[Federal Register Volume 76, Number 194 (Thursday, October 6, 2011)]
[Proposed Rules]
[Pages 62166-62212]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-25471]
[[Page 62165]]
Vol. 76
Thursday,
No. 194
October 6, 2011
Part II
Department of the Interior
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Fish and Wildlife Service
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50 CFR Part 17
Endangered and Threatened Wildlife and Plants; 12-Month Finding on a
Petition To List Texas Fatmucket, Golden Orb, Smooth Pimpleback, Texas
Pimpleback, and Texas Fawnsfoot as Threatened or Endangered; Proposed
Rule
Federal Register / Vol. 76 , No. 194 / Thursday, October 6, 2011 /
Proposed Rules
[[Page 62166]]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[FWS-R2-ES-2011-0079; MO 92210-0-0008 B2]
Endangered and Threatened Wildlife and Plants; 12-Month Finding
on a Petition To List Texas Fatmucket, Golden Orb, Smooth Pimpleback,
Texas Pimpleback, and Texas Fawnsfoot as Threatened or Endangered
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of 12-month petition finding.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce a
12-month finding on a petition to list five mussel species in Texas as
threatened or endangered and to designate critical habitat under the
Endangered Species Act of 1973, as amended (Act). The five species are
Texas fatmucket (Lampsilis bracteata), golden orb (Quadrula aurea),
smooth pimpleback (Q. houstonensis), Texas pimpleback (Q. petrina), and
Texas fawnsfoot (Truncilla macrodon). After review of all available
scientific and commercial information, we find that listing these five
mussel species is warranted. Currently, however, listing of these
species is precluded by higher priority actions to amend the Federal
Lists of Endangered and Threatened Wildlife and Plants. Upon
publication of this 12-month petition finding, we will add these five
species to our candidate species list. We will develop a proposed rule
to list these species as our priorities allow. We will make any
determination on critical habitat during development of the proposed
listing rule. In any interim period, we will address the status of the
candidate taxa through our annual Candidate Notice of Review.
DATES: The finding announced in this document was made on October 6,
2011.
ADDRESSES: This finding is available on the Internet at http://www.regulations.gov at Docket Number FWS-R2-ES-2011-0079. Supporting
documentation we used in preparing this finding is available for public
inspection, by appointment, during normal business hours at the U.S.
Fish and Wildlife Service, 1505 Ferguson Lane, Austin, TX 78754. Please
submit any new information, materials, comments, or questions
concerning this finding to the above address.
FOR FURTHER INFORMATION CONTACT: Gary Mowad, Texas State Administrator,
U.S. Fish and Wildlife Service (see ADDRESSES); by telephone at 512-
927-3557; or by facsimile at 512-927-3592. If you use a
telecommunications device for the deaf (TDD), please call the Federal
Information Relay Service (FIRS) at 800-877-8339.
SUPPLEMENTARY INFORMATION:
Background
Section 4(b)(3)(B) of the Act (16 U.S.C. 1531 et seq.) requires
that, for any petition to revise the Federal Lists of Endangered and
Threatened Wildlife and Plants that contains substantial scientific or
commercial information that listing the species may be warranted, we
make a finding within 12 months of the date of receipt of the petition.
In this finding, we will determine that the petitioned action is: (1)
Not warranted, (2) warranted, or (3) warranted, but the immediate
proposal of a regulation implementing the petitioned action is
precluded by other pending proposals to determine whether species are
threatened or endangered, and expeditious progress is being made to add
or remove qualified species from the Federal Lists of Endangered and
Threatened Wildlife and Plants. Section 4(b)(3)(C) of the Act requires
that we treat a petition for which the requested action is found to be
warranted but precluded as though resubmitted on the date of such
finding, that is, requiring a subsequent finding to be made within 12
months. We must publish these 12-month findings in the Federal
Register.
Previous Federal Actions
This 12-month petition finding covers five species of mussels that
are grouped together because of their overlapping or proximate ranges
within the river basins of central Texas. The petitions for listing
these five species were parts of two multi-species petitions, dated
June 18, 2007, and October 9, 2008. The other species from those
petitions, including other Texas mussels, will be considered in
separate petition findings.
On June 25, 2007, we received a formal petition dated June 18,
2007, from Forest Guardians (now WildEarth Guardians), requesting that
we: (1) Consider all full species in our Southwest Region ranked as G1
or G1G2 by the organization NatureServe, except those that are
currently listed, proposed for listing, or candidates for listing; and
(2) List each species as either threatened or endangered with critical
habitat. The petitioned group of species included four Texas mussels,
two of which are included in this finding: the Texas fatmucket and
golden orb. Two additional mussels from eastern Texas, the Texas
heelsplitter (Potamilus amphichaenus) and Salina mucket (P.
metnecktayi), were also included in this petition. The petition
incorporated all analyses, references, and documentation provided by
NatureServe in its online database at http://www.natureserve.org/ into
the petition. Included in NatureServe was supporting information
regarding the species' taxonomy and ecology, historical and current
distribution, present status, and actual and potential causes of
decline. We sent a letter dated July 11, 2007, to Forest Guardians
acknowledging receipt of the petition and stating that the petition was
under review by staff in our Southwest Regional Office.
On October 15, 2008, we received a petition dated October 9, 2008,
from WildEarth Guardians, requesting that the Service list as
threatened or endangered and designate critical habitat for six species
of freshwater mussels, including the smooth pimpleback, Texas
pimpleback, and Texas fawnsfoot. Two additional mussels from the Rio
Grande basin, the false spike (Quincuncina mitchelli) and Mexican
fawnsfoot (Truncilla congata), were also included in this petition. In
addition to other information, the petition incorporated all analyses,
references, and documentation provided by NatureServe in its online
database at http://www.natureserve.org/. In a November 26, 2008, letter
to the petitioner, we acknowledged receipt of the second petition and
stated that the petition for the six mussel species was under review by
staff in our Southwest (Region 2) and Southeast (Region 4) Regional
Offices. The southern hickorynut (Obovaria jacksoniana) was also
included in this 2008 petition, and on March 23, 2010 (75 FR 13717), we
found that the petition did not present substantial information
supporting that that species may be endanagered or threatened.
On December 15, 2009, we published our 90-day finding that the
petitions presented substantial scientific information indicating that
listing nine Texas mussels may be warranted (74 FR 66260). As a result
of the finding, we initiated a status review for all nine species. This
notice constitutes the 12-month finding on the June 18, 2007, petition
to list the Texas fatmucket and golden orb and the October 9, 2008,
petition to list the smooth pimpleback, Texas pimpleback, and Texas
fawnsfoot as threatened or endangered. Our petition findings for the
remaining Texas mussel species will be published at a later time.
[[Page 62167]]
Summary of Procedures for Determining the Listing Status of Species
Review of Status Based on Five Factors
Section 4 of the Act (16 U.S.C. 1533) and implementing regulations
(50 CFR part 424) set forth procedures for adding species to, removing
species from, or reclassifying species on the Federal Lists of
Endangered and Threatened Wildlife and Plants. Under section 4(a)(1) of
the Act, a species may be determined to be endangered or threatened
based on any of the following five factors:
(A) The present or threatened destruction, modification, or
curtailment of its habitat or range;
(B) Overutilization for commercial, recreational, scientific, or
educational purposes;
(C) Disease or predation;
(D) The inadequacy of existing regulatory mechanisms; or
(E) Other natural or manmade factors affecting its continued
existence.
In making these findings, we discuss below information pertaining
to each species in relation to the five factors provided in section
4(a)(1) of the Act. In considering what factors might constitute
threats to a species, we must look beyond the exposure of the species
to a particular factor to evaluate whether the species may respond to
the factor in a way that causes actual impacts to the species. If there
is exposure to a factor and the species responds negatively, the factor
may be a threat, and during the status review, we attempt to determine
how significant a threat it is. The threat is significant if it drives
or contributes to the risk of extinction of the species such that the
species warrants listing as endangered or threatened as those terms are
defined by the Act. However, the identification of factors that could
impact a species negatively may not be sufficient to compel a finding
that the species warrants listing. The information must include
evidence sufficient to suggest that the potential threat has the
capacity (i.e., it should be of sufficient magnitude and extent) to
affect the species' status such that it meets the definition of
endangered or threatened under the Act.
Evaluation of the Status of Each of the Five Mussel Species
In this finding, we first provide a description of general mussel
biology. Then, for each of the five species, we describe the species,
its life history, and habitat; evaluate listing factors for that
species; and present our finding that the petitioned action is
warranted or not for that species. We follow these descriptions,
evaluations, and findings with a discussion of the priority and
progress of our listing actions.
General Mussel Biology
All five species are freshwater mussels in the family Unionidae and
occur only in Texas, in portions of the Colorado, Guadalupe, Nueces-
Frio, and Brazos River systems (Howells et al. 1996, p. 1). Adult
freshwater mussels are suspension feeders, drawing in food and oxygen
through their incurrent siphon (tube that draws water into the shell).
They may also feed on organic particles in sediment using the large,
muscular foot (an organ used to anchor the mussel in the substrate or
for locomotion) (Raikow and Hamilton 2001, p. 520). Adults feed on
algae, bacteria, detritus (dead organic material), microscopic animals,
and dissolved organic matter (Fuller 1974, pp. 221-222; Silverman et
al. 1997, p. 1862; Nichols and Garling 2000, pp. 874-876; Christian et
al. 2004, p. 109). For their first several months, as they inhabit
interstitial spaces (small spaces between sediment particles) within
the substrate, juvenile mussels feed using cilia (fine hairs) on the
foot to capture suspended as well as depositional material, such as
algae and detritus (Yeager et al. 1994, pp. 253-259). Mussels tend to
grow relatively rapidly for the first few years, and then slow
appreciably at sexual maturity, when energy presumably is being
diverted from growth to reproductive activities (Baird 2000, pp. 66-
67).
As a group, mussels are extremely long lived, living from two to
several decades (Rogers et al. 2001, p. 592), and possibly up to 200
years in extreme instances (Bauer 1992, p. 427). Most mussel species,
including the five in this finding, have distinct forms of males and
females. During reproduction, males release clouds of sperm into the
water column, which females draw in through their siphons.
Fertilization takes place internally, and the resulting eggs develop
into specialized larvae (called glochidia) within the female gills. The
females release matured glochidia individually, in small groups, or
embedded in larger mucus structures called conglutinates.
The glochidia of freshwater mussels are obligate parasites (cannot
live independently of their hosts) on the gills or fins of fishes
(Vaughn and Taylor 1999, p. 913). Glochidia die if they fail to find a
host fish, attach to a fish that has developed immunity from prior
infestations, or attach to the wrong location on a host fish (Neves
1991, p. 254; Bogan 1993, p. 299). Glochidia encyst (enclose in a cyst-
like structure) on the host's tissue and develop into juvenile mussels
weeks or months after attachment (Arey 1932, pp. 214-215). Mussels
experience their primary opportunity for dispersal and movement within
the stream as glochidia attached to a host fish (Smith 1985, p. 105).
Upon release from the host, newly transformed juveniles drop to the
substrate on the bottom of the stream. Those juveniles that drop in
unsuitable substrates die because their immobility prevents them from
relocating to more favorable habitat. Juvenile freshwater mussels
burrow into interstitial substrates and grow to a larger size that is
less susceptible to predation and displacement from high flow events
(Yeager et al. 1994, p. 220). Throughout the rest of their life cycle,
mussels generally remain within the same small area where they released
from the host fish.
Species Information for Texas Fatmucket
Species Description
The Texas fatmucket is a large, elongated mussel that reaches a
maximum length of 100 millimeters (mm) (3.94 inches (in)) (Howells
2010c, p. 2). The shell is oval to elliptical or somewhat rhomboidal
and tan to greenish-yellow with numerous irregular, wavy, and broad and
narrow dark brown rays, with broad rays widening noticeably as they
approach the ventral (underside) margin. The nacre (inside of the
shell) is white with occasional yellow or salmon coloration and
iridescent posteriorly (Howells 2010c, p. 2). Females have mantle flaps
(extensions of the tissue that covers the visceral mass) that often
resemble minnows, including eye spots, lateral line, and fins (Howells
2010c, p. 2).
Taxonomy
The Texas fatmucket was first described in 1855 by Gould as Unio
bracteatus and later moved to the genus Lampsilis by Simpson (1900, p.
543). Some forms found in headwater streams were historically split
into a different species, L. elongatus, but they have since been
determined to be ecophenotypes (individuals whose shape is determined
by their environment) of L. bracteata (Howells 2010c, p. 5). The Texas
fatmucket is recognized by the Committee on Scientific and Vernacular
Names of Mollusks of the Council of Systematic Malacologists, American
Malacological Union (Turgeon et al. 1998, p. 34), and we recognize it
as a valid species.
[[Page 62168]]
Biology and Life History
Although there is no specific information on age and size of
maturity of the Texas fatmucket, it is likely similar to a related
species, the Louisiana fatmucket (L. hydiana), which reaches sexual
maturity around 36 mm (1.4 in) (Howells 2000b, pp. 35-48; Howells
2010c, p. 3). Texas fatmucket females have been found gravid (with
glochidia in the gill pouch) from July through October, although
brooding may continue throughout much of the year (Howells 2010c, p.
3). Texas fatmucket females display a mantle lure to attract host fish,
releasing glochidia when the lure is bitten or struck by the fish.
Bluegill (Lepomis macrochirus) and green sunfish (L. cyanellus) have
been successful hosts in laboratory studies (Howells 1997b, p. 257).
Hosts such as these sunfishes are common, widely distributed species in
Texas that occur in an array of habitat types (Hubbs et al. 2008, p.
45) and would not generally be expected to be a limiting factor in
Texas fatmucket reproduction and distribution (Howells 2010c, p. 3).
Habitat
The Texas fatmucket occurs in moderately sized rivers in mud, sand,
or gravel, or mixtures of these substrates (Howells 2010c, p. 4) and
sometimes in narrow crevices between bedrock slabs (Howells 1995, p.
21). Live individuals have been found in relatively shallow water,
rarely more than 1.5 meters (m) (4.9 feet (ft)) deep, and usually less.
Remaining populations typically occur at sites where one or both banks
are relatively low, allowing floodwaters to spread out over land and
thereby reducing damage from scouring (Howells 2010c, p. 4). The
species does not occur in ponds, lakes, or reservoirs, suggesting that
it is intolerant of deep, low-velocity water created by artificial
impoundments.
Distribution and Abundance
Historical Distribution
The Texas fatmucket historically had populations in at least 18
rivers in the upper Colorado, Guadalupe, and San Antonio River systems
in the Texas Hill Country and east-central Edwards Plateau region of
central Texas. In the Colorado River, it ranged from Travis County
upstream approximately 320 kilometers (km) (200 miles (mi)) to Runnels
County in the Colorado River. It was also found in many tributaries,
including the Pedernales, Llano, San Saba, and Concho Rivers, and Jim
Ned, Elm, and Onion Creeks (Howells et al. 1996, p. 61).
In the Guadalupe-San Antonio River basin, the Texas fatmucket
occupied approximately 240 km (150 mi) of the Guadalupe River, from
Gonzales County upstream to Kerr County, including the North Guadalupe
River, Johnson Creek, and the Blanco River. In the San Antonio River,
it ranged from its confluence with the Medina River in Bexar County
upstream to the City of San Antonio, as well as in the Medina River and
Cibolo Creek (Howells et al. 1996, p. 61; Howells 2010c, p. 6).
Strecker (1931, pp. 66-68) reported Texas fatmucket from a lake in
Victoria County in the lower Guadalupe River drainage (Howells 2010c,
p. 6), but this is probably a misidentified Louisiana fatmucket, which
occurs in lakes or impoundments. A Salado Creek record from Bell County
(Strecker 1931, pp. 62-63) is also probably a misidentified Louisiana
fatmucket, since the Texas fatmucket is not known to occur in the
Brazos River basin or its western tributaries (Howells et al. 1996, p.
61; Howells 2010c, p. 6).
Current Distribution
Based on historical and current data, the Texas fatmucket has
declined significantly rangewide and is now known from only nine
streams in the Colorado and Guadalupe River systems in very limited
numbers. All existing populations are represented by only one or two
individuals and are likely not stable or recruiting (juvenile mussels
joining the adult population). In the streams where the species is
extant (surviving), populations are highly fragmented and restricted to
short reaches with few exceptions. The Texas fatmucket has been
considered a species of special concern by some malacologists for
several decades (Athearn 1970, p. 28).
Colorado River System
The Texas fatmucket was historically known to occur throughout the
Colorado River and numerous tributaries (Randklev et al. 2010c, p. 4).
However, in the mainstem Colorado River, the Texas fatmucket has not
been found, live or dead, in several decades despite numerous surveys
(Howells 1994, p. 4; 1995, pp. 20-21, 25, 29; 1996, pp. 20, 23; 1997a,
pp. 27, 31, 34-35; 1998, p. 10; 1999, p. 18; 2000a, pp. 25-27; 2002a,
pp. 6-7; 2004, pp. 7, 10-11; 2005, p. 6; Johnson 2009, p. 1; Burlakova
and Karatayev 2010a, p. 12), and thus is considered extirpated
(eliminated from) from the Colorado River mainstem. Within this system,
the species is only known from sparse populations in Colorado River
tributaries, including the South Concho River, Spring Creek, Llano
River (including Threadgill Creek), Pedernales River (including Live
Oak Creek), Onion Creek, Jim Ned Creek, Elm Creek, and the San Saba
River.
Evidence of persisting Texas fatmucket populations has been found
in Spring Creek, a tributary to the Middle Concho River, which flows
into the Concho River, a large tributary of the Colorado River.
Historically, Spring Creek harbored Texas fatmucket in Irion and Tom
Green Counties (Randklev et al. 2010c, p. 1). In 1993, discovery of
shell material prompted additional surveys, and in 1997, one live
individual was found in Irion County (Howells 1998, p. 13). Farther
downstream, in Tom Green County, two live individuals were recorded in
1997, upstream of Twin Buttes Reservoir (Howells 1998, pp. 13-14), but
no evidence of this population was found in 2008 (Burlakova and
Karatayev 2010a, p. 12). Spring Creek was reported to have dried in
1999 and 2000, which may have eliminated the population there (Howells
et al. 2003, p. 5).
In the Llano River, there are three areas that are currently known
to contain Texas fatmucket populations. The species occurred throughout
the length of the river historically (Ohio State University Museum
(OSUM) 2011a, p. 1). A single shell was collected in Llano County in
1992 (Howells 1994, p. 6), and eight live individuals were found in
2011 (Burlakova and Karatayev 2011, p. 1). Individuals were small in
size, indicating a potentially reproducing population. The species also
persists in Mason County, where two shell fragments of recently dead
Texas fatmucket were found in 1995 (Howells 1996, p. 22), and two live
individuals were collected at the same site in 2009 (Burlakova and
Karatayev 2010a, pp. 12-13). The species also appears to persist in
Kimble County, where one live Texas fatmucket was recorded in 2009
(Burlakova and Karatayev 2010a, pp. 12-13).
In 2004, four live Texas fatmucket were recorded from Threadgill
Creek, a tributary to the Llano River in Gillespie and Mason Counties
(Howells 2005, pp. 6-7). This population is on private land, which
limits survey access, but Howells (2009, p. 5) indicates it likely
persists due to favorable land management.
Live Oak Creek, a tributary to the Pedernales River in Gillespie
County, also contains a sparse Texas fatmucket population. In 2002, 11
shells were discovered, and in 2003, one live individual was recorded,
confirming the species persisted in low numbers (Howells 2003, p. 10;
Howells 2004, pp. 8-9). Since that time, surveys have been
[[Page 62169]]
conducted in Live Oak Creek on a fairly regular basis. The stream was
visited in two different occasions in 2004, with only shell material
found (Howells 2005, pp. 7-8), and again in 2005, when two live
individuals were recorded (Burlakova and Karatayev 2010a, p. 12). The
stream was surveyed in 2007 and 2008, but no evidence of the species
was found (Howells 2009, p. 5). This population is presumed to be small
but persisting.
Original records of speckled pocketbook (Lampsilis streckeri) from
Onion Creek in Travis County in 1931 are now believed to have been
misidentified; instead they represent records of Texas fatmucket
(Howells 2010c, p. 6; Randklev et al. 2010c, p. 4). The stream was
surveyed in 1993, and no live freshwater mussels were found (Howells
1995, p. 28). However, in 2010, several live Texas fatmucket were found
during a survey near Highway 71 (Groce 2011, pers. comm.), indicating
the species persists there.
Elm Creek, a tributary to the Colorado River, has been known to
harbor a Texas fatmucket population since 1993, when 10 live
individuals were recorded (Howells 1995, p. 21). Since that time, the
population has declined, with two individuals found in 1995 (Howells
1996, pp. 19-20), and no live individuals found in 2001 or 2005
(Howells 2002a, p. 5; 2006, p. 63). In 2008, additional sites
downstream of the known population were surveyed and one live
individual was recorded after 15 person-hours of searching (Burlakova
and Karatayev 2010a, p. 12), indicating that the species continues to
persist in Elm Creek, although in very low numbers.
Texas fatmucket also persist in the San Saba River, where the
species has been known to occur historically (Randklev et al. 2010c, p.
2; OSUM 2011a, p. 1). The river was surveyed in 1997, and three live
individuals were found (Howells 1998, p. 16). In 2000 and 2004, no
Texas fatmucket were found in this stretch of river (Howells 2001, p.
29; Howells 2005, pp. 8-9). One live individual was found in 2005
(Howells 2006, p. 64), and, in 2008, only one shell of a recently dead
individual was found (Burlakova and Karatayev 2010a, p. 12). In 2005,
the number of mussels of all species collected was about 40 percent of
the 1997 numbers (Howells 2006, p. 64), indicating an overall decline
in the freshwater mussel fauna. Aquatic macrophyte (aquatic plants
larger than algae) abundance has increased in this river, confounding
survey efforts and degrading mussel habitat (Howells 2006, p, 64).
Texas fatmucket have not been found alive in the Pedernales River
since 1978 (Howells 1999, p. 16). In 1992, a thorough search of the
habitat yielded no live Texas fatmuckets, with only very old dead shell
material collected in the banks above the normal high water line
(Howells 1994, p. 4). Because the species was documented from Blanco
County by museum records (OSUM 2011a, p. 1), additional sections of the
river were also surveyed in 1992, with no evidence of Texas fatmucket
found, although in 1993, very old Texas fatmucket shell fragments were
discovered in Pedernales Falls State Park (Howells 1995, p. 28). Mussel
habitat in this area is poor, and it is unlikely the species persists
there. Subsequent searches of the river in 1998 yielded only dead shell
material (Howells 1999, p. 16).
The Texas fatmucket is considered extirpated from the South Concho
River and Jim Ned Creek. In the South Concho River, old Texas fatmucket
shell fragments were found in gravel bars in Tom Green County in 1997,
but there has been no additional evidence of the species (Howells 1998,
p. 12). Additionally, three live individuals were recorded from Jim Ned
Creek in Brown County in 1979 (Randklev et al. 2010c, p. 3), but the
species has not been found in this stream since then (Howells 1997a,
pp. 29-30).
Guadalupe River System
While the Texas fatmucket was never widely distributed in the
Guadalupe River system, the only remaining populations are in the
mainstem Guadalupe River and possibly the North Fork Guadalupe River.
It is presumed extirpated from the entire San Antonio River system, as
well as the Blanco River and Johnson Creek.
In the mainstem Guadalupe River, Texas fatmucket historically
occurred in Kerr County (OSUM 2011a, p. 1). In 1992 and 1995, surveys
yielded no evidence of the species (Howells 1994, pp. 7-8; Howells
1996, p. 25), although shell fragments collected in 1993 in Guadalupe
County may have been Texas fatmucket but were too weathered for an
accurate determination (Howells 1995, p. 31). In 1996, two live
individuals were recorded in Kerr County directly below a dam (Howells
1997a, p. 36), and in 1997, three shells were found at the same site
following a flood (Howells 1998, p. 18). No Texas fatmucket or other
freshwater mussels have been found at that site since, and it is
unlikely that Texas fatmucket persist there (Howells 2006, p. 71).
However, 20 recently dead individuals were discovered approximately 1
km (0.6 mi) downstream in Louise Hayes Park during a drawdown (Howells
1999, pp. 18-19), and 6 live individuals were found at the same
location in 2005 (Howells 2006, pp. 71-72). Surveys in 2007 and 2008
yielded no live or recently dead individuals (Burlakova and Karatayev
2010a, p. 12). It is likely that the species persists in the vicinity.
There has been no other evidence of Texas fatmucket in the mainstem
Guadalupe River in recent years.
In 1999, two recently dead Texas fatmucket were found in North Fork
Guadalupe River (Howells 2000a, p. 27). This river was surveyed again
in 2000 and 2003 at several sites, and no Texas fatmucket were found
(Howells 2001, p. 31; Howells 2004, pp. 13-14).
Johnson Creek was a historical location for Texas fatmucket, but no
live freshwater mussels of any species have been found in this stream
for decades (Howells 1996, p. 25; Howells 1998, p. 18; Howells 2002a,
p. 8). Additionally, the Blanco River has been surveyed extensively
since 1992, and no evidence of Texas fatmucket has been collected, nor
is suitable habitat present (Howells 1994, p. 9; Howells 1995, pp. 32-
33; Howells 1996, p. 28; Johnson 2011, p. 1). The last collection of
Texas fatmucket from the Blanco River occurred in the 1970s or 1980s
(Howells 2005, p. 10).
Texas fatmucket have also been extirpated from the entire San
Antonio River system. The mainstem San Antonio River was surveyed in
1993 and 1996, and no live or dead Texas fatmucket were found (Howells
1995, p. 35; 1997a, pp. 41-42). It was known from the Medina River, a
tributary to the San Antonio River, historically (Randklev et al.
2010c, p. 3), but no mussels of any species have been found in this
river in recent years (May 2011, pers. comm.). Additionally, although
Texas fatmucket were collected from Cibolo Creek historically (OSUM
2011a, p. 1) and shell material, likely from Texas fatmucket, was found
in 1993 (Howells 1995, p. 36), no live freshwater mussels have been
found in Cibolo Creek since (Howells 1997a, pp. 40-41).
Summary
Based on historical and current data, the Texas fatmucket has
declined significantly rangewide and has been extirpated from most of
the Guadalupe River system and hundreds of miles of the Colorado River,
as well as from numerous tributaries. Extant populations are
represented by only a few individuals, and they are highly disjunct and
restricted to short reaches. Two of the populations considered extant
in recent years may now be
[[Page 62170]]
extirpated, and the remaining seven populations are extremely small and
likely not stable. No evidence of recent recruitment has been found in
any of the populations, with the possible exception of the Llano River.
Species Information for Golden Orb
Species Description
The golden orb is small, usually less than 82 mm (3.2 in), with an
oval to nearly round, smooth, and unsculptured shell, except for
concentric growth rings (Howells 2002b, p. 6). External shell
coloration varies from yellow-brown, gold, or orangish-brown to dark
brown or black, and some individuals may show faint greenish rays.
Internally, the nacre is white to bluish-white (Howells 2002b, p. 6).
Taxonomy
The golden orb was originally described as Unio aureas by Lea in
1859 and later moved to the genus Quadrula in 1900 (Simpson 1900, p.
783). Graf and Cummings (2007, p. 18) have proposed moving it to the
genus Amphinaias, but other freshwater mussel taxonomists recommend
waiting for additional work to be completed on members of Quadrula
before splitting the genus (Bogan 2011, pers. comm.). Because the
golden orb can exhibit an elongated shell structure in headwater
riffles, old records of Unio bolli in the Colorado River (Dall 1882, p.
956) are very likely elongated forms of golden orb (Howells 2010a, p.
5). The golden orb is recognized by the Committee on Scientific and
Vernacular Names of Mollusks of the Council of Systematic
Malacologists, American Malacological Union (Turgeon et al. 1998, p
36), and we recognize it as a valid species.
Biology and Life History
There is no specific information on age, size of maturity, or host
fish use for golden orb. Other species in the genus Quadrula
successfully parasitize catfish, and it is likely golden orb do as well
(Howells 2010a, p. 3). Gravid females have been found from May through
August (Howells 2000b, p. 38). Mussels in the genus Quadrula are short-
term brooders, which are species that hold fertilized eggs and
glochidia for a short period, usually 3 to 6 weeks, before releasing
glochidia (Gorden and Layzer 1989, p. 6; Garner et al. 1999, p. 277).
Habitat
The golden orb has been found almost exclusively in flowing waters
in moderately sized rivers (Howells 2010a, p. 3). It has been found in
only one reservoir in the lower Nueces River (Lake Corpus Christi),
where wave action may simulate flowing water conditions (Howells 2010a,
p. 3). This species is found in substrates of firm mud, sand, and
gravel, and it does not appear to tolerate more unstable substrates
such as loose sand or silt (Howells 2002b, p. 6).
Distribution and Abundance
Historical Distribution
The golden orb is endemic (native) to nearly the entire lengths of
the Guadalupe, San Antonio, and Nueces-Frio River basins in central
Texas (Howells 2010a, p. 5), including the Guadalupe, Medina, San
Antonio, Frio, and Nueces Rivers and Cibolo Creek. It was originally
reported from four sites in the Brazos River system (Strecker 1931, p.
63), but these are almost certainly misidentified smooth pimpleback
(Howells 2002b, p. 5) based on numerous mussel surveys throughout the
Brazos River system since the 1970s that failed to find any golden orb.
The species has not been found in studies of archaeological specimens
from the Brazos River (Howells 2010a, p. 5), further indicating golden
orb did not historically occur in the Brazos River system.
The golden orb has also been reported from the upper Colorado River
drainage (Howells et al. 1996, pp. 108-109; Randklev et al. 2010c, p.
4), but these appear to have been misidentified Texas pimpleback
(Howells 2010a, p. 5). Since no other golden orb have been reported
from the Colorado River system, we do not believe it occurred in that
basin.
Current Distribution
Based on historical and current data, the golden orb has declined
significantly rangewide and is now known from only four streams in
disjunct locations. Despite mussel surveys across the historical range,
since 1995 golden orb has only been found in Lake Corpus Christi and
the Guadalupe, lower San Marcos, and lower San Antonio Rivers. The
species has been extirpated from the entire Nueces-Frio River basin,
except at the extreme downstream end of the Nueces River, where a
population persists in Lake Corpus Christi. Aside from the upper
Guadalupe River, all existing populations occur in the lower portion of
occupied basins in a small geographical area; only about 130 km (80 mi)
separate the farthest two populations. Only four populations appear to
be relatively stable and recruiting, while the remaining five
populations are represented by only a few individuals.
Guadalupe River System
In the Guadalupe River system, the golden orb historically ranged
throughout the length of the Guadalupe, San Antonio, and San Marcos
Rivers. Currently in this basin, the species only persists in the
uppermost Guadalupe River and lower San Marcos, San Antonio, and
Guadalupe Rivers. The lower portion of this basin (within approximately
120 km (75 mi) of the Gulf of Mexico) harbors all four of the large,
presumably reproducing populations of golden orb.
Historically known from the mainstem Guadalupe River (Howells
2002a, p. 8), the golden orb was not seen in the upper Guadalupe River
in Kerr County again, despite repeated surveys (Howells 1994, pp. 7-8;
1996, p. 30; 1997a, p. 36), until 1997, when three shells were
discovered (Howells 1998, p. 18). No live freshwater mussels of any
species have been found in this area, just downstream of a dam, since
1997 (Howells 1999, p. 18; Howells 2006, p. 71), and it is unlikely
golden orb persists there. However, upstream of this area, above the
dam and impounded reach, a single recently dead individual was found in
1998 during an extended drawdown of the river to construct a footbridge
in a local park (Howells 1999, pp. 18-19). In 2005, two live
individuals were also found at this site (Howells 2006, pp. 71-72),
showing that the species had survived the drawdown and persists at the
site.
Golden orb also occurs farther downstream in the mainstem Guadalupe
River, near Lake Gonzales in Gonzales County. Upstream of the
reservoir, subfossil shells (very old shells that are brittle,
crumbling, and with extensive erosion) were found in 1993 (Howells
1995, p. 31), but the species has not been found there since. However,
below the reservoir, one recently dead individual was collected in 1995
(Howells 1996, pp. 26-27), and in 1996, 25 live golden orb were
recorded at two sites in this area (Howells 1997a, pp. 37-38). Later,
in 2006, three live golden orb were also found in this area (Howells
2006, pp. 85-86). A small population apparently continues to persist
below Lake Gonzales.
A large golden orb population occurs farther downstream in the
mainstem Guadalupe River, below Lake Wood, also in Gonzales County.
Although none were found during a survey in 1995 (Howells 1996, p. 27),
36 live golden orb were found at two sites below Lake Wood in 1996
(Howells 1997a, pp. 38-40). Density estimates were calculated based on
the quantitative information collected from these surveys, but they
[[Page 62171]]
were not considered statistically valid (Howells 1997a, p. 40) and so
are not reported here. Only one live golden orb was found at this site
in 2002 (Howells 2003, p. 11), but a relatively large population
continues to persist; a total of around 100 live golden orb were found
at three sites within 2 km (1.2 mi) of the Lake Wood Dam in 2006
(Howells 1996, pp. 87-91). Also, in 2008, 33 golden orb were recorded
alive downstream of Lake Wood (Burlakova and Karatayev 2010a, p. 14).
This portion of the Guadalupe River supports a relatively large
population of golden orb, and it also contains one of the most abundant
freshwater mussel communities in Texas (Burlakova and Karatayev 2010a,
p. 14).
In 2009, a large population of golden orb was discovered farther
downstream in the mainstem Guadalupe River in Victoria County, when
over 100 individuals were found (Johnson 2009, p. 1). Multiple size
classes were observed, including juveniles, indicating this population
is reproducing and recruiting new individuals into the population. A
large number of shells was collected upstream of this site in 1994
(Burlakova and Karatayev 2010c, p.1), but no golden orb were seen alive
until 2009.
The San Marcos River, a tributary to the Guadalupe River, also
supports a large golden orb population near its confluence with the
tailwaters (outflow) of Lake Wood Dam. Although much of the San Marcos
River has been extensively surveyed, with very few freshwater mussels
present of any species (Howells 1995, pp. 33-34; 1997a, p. 40; 2004,
pp. 15-16, 18; 2005, p. 10), one old golden orb shell was found near
the town of Staples (Howells 1998, p. 19), and a single live individual
was found near the town of Luling (Howells 1999, p. 28). Downstream
from these locations, a large population persists in the vicinity of
Palmetto State Park in Gonzales County. In 1995, a recently dead
individual was discovered downstream of the park, indicating the recent
presence of the species (Howells 1996, p. 28), and, based on surveys
from 2000-2006, a relatively large population was confirmed to be in
the area (Howells 2001, pp. 32-33; 2006, pp. 72-73; 2006, p. 91;
Burlakova and Karatayev 2010a, pp. 14-15).
Historically, golden orb were numerous in the San Antonio River in
Karnes County (OSUM 2011b, p. 1), but only a single subfossil shell was
found at each of two sites in Karnes County in 1996 (Howells 1997a, pp.
41-42). No live animals have been found there since, although abundant
shell material remains present (Karatayev and Burlakova 2008, p. 40).
The lower portion of the San Antonio River supports the largest
known golden orb population. In 2007, 37 live golden orb were recorded
near Goliad in Goliad County, both within and downstream of Goliad
State Park (Howells 2009, p. 11). The following year, 285 live golden
orb were found within the park and downstream surrounded by private
lands (Burlakova and Karatayev 2010a, p. 15). This site represents the
largest known population of golden orb.
In 2009, a single live golden orb was discovered in the lower San
Antonio River south-southwest of Victoria in Victoria County (Johnson
2009, p. 1); this site has not been surveyed since. We presume golden
orb may persist in this stretch of river.
The golden orb appears to have been extirpated from the Medina
River. The species historically occurred in Medina and Bexar Counties
(Randklev et al. 2010b, p. 4; OSUM 2011b, p. 1), but no live or dead
mussels of any species have been found in this river in recent years
(May 2011, pers. comm.).
Cibolo Creek, a tributary to the San Antonio River, was extensively
surveyed in the 1990s, with only old golden orb shells collected in
Wilson County (Howells 1995, pp. 35-37; 1997a, pp. 40-41). In 2006 and
2007, Burlakova and Karatayev (2010b, p. 1) surveyed this same general
area and found only shell material. It is unlikely golden orb remain in
Cibolo Creek.
Nueces-Frio River System
Information is limited on the occurrence of golden orb in the
Nueces River. Other than a population that occurs in a reservoir on the
lower Nueces River (Lake Corpus Christi), the species appears to be
extirpated from the remainder of the basin.
Historically, the golden orb occurred in the Nueces River in Live
Oak County (OSUM 2011b, p. 1). It was last seen alive in the Nueces
River in 1993, when unreported numbers were found in the same area
(Burlakova and Karatayev 2010c, p. 1). A shell was collected in the
same general area in 1995 (Burlakova and Karatayev 2010c, p. 1), but
additional surveys in 1996 and 1997 found no evidence of the species
(Howells 1997a, pp. 43-44; 1998, p. 20). We presume the species no
longer occurs in the upper portions of the Nueces River.
An anomalous (odd) population of golden orb has persisted in Lake
Corpus Christi Reservoir in the lower Nueces River. While the species
does not typically inhabit lentic (ponded) water, wave action is
presumed to simulate flowing water conditions and has supported a
golden orb population since at least the 1970s (OSUM 2011b, p. 1). A
few live individuals of golden orb have been found within the reservoir
consistently since 1994 (Howells 1995, p. 39; 1996, pp. 30-31;
Burlakova and Karatayev 2010c, p. 1). Numbers of golden orb collected
increased in 1996, when 86 live golden orb were found at three
different locations within the reservoir (Howells 1996, pp. 30-31).
However, a drawdown of the lake in 1996 resulted in large numbers of
golden orb stranded and killed (Howells 2010a, p. 9), and in 1998 no
live individuals were found (Howells 1999, p. 19). Again in 2005, no
live individuals were found during surveys, but in 2006, a total of
nine were collected at three different sites within the reservoir
(Howells 2006, pp. 73-76, 91-93). A small golden orb population likely
persists in the reservoir.
Very little information is available on the distribution of golden
orb in the Frio River. Shells were last seen in McMullen County in 1994
(Burlakova and Karatayev 2010c, p. 1), but no evidence of the species
has been found in this river since (Howells 1995, pp. 37-38; 1996, p.
29; 2002a, pp. 9-10; 2004, pp. 19-20).
Summary
Based on historical and current data, the golden orb has declined
rangewide and is now known from only nine populations in four rivers
and has been eliminated from nearly the entire Nueces-Frio River
system. Four of these populations appear to be stable and reproducing;
the remaining five populations are small and isolated and show no
evidence of recruitment. Only the populations in the middle Guadalupe
River and lower San Marcos River are likely connected; the remaining
extant populations are highly fragmented and restricted to short
reaches.
Species Information for Smooth Pimpleback
Species Description
The smooth pimpleback is a nearly round, thick-shelled freshwater
mussel that generally reaches at least 60 mm (2.6 in) in length
(Howells 2010b, p. 4). It is moderately thick, solid, and inflated.
Externally, the smooth pimpleback, like its name suggests, is
relatively smooth with minute sculpturing; it may or may not have a few
small pustules (raised bumps) (Howells 2010b, p. 2). The external
coloration of the shell ranges from tan
[[Page 62172]]
to light brown, dark brown, and black with no rays (Howells 2010b, p.
4).
Taxonomy
The smooth pimpleback was originally described by Lea in 1859 as
Unio houstonensis. It was later placed in the genus Margaron and
ultimately moved to Quadrula by Simpson (1900, p. 782). Graf and
Cummings (2007, p. 18) have proposed moving it to the genus Amphinaias,
but other freshwater mussel taxonomists recommend waiting for
additional work to be completed on members of Quadrula before splitting
the genus (Bogan 2011, pers. comm.). The smooth pimpleback is
recognized by the Committee on Scientific and Vernacular Names of
Mollusks of the Council of Systematic Malacologists, American
Malacological Union (Turgeon et al. 1998, p 37), and we recognize it as
a valid species.
Biology and Life History
There is no specific information on age, size of maturity, or host
fish use for smooth pimpleback. Numerous individuals were examined for
gravidity between June and November, with no evidence of eggs or
glochidia (Howells 2000b, p. 38). Other species in the genus Quadrula
successfully parasitize catfish, and it is likely smooth pimpleback
does as well (Howells 2010b, p. 2); additionally, mussels in the genus
Quadrula are typically short-term brooders (Gorden and Layzer 1989, p.
6; Garner et al. 1999, p. 277), and we expect the same of the smooth
pimpleback.
Habitat
The smooth pimpleback has been found in mud, sand, and fine gravel
in medium-to-large rivers and some reservoirs (Howells 2010b, p. 3).
Unlike most other Quadrula species in central Texas, smooth pimpleback
do occur in some reservoirs (Howells 2002b, p. 8; 2010b, p. 3).
Distribution and Abundance
Historical Distribution
The smooth pimpleback is native to the central and lower Brazos and
Colorado Rivers and their tributaries in central Texas (Howells 2010b,
p. 4). The smooth pimpleback has also been reported from the Trinity
River and other drainages in Texas, as well as from areas outside of
Texas, including southern Arkansas and the Verdigris River in Kansas.
These reports are likely misidentifications of other pimpleback species
that can sometimes closely resemble smooth pimpleback (Howells 2010b,
pp. 4-5). The smooth pimpleback was historically uncommon where it
occurred; from the 1960s through the 1990s, experts failed to find
large populations persisting throughout its range (Howells 2009, p.
12).
In the Colorado River, historical reports indicate that the smooth
pimpleback occurred from San Saba County downstream to Wharton County,
as well as in the Llano River and Onion and Skull Creeks. Within the
Brazos River basin, the species historically occurred throughout the
length of the mainstem of the Brazos River (Howells 2009, p. 12), as
well as in the Clear Fork Brazos, Leon, Navasota, Little Brazos, San
Gabriel, Lampasas, and Little Rivers and Yegua Creek (Howells 2010b,
pp. 4-6; Randklev et al. 2010b, p. 20).
Current Distribution
The smooth pimpleback has been nearly extirpated from the Colorado
River basin, and a few small populations persist in the Brazos River
basin. Recent surveys suggest a greater abundance and distribution of
the smooth pimpleback in the central Brazos River drainage than was
indicated by collections from the past 40 years, with five populations
represented by more than a few individuals.
Colorado River System
The smooth pimpleback historically occurred throughout the mainstem
Colorado River as well as several tributaries, but it is currently
restricted to one mainstem reservoir, two sites on the mainstem
Colorado River, and the San Saba River. Populations in all of the other
historically occupied tributaries and two reservoirs appear to have
been extirpated.
In the mainstem Colorado River, smooth pimpleback were historically
known from much of the length of the river (Howells 1996, p. 21; 1997a,
pp. 34-35; Randklev et al. 2010c, p. 4; OSUM 2011c, p. 1). Numerous
surveys in many locations on the Colorado River occurred between 1993
and 2009, and no evidence of smooth pimpleback was found (Howells 1995,
p. 29; 1996, p. 23; 1997a, pp. 27, 31; 2002a, p. 6; 2004, p. 7, 11;
2005, p. 6; Burlakova and Karatayev 2010a, pp. 15-16), except for in
Colorado County in 1999, when three live smooth pimpleback were found
(Howells 2000a, p. 27). During two surveys in 2009, live smooth
pimpleback were found in the same general area as in 1999 (Burlakova
and Karatayev 2010a, p. 16; Johnson 2009, p. 1). Farther downstream, in
Wharton County, live smooth pimpleback were found at two sites in 2009
(Burlakova and Karatayev 2010a, p. 16), despite having been surveyed in
1995 and none found (Howells 1996, p. 23).
Inks Lake is a small mainstem reservoir on the Colorado River in
Burnet County. Several live smooth pimpleback were found in 1992
(Howells 1994, p. 4); however, since that time only shell material has
been found during four separate surveys between 1996 and 2005 (Howells
1997a, pp. 32-33; 1999, p. 16; 2005, p. 8; 2006, p. 67). Frequent
drawdowns in this lake appear to have affected all species of
freshwater mussels, as there has been a sharp decline in the overall
mussel community (Howells 1999, p. 16).
One live smooth pimpleback was found in Lake Lyndon B. Johnson, a
large mainstem reservoir on the Colorado River, in 2001, but no live
individuals have been found since (Howells 2002a, pp. 6-7; 2006, pp.
68-69). Farther downstream, in Lake Marble Falls, 13 live smooth
pimpleback were found in 1995 during a drawdown of lake levels (Howells
1996, p. 22), but subsequent surveys in 1996 failed to find any
additional living animals (Howells 1997a, p. 33). The small recent
survey effort is not sufficient to conclude that the smooth pimpleback
no longer occur in these lakes, and small populations may still persist
there.
Smooth pimpleback were recently found in the San Saba River in San
Saba County, when 29 individuals were found at two locations (Burlakova
and Karatayev 2011, p. 5). Various size and age classes were
represented, indicating a reproducing, recruiting population (Burlakova
and Karatayev 2011, p. 5). Even more recently, 206 smooth pimpleback,
including adults and juveniles, were recorded in this same area in
riffle and pool habitat (Randklev 2011b, p. 1).
No smooth pimpleback populations remain in any of the Colorado
River tributaries in which the species was historically known to occur,
including the full length of the Llano River (Howells 1996, pp. 21-22;
1998, p. 17; 2000a, p. 25; 2005, p. 8; Randklev et al. 2010c, p. 4;
OSUM 2011c, p. 1). A single subfossil shell, likely a smooth
pimpleback, was found in the Llano River in Kimble County in 1995
(Howells 1996, pp. 21-22), but no other evidence of the species has
been found in the Llano River in recent years. Additionally, although
Onion and Skull Creeks were historically occupied by smooth pimpleback
(Randklev et al. 2010c, p. 4), the species has not been found recently
in either stream (Howells 1995, pp. 28-29).
[[Page 62173]]
Brazos River System
The smooth pimpleback historically occurred in the Brazos River
system from Palo Pinto County downstream to Austin and Waller Counties,
as well as in numerous tributaries. The species has been extirpated
from the upstream half of the mainstem Brazos River and from at least
three tributaries. Substantial populations persist in the Leon River,
Navasota River, and Yegua Creek, and small populations remain in the
lower Brazos and Little Brazos Rivers.
In the mainstem Brazos River, surveys in Palo Pinto, Somervell, and
Bosque Counties between 1996 and 2000 indicate that the smooth
pimpleback has been extirpated from the upstream portion of the river
(Howells 1997a, pp. 16, 18-19; 1999, pp. 11-12; 2001, p. 19). Despite
surveys in 1996 and 1998 in which no individuals were found (Howells
1997a, p. 21; 1999, p. 12), a single live smooth pimpleback was found
in McLennan County in the middle Brazos River in 2005 (Howells 2010b,
p. 5), and two live individuals were recorded in Falls County in 2006
(Karatayev and Burlakova 2008, pp. 6-10).
Although not extirpated from the middle Brazos River, the smooth
pimpleback occurs only in low numbers. In Milam and Robertson Counties,
no smooth pimpleback were found in 1998 (Howells 1999, p. 13), but
eight live individuals were found in 2006 (Burlakova and Karatayev
2010b, p. 1). More recently, in 2008, 13 live smooth pimpleback were
found at the same site (Randklev et al. 2009, p. 18). Additionally,
downstream in Burleson and Brazos Counties, which were historically
occupied by the smooth pimpleback (OSUM 2011c, p. 1), a small
population persists. In 1995, one live and one recently dead individual
were collected within Brazos County (Howells 1996, pp. 17-18). Although
none were found here in 1999 (Howells 2000a, pp. 21-22), in 2006 a
single live smooth pimpleback was collected at this site (Karatayev and
Burlakova 2008, pp. 6-10). Additionally, further downstream in Grimes
and Waller Counties, a single live individual was found in 2006
(Burlakova and Karatayev 2010b, p. 1) and again in 2008 (Randklev et
al. 2009, p. 18). Smooth pimpleback are more numerous in the lower
mainstem Brazos River, in Austin and Waller Counties, where 38 live
individuals were found in 2006 (Karatayev and Burlakova 2008, pp. 6-
10).
Tributaries to the Brazos River also contain smooth pimpleback
populations. The Leon River, in the Little River drainage of the
Brazos, historically contained smooth pimpleback throughout its length
in Hamilton, Coryell, and Bell Counties (Howells 1994, p. 19, 1997a, p.
20; Randklev et al. 2010c, p. 4; OSUM 2011c, p. 1). Currently, a smooth
pimpleback population persists in Hamilton County, where numerous live
individuals were found in 2006 and 2011 (Howells 2006, pp. 82-83;
Randklev 2011a, p. 1), as well as several locations in Coryell County,
where numerous individuals were also recently found (Randklev 2011a, p.
1).
Only subfossil smooth pimpleback shells have been found in the
Lampasas River in Bell County in 1996 (Howells 1997a, pp. 20, 23).
Subsequent surveys of the river in both Bell and Lampasas Counties
yielded no evidence of smooth pimpleback (Howells 1999, p.14; 2001, p.
20), and the species has likely been extirpated from the Lampasas
River.
The Little River in Milam County is also a historical location for
the smooth pimpleback (Randklev et al. 2010c, p. 4). Old shells were
found at this site in 1996 (Howells 1997a, p. 22), and a single live
individual was found here in 2006 (Karatayev and Burlakova 2008, p. 6).
Farther downstream, at the confluence with the Brazos River, none have
been found (Howells 1996, p. 17).
A single old smooth pimpleback shell has been found in the San
Gabriel River in Milam County (Howells 1997a, p. 23), and it is likely
the species has been extirpated from this Brazos River tributary as
well.
In the Little Brazos River, the smooth pimpleback appears to
persist in low numbers. Although none were found in Robertson County in
1993 and there had appeared to be a die off of numerous freshwater
mussel species (Howells 1995, p. 18), one live smooth pimpleback was
found during a 2006 survey (Karatayev and Burlakova 2008, p. 6).
Farther downstream in Brazos County, recently dead individuals were
discovered in 2001 (Howells 2002a, pp. 4-5). The species occurred in
this area historically (Randklev et al. 2010c, p. 4), and reports of
mussels in the Little Brazos River from the 1950s described the
freshwater mussel community as numerous, including smooth pimpleback
(Gentner and Hopkins 1966, pp. 458-459), but no live individuals have
been collected in this area in recent years (Howells 1996, p. 18; 1999,
p. 14).
The smooth pimpleback has been extirpated from the Clear Fork
Brazos River. Although this species was originally documented from this
river in Shackelford County in 1893 (Randklev et al. 2010c, p. 4), none
have been found in this stream since (Howells 1999, p. 19).
In the Navasota River, smooth pimpleback historically occurred in
Leon, Brazos, Grimes, and Washington Counties (Randklev et al. 2010c,
p. 4; OSUM 2011c, p. 1). Currently, the species persists in each of
those counties, with a large population occurring in the lower river.
In Leon County three recently dead smooth pimpleback shells were found
in 2000 (Howells 2001, p. 23), indicating that a few individuals may
persist in the area. However, one of the largest known populations
occurs farther downstream near the confluence of the Navasota and
Brazos Rivers. Nine live individuals were found in this area in 2006
(Karatayev and Burlakova 2008, pp. 6-10), and in 2008 a total of 117
live smooth pimpleback were recorded at 3 different locations within
Washington and Grimes Counties (Randklev et al. 2009, pp. 6, 18). A
large population continues to persist in the Navasota River, with a
total of 314 smooth pimpleback recorded at two sites in 2011 (Randklev
2011a, p. 1).
In Yegua Creek, no smooth pimpleback were found during several
surveys between 1996 and 2003 (Howells 1997a, pp. 24-26; 2001, p. 22;
2004, p. 6), although subfossil shells were found in Washington County
in 1996. However, in 2006, a live individual was discovered (Karatayev
and Burlakova 2008, pp. 6-10), which prompted further surveys in 2008.
Numerous smooth pimpleback were found during subsequent surveys at four
different locations within Washington and Burleson Counties (Randklev
et al. 2009, pp. 16-18; Randklev 2011a, p. 1), indicating the presence
of a potentially large population in this stream.
Summary
Based on historical and current data, the smooth pimpleback has
declined rangewide and is now known from only nine locations. The
species has been eliminated from nearly the entire Colorado River and
all but one of its tributaries, as well as from the upper Brazos River
and several tributaries. The San Saba River, lower Brazos River,
Navasota River, Leon River, and Yegua Creek populations appear to be
stable and reproducing, but the remaining populations are small,
isolated, and represented by only a few individuals.
Species Information for Texas Pimpleback
Species Description
The Texas pimpleback is a large pimpleback species with a
moderately
[[Page 62174]]
inflated shell that generally reaches 60-90 mm (2.4-3.5 in) (Howells
2002b, pp. 3-4). With the exception of growth lines, the shell of the
Texas pimpleback is generally smooth and moderately thick (Howells
2002b, p. 4). Externally, coloration ranges from yellowish-tan to dark
brown with some individuals mottled or with dark green rays.
Internally, the nacre is white and iridescent posteriorly (Howells
2002b, p. 4).
Taxonomy
The Texas pimpleback was originally described as Unio petrinus by
Gould in 1855. It was placed in the genus Margaron by Lea in 1870 and
ultimately moved to Quadrula by Simpson in 1900 (Simpson 1900, p. 783).
Graf and Cummings (2007, p. 18) have proposed moving it to the genus
Amphinaias, but other freshwater mussel taxonomists recommend waiting
for additional work to be completed on members of Quadrula before
splitting the genus (Bogan 2011, pers. comm.). The Texas pimpleback is
recognized by the Committee on Scientific and Vernacular Names of
Mollusks of the Council of Systematic Malacologists, American
Malacological Union (Turgeon et al. 1998, p. 37), and we recognize it
as a valid species.
Biology and Life History
There is very little specific information on age, size of maturity,
or host fish use for Texas pimpleback. Gravid females have been found
from June through August, and the smallest documented gravid female was
45 mm (1.8 in) long (Howells 2000b, p. 38). Glochidia are hookless and
elliptical in shape (Howells et al. 1996, p. 120). To date, no host
fish have been confirmed for the Texas pimpleback; however, glochidia
have been reported attached to and encysted on flathead catfish
(Pylodictis olivaris), yellow bullhead (Ameiurus natalis), and bluegill
in laboratory settings, although none transformed to the juvenile stage
(Howells 2010e, p. 3). This is consistent with other species in the
genus Quadrula, which also parasitize catfish species.
Habitat
The Texas pimpleback typically occurs in moderately sized rivers,
usually in mud, sand, gravel, and cobble, and occasionally in gravel-
filled cracks in bedrock slab bottoms (Horne and McIntosh 1979, p. 122;
Howells 2002b, p. 4). The species has not been found in water depths
over 2 m (6.6 ft). Texas pimpleback have not been found in reservoirs,
which indicates that this species is intolerant of deep, low-velocity
waters created by artificial impoundments (Howells 2002b, p. 4). In
fact, Texas pimpleback appear to tolerate faster water more than many
other mussel species (Horne and McIntosh 1979, p. 123).
Distribution and Abundance
Historical Distribution
The Texas pimpleback is endemic to the Colorado and Guadalupe-San
Antonio River basins of central Texas (Howells 2002b, p. 3). In the
Colorado River basin, Texas pimpleback occurred throughout nearly the
entire mainstem, as well as numerous tributaries, including the Concho,
North Concho, San Saba, Llano, and Pedernales Rivers, and Elm and Onion
Creeks (Howells 2010e, p. 5; Randklev et al. 2010c, p. 4; OSUM 2011d,
p. 1). Within the Guadalupe-San Antonio River basin, it occurred
throughout most of the length of the Guadalupe River, as well as in the
San Antonio, San Marcos, Blanco, and Medina Rivers (Horne and McIntosh
1979, p. 122; Howells 2010e, p. 5; OSUM 2011d, p. 1).
Current Distribution
The Texas pimpleback has declined significantly rangewide, and only
four streams--the San Saba River, Concho River, Guadalupe River, and
San Marcos River--are known to harbor persisting Texas pimpleback
populations. These populations are disjunct, small, and isolated. The
species has been extirpated from the remainder of its historical range.
Colorado River System
In the Colorado River system, Texas pimpleback once occurred
throughout the mainstem and in many major tributaries. Currently, the
species has been extirpated from the Pedernales, North Concho, and
Llano Rivers, as well as Onion Creek. It has also likely been
extirpated from the mainstem Colorado River and Elm Creek. The Concho
River contains the most abundant population of Texas pimpleback and one
of only two populations of the species likely to be remaining in the
Colorado River system, but most individuals are old and there has been
very little evidence of recruitment.
In the mainstem Colorado River, Texas pimpleback historically
occurred from Runnels County downstream to Colorado County (Howells
2010e, p. 5; Randklev et al. 2010c, pp. 3-4; OSUM 2011d, p. 1).
However, surveys in numerous locations along the river yielded no
evidence of the species anywhere except in Runnels and San Saba
Counties (Howells 1995, pp. 20, 29; 1997a, pp. 27, 31, 35; 2000a, p.
27; 2002a, p. 7). In Runnels County, Texas pimpleback shells were found
in 1993 (Howells 1995, p. 20), but several subsequent surveys between
1996 and 2008 detected no further evidence of the species (Howells
1997a, p. 27; 1998, p. 10; 2002a, p. 7; 2004, p. 7; Burlakova and
Karatayev 2010a, p. 10). In San Saba County, a single shell was
collected in 1989 (Howells 2002b, p. 6), and three recently dead
individuals were found in 1999 (Howells 2000a, pp. 25-26). An
additional shell was collected in 2001 (Howells 2002a, p. 6). No live
individuals have been collected from this reach of the Colorado River.
In Runnels County, Elm Creek once supported a Texas pimpleback
population. Small numbers of Texas pimpleback were found in 1993 and
1995 (Howells 1995, p. 21; 1996, p. 20), but none were found in 1997,
2001, or 2003 (Howells 1998, p. 11; 2002a, p. 5; 2004, p. 7). In 2005
and 2008, only dead individuals were collected (Howells 2006, pp. 63-
64; Burlakova and Karatayev 2010a, p. 10). No live individuals have
been found in over a decade despite repeated sampling efforts, and it
is likely the Texas pimpleback has been extirpated from this stream.
The Concho River in Concho County supports the largest Texas
pimpleback population. Thirteen and 28 individuals were collected in
1993 and 1994, respectively (Howells 1995, pp. 24-25; 2006, p. 61).
However, low water and high temperatures in 1997 killed large numbers
of many freshwater mussel species in the area up and downstream of
Paint Rock, and 63 recently dead Texas pimpleback were found (Howells
1998, pp. 14-15). A severe drought in 1999 resulted in this area of the
Concho River being reduced to a series of small pools. Few live Texas
pimpleback were collected during this drought, in addition to many
recently dead individuals (Howells 2000a, p. 23). No evidence of the
species was found in 2004 (Howells 2005, p. 9), but eight live
individuals were found in 2005 (Howells 2006, p. 60), evidence that the
species had survived the extreme dewatering of the river. In 2008, 61
live Texas pimpleback were collected in this same area, and the
population was estimated to contain approximately 4,000 individuals
(Burlakova and Karatayev 2010a, p. 10; 2010b, p. 1). However, the
average length of individuals collected at this site was over 90 mm
(3.5 in), indicating that reproduction is limited in this population.
Further, although no mussel surveys occurred in 2009 and 2010, the
[[Page 62175]]
river was reported to be extremely low during this time (Howells 2010e,
p. 6); the result of this additional dewatering on the population is
unknown.
The San Saba River historically contained Texas pimpleback
(Randklev et al. 2010c, p. 2), but no live individuals had been
collected in over a decade until recently when shells were collected in
1992 and 1995 (Howells 1994, p. 7; 1996, p. 21), and five live
individuals were collected in 1997 (Howells 1998, p. 16). However,
subsequent surveys were conducted in 2000, 2004, and 2005, with only
shell material being found in 2000 (Howells 2001, pp. 28-29), and no
evidence of Texas pimpleback was found in 2004 and 2005 (Howells 2005,
pp. 8-9; 2006, pp. 64-65). A single shell was collected in 2008
(Burlakova and Karatayev 2010b, p. 1). However, in 2011, 39 live
individuals were found at two sites in San Saba County (Burlakova and
Karatayev 2011, p. 3). The individuals found were of various sizes and
ages, indicating a reproducing population (Burlakova and Karatayev
2011, p. 4). Further surveys at this site confirm a large population in
the area, with 140 individuals, including many juveniles, found here
(Randklev 2011b, p. 1).
The Texas pimpleback also historically occurred in the North
Concho, Pedernales, and Llano Rivers, as well as Onion Creek (Howells
2010e, p.5; Randklev et al. 2010c, p. 4; OSUM 2011d, p. 1); all are
tributaries within the Colorado River system. In the North Concho
River, all freshwater mussels are presumed extirpated from historically
occupied areas (Howells 1995, pp. 22-23). The Pedernales River
historically harbored a Texas pimpleback population (OSUM 2011d, p. 1),
but only old shells have been collected in this river in recent years
(Howells 1994, p. 5). Since 1993, no evidence of Texas pimpleback has
been found (Howells 1995, pp. 27-28; 1999, p. 16), and the species is
presumed to be extirpated. Additionally, repeated surveys in the Llano
River in Kimble and Mason Counties consistently failed to collect live
Texas pimpleback, with shells found only in Llano County in 1997
(Howells 1996, pp. 21-22; 1998, p. 17; 2005, p. 8). The Texas
pimpleback is likely extirpated from all of these streams.
Guadalupe River System
In the Guadalupe River system, the Texas pimpleback has been
extirpated from nearly the entire reach of the mainstem Guadalupe, San
Antonio, and Blanco Rivers. Very small populations remain only in the
lower Guadalupe and San Marcos Rivers, represented by one or two
individuals in each.
In the mainstem Guadalupe River, the Texas pimpleback was
historically known throughout the length of the river, from as long ago
as 1905 (Randklev et al. 2010c, p. 1; OSUM 2011d, p. 1). Numerous
surveys between 1992 and 2005 have not yielded any evidence of the
species anywhere but in Victoria County (Howells 1994, pp. 7-9; 1995,
pp. 30-32; 1996, pp. 25-27; 1997a, pp. 37-40; 1999, pp. 18-19; 2002a,
p. 8; 2003, pp. 15, 17; 2006, pp. 71-72; Johnson 2009, p. 1), where two
live individuals were collected in 2009. A small population may remain
in the lower Guadalupe River.
In the San Marcos River near the confluence with the Blanco River
in Hays County, repeated surveys between 1992 and 2000 yielded no
evidence of Texas pimpleback (Howells 1994, pp. 9-10; 1995, pp. 33-34;
1996, p. 27; 1997a, p. 40; 2000a, p. 28; 2001, pp. 32-33). However, in
2003 two shells were collected (Howells 2004, p. 16), and in 2004, a
single live individual was found (Howells 2005, p. 10). The Texas
pimpleback likely persists in this river in very low numbers.
The Texas pimpleback appears to be extirpated from the San Antonio
River, with only shell fragments found near the City of San Antonio in
Bexar County in 1993 (Howells 1995, p. 35). No evidence of the species
was found downstream in Karnes County in 1996 (Howells 1997a, pp. 41-
42).
The Texas pimpleback was once described as abundant in the Blanco
River just upstream of its confluence with the San Marcos River in Hays
County (Horne and Mcintosh 1979, p. 126), but repeated surveys of this
area between 1992 and 1995 yielded no recent evidence of the species
(Howells 1994, p. 9; 1995, pp. 32-33; 1996, p. 27), with only a
subfossil shell collected in 1993 (Howells 1995, p. 33). No shell
material or live individuals were found in additional surveys in 2011
(Johnson 2011, p. 1).
Summary
The Texas pimpleback has been eliminated from long reaches of
former habitat in hundreds of miles of the Colorado and Guadalupe River
systems. Only two populations appear large enough to be stable, but
evidence of recruitment in the Concho River population is limited. The
San Saba River population may be the only remaining recruiting
population of Texas pimpleback. Two additional populations are
represented by one or two individuals; all populations are highly
disjunct.
Species Information for Texas Fawnsfoot
Species Description
The Texas fawnsfoot is a small, relatively thin-shelled freshwater
mussel that can reach 60 mm (2.4 in) in length but is usually much
smaller (Howells 2010d, p. 2). The shell is long and oval, generally
free of external sculpturing, with external coloration that varies from
yellowish- or orangish-tan, brown, reddish-brown, to smoky-green with a
pattern of broken rays or irregular blotches (Howells 2010d, p. 2). The
nacre is bluish-white or white and iridescent posteriorly (Howells
2010d, p. 2).
Taxonomy
The Texas fawnsfoot was first described as Unio macrodon by Lea in
1859 and was subsequently placed in the genus Margaron by Lea in 1870
and then moved to Plagiola by Simpson (1900, p. 605). Ultimately the
species was placed in the genus Truncilla by Strecker (1931, pp. 63,
65). The Texas fawnsfoot is recognized by the Committee on Scientific
and Vernacular Names of Mollusks of the Council of Systematic
Malacologists, American Malacological Union (Turgeon et al. 1998, p.
37), and we recognize it as a valid species.
Biology and Life History
There is no specific information on age, size of maturity, or host
fish use for Texas fawnsfoot. However, other species in the genus
Truncilla parasitize freshwater drum (Aplodinotus grunniens) (OSUM
2011f, p. 1), and it is likely the Texas fawnsfoot does as well.
Freshwater drum are ubiquitous throughout the range of Texas fawnsfoot
(Hubbs et al. 2008, p. 53).
Habitat
Since Texas fawnsfoot were not found alive for many years, very
little information is available about its habitat preferences. In the
past only Texas fawnsfoot shells and recently dead individuals were
occasionally found along rivers following drought-related dewatering or
bank deposition after high floods. These shells and recently dead
individuals indicated that the Texas fawnsfoot occurs in flowing water,
as it was never found in ponds, lakes, or reservoirs, suggesting that
it is intolerant of deep, low-velocity waters created by artificial
impoundments (Howells 2010d, p. 3). The recently discovered live
population in the Brazos River indicates that the species occurs in
rivers with soft, sandy sediment with moderate water flow (Randklev and
[[Page 62176]]
Lundeen 2010, p. 1; Randklev et al. 2010a, p. 298; Johnson 2011, p. 1).
Distribution and Abundance
Historical Distribution
The Texas fawnsfoot is endemic to the Brazos and Colorado Rivers of
central Texas (Howells et al. 1996, p. 143; Randklev et al. 2010a, p.
297). From the 1960s to the 1990s, malacologists working in central
Texas found few individuals and few new population locations (Howells
2010d, p. 6). Historical records suggest the Texas fawnsfoot inhabited
much of the Colorado River, from Wharton County upstream as far as the
North Fork Concho River in Sterling County, as well as throughout the
Concho, San Saba, and Llano Rivers and Onion Creek within the Colorado
River basin (Howells 2010d, p. 4; Randklev et al. 2010b, p. 24). In the
Brazos River, the species occurred from Fort Bend County upstream to
the lower reaches of the Clear Fork Brazos River in Shackelford County,
as well as in the Leon River, Little River, San Gabriel River, Deer
Creek, and Yegua Creek (Howells 2010d, pp. 4-5; Randklev et al. 2010b,
p. 24). Species reports from the Trinity River and other east Texas
locations are of misidentified fawnsfoot (Truncilla donaciformis)
(Howells 2010d, p. 4).
Current Distribution
Relatively few Texas fawnsfoot have been documented since this
species was first described in 1859, and very few live individuals have
been found in recent decades (Randklev et al. 2010a, p. 297). All of
these animals were flood deposited on gravel bars and near death just
prior to collection (Randklev et al. 2010a, p. 297), preventing
information from being gathered about population size, preferred
habitat, and other parameters. A live population of Texas fawnsfoot was
not discovered until 2008 in the Brazos River near its confluence with
the Navasota River (Randklev et al. 2010a, p. 297). A second live
population was found in 2009 in the Colorado River (Johnson 2009, p.
1). These two locations contain the only confirmed populations of the
species to date. Evidence of other remnant populations has also been
found in the Clear Fork Brazos River, San Saba River, and Deer Creek.
Colorado River System
The Texas fawnsfoot has been eliminated from almost all of the
Colorado River system. Live individuals were found in the lower
mainstem Colorado River in 2009, and the only other evidence of current
occurrence of Texas fawnsfoot in the Colorado River basin is in the San
Saba River, where a population persists.
In the mainstem Colorado River, the Texas fawnsfoot historically
occurred from Wharton County upstream into the headwaters (Randklev et
al. 2010c, p. 4; OSUM 2011e, p. 1). Surveys throughout the upper
Colorado River between 1993 and 2009 yielded no evidence of Texas
fawnsfoot (Howells 1994, pp. 20-21, 29; 1996, pp. 20-21, 23; 1997a, pp.
27, 31, 34-35; 1998, p. 10; 2000a, p. 27; 2002a, p. 6; 2004, p. 7;
Burlakova and Karatayev 2010a, p. 16), except for one recently dead
individual found in 1999 in San Saba County when the entire river was
dewatered and all mussels were eliminated from the area (Howells 2000a,
pp. 25-26; 2009, p. 17). The lack of evidence of the species since that
time indicates that the population may have been lost. In the lower
Colorado River in Colorado County, several old shells of Texas
fawnsfoot were found at several sites in 1996 (Howells 1997a, p. 35),
and, subsequently in 2009, two live individuals were discovered
(Johnson 2011, p. 1). The population was later estimated to be
approximately 2,800 individuals, with individuals ranging in size from
21 to 38 mm (0.8-1.5 in) (Burlakova and Karatayev 2010a, p. 17),
indicating that reproduction and recruitment is occurring.
Texas fawnsfoot were not known to occur in the San Saba River until
a single live individual was collected in 2011 (Burlakova and Karatayev
2011, p. 6). Additional surveys yielded 16 Texas fawnsfoot of various
ages collected at the site (Randklev 2011b, p. 1), indicating a
persistent, recruiting population.
Texas fawnsfoot is presumed extirpated from the remainder of the
Colorado River basin. Although historical records exist in the North
Concho, Concho, and Llano Rivers and in Onion Creek (Randklev et al.
2010c, p. 4), numerous surveys of these streams indicate the
extirpation of the species (Howells 1994, pp. 5-6; 1995, pp. 22-25, 28-
29; 1996, pp. 21-22; 1998, pp. 14-17; 1999, pp. 15-16; 2000a, pp. 23,
25; 2001, p. 27; 2005, p. 9; Burlakova and Karatayev 2011, p. 6).
Brazos River System
In the Brazos River system, the Texas fawnsfoot persists in the
mainstem Brazos River, Clear Fork Brazos River, Navasota River, and
possibly in Deer Creek. The species has been extirpated from the Leon
River, Little River, San Gabriel River, and Yegua Creek.
In the mainstem Brazos River, the Texas fawnsfoot historically
occurred throughout the length of the river, from Palo Pinto County
downstream to Fort Bend County (Randklev et al. 2010c, pp. 2-4;
Burlakova and Karatayev 2010b, p. 1; OSUM 2011e, p. 1). While the
species appears to have retained its range through the length of the
Brazos River, occurrences are represented by very few live or recently
dead individuals. In the upper Brazos River in Palo Pinto and Parker
Counties, two live individuals were found at each of two sites in 1996,
as well as numerous shells (Howells 1997a, pp. 16, 17). A survey in
2000 yielded no evidence of Texas fawnsfoot in this area (Howells 2001,
p. 19). Nearby, in Somervell County, four recently dead individuals
were found in the mainstem Brazos River in 1996 (Howells 1997a, pp. 18-
19. In 2007, only one old shell was found in the same area (Burlakova
and Karatayev 2010b, p. 1).
Surveys in Milam and Falls Counties have not yielded any evidence
of Texas fawnsfoot, indicating the species has been extirpated from
this section of the Brazos River (Howells 1995, p. 17; 1999, pp. 12-
13).
In the middle Brazos River, Texas fawnsfoot persists in low numbers
in the vicinity of Brazos County. One live individual was found in 1994
(Howells 1996, pp. 17-18), representing the first live collection of
the species anywhere since the 1970s. In 1999, numerous recently dead
Texas fawnsfoot of mixed sizes and ages were found at several sites in
Burleson and Brazos Counties (Howells 2000a, pp. 21-22), indicating a
recruiting population existed in the area. The species has been
documented here in repeated surveys in 2000, 2003, and 2006 (Howells
2001, p. 22; Karatayev and Burlakova 2008, p. 7; Howells 2009, p. 17),
indicating that the species continues to persist in the area.
The first account of a living population of Texas fawnsfoot
(animals living in situ rather than deposited on or near the banks by
floods) occurred in 2008 in the lower Brazos River near its confluence
with the Navasota River (Randklev et al. 2010a, p. 297). Ten live
individuals were collected, and all were small, indicating successful
reproduction and recent recruitment. An additional Texas fawnsfoot was
found in this area in 2011 (Randklev 2011a, p. 1).
The farthest downstream collection of Texas fawnsfoot in the Brazos
River in recent years was in Austin and Waller Counties, when one live
individual was found in 2006 (Karatayev and Burlakova 2008, p. 39). It
is likely the species occurs sporadically through the section of the
Brazos River between Brazos and Austin Counties.
[[Page 62177]]
Texas fawnsfoot was first discovered in the Navasota River in 2011,
when three individuals were found in Washington and Grimes Counties
(Randklev 2011a, p. 1). Previous surveys had not yielded evidence of
the species in this river (Howells 2001, p. 23).
In Deer Creek, a tributary to the Brazos River in Falls County, a
recently dead Texas fawnsfoot was collected in 2006 (Burlakova and
Karatayev 2010b, p.1), despite previous surveys that yielded no
evidence of the species (Howells 1999, p. 12).
Additionally, a Texas fawnsfoot population persists in the Clear
Fork Brazos River. Recently dead Texas fawnsfoot have been collected in
several locations along the length of the river, in Shackelford,
Stephens, and Young Counties (Randklev et al. 2010c, p. 4; Randklev
2011, pers. comm.). Several other tributaries to the Brazos River that
historically contained Texas fawnsfoot appear to no longer support the
species after numerous surveys reveal no living or dead individuals,
including the Leon River (Howells 1994, pp. 18-20; 1997a, pp. 19-20),
the Little River (Howells 1997a, pp. 22-23), the San Gabriel River
(Howells 1997a, p. 23), and Yegua Creek (Howells 1997a, pp. 24, 25-26;
1999, p. 14; 2001, p. 22; 2004, p. 6).
Summary
The Texas fawnsfoot has declined rangewide and is now known from
only five populations. The species has been extirpated from nearly all
of the Colorado River basin and from much of the Brazos River basin. Of
the populations that remain, only the Colorado, San Saba, and Brazos
River populations are likely to be stable and recruiting; the remaining
populations are disjunct and restricted to short stream reaches.
Five-Factor Evaluation and Findings
Texas fatmucket, golden orb, smooth pimpleback, Texas pimpleback,
and Texas fawnsfoot all occur in central Texas across four major river
basins (Brazos, Colorado, Guadalupe, and Nueces-Frio River basins).
These species depend on similar physical and biological features and on
the successful functioning of riverine ecosystems to survive. Many of
the species face the same or very similar threats. For each species, we
identified and evaluated all the factors that may be threatening the
species. However, to avoid redundancy of information when the analysis
of the threats is the same between species, we referenced the reader to
the initial description of the common threats. For example, the
degradation of habitat and habitat loss due to dams and impoundments is
a common threat to all five species, so a full description of the
threat was provided for the Texas fatmucket, and for the remaining
species the initial description was referenced with species-specific
information provided, as available.
Five-Factor Evaluation for Texas Fatmucket
Information pertaining to the Texas fatmucket in relation to the
five factors provided in section 4(a)(1) of the Act is discussed below.
Factor A. The Present or Threatened Destruction, Modification, or
Curtailment of Its Habitat or Range.
The decline of mussels in Texas and across the United States is
primarily the result of habitat loss and degradation (Neves 1991, pp.
252, 265; Howells et al. 1996, pp. 21-22). Chief among the causes of
mussel decline in Texas are the effects of impoundments, sedimentation,
dewatering, sand and gravel mining, and chemical contaminants (Neck
1982a, pp. 33-35; Howells et al. 1996, pp. 21-22; Winemiller et al. pp.
17-18). These threats are discussed below.
Impoundments
A major factor in the decline of freshwater mussels across the
United States has been the large-scale impoundment of rivers (Vaughn
and Taylor 1999, p. 913). Dams are the source of numerous threats to
freshwater mussels: They block upstream and downstream movement of
species by blocking host fish movement; they eliminate or reduce river
flow within impounded areas, thereby trapping silts and causing
sediment deposition; and dams change downstream water flow timing and
temperature, decrease habitat heterogeneity, and affect normal flood
patterns (Layzer et al. 1993, pp. 68-69; Neves et al. 1997, pp. 63-64;
Watters 2000, pp. 261-264; Watters 1996, p. 80). Within reservoirs (the
impounded waters behind dams), the decline of freshwater mussels has
been attributed to sedimentation, decreased dissolved oxygen, and
alteration of resident fish populations (Neves et al. 1997, pp. 63-64;
Pringle et al. 2000, pp. 810-815; Watters 2000, pp. 261-264). Dams
significantly alter downstream water quality and stream habitats (Allan
and Flecker 1993, p. 36; Collier et al. 1996, pp. 1, 7) resulting in
negative effects to tailwater (the area downstream of a dam) mussel
populations (Layzer et al. 1993, p. 69; Neves et al. 1997, p. 63;
Watters 2000, pp. 265-266). Below dams, mussel declines are associated
with changes and fluctuation in flow regime, scouring and erosion of
stream channels, reduced dissolved oxygen levels and water
temperatures, and changes in resident fish assemblages (Williams et al.
1992, p. 7; Layzer et al. 1993, p. 69; Neves et al. 1997, pp. 63-64;
Pringle et al. 2000, pp. 810-815; Watters 2000, pp. 265-266). Numerous
dams have been constructed throughout the Colorado, Guadalupe, Brazos,
and Nueces-Frio River systems within the range of all five mussels
addressed in this finding (Stanley et al. 1990, p. 61).
Population losses due to the effects of dams and impoundments have
likely contributed more to the loss of diversity and abundance of
freshwater mussels across Texas, including the Texas fatmucket, than
any other factor. Stream habitat throughout nearly all of the range of
Texas fatmucket has been affected by numerous impoundments, leaving
generally short, isolated patches of remnant habitat between dams.
Impoundments have resulted in profound changes to the nature of the
rivers, primarily replacing free-flowing river systems with a series of
large reservoirs.
There are no natural lakes within the range of the Texas fatmucket,
nor has it ever been found in reservoirs. Surveys of the reservoirs on
the Guadalupe and Colorado Rivers have been ongoing since at least
1992, and no evidence of live or dead Texas fatmucket has been found in
any reservoir (Howells 1994, pp. 1-20; 1995, pp. 1-50; 1996, pp. 1-45;
1997a, pp. 1-58; 1998, pp. 1-30; 1999, pp. 1-34; 2000a, pp. 1-56; 2001,
pp. 1-50; 2002a, pp. 1-28; 2003, pp. 1-42; 2004, pp. 1-48; 2005, pp. 1-
23; 2006, pp. 1-106; Karatayev and Burlakova 2008, pp. 1-47; Burlakova
and Karatayev 2010a, pp. 1-30; 2011, pp. 1-8), further indicating this
species is not tolerant of impoundments.
Impoundments occur throughout the range of the Texas fatmucket. The
majority of the Nueces-Frio, Guadalupe, San Antonio, Colorado, and
Brazos Rivers, as well as many tributaries, are now impounded. There
are 31 major reservoirs within the Colorado River basin, with another
reservoir (Goldthwaite Reservoir) being considered on the Colorado
River in Mills and San Saba Counties; this reservoir was the number one
recommendation in the water plan for the region (Texas Water
Development Board (TWDB) 2011, p. 4-85). There are 29 reservoirs
throughout the Guadalupe River basin and 34 reservoirs throughout the
San Antonio River basin, each with a storage capacity of 3000 acre-feet
or more, and many smaller reservoirs (Exelon 2010, p. 2.3-4). The
majority of the large dams were
[[Page 62178]]
constructed for power generation, flood control, and water supply,
primarily by the Lower Colorado River and Guadalupe-Blanco River
Authorities, beginning in the early twentieth century (Guadalupe-Blanco
River Authority 2011, p. 1; Lower Colorado River Authority (LCRA)
2011a, p. 1). These, and numerous smaller dams, occur throughout the
Colorado and Guadalupe River basins and have resulted in ongoing
destruction and modification of Texas fatmucket habitat and the
curtailment of its range.
Dams threaten freshwater mussels in several ways. First, they can
prevent the movement of freshwater mussel host fish. The overall
distribution of mussels is a function of the dispersal of their hosts
(Watters 1996, p. 83). For example, Watters (1996, p. 80) found that
the distributions of the fragile papershell (Leptodea fragilis) and
pink heelsplitter (Potamilus alatus) in five midwestern rivers were
determined by the presence of low-head dams. These dams were non-
navigable (without locks), lacked fish ladders, and varied in height
from 1 to 17.7 m (3 ft to 58 ft), and the host fish could not disperse
through them. Although the distribution of mussels may depend on many
ecological factors, the evidence presented in Watters (1996, pp. 79-85)
illustrates that dams as small as 1 m (3 ft) high can limit the
distribution of mussels. There are many dams that occur throughout the
range of the Texas fatmucket that lack fish ladders and may be a
barrier to the movement of fish hosts and, therefore, the distribution
of mussels. Because the Texas fatmucket populations are all separated
by dams of various sizes that are not passable by fish, the mussel is
unable to disperse from its current occupied range through host fish
migration.
Dams also alter aquatic habitat within the resulting impoundments.
It is well documented that many mussel species that are adapted to
flowing water stream environments do poorly in the altered aquatic
conditions found within impoundments (Williams et al. 1992, p. 7;
Vaughn and Taylor 1999, p. 913). Once a dam is constructed, the
original river channel upstream remains intact but under much deeper
water with much lower velocities. As water velocity decreases, water
loses its ability to carry sediment; sediment falls to the substrate,
eventually smothering mussels that cannot adapt to soft substrates
(Watters 2000, p. 263). Over time, the original mussel species
composition of the stream channel may be eliminated or changed in favor
of silt-tolerant species (Watters 2000, p. 264). The mussel community
may be altered from one with many different species to a community
dominated by one to several very common species (Neck 1982b, p. 174).
Texas fatmucket does not occur in reservoirs, indicating it is not
tolerant of lentic conditions, and it is now extirpated from impounded
areas where it occurred prior to inundation. The inundation of stream
habitat by impoundments is a likely cause of the reduction in the
distribution of the Texas fatmucket. The presence of the impoundments
has caused the permanent loss of Texas fatmucket habitat throughout its
range.
The loss of seven freshwater mussel species native to Texas,
including Texas fatmucket and golden orb, due to impoundment
construction was documented on the Medina River (Neck 1989, p. 323).
The Medina River was impounded in 1913 by construction of Medina Dam,
and now only three different species of mussels, all of which are
tolerant of lentic habitats, occur in the impounded area. The bottom of
Medina Lake now consists of moderate and steep limestone slopes and
excessive silt deposits, whereas before it was most likely made up of a
combination of silt, sand, and gravel substrates. Most mussels native
to the Medina River were unable to adapt to the change in flowing water
and substrate conditions (Neck 1989, p. 323), including the Texas
fatmucket, which is no longer found in the river.
Mussels downstream of impoundments are often affected through
changes in fish host availability, water quality (particularly lower
water temperatures), habitat structure, and stream channel scouring
(Vaughn and Taylor 1999, p. 916). The release of cold water from the
hypolimnion (deeper and colder layer of water in reservoirs) can
decrease the occurrence of fish species adapted to warm water and
increase the occurrence of fish species adapted to colder water
(Edwards 1978, pp. 73-75). This changes the species composition of
suitable host fish and may prevent mussels from completing an essential
part of their reproductive cycle. This has been demonstrated by the
extirpation of mussel species from several rivers on the eastern
seaboard of the United States, which has been linked to the
disappearance of appropriate host fish; the reintroduction of the host
fish to rivers has enabled mussel species to recolonize areas (Kat and
Davis 1984, p. 174). In addition, because mussel reproduction is
temperature dependent (Watters and O'Dee 1999, pp. 455-456), it is
likely that individual mussels living in cold waters downstream of dam
releases may reproduce less frequently, if at all (Layzer et al. 1993,
p. 69). Low water temperatures can also significantly delay or prevent
metamorphosis (Watters and O'Dee 1999, pp. 454-455) and glochidial
release, which is often triggered by water temperature (Watters and
O'Dee 2000, p. 136).
Similar changes in water temperatures downstream of dams may be
responsible for the loss of some Texas fatmucket populations. For
example, Canyon Reservoir on the Guadalupe River in Comal County is a
deep impoundment built in 1964 that has hypolimnetic water releases.
Temperature monitoring stations throughout the Guadalupe River basin
show that maximum temperatures above Canyon Reservoir averaged 29.6
degrees Celsius ([deg]C) (85.3 degrees Fahrenheit ([deg]F)); the
maximum stream temperatures below the reservoir averaged only 19.7
[deg]C (67.5 [deg]F) (Edwards 1978, p. 72). After impoundment,
dissolved oxygen and water temperature dropped, with an accompanying
drop in mussel numbers and species diversity (Young et al. 1976, p.
216). According to historical museum records analyzed by Randklev et
al. (2010b, pp. 1-32), the Texas fatmucket once occurred in this area
of the Guadalupe River prior to the construction of Canyon Reservoir.
The Guadalupe River and Canyon Lake in Comal and Kendall Counties were
surveyed in 2009, and no live or recently dead Texas fatmucket were
found (Burlakova and Karatayev 2010a, pp. 12-13). We reasonably
conclude that the loss of the Texas fatmucket from this area was caused
by the changes to the aquatic habitat of the Guadalupe River from the
effects of Canyon Reservoir. Many of the dams throughout the range of
Texas fatmucket have hypolimnetic water releases, including Canyon
Reservoir on the Guadalupe River (Magnelia 2001, p. 1), and Inks Lake,
Lake LBJ (Schnoor and Fruh 1979, p. 506), and Lake Travis (Texas
Natural Resource Conservation Commission 2001, p. 4) on the Colorado
River, among others. We anticipate that changes in water temperatures
from water released by these and other reservoirs also alter mussel
habitats in streams, causing the elimination of mussel populations
downstream.
In addition to the temperature of water released from dams, highly
fluctuating, turbulent tailwaters devoid of sediment will scour the
riverbed downstream of dams, rendering the area without mussel habitat
(Layzer et al. 1993, p. 69). Depending on the use of the dam, water
levels may fluctuate on a regular interval (for hydroelectric purposes)
or at random (for flood
[[Page 62179]]
control) (Watters 2000, p. 265). On the Colorado River, Inks Lake, Lake
Marble Falls, Lake Buchanan, Lake Austin, Lake Travis, and Lady Bird
Lake are each used for one or both of these purposes. Mortality of
another rare mussel species in Texas, the Texas heelsplitter (Potamilus
amphichaenus) was attributed to scheduled dewatering of the Neches
River below B.A. Steinhagen Reservoir in east Texas (Neck and Howells
1994, p. 15).
Fluctuating water levels below dams also result in dramatic changes
in water velocity. Downstream of Lake Livingston on the Trinity River
in east Texas, for example, high-volume water discharges and abrupt
stoppages of flow resulted in a river bed composed of large rocks and
shifting sand (Neck and Howells 1994, p. 14); these kinds of habitat
changes would be inhospitable to Texas fatmucket below the dams within
its range. In some rivers this unstable zone may be extensive. For
example, on the Brazos River downstream of Possum Kingdom Reservoir in
Texas exhibited unstable substrate for 150 km (240 mi) below the dam
(Yeager 1993, p. 68).
In one study of the downstream effects of dams, Vaughn and Taylor
(1999, p. 915) found a strong, gradual, linear increase in mussel
species richness and abundance at sites on the Little River in Oklahoma
downstream from Pine Creek Reservoir. Their research revealed that
mussel species richness and total abundance did not begin to rebound
until 20 km (12 mi) downstream of the impoundment and did not peak
until 53 km (33 mi) downstream. They noted the most obvious difference
since reservoir construction has been the alteration of the flow and
temperature regimes, which gradually return to pre-impoundment levels
with downstream distance from the dam. These alterations appear to have
produced an extinction gradient of mussels that is most severe near the
dam (Vaughn and Taylor 1999, p. 915). We expect similar effects on the
Texas fatmucket and other Texas mussels downstream of dams.
In one area on the Guadalupe River in Kerr County, a Texas
fatmucket population once existed directly below a small dam (Howells
1997a, p. 36), indicating the effects of the dam construction and
closure were not immediately lethal. However, the population has been
presumed extirpated since 1998 (Howells 2006, p. 71), and it is likely
that fluctuating downstream flows from the dam contributed to the loss
of this population.
Dam construction also fragments the range of Texas fatmucket,
leaving remaining habitats and populations isolated by the structures
as well as by extensive areas of deep uninhabitable, impounded waters.
These isolated populations are unable to naturally recolonize suitable
habitat that may be impacted by temporary but devastating events, such
as severe drought, floods, or pollution. Dams impound river habitats
throughout almost the entire range of the species, and these
impoundments have left short and isolated patches of remnant habitat,
typically between impounded reaches.
In summary, the widespread construction of dams has affected the
Texas fatmucket throughout its range by significantly altering stream
habitat both upstream and downstream of the dams by changing fish
assemblages, water depths and velocities, water temperature, dissolved
oxygen, substrate, and stream channels. The effects of dams are ongoing
and continue to negatively impact the Texas fatmucket rangewide.
Because of this loss of habitat and its effects on the populations, we
find that the effects of impoundments are a threat to the Texas
fatmucket.
Sedimentation
Siltation and general sediment runoff is a pervasive problem in
streams and has been implicated in the decline of stream mussel
populations (Ellis 1936, pp. 39-40; Vannote and Minshall 1982, p. 4105;
Dennis 1984, p. ii; Brim Box and Mossa 1999, p. 99; Fraley and Ahlstedt
2000, pp. 193-194). Specific biological effects on mussels from
excessive sediment include reduced feeding and respiratory efficiency
from clogged gills (Ellis 1936, p. 40), disrupted metabolic processes,
reduced growth rates, increased substrate instability, limited
burrowing activity (Marking and Bills 1979, pp. 208-209; Vannote and
Minshall 1982, p. 4106), physical smothering, and disrupted host fish
attractant mechanisms (Hartfield and Hartfield 1996, p. 373). The
primary effects of excess sediment on mussels are sublethal, with
detrimental effects not immediately apparent (Brim Box and Mossa 1999,
p. 101).
The physical effects of sediment on mussel habitats are multifold
and include changes in suspended material load; changes in streambed
sediment composition from increased sediment production and runoff in
the watershed; changes in the form, position, and stability of stream
channels; changes in water depth or the width-to-depth ratio, which
affects light penetration and flow regime; actively aggrading (filling)
or degrading (scouring) channels; and changes in channel position that
may leave mussels stranded (Brim Box and Mossa 1999, pp. 109-112).
Increased sedimentation and siltation may explain, in part, why
Texas fatmucket appear to be experiencing recruitment failure in some
streams. Interstitial spaces (small openings between rocks and gravels)
in the substrate provide essential habitat for juvenile mussels. When
clogged with sand or silt, interstitial flow rates and spaces may
become reduced (Brim Box and Mossa 1999, p. 100), thus reducing
juvenile habitat availability. Juvenile freshwater mussels, including
Texas fatmucket juveniles, burrow into interstitial substrates, making
it particularly susceptible to degradation of this habitat.
Even in 1959, both the Colorado and Guadalupe Rivers were noted as
having high sedimentation rates from agricultural activities (Soil
Conservation Service 1959, pp. 56, 59). Approximately 40 percent of
U.S. river miles do not meet Clean Water Act standards due to excessive
sediment loads (Environmental Protection Agency (EPA) 2000, p. 1), with
agricultural activities being the primary source of sediment in streams
(Waters 1995, p. 170). In general, sedimentation, resulting from
unrestricted access by livestock, has been shown to be a significant
threat to many streams and their mussel populations (Fraley and
Ahlstedt 2000, p. 193). A primary land use throughout the range of the
Texas fatmucket is grazing by cattle, sheep, and goats (Hersh 2007, p.
11). Soil compaction, which reduces vegetative growth, from intensive
grazing may reduce infiltration rates and increase runoff and erosion,
and trampling of riparian vegetation increases the probability of
erosion (Armour et al. 1994, p.10; Brim Box and Mossa 1999, p. 103).
Another cause of increased sediments in streams is widespread brush
removal, such as that of the native plant, Juniperus ashei (Ashe
juniper), throughout central Texas. Juniperus ashei removal can cause a
marked increase in sediment runoff into streams (Greer 2005, p. 76).
The Texas State Soil and Water Conservation Board has a funding program
specifically for Juniperus ashei removal in Blanco, Gillespie, Kerr,
Kendall, and Travis Counties (Gillespie County Soil and Water
Conservation District 2011, p. 1), which includes the watersheds of
three known Texas fatmucket populations in Live Oak Creek, Threadgill
Creek, and the upper Guadalupe River. In one example, Howells (2010f,
p. 6) noted
[[Page 62180]]
increased sediment deposition after widespread Juniperus ashei removal
upstream of the Texas fatmucket population in Live Oak Creek.
Sedimentation may become an increasing threat to the Texas
fatmucket in the Colorado and Guadalupe River basins as the Austin and
San Antonio metro areas continue to expand. Activities associated with
urbanization, such as road construction and increased impervious
surfaces (surfaces that do not allow infiltration of rain water), can
be detrimental to stream habitats (Couch and Hamilton 2002, p. 1).
Runoff from increased impervious surfaces increases sediment loads in
streams and destabilizes stream channels (Pappas et al. 2008, p. 151).
Impervious surfaces also result in channel instability by accelerating
stormwater runoff, which increases bank erosion and bed scouring,
thereby further increasing downstream sedimentation (Brim Box and Mossa
1999, p. 103). While erosion and sedimentation associated with road
construction may be temporary, the existence of road crossings is shown
to have ongoing impacts to mussel habitat. For example, in the
Guadalupe River, road crossings were found to cause a long-term
increase in sedimentation both upstream and downstream, as channel
constriction reduced flow upstream, causing sediment deposition, and
runoff from the road increased sedimentation downstream (Keen-Zebert
and Curran 2009, p. 301). Urban development activities may also affect
streams and their mussel fauna where adequate streamside buffers are
not maintained and erosion from adjacent land is allowed to enter
streams (Brainwood et al. 2006, p. 511).
Large projects that reduce vegetative cover within the watersheds
supporting Texas fatmucket populations can also increase sedimentation
flowing into streams. For example, the Lower Colorado River Authority
Transmission Services Corporation (LCRA TSC) is proposing to construct
two new 345-kilovolt (kV) electric transmission line facilities between
Tom Green (in the Colorado River basin near San Angelo) and Kendall
Counties (in the Guadalupe River basin north of San Antonio) to provide
electrical power to accommodate increased human populations (Clary
2010, p. 1). All of the proposed project routes occur within the range
of the Texas fatmucket. Two proposed segments would cross through Live
Oak Creek, one through the San Saba River, and one through the upper
Guadalupe River; all of these streams contain populations of the Texas
fatmucket. The proposed project could negatively affect Texas fatmucket
habitat if construction or maintenance of the transmission line
requires removal of vegetation within the riparian zone and that
removal results in an increase in sediment runoff into Live Oak Creek
and the Guadalupe and San Saba Rivers (Clary 2010, pp. 7, 9, 15).
Similar infrastructure development activities to accommodate Texas
population growth are expected to be undertaken across the species'
range and will likely lead to additional sources of sediment in the
streams inhabited by the Texas fatmucket.
Streams occupied by Texas fatmucket are subject to increasing
levels of sedimentation from agricultural activities, instream sand and
gravel mining, vegetation removal, and urbanization. All of these
activities are ongoing throughout the range of the Texas fatmucket and
are unlikely to decrease, resulting in significant threats to the Texas
fatmucket.
Dewatering
River dewatering can occur in several ways: Anthropogenic
activities such as surface water diversions and groundwater pumping,
and natural events, such as drought. Surface water diversions and
groundwater pumping can lower water tables, reducing river flows and
reservoir levels. When water levels in streams and reservoirs are
lowered dramatically, it can result in mussels being stranded and dying
in previously wetted areas. This is a particular concern within and
below reservoirs where water levels are managed for purposes that
result in water levels in the reservoir or downstream to rise or fall
in very short periods of time, such as when hydropower facilities
release water during peak energy demand periods. Rivers can also be
dewatered to expedite construction activities, which happened in the
upper Guadalupe River in Kerr County in 1998 for bridge construction;
numerous Texas fatmuckets were exposed and desiccated (dried out and
died) (Howells 1999, pp. 18-19).
Drought can also severely affect Texas fatmucket populations. For
example, near-record dry conditions in 2008, followed by a pattern of
below-normal rainfall during the winter and spring of 2009, led to one
of the worst droughts in recorded history for most of central Texas,
including the range of the Texas fatmucket (Nielsen-Gammon and
McRoberts 2009, p. 2). This drought's severity was exacerbated by
abnormally high air temperatures, a likely effect of climate change,
which has increased average air temperatures in Texas by at least 1
[deg]C (1.8 [deg]F) (Nielsen-Gammon and McRoberts 2009, p. 22). The
reservoirs within the Colorado River basin were extremely low during
this time due to the drought (Clean Water Action 2011, p. 1), as were
river levels. Minimal to no flow was recorded at numerous sites within
the basin (U.S. Geological Survey (USGS) 2011a, p. 1). Four of the five
current sites of the Texas fatmucket may have had very low flows during
the 2009 drought, including populations in the San Saba, Llano,
Pedernales, and Guadalupe Rivers (Howells 2010c, pp. 9-10). As low
flows persist, mussels face oxygen deprivation, increased water
temperature, and, ultimately, stranding (Golladay et al. 2004, p. 501).
Only the Llano River has been surveyed since 2009, and the species
persists in that river (Burlakova and Karatayev 2011, p. 1). Central
Texas is currently experiencing another extreme drought, with rainfall
between October 2010 and July 2011 being the lowest on record during
those months (LCRA 2011c, p. 1), and the effects of this drought are
being observed but are not yet fully known. As of the date of
publication of this finding, the Llano River has nearly stopped flowing
(Mashhood 2011, p. 1); this has undoubtedly affected Texas fatmucket
populations in this river.
We do not know the extent of the impacts of stream dewatering on
the Texas fatmucket; however, because this species' populations are so
small and isolated, the loss of numerous individuals at a site can have
dramatic consequences to the population. Hydropower facilities,
construction, surface water diversions, groundwater pumping, and
drought are occurring throughout the range of the Texas fatmucket;
therefore, the effects of dewatering are ongoing and unlikely to
decrease in the future, resulting in significant threats to the Texas
fatmucket.
Sand and Gravel Mining
Sand and gravel mining (removing bed materials from streams) has
been implicated in the destruction of mussel populations across the
United States (Hartfield 1993, pp. 136-138). Sand and gravel mining
causes stream instability by increasing erosion and turbidity (a
measure of water clarity) and causing subsequent sediment deposition
downstream (Meador and Layher 1998, pp. 8-9). These changes to the
stream can result in large-scale changes to aquatic fauna, by altering
habitat and affecting spawning of fish, mussels, and other aquatic
species (Kanehl and Lyons 1992, pp. 4-11).
Sedimentation and increased turbidity can accrue from instream
mining activities. In the Brazos River, a gravel dredging operation was
[[Page 62181]]
documented as depositing sediment as far as 1.6 km (1 mi) downstream
(Forshage and Carter 1973, p. 697). Accelerated streambank erosion and
downcutting of streambeds are common effects of instream sand and
gravel mining, as is the mobilization of fine sediments during sand and
gravel extraction (Roell 1999, p. 7).
Mining activities may threaten some local Texas fatmucket
populations. Currently, one mining operation is permitted near the
population in Onion Creek (TPWD 2008c, p. 1), and another in the Llano
River watershed in Kimble County (TPWD 2008a, p. 1). The permits allow
for repeated removal of sand and gravel at various instream locations.
Two additional mining operations occur in historical habitat for the
species--the mainstem Colorado River (U.S. Army Corps of Engineers
(USACE) 2010, p. 2) and Johnson Creek (TPWD 2007a, p. 1).
In areas where repeated mining occurs, an upstream progression of
channel degradation and erosion (called headcutting) can occur (Meador
and Layher 1998, p. 8). Headcutting may move miles upstream in a
zipper-like fashion as the upper boundary of the modified area
collapses. Headcutting can be found within the majority of rivers and
streams in Texas, including within the Texas fatmucket's current and
historical range (Kennon et al. 1967, p. 22). Headcuts induced by sand
and gravel mining can cause dramatic changes in streambank and channel
shape that may affect instream flow, water chemistry and temperature,
bank stability, and siltation (Meador and Layher 1998, p. 8), all of
which are harmful to freshwater mussels. Mussels are particularly
vulnerable to channel degradation and sedimentation processes
associated with headcutting due to their immobility (Pringle 1997, p.
429).
In addition to headcutting, mines that are located near stream
channels are subject to the gravel pit being captured by the stream
during flood events or due to gradual channel migration (Simmang and
Curran 2006, p. 1). For example, two gravel mines along the Colorado
River downstream of Austin were inundated; one by stream channel
migration in 1984, one by stream capture in 1991 (Simmang and Curran
2006, p. 1). Once captured by the mainstem river, gravel mines
contribute large amounts of suspended sediment to the river, causing
additional turbidity and sedimentation and further degrading mussel
habitat.
Two Texas fatmucket populations in the mainstem Colorado River and
Johnson Creek may be currently affected by sand and gravel mining.
These activities occur over a long period of time, destabilizing
habitat and altering substrates and banks both upstream and downstream.
Altered habitat will cause a decrease in the likelihood of
recolonization by mussels after the activity has been completed.
Therefore, the effects of sand and gravel mining are an ongoing threat
to the Texas fatmucket.
Chemical Contaminants
Chemical contaminants are ubiquitous throughout the environment and
are a major reason for the decline of freshwater mussel species
nationwide (Richter et. al. 1997, p. 1081; Strayer et al. 2004, p. 436;
Wang et al. 2007a, p. 2029). Chemicals enter the environment through
both point and nonpoint discharges, including spills, industrial
sources, municipal effluents, and agriculture runoff. These sources
contribute organic compounds, heavy metals, pesticides, herbicides, and
a wide variety of newly emerging contaminants to the aquatic
environment. As a result, water quality can be degraded to the extent
that mussel populations are adversely affected.
Chemical and oil spills can be especially devastating to mussels
because they may result in exposure of a relatively immobile species to
elevated concentrations that far exceed toxic levels. Acute and chronic
exposure to oil spills in freshwater systems is largely understudied;
therefore, little information is available on effects of oil spills on
freshwater ecosystems (Harrel 1985, p. 223; Bhattacharyya et al. 2002,
p. 205). Oil is retained much longer in marshes and other low-energy
environments, such as slow-moving streams and rivers, than on wave-
swept coasts (Bhattacharyya et al. 2002, p. 205). Oils have been found
in sediments at low energy sites as much as 5 years after the
occurrence of spills, and they may be released into the water column
long after the initial spill. Oil may have various chronic effects on
water-column and benthic (bottom-dwelling) species. These effects
include sensory disruption, behavioral and developmental abnormalities,
and reduced fertility (Bhattacharyya et al. 2002, p. 205). Oil spilled
on the water surface may also limit oxygen exchange, coat the gills of
aquatic organisms, and cause pathological lesions on respiratory
surfaces, thereby affecting respiration in aquatic organisms. Effects
of oil on freshwater mussels may result from oil settling on the
sediment surfaces and accumulating in the sediment. This can prevent
invertebrate colonization (Bhattacharyya et al. 2002, p. 205). Complete
recovery of benthic communities may be a matter of years, with
communities in the meantime consisting solely of pollutant-tolerant
organisms (Bhattacharyya et al. 2002, p. 205). Oil spills can occur
from on-site accidents (tank, pipeline spills) or from tanker truck
accidents within watersheds occupied by Texas fatmucket. For example,
450 gallons of oil were spilled into Lake Bastrop, a reservoir on a
tributary to the Colorado River, in February 2011 (Cihock 2011, p. 1).
Exposure of mussels to persistent low concentrations of
contaminants likely to be found in aquatic environments can also
adversely affect mussels and their populations. Such concentrations may
not be immediately lethal, but over time can result in mortality,
reduced filtration efficiency, reduced growth, decreased reproduction,
changes in enzyme activity, and behavioral changes to all mussel life
stages (Naimo 1995, pp. 351-352; Baun et al. 2008, p. 392). Frequently,
procedures that evaluate the ``safe'' concentration of an environmental
contaminant (for example, national water quality criteria) do not have
data for freshwater mussel species or do not consider data that are
available for freshwater mussels (March et al. 2007, pp. 2066-2067,
2073).
One chemical that is particularly toxic to early life stages of
mussels is ammonia. Sources of ammonia include agricultural activities
(animal feedlots and nitrogenous fertilizers), municipal wastewater
treatment plants, and industrial waste (Augspurger et al. 2007, p.
2026), as well as precipitation and natural processes (decomposition of
organic nitrogen) (Goudreau et al. 1993, p. 212; Hickey and Martin
1999, p. 44; Augspurger et al. 2003, p. 2569; Newton 2003, p. 2543).
Therefore, ammonia is considered a limiting factor for survival and
recovery of some mussel species due to its ubiquity in aquatic
environments, high level of toxicity, and because the highest
concentrations typically occur in mussel microhabitats (Augspurger et
al. 2003, p. 2574). In addition, studies have shown that ammonia
concentrations increase with increasing temperature and low-flow
conditions (Cherry et al. 2005, p. 378; Cooper et al. 2005, p. 381),
which may be exacerbated during low-flow events in streams. Within the
range of Texas fatmucket, high ammonia levels are common, either
chronically, such as in Elm Creek, which is listed as impaired due to
high ammonia concentrations (Texas Commission on Environmental Quality
(TCEQ) 2010a, p. 294), or due to spills. A wastewater leak in August
2010 spilled approximately 380,000
[[Page 62182]]
liters (L) (100,000 gallons (gal)) of sewage into Elm Creek (Bramlette
and Cosel 2010, p. 1); ammonia is present in high concentrations in
sewage, among other pollutants. Additionally, a sewage spill in 2008 in
Onion Creek discharged nearly 380,000 L (100,000 gal), and another
sewage spill occurred in April 2011 in Quinlan Creek, a tributary to
the Guadalupe River near the Kerr County population (MacCormack 2011,
p. 1). High ammonia levels from chronic sources as well as from spills
may be affecting Texas fatmucket populations.
In addition to ammonia, agricultural sources of chemical
contaminants include two broad categories that have the potential to
adversely affect mussel species: Nutrients and pesticides. High amounts
of nutrients, such as nitrogen and phosphorus, in streams can stimulate
excessive plant growth (algae and periphyton, among others), which in
turn can reduce dissolved oxygen levels when dead plant material
decomposes. Nutrient over-enrichment in streams is primarily a result
of runoff of fertlizer and animal manure from livestock farms,
feedlots, and heavily fertilized row crops (Peterjohn and Correll 1984,
p. 1471). Over-enriched conditions are exacerbated by low-flow stream
conditions, such as those experienced during typical summer season
flows. Bauer (1988, p. 244) found that excessive nitrogen
concentrations can be detrimental to the adult freshwater pearl mussel
(Margaritifera margaritifera), as was evident by the positive linear
relationship between mortality and nitrate concentrations. Also, a
study of mussel life span and size (Bauer 1992, p. 425) showed a
negative correlation between growth rate and high nutrient
concentrations, and longevity was reduced as the concentration of
nitrates increased. Juvenile mussels in interstitial habitats are
particularly affected by depleted dissolved oxygen levels resulting
from nutrient over-enrichment (Sparks and Strayer 1998, p. 133). The
Texas fatmucket occurs within the Concho River watershed, which has
been documented as having particularly high nitrates for nearly 20
years, likely due to intensive agriculture in the area (Texas Clean
Rivers Program 2008, p. 2), which may be affecting the Texas fatmucket
population.
Mussels are also affected by metals (Keller and Zam 1991, p. 543)
such as cadmium, chromium, copper, mercury, and zinc, which can
negatively affect biological processes such as growth, filtration
efficiency, enzyme activity, valve closure, and behavior (Keller and
Zam 1991, p. 543; Naimo 1995, pp. 351-355; Jacobson et al. 1997, p.
2390; Valenti et al. 2005, p. 1244). Metals occur in industrial and
wastewater effluents and are often a result of atmospheric deposition
from industrial processes and incinerators. Studies have shown that
copper can have toxic effects on glochidia and juvenile freshwater
mussels (Wang et al. 2007a, pp. 2036-2047; Wang et al. 2007b, pp. 2048-
2056). In the range of Texas fatmucket, high copper concentrations have
been recorded in fish in the lower Guadalupe River and San Antonio
River (Lee and Schultz 1994, p. 8). While these high levels of copper
in fish are not directly informative of the level of copper within the
habitat of the Texas fatmucket, these observations demonstrate that
copper levels are likely high in the lower Guadalupe and San Antonio
Rivers. Because we know that copper contamination in water can lead to
death of mussels, we conclude that the copper may be adversely
affecting Texas fatmucket.
Mercury is another heavy metal that has the potential to negatively
affect mussel populations, and it is widely distributed in the
environment. Mercury has been detected throughout aquatic environments
as a product of municipal and industrial waste and atmospheric
deposition from coal burning plants. Rainbow mussel (Villosa iris)
glochidia have been demonstrated to be more sensitive to mercury than
juvenile mussels, with the median lethal concentration value of 14
parts per billion (ppb) for glochidia, compared to 114 ppb for the
juvenile life stages (Valenti 2005, p. 1242). The chronic toxicity
tests conducted determined that juveniles exposed to mercury greater
than or equal to 8 ppb exhibited reduced growth. Acute mercury toxicity
was determined to be the cause of extirpation of a diverse mussel
community for a 112 km (70 mi) portion of the North Fork Holston River
in Virginia (Brown et al. 2005, pp. 1455-1457). Mercury has been
documented throughout the Guadalupe and San Antonio Rivers, with
particularly high concentrations in fish in the upper reaches of both
rivers (Lee and Schultz 1994, p. 8). As with copper, we do not have
information on the concentration of mercury that Texas fatmucket is
being exposed to in these streams, but the higher than expected levels
in fish indicate high mercury levels in the area, which may be
adversely affecting Texas fatmucket.
Pesticides are another source of contaminants in streams. Elevated
concentrations of pesticides frequently occur in streams due to
pesticide runoff, overspray application to row crops, and lack of
adequate riparian buffers. The timing of agricultural pesticide
applications in the spring often coincides with the reproductive and
early life stages of mussels, which may increase the vulnerability of
mussels to pesticides (Bringolf et al. 2007a, p. 2094). Little is known
regarding the effect of currently used pesticides to freshwater mussels
even though some pesticides, such as glyphosate (active ingredient in
Roundup[supreg]), are used globally. Recent studies tested the toxicity
of glyphosate, its formulations, and a surfactant (MON 0810) used in
several glyphosate formulations, to early life stages of the fatmucket
(Lampsilis siliquoidea) (Bringolf et al. 2007a, p. 2094), a freshwater
mussel closely related to the Texas fatmucket. Studies conducted with
fatmucket juveniles and glochidia determined that the surfactant was
the most toxic of the compounds tested and that fatmucket glochidia
were the most sensitive organisms tested to date (Bringolf et al.
2007a, p. 2094). Roundup[supreg], technical grade glyphosate
isopropylamine salt, and isopropylamine were also acutely toxic to
juveniles and glochidia (Bringolf et al. 2007a, p. 2097). These
commonly applied pesticides may be adversely affecting Texas fatmucket
populations.
The effects of other widely used pesticides, including atrazine,
chlorpyrifos, and permethrin, on glochidia and juvenile life stages
have also recently been studied (Bringolf et al. 2007b, p. 2101).
Environmentally relevant concentrations (concentrations that may be
found in streams) of permethrin and chlorpyrifos were found to be toxic
to glochidia and juvenile fatmucket (Bringolf et al. 2007b, pp. 2104-
2106). Commonly applied pesticides are a threat to mussels as a result
of their widespread use. All of these pesticides are commonly used on
agricultural lands throughout the range of the Texas fatmucket, which
may be adversely affecting the species.
A potential, but undocumented, threat to freshwater mussels,
including Texas fatmucket, are compounds referred to as ``emerging
contaminants'' that are being detected in aquatic ecosystems at an
increasing rate. These include pharmaceuticals, hormones, and other
organic contaminants that have been detected downstream from urban
areas and livestock production (Kolpin et al. 2002, p. 1202) and have
been shown to affect fish behavior (TCEQ 2010b, p. 3). In samples of
the Trinity River, for example, compounds such as antidepressants,
antihistamines, blood pressure lowering medication, anti-seizure
medication, and antimicrobial compounds were all detected during a 2006
study (TCEQ 2010b, pp. 27-28). A
[[Page 62183]]
large potential source of these emerging contaminants is wastewater
being discharged through both permitted (National Pollutant Discharge
Elimination System (NPDES)) and non-permitted sites within the Colorado
and Guadalupe River systems. Although streams within the range of Texas
fatmucket have not been tested for these emerging contaminants,
permitted discharge sites are ubiquitous in watersheds with Texas
fatmucket populations, providing many opportunities for contaminants to
impact the species.
A study in the Blanco River found that mussels may be adversely
affected by sewage effluent (Horne and McIntosh 1979, p. 132). Ammonia
levels below the outfall were three times higher than the levels above
the outfall and were higher than recently determined toxicity values of
ammonia for mussels (Augsperger et al. 2003, p. 2572). The river was
nutrient-enriched for miles downstream, and mussels were less abundant
below the outfall than above (Horne and McIntosh 1979, pp. 124-125,
132). Texas fatmucket have not been found alive in the Blanco River
since 1978.
Texas Commission on Environmental Quality (TCEQ) data for 2010
indicated that 26 of the 98 assessed water bodies within the Texas
fatmucket's historical and current range did not meet surface water
quality standards and were classified as impaired water bodies under
the Clean Water Act (Texas Clean Rivers Program 2010a, p. 5; 2010b, p.
13), including Elm Creek, due to high ammonia. These water bodies were
impaired with dissolved solids, nitrates, bacteria, low dissolved
oxygen, aluminum, sulfates, selenium, chloride, and low pH associated
with agricultural, urban, municipal, and industrial runoff. Of these,
nitrates and low dissolved oxygen pose the greatest threat to Texas
fatmucket, as discussed above. Chemical contaminants, such as oil,
ammonia, copper, mercury, nutrients, pesticides, and other compounds,
are currently a threat to the Texas fatmucket. The species is
vulnerable to acute contamination from spills, which have been
documented in four of the seven remaining populations, as well as
chronic contaminant exposure, which is occurring rangewide.
Summary of Factor A
The reduction in numbers and range of the Texas fatmucket is
primarily the result of the long-lasting effects of habitat alterations
such as the effects of impoundments, sedimentation, dewatering, sand
and gravel mining, and chemical contaminants. Impoundments occur
throughout the range of the species and have far-reaching effects both
up- and downstream. Both the Colorado and Guadalupe River systems have
experienced a large amount of sedimentation from agriculture, mining,
urban development, and widespread Juniperus ashei removal. Sand and
gravel mining affects Texas fatmucket habitat by increasing
sedimentation and channel instability downstream and causing
headcutting upstream. Finally, chemical contaminants have been
documented throughout the range of the species and are significant
concern to Texas fatmucket. Based upon our review of the best
commercial and scientific data available, we conclude that the present
or threatened destruction, modification, or curtailment of its habitat
or range is an immediate threat of high magnitude to the Texas
fatmucket.
Factor B. Overutilization for Commercial, Recreational, Scientific,
or Educational Purposes.
The Texas fatmucket is not a commercially valuable species and has
never been harvested in Texas as a commercial mussel species (Howells
2010c, p. 11), although in the Llano River shells were found that were
apparently collected by anglers for use as bait (Howells 1996, p. 22;
2010c, p. 11). Additionally, the Elm Creek population is suspected to
have declined in part due to the publication of detailed location
information, which may have inspired collectors to visit the site
(Howells 2009, pp. 5-6). Scientific collecting is not likely to be a
significant threat to the status of the species, although disturbing
gravid females can result in glochidial loss and subsequent
reproductive failure. Additionally, handling has been shown to reduce
shell growth in other mussel species, including several other species
of Lampsilis (Haag and Commens-Carson 2008, pp. 505-506). Repeated
handling by researchers may adversely affect Texas fatmucket
individuals, but these activities are occurring rarely and are not
likely to be a threat to populations. Handling for scientific purposes
contributes to the long-term conservation of the species.
We do not have any evidence of risks to the Texas fatmucket from
overutilization for commercial, recreational, scientific, or
educational purposes, and we have no reason to believe this factor will
become a threat to the species in the future. Based upon the best
scientific and commercial information available, we conclude that
overutilization for commercial, recreational, scientific, or
educational purposes does not pose a significant threat to the Texas
fatmucket.
Factor C. Disease and Predation.
Disease
Little is known about disease in freshwater mussels. However,
disease is believed to be a contributing factor in documented mussel
die-offs in other parts of the United States (Neves 1987, pp. 11-12).
Diseases have not been documented or observed during any studies of
Texas fatmucket.
Predation
Raccoons have preyed on individual Texas fatmuckets stranded by low
waters or deposited in shallow water or on bars following flooding or
low water periods (Howells 2010c, p. 12). Predation of Texas fatmucket
by raccoons may be occurring occasionally but there is no indication it
is a significant threat to the status of the species.
Some species of fish feed on mussels, such as common carp (Cyprinus
carpio), freshwater drum, and redear sunfish (Lepomis microlophus), all
of which are common throughout the range of Texas fatmucket (Hubbs et
al. 2008, pp. 19, 45, 53). Common species of flatworms are voracious
predators of newly metamorphosed juvenile mussels of many species
(Zimmerman et al. 2003, p. 30), including other species in the genus
Lampsilis (Delp 2002, pp. 12-13). Predation is a normal aspect of the
population dynamics of a healthy mussel population; however, predation
may amplify declines in small populations.
Summary of Factor C
Disease in freshwater mussels is poorly known, and we do not have
any information indicating it is a threat to the Texas fatmucket.
Additionally, while predation is likely occurring within Texas
fatmucket populations, it is a natural ecological interaction and we
have no information indicating the extent of such predation is large
enough to be a threat to populations of Texas fatmucket. Based upon the
best scientific and commercial information available, we conclude that
disease or predation is not a threat to the Texas fatmucket.
Factor D. The Inadequacy of Existing Regulatory Mechanisms.
The Act requires us to examine the adequacy of existing regulatory
mechanisms with respect to threats that may place the Texas fatmucket
in danger of extinction or increase its likelihood of becoming so in
the future. Existing regulatory mechanisms that could affect threats to
the Texas
[[Page 62184]]
fatmucket include State and Federal laws such as the Texas Threatened
and Endangered Species regulations, Texas freshwater mussel
sanctuaries, State and Federal sand and gravel mining regulations, and
regulation of point and non-point source pollution.
Texas Threatened and Endangered Species Regulations
On January 8, 2010, the Texas Parks and Wildlife Commission placed
15 species of freshwater mussels, including the Texas fatmucket, on the
State threatened list (Texas Register 2010, pp. 6-10). Section 68.002
of the Texas Parks and Wildlife (TPW) Code and Section 65.171 of the
Texas Administrative Code (TAC) prohibit the direct take of a
threatened species, except under issuance of a scientific collecting
permit. ``Take'' is defined in Section 1.101(5) of the TPW Code as
collect, hook, hunt, net, shoot, or snare, by any means or device, and
includes an attempt to take or to pursue in order to take. While this
law protects individuals from take, it is difficult to enforce and does
not provide any protection for Texas fatmucket habitat. Moreover, our
assessment finds that the species is not threatened by take (see Factor
B above). There are no State provisions under the Texas Threatened and
Endangered Species Regulations for reducing or eliminating the threats
(see Factor A above) that may adversely affect Texas fatmucket or its
habitat. In addition, these State regulations do not call for
development of a recovery plan that will restore and protect existing
habitat for the species. For these reasons, we find that existing Texas
regulatory mechanisms for State-listed threatened species are currently
inadequate to protect Texas fatmucket and its habitat or to prevent
further decline of the species.
Freshwater Mussel Sanctuaries
The TPWD has designated specific areas of streams and reservoirs as
no-harvest mussel sanctuaries (31 TAC, part 2, chapter 57, subpart B,
Rule 57.157). The locations of the designated mussel sanctuaries were
selected because they support populations of rare and endemic mussel
species or are important for maintaining, repopulating, or allowing
recovery of mussels in watersheds where they have been depleted. As a
result of the designation of mussel sanctuaries, four of the Texas
fatmucket populations are protected from harvesting disturbance of
other species (Howells 2010f, p. 12). Unfortunately, mussel sanctuaries
only restrict the harvest of mussels and do not address other
activities that may affect mussels or their habitats. Therefore, these
designations provide no regulatory mechanisms to protect Texas
fatmucket from habitat alteration.
State Sand and Gravel Mining Regulations
TPWD has been responsible for regulating the ``disturbance of
taking'' streambed materials since 1911 (Meador and Layher 1998, p. 11)
and has issued several permits for ongoing activities within the Texas
fatmucket range (for more information on the effects of sand and gravel
mining on Texas fatmucket, please refer to ``Sand and Gravel Mining''
under Factor A in Five-Factor Evaluation for Texas Fatmucket). In
addition to authorized activities, there are ongoing unauthorized sand
and gravel mining activities within the range of Texas fatmucket. For
example, the LCRA, which monitors water quality permit applications
submitted through other agencies (LCRA 2011b, p. 1), found unpermitted
sand removal from the Llano River in Llano County during a site visit
in 2010 (Lehman 2010, p. 1). This site is located upstream from a known
population of the Texas fatmucket and other rare mussels (Howells 1994,
p. 6), and the sand removal may have increased turbidity and
sedimentation downstream within Texas fatmucket habitat. Sand and
gravel mining may be one of the least regulated of all mining
activities (Meador and Layher 1998, p. 10).
Clean Water Act
The U.S. Army Corps of Engineers (USACE) retains oversight
authority and requires a permit for gravel and sand mining activities
that deposit fill into streams under section 404 of the Clean Water Act
(33 U.S.C. 1251 et seq.). Additionally, a permit is required under
section 10 of the Rivers and Harbors Act (33 U.S.C. 401 et seq.) for
navigable waterways. However, many mining operations do not fall under
these two categories. For example, nationwide permits are issued by the
USACE for types of projects that are presumed to have minimal
environmental impacts. However, projects permitted by nationwide
permits, such as small mining operations, may have cumulative effects
on aquatic species like the Texas fatmucket through increased
sedimentation and channel instability.
Point source discharges of potential contaminants within the range
of the Texas fatmucket have been reduced since the inception of the
Clean Water Act, but this reduction may not provide adequate protection
for filter-feeding organisms that can be affected by extremely low
levels of contaminants (see ``Chemical Contaminants'' under Factor A in
the Five-Factor Evaluation for Texas Fatmucket section). The EPA's
established water quality criteria may not be protective of mussels.
Current water quality standards applied by EPA were established to be
protective of aquatic life; however, freshwater mussels were not used
to develop these standards (EPA 2005, p. 5), and current research
reveals mussels to be more sensitive to many aquatic pollutants than
the tested organisms (Augsperger et al. 2007, p. 2025). For example,
Augspurger et al. (2003, p. 2572) and Sharpe (2005, p. 28) suggested
that the criteria for ammonia may not be sufficient to prevent impacts
to mussels under current and future climate conditions. In addition,
chronic copper concentrations lethal to juvenile freshwater mussels
have been shown to be less than the EPA's 1996 chronic water quality
criterion for copper (Wang et al. 2007b, pp. 2052-2055), and, as stated
above (see ``Chemical Contaminants'' under Factor A in Five-Factor
Evaluation for Texas Fatmucket), high copper concentrations have been
documented in the lower Guadalupe and San Antonio Rivers (Lee and
Schultz 1994, p. 8). Based on this information, the existing EPA water
quality criteria may not be sufficient to prevent negative effects to
the Texas fatmucket.
Nonpoint source pollution such as sedimentation and chemical
contaminantation is considered a significant threat to Texas fatmucket
habitat; however, the Clean Water Act does not adequately protect Texas
fatmucket habitat from nonpoint source pollution, because most
activities that cause nonpoint source pollution are not regulated under
the Clean Water Act.
Summary of Factor D
Despite some State and Federal laws protecting the species and
water quality, the Texas fatmucket continues to decline due to the
effects of habitat destruction, poor water quality, contaminants, and
other factors. The regulatory measures described above are not
sufficient to significantly reduce or remove the threats to the Texas
fatmucket. Based upon our review of the best commercial and scientific
data available, we conclude that the lack of existing regulatory
mechanisms is an immediate threat of moderate magnitude to the Texas
fatmucket.
Factor E. Other Natural or Manmade Factors Affecting Its Continued
Existence.
Other natural and manmade factors that threaten the Texas fatmucket
[[Page 62185]]
include climate change, population fragmentation and isolation, and
nonnative species.
Climate Change
It is widely accepted that changes in climate are occurring
worldwide (International Panel on Climate Change (IPCC) 2007, p. 30).
Understanding the effects of climate change on the Texas fatmucket is
important because the disjunct nature of the remaining Texas fatmucket
populations, coupled with the limited ability of mussels to migrate,
makes it unlikely that the Texas fatmucket can adjust its range in
response to changes in climate (Strayer 2008, p. 30). For example,
changes in temperature and precipitation can increase the likelihood of
flooding or increase drought duration and intensity, resulting in
direct effects to freshwater mussels like the Texas fatmucket (Hastie
et al. 2003, pp. 40-43; Golloday et al. 2004, p. 503). Because the
range of the Texas fatmucket has been reduced to isolated locations
with low population numbers in small rivers and streams, the Texas
fatmucket is vulnerable to climatic changes that could decrease the
availability of water or produce more frequent scouring flood events.
Indirect effects of climate change may include declines in host fish
populations, habitat reduction, and changes in human activity in
response to climate change (Hastie et al. 2003, pp. 43-44).
For the next two decades, a warming of about 0.2 [deg]C (0.4
[deg]F) per decade is projected across the United States (IPCC 2007, p.
12), and hot extremes, heat waves, and heavy precipitation and flooding
are expected to increase in frequency (IPCC 2007, p. 18). As with many
areas of North America, central Texas is projected to experience an
overall warming trend in the range of 2.5 to 3.3 [deg]C (4.5 to 6
[deg]F) over the next 50 to 200 years (Mace and Wade 2008, p. 656).
Even under lower greenhouse gas emission scenarios, recent projections
forecast a 2.8 [deg]C (5 [deg]F) increase in temperature and a 10
percent decline in precipitation in central Texas by 2080-2099 (Karl et
al. 2009, pp. 123-124). Based on our current understanding of climate
change, air temperatures are expected to rise and precipitation
patterns are expected to change in areas occupied by the Texas
fatmucket. Karl et al. (2009, p. 12) also suggests that climate change
impacts on water resources in the southern Great Plains (including
central Texas) are expected as rising temperatures and decreasing
precipitation exacerbate an area already plagued by low rainfall, high
temperatures, and unsustainable water use practices.
One preliminary study forecasting the possible hydrological impacts
of climate change on the annual runoff and its seasonality in the upper
Colorado River watershed was conducted by CH2M HILL (2008). In this
initial evaluation, four modeling scenarios (chosen to represent a
range of possible future climatic conditions) were each run under a
2050 and 2080 time scenario, producing annual surface water runoff
estimates at multiple sites with stream gages in the Colorado River
basin. For the 2050 scenarios, the results from all four climate change
scenarios predicted significant decreases in annual runoff totals
compared to historic averages (CH2M HILL 2008, pp. 7-30--7-32). For the
2080 scenarios, one model predicted increases in annual runoff; the
other three 2080 scenarios predicted decreases in annual runoff (CH2M
HILL 2008, pp. 7-30--7-33). The modeling efforts from this study focus
on annual averages and cannot necessarily account for the seasonal
variations in flooding events or long periods of drought. However, the
study demonstrates the potential effects of climate change on surface
water availability, which is forecasted to result in an overall decline
in stream flows in the region where the Texas fatmucket occurs.
In summary, climate change could affect the Texas fatmucket through
the combined effects of global and regional climate change, along with
the increased probability of long-term drought. Climate change
exacerbates threats such as habitat degradation from prolonged periods
of drought, increased water temperature, and the increased allocation
of water for municipal, agricultural, and industrial use. As such,
climate change, in and of itself, may affect the Texas fatmucket, but
the magnitude and imminence (when the effects occur) of the effects
remain uncertain. Based upon our review of the best commercial and
scientific data available, we conclude that the effects of climate
change in the future will likely exacerbate the current and ongoing
threats of habitat loss and degradation caused by other factors, as
discussed above.
Population Fragmentation and Isolation
All of the remaining populations of the Texas fatmucket are small
and geographically isolated and thus are susceptible to genetic drift
(change of gene frequencies in a population over time), inbreeding
depression, and random or chance changes to the environment, such as
toxic chemical spills (Watters and Dunn 1995, pp. 257-258) or
dewatering. Inbreeding depression can result in death, decreased
fertility, smaller body size, loss of vigor, reduced fitness, and
various chromosomal abnormalities (Smith 1974, pp. 350). Despite any
evolutionary adaptations for rarity, habitat loss and degradation
increase a species' vulnerability to extinction (Noss and Cooperrider
1994, pp. 58-62). Numerous authors (including Noss and Cooperrider
1994, pp. 58-62; Thomas 1994, p. 373) have indicated that the
probability of extinction increases with decreasing habitat
availability. Although changes in the environment may cause populations
to fluctuate naturally, small and low-density populations are more
likely to fluctuate below a minimum viable population (the minimum or
threshold number of individuals needed in a population to persist in a
viable state for a given interval) (Gilpin and Soule 1986, pp. 25-33;
Shaffer 1981, p. 131; Shaffer and Samson 1985, pp. 148-150).
The Texas fatmucket was widespread throughout much of the Colorado
and Guadalupe River systems when few natural barriers existed to
prevent migration (via host species) among suitable habitats.
Construction of dams, however, likely destroyed many Texas fatmucket
populations through drastic habitat changes and isolated the remnant
populations from each other. For fertilization, Texas fatmucket females
need an upstream male to release sperm; populations with few
individuals reduce the likelihood that females will be exposed to sperm
while siphoning. Therefore, recruitment failure is a potential problem
for many small populations rangewide, a potential condition exacerbated
by its reduced range and increasingly isolated populations. If downward
population trends continue, further significant declines in total Texas
fatmucket population size and consequent reduction in long-term
survivability may soon become apparent.
The small, isolated nature of the Texas fatmucket's remaining
populations also increases the species' vulnerability to stochastic
(random) natural events. When species are limited to small, isolated
habitats, as the Texas fatmucket is, they are more likely to become
extinct due to a local event that negatively effects the population
(McKinney 1997, p. 497; Minckley and Unmack 2000, pp. 52-53; Shepard
1993, pp. 354-357). While the populations' small, isolated nature does
not represent an independent threat to the species, it does
substantially increase the risk of extirpation from the effects of all
other threats, including those addressed in
[[Page 62186]]
this analysis, and those that could occur in the future from unknown
sources.
Based upon our review of the best commercial and scientific data
available, we conclude that fragmentation and isolation of small
remaining populations of the Texas fatmucket exacerbate ongoing threats
to the species throughout all of its range and are expected to
continue.
Nonnative Species
Various nonnative species of aquatic organisms are firmly
established within the range of the Texas fatmucket and pose a threat
to the species. Golden algae (Prymnesium parvum) is a microscopic algae
considered to be one of the most harmful algal species to fish and
other gill-breathing organisms (Lutz-Carrillo et al. 2010, p. 24).
Golden algae was first discovered in Texas in 1985 and is presumed to
have been introduced from western Europe (Lutz-Carrillo et al. 2010, p.
30). Since its introduction, golden algae has been found in Texas
rivers and lakes, including two lakes in central Texas (Baylor
University 2009, p. 1). Under certain environmental conditions, this
algae can produce toxins that can cause massive fish and mussel kills
(Barkoh and Fries 2010, p. 1; Lutz-Carrillo et al. 2010, p. 24).
Evidence shows that golden algae probably caused fish kills in Texas as
early as the 1960s, but the first documented fish kill due to golden
algae in inland waters of Texas occurred in 1985 on the Pecos River in
the Rio Grande basin (TPWD 2002, p. 1). The range of golden algae has
increased to include portions of the Brazos and Colorado River basins,
among others, and it has been responsible for killing more than 8
million fish in the Brazos River since 1981 and more than 2 million
fish in the Colorado River since 1989 (TPWD 2010a, p. 1). Although
actual mussel kills in Texas due to golden algae have not been recorded
in the past, the toxin can kill mussels. Therefore, the elimination of
host fish and the poisonous nature of the toxin to mussels make future
golden algae blooms a threat to the Texas fatmucket.
An additional nonnative species, the zebra mussel (Dreissena
polymorpha), poses a potential threat to the Texas fatmucket. This
invasive species has been responsible for the extirpation of freshwater
mussels in other regions of the United States, including the Higgin's
eye (Lampsilis higginsii) in Wisconsin and Iowa (Service 2006, pp. 9-
10). Zebra mussels attach in large numbers to the shells of live native
mussels and are implicated in the loss of entire native mussel beds
(Ricciardi et al. 1998, p. 615). This fouling impedes locomotion (both
laterally and vertically), interferes with normal valve movements,
deforms valve margins, and essentially suffocates and starves the
native mussels by depleting the surrounding water of oxygen and food
(Strayer 1999, pp. 77-80). Heavy infestations of zebra mussels on
native mussels may overly stress the animals by reducing their energy
reserves. Zebra mussels may also filter the sperm and possibly
glochidia of native mussels from the water column, thus reducing
reproductive potential. Habitat for native mussels may also be degraded
by large deposits of zebra mussel pseudofeces (undigested waste
material passed out of the incurrent siphon) (Vaughan 1997, p. 11).
Zebra mussels are not currently found within the range of the Texas
fatmucket. However, a live adult zebra mussel was first documented in
Lake Texoma on the Red River (on the north Texas border with Oklahoma)
in 2009 (TPWD 2009a, p. 1). Since that time, additional zebra mussels
have been reported from Lake Texoma, where they are now believed to be
well established (TPWD 2009c, p. 1). Zebra mussels are likely to spread
to many other Texas reservoirs through accidental human transport
(Schneider et al. 1998, p. 789). Although zebra mussels tend to
proliferate in reservoirs or large pools, released zebra mussel larvae,
called veligers, float downstream and attach to any hard surface
available, rendering downstream Texas fatmucket populations extremely
vulnerable to attachment and fouling. Because zebra mussels are so
easily introduced to new locations, the potential for zebra mussels to
continue to expand in Texas and invade the range of the Texas fatmucket
is high. If this occurs, the Texas fatmucket is vulnerable to zebra
mussel attachment and subsequent deprivation of oxygen, food, and
mobility.
A molluscivore (mollusk eater), the black carp (Mylopharyngodon
piceus) is a potential threat to the Texas fatmucket. The species has
been commonly used by aquaculturists to control snails or for research
in fish production in several States, including Texas (72 FR 59019,
October 18, 2007). Black carp can reach more than 1.3 m (4 ft) in
length and 150 pounds (68 kilograms (kg)) (Nico and Williams 1996, p.
6). Foraging rates for a 4-year-old fish average 3 to 4 pounds (1.4
to1.8 kg) a day, indicating that a single individual could consume 10
tons (9,072 kg) of native mollusks over its lifetime (Mississippi
Interstate Cooperative Resource Association (MICRA) 2005, p. 1). Black
carp can escape from aquaculture facilities. For example, in 1994 30
black carp escaped from an aquaculture facility in Missouri during a
flood. Other escapes into the wild by non-sterile carp are likely to
occur. Because of the high risk to freshwater mussels and other native
mollusks, the Service recently listed black carp as an injurious
species under the Lacey Act (72 FR 59019, October 18, 2007), which
prevents importations and interstate transfer of this harmful species,
but does not prevent its release into the wild once it is in the State.
If the black carp were to escape within the range of the Texas
fatmucket, it would likely negatively affect native mussels, including
the Texas fatmucket.
Based upon our review of the best commercial and scientific data
available, we conclude that golden algae is an ongoing threat to the
Texas fatmucket, and other nonnative species, such as zebra mussels and
black carp, are a potential future threat to the Texas fatmucket that
is likely to increase as these exotic species expand their occupancy
within the range of the Texas fatmucket.
Summary of Factor E
The effects of climate change, while difficult to quantify at this
time, are likely to exacerbate the current and ongoing threat of
habitat loss caused by other factors, and the small sizes and
fragmented nature of the remaining populations render them more
vulnerable to extirpation. In addition, nonnative species, such as
golden algae, currently threaten the Texas fatmucket, and the potential
introduction of zebra mussels and black carp are potential future
threats. Based upon our review of the best commercial and scientific
data available, we conclude that other natural or manmade factors are
immediate threats of moderate magnitude to the Texas fatmucket.
Finding for Texas Fatmucket
As required by the Act, we considered the five factors in assessing
whether Texas fatmucket is threatened or endangered throughout all of
its range. We examined the best scientific and commercial information
available regarding the past, present, and future threats faced by the
Texas fatmucket. We reviewed the petition, information available in our
files, and other available published and unpublished information, and
we consulted with recognized Texas fatmucket experts and other Federal
and State agencies.
This status review identified threats to the Texas fatmucket
attributable to Factors A, D, and E. The primary threat to the species
is from habitat destruction and modification (Factor A) from
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impoundments, which scour riverbeds, thereby removing mussel habitat,
decrease water quality, modify stream flows, and prevent fish host
migration and distribution of freshwater mussels, as well as
sedimentation, dewatering, sand and gravel mining, and chemical
contaminants. Additionally, most of these threats may be exacerbated by
the current and projected effects of climate change (discussed in
Factor E). Threats to the Texas fatmucket and its habitat are not being
adequately addressed through existing regulatory mechanisms (Factor D).
Because of the limited distribution of this endemic species and its
lack of mobility, these threats are likely to result in the extinction
of the Texas fatmucket in the foreseeable future.
On the basis of the best scientific and commercial information
available, we find that the petitioned action to list the Texas
fatmucket under the Act is warranted. We will make a determination on
the status of the species as threatened or endangered when we complete
a proposed listing determination. When we complete a proposed listing
determination, we will examine whether the species may be endangered or
threatened throughout all of its range or whether the species may be
endangered or threatened in a significant portion of its range.
However, as explained in more detail below, an immediate proposal of a
regulation implementing this action is precluded by higher priority
listing actions, and progress is being made to add or remove other
qualified species from the Lists of Endangered and Threatened Wildlife
and Plants.
We reviewed the available information to determine if the existing
and foreseeable threats render the Texas fatmucket at risk of
extinction now such that issuing an emergency regulation temporarily
listing the species under section 4(b)(7) of the Act is warranted. We
determined that issuing an emergency regulation temporarily listing the
species is not warranted for the Texas fatmucket at this time, because
we have not identified a threat or activity that poses a significant
risk, such that losses to the species during the normal listing process
would endanger the continued existence of the entire species. However,
if at any time we determine that issuing an emergency regulation
temporarily listing Texas fatmucket is warranted, we will initiate this
action at that time.
Listing Priority Number for Texas Fatmucket
The Service adopted guidelines on September 21, 1983 (48 FR 43098),
to establish a rational system for utilizing available resources for
the highest priority species when adding species to the Lists of
Endangered and Threatened Wildlife and Plants or reclassifying species
listed as threatened to endangered status. These guidelines, titled
``Endangered and Threatened Species Listing and Recovery Priority
Guidelines,'' address the immediacy and magnitude of threats, and the
level of taxonomic distinctiveness by assigning priority in descending
order to monotypic genera (genus with one species), full species, and
subspecies (or equivalently, distinct population segments of
vertebrates).
As a result of our analysis of the best available scientific and
commercial information, we have assigned the Texas fatmucket a Listing
Priority Number (LPN) of 2, based on our finding that the species faces
threats that are of high magnitude and are imminent. These threats
include habitat loss and degradation from impoundments, sedimentation,
sand and gravel mining, and chemical contaminants; other natural or
manmade factors such as climate change, small, isolated populations,
and nonnative species; and the fact that the threats to the species are
not being adequately addressed by existing regulatory mechanisms. Our
rationale for assigning the Texas fatmucket an LPN of 2 is outlined
below.
Under the Service's guidelines, the magnitude of threat is the
first criterion we look at when establishing a listing priority. The
guidance indicates that species with the highest magnitude of threat
are those species facing the greatest threats to their continued
existence. These species receive the highest listing priority. We
consider the threats that the Texas fatmucket faces to be high in
magnitude. Habitat loss and degradation from impoundments,
sedimentation, sand and gravel mining, and chemical contaminants are
widespread throughout the range of the Texas fatmucket and profoundly
affect its survival and recruitment. Remaining populations are small,
isolated, and highly vulnerable to stochastic events.
Under our LPN guidelines, the second criterion we consider in
assigning a listing priority is the immediacy of threats. This
criterion is intended to ensure that the species facing actual,
identifiable threats are given priority over those for which threats
are only potential or that are intrinsically vulnerable but are not
known to be presently facing such threats. We consider the threats to
the Texas fatmucket as described under Factors A, D, and E in the Five-
Factor Evaluation for Texas Fatmucket section to be imminent because
these threats have affected the species in the past, are ongoing, and
will continue in the foreseeable future. Habitat loss and destruction
have already occurred and will continue as the human population
continues to grow in central Texas. Texas fatmucket populations may
already be below the minimum viable population requirement, which would
cause a reduction in the number of populations and an increase in the
species' vulnerability to extinction. These threats are exacerbated by
climate change, which will increase the frequency and magnitude of
droughts. Therefore, we consider these threats to be imminent.
The third criterion in our Listing Priority Number guidance is
intended to devote resources to those species representing highly
distinctive or isolated gene pools as reflected by taxonomy. The Texas
fatmucket is a valid taxon at the species level and, therefore,
receives a higher priority than subspecies, but a lower priority than
species in a monotypic genus. Therefore, we assigned Texas fatmucket an
LPN of 2.
We will continue to monitor the threats to the Texas fatmucket and
the species' status on an annual basis, and should the magnitude or
imminence of the threats change, we will revisit our assessment of the
LPN.
While we conclude that listing the Texas fatmucket is warranted, an
immediate proposal to list this species is precluded by other higher
priority listings, which we address in the Preclusion and Expeditious
Progress section below. Because we have assigned the Texas fatmucket an
LPN of 2, work on a proposed listing determination for the species is
precluded by work on higher priority listing actions with absolute
statutory, court-ordered, or court-approved deadlines and final listing
determinations for those species that were proposed for listing with
funds from Fiscal Year (FY) 2011. This work includes all the actions
listed in the tables below under Preclusion and Expeditious Progress.
Five-Factor Evaluation for Golden Orb
Information pertaining to the golden orb in relation to the five
factors provided in section 4(a)(1) of the Act is discussed below.
Factor A. The Present or Threatened Destruction, Modification, or
Curtailment of Its Habitat or Range.
As discussed above, the decline of mussels in Texas and across the
United States is primarily the result of habitat
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loss and degradation. Chief among the causes of decline of the golden
orb in Texas are the effects of impoundments, dewatering,
sedimentation, sand and gravel mining, chemical contaminants, and off-
road vehicle use. These threats are discussed below.
Impoundments
For general information on the effects of impoundments on
freshwater mussels, please refer to ``Impoundments'' under Factor A in
Five-Factor Evaluation for Texas Fatmucket. Golden orb occur in one
impoundment, Lake Corpus Christi, indicating that inundation may not be
as detrimental to this species as it is to other, more flow-dependent
mussel species. However, dams continue to fragment golden orb
populations. There are 29 reservoirs, each with a storage capacity of
3,000 acre-feet or more, within the Guadalupe River basin and 34 within
the San Antonio River basin, in addition to many other smaller
reservoirs in these basins (Exelon 2010, p. 2.3-4). Three large
reservoirs exist within the Nueces River basin.
Historical records showed that the golden orb once occurred in the
Guadalupe River in Comal County before the Canyon Reservoir was
constructed in 1964 (Randklev et al. 2010c, p. 4). No live or recently
dead golden orb have been found in this reach since the reservoir was
completed (Burlakova and Karatayev 2010a, pp. 14-15), and we presume
the species is extirpated from this reach because of the effects of the
reservoir. Surveys of the reservoirs in the Guadalupe River system have
been ongoing since at least 1992, and no evidence of live or dead
golden orb has been found in any of the reservoirs (Howells 1994, pp.
1-20; 1995, pp. 1-50; 1996, pp. 1-45; 1997a, pp. 1-58; 1998, pp. 1-30;
1999, pp. 1-34; 2000a, pp. 1-56; 2001, pp. 1-50; 2002a, pp. 1-28; 2003,
pp. 1-42; 2004, pp. 1-48; 2005, pp. 1-23; 2006, pp. 1-106; Karatayev
and Burlakova 2008, pp. 1-47; Burlakova and Karatayev 2010a, pp. 1-30;
2011, pp. 1-8).
For species such as golden orb that may be able to survive the
initial inundation of reservoirs, conditions within the reservoir are
likely to become uninhabitable. The deep water in reservoirs is very
cold and often devoid of oxygen and necessary nutrients (Watters 2000,
p. 264). Cold water (less than 11 [deg]C (52 [deg]F)) has been shown to
stunt mussel growth (Hanson et al. 1988, p. 352). Because mussel
reproduction is temperature dependent (Watters and O'Dee 1999, p. 455),
it is likely that individuals living in the constantly cold hypolimnion
in these channels may never reproduce, or reproduce less frequently
(Watters 2000, p. 264). Any golden orb that survived the initial
inundation may have been unable to reproduce, eventually eliminating
the species from large areas of the reservoir. The same would be true
for mussels living in cold-water discharges downstream of large
impoundments (Watters 2000, p. 264).
Dam construction also fragments the range of golden orb, leaving
remaining habitats and populations isolated by the structures, as well
as by extensive areas of deep, uninhabitable, impounded waters. These
isolated populations are unable to naturally recolonize suitable
habitat that may be impacted by temporary but devastating events, such
as severe drought, chemical spills, or unauthorized discharges. Dams
impound river habitats throughout almost the entire range of the
species. These impoundments have left short and isolated patches of
remnant habitat, typically in between impounded reaches, such as the
golden orb population on the Guadalupe River within about one mile (1.6
km) downstream of Lake Wood. This population is subject to dramatic
flow fluctuations from the hydroelectric facility associated with the
dam (Howells 2010a, p. 4), which can leave individuals stranded when
water levels are quickly lowered or wash individuals downstream when
flow is increased.
The widespread construction of dams throughout the range of golden
orb has significantly altered stream habitat both upstream and
downstream of the dams by changing fish assemblages, temperature,
dissolved oxygen, and substrate. The effects of dams on the golden orb
are expected to be ongoing decades after construction and are presumed
to be continuing today. Because of this loss of habitat and its
widespread effects on the populations, we conclude that the effects of
dams are a threat to the golden orb.
Sedimentation
For general information on the effects of sedimentation on
freshwater mussels like the golden orb, please refer to
``Sedimentation'' under Factor A in Five-Factor Evaluation for Texas
Fatmucket.
As with other freshwater mussel species, the golden orb is affected
by excessive sedimentation in streams. Even in 1959, the Guadalupe
River was noted as having high sedimentation rates from agricultural
activities (Soil Conservation Service 1959, p. 59). Turbidity has also
been recorded as high in the Guadalupe River near Victoria (Exelon
2010, p. 2.3-186), indicating a large amount of suspended sediment
where a small golden orb population was recently found. Sedimentation
can occur from agricultural activities, sand and gravel mining, urban
runoff, and construction activities, among other sources.
One example of a proposed project that could lead to localized
increases in sedimentation within the range of the golden orb is the
LCRA TSC. This project proposes to construct two new, 345-kV electric
transmission line facilities between Tom Green (in the Colorado River
basin near San Angelo) and Kendall Counties (in the Guadalupe River
basin north of San Antonio) to provide electrical power to accommodate
increased human populations (Clary 2010, p. 1). One of the proposed
transmission lines would cross the upper Guadalupe River in Kerr
County, which contains a small population of golden orb. The proposed
project could negatively affect golden orb habitat by clearing land
within the riparian zone and may increase sediment runoff into the
Guadalupe River (Clary 2010, p. 7). Similar activities to accommodate
Texas population growth are expected to be undertaken across the
species' range and will likely lead to additional sources of sediment
in the streams inhabited by the golden orb.
Streams occupied by golden orb are subject to increasing levels of
sedimentation from agriculture, urbanization, and sand and gravel
mining. Agriculture is a common land use in the Guadalupe and San
Antonio River basins. Sedimentation may become an increasing threat to
the golden orb in the Guadalupe River basin as the San Antonio metro
area continues to expand. Activities associated with urbanization, such
as road construction, increased impervious surfaces, and road
construction can be detrimental to stream habitats (Couch and Hamilton
2002, p. 1), and the City of San Antonio, the second largest city in
Texas, continues to grow (City of San Antonio 2010, p. 5).
Sedimentation from agriculture, urbanization, and sand and gravel
mining is widespread in the range of the golden orb will continue to
threaten the species.
Dewatering
River dewatering can occur in several ways: anthropogenic
activities such as surface water diversions and groundwater pumping,
and natural events, such as drought, which can result in mussels
stranded in previously wetted areas. This is a particular concern
within and below reservoirs, whose water levels are managed for
[[Page 62189]]
various purposes that can cause water levels in the reservoir or
downstream to rise or fall in very short periods of time, such as when
hydropower facilities release water during peak energy demand periods.
For example, Lake Corpus Christi reservoir has experienced several
drawdowns of lake levels to reduce salinity levels in the reservoir,
such as in 1996 and 2006. Golden orb have been stranded above the water
line during both drawdowns, killing the exposed mussels (Howells 2006,
pp. 75-76). Rivers can also be dewatered to facilitate construction
activities, such as in the upper Guadalupe River in Kerr County, which
was dewatered in 1998 for bridge construction, which exposed and killed
golden orb (Howells 1999, pp. 18-19).
Drought can also severely impact golden orb populations. Central
Texas, including the Guadalupe River basin, experienced a major drought
in the late 1970s (Lewis and Oliveria 1979, p. 243). Near record dry
conditions in 2008 followed by a pattern of below-normal rainfall
during the winter and spring of 2009 led to one of the worst droughts
in recorded history for most of central Texas, including the range of
the golden orb (Nielsen-Gammon and McRoberts 2009, p. 2). This
drought's severity was exacerbated by abnormally high air temperatures,
a likely effect of climate change, which has already increased average
air temperatures in Texas by at least 1 [deg]C (1.8 [deg]F) (Nielsen-
Gammon and McRoberts 2009, p. 22). The Guadalupe River in Kerr County
experienced minimal to no flow during periods of the 2009 drought (USGS
2011b, p. 2), which may have negatively affected this golden orb
population. Central Texas is currently experiencing another extreme
drought, with rainfall between October 2010 and July 2011 being the
lowest on record during those months (LCRA 2011c, p. 1); the effects of
this drought are being observed but are not yet fully known.
We do not know the extent of the impacts of stream dewatering on
the golden orb; however, because several populations are small and
isolated, the loss of numerous individuals at a site can have dramatic
consequences to the population. Hydropower facilities, construction,
and drought are occurring throughout the range of the golden orb;
therefore, the effects of dewatering are ongoing and unlikely to
decrease, resulting in significant threats to the golden orb.
Sand and Gravel Mining
For general information on the effects of sand and gravel mining on
freshwater mussels, please refer to ``Sand and Gravel Mining'' under
Factor A in Five-Factor Evaluation for Texas Fatmucket.
In 1995, the reach of the Guadalupe River near Victoria, which
contains a golden orb population, was described as having numerous
current and abandoned sand and gravel mining areas (USACE 1995, p. 7).
Currently, TPWD has permitted one sand mining activity within the
existing range of golden orb, in the Guadalupe River basin in Comal
County (TPWD 2009b, p. 1); golden orb populations occur upstream and
downstream of this area in the Guadalupe River. The permit allows for
the repeated removal of sand and gravel at various locations within the
stream.
Headcuts from sand and gravel mining operations have been
documented in the San Antonio River basin in Karnes County from as
early as 1967, with downstream channels having steep, eroded banks
(Kennon et al. 1967, p. 22). The golden orb has not been documented
from this area since 1996, and only an old, eroded shell was collected
at that time (Howells 1997a, pp. 41-42).
The golden orb populations in the Guadalupe River may be currently
threatened by sand and gravel mining. These activities occur over a
long period of time, destabilizing habitat both upstream and
downstream, which decreases the likelihood of recolonization after the
activity has been completed. Therefore, the effects of sand and gravel
mining are an ongoing threat to the golden orb.
Chemical Contaminants
For general information on the effects of chemical contaminants on
freshwater mussels, please refer to ``Chemical Contaminants'' under
Factor A in Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussel species, the golden orb is also
threatened by chemical contaminants. TCEQ water quality standards for
2010 indicated the majority of the assessed water bodies within the
golden orb's historical and current range did not meet surface water
quality standards and were classified as impaired water bodies (Nueces
River Authority 2010, pp. 1-37; Texas Clean Rivers Program 2010b, p.
13). These water bodies were impaired with dissolved solids, nitrates,
bacteria, low dissolved oxygen, sulfates, phosphates, chloride,
chlorophyll-a, and low pH associated with agricultural, urban,
municipal, and industrial runoff. Of these, nitrates and low dissolved
oxygen pose the greatest threat to the golden orb. Additionally,
several streams within the range of the golden orb have been listed as
impaired due to high ammonia concentrations, including Elm Creek in the
Guadalupe River basin (TCEQ 2010a, p. 294). High copper concentrations
have been recorded in the lower Guadalupe and San Antonio Rivers (Lee
and Schultz 1994, p. 8), and mercury has been documented throughout the
Guadalupe and San Antonio Rivers, with particularly high concentrations
found in fish tissues from the upper reaches of both rivers (Lee and
Schultz 1994, p. 8). Row crop agriculture and wastewater discharges are
prominant within the range of the golden orb. These activities result
in chronic contamination from agricultural pesticides and emerging
contaminants of rivers inhabited by the species and are a threat to
golden orb.
Numerous spills of potential contaminant materials have occurred
within the range of the golden orb. These can occur from on site
accidents (tank, pipeline spills) or from tanker truck accidents within
watersheds occupied by golden orb. For example, 100,000 gallons of
sewage spilled into the San Antonio River near the City of San Antonio
when a pipeline collapsed in October 2010 (San Antonio Water System
2010, p. 1). The largest known golden orb population occurs downstream
of this location. Raw sewage contains very high ammonia levels, which
is toxic to freshwater mussels, as well as other pollutants.
Additionally, 300 gallons of diesel fuel spilled into the San Antonio
River near the same location in May 2011 (Serna 2011, p. 1). Another
sewage spill occurred in April 2011 in Quinlan Creek, a tributary to
the Guadalupe River near the Kerr County population of golden orb
(MacCormack 2011, p. 1). The actual effects on the golden orb of spills
such as these recent examples are unknown, but there are likely to be
negative consequences.
Because of the risk of spills as well as chronic contamination,
chemical contaminants, such as oil, ammonia, copper, mercury,
nutrients, pesticides, and other compounds are currently a threat to
the golden orb. The species is vulnerable to acute contamination from
spills as well as chronic contaminant exposure, which is occurring
rangewide.
Summary of Factor A
The reduction in numbers and range of the golden orb is primarily
the result of the long-lasting effects of habitat alterations such as
the effects of impoundments, sedimentation, dewatering, sand and gravel
mining, and chemical contaminants. Impoundments occur throughout the
range of the species and have far-reaching effects both up- and
[[Page 62190]]
downstream. Both the Colorado and Guadalupe River systems experience a
large amount of sedimentation from agriculture, instream mining, and
urban development. Sand and gravel mining affects golden orb habitat by
causing headcutting upstream, increasing sedimentation concentrations
in the water downstream, and causing channel instability downstream.
Chemical contaminants have been documented throughout the range of the
species and may represent a significant threat to the golden orb.
However, the large populations in the middle and lower Guadalupe River,
lower San Antonio River, and San Marcos River indicate that some golden
orb populations are not currently as vulnerable to habitat loss as
others. Based upon our review of the best commercial and scientific
data available, we conclude that the present or threatened destruction,
modification, or curtailment of its habitat or range is an immediate
threat of moderate magnitude to golden orb populations rangewide.
Factor B. Overutilization for Commercial, Recreational, Scientific,
or Educational Purposes.
The golden orb is not a commercially valuable species and has never
been harvested in Texas as a commercial mussel species (Howells 2010a,
p. 12). Some scientific collecting occurs but is not likely to be a
significant threat to the species because it occurs only rarely.
However, handing mussels can disturb gravid females and result in
glochidial loss and subsequent reproductive failure (Waller et. al
1995, p. 205). Additionally, handling has also been shown to reduce
shell growth across mussel species, including several species of
Lampsilis (Haag and Commens-Carson 2008, pp. 505-506). Repeated
handling by researchers may adversely affect golden orb individuals,
but these activities are occurring rarely and are not likely to
threaten populations. Handling for scientific purposes contributes to
the long-term conservation of the species.
We do not have any evidence of risks to the golden orb from
overutilization for commercial, recreational, scientific, or
educational purposes, and we have no reason to believe this factor will
become a threat to the species in the future. Based upon the best
scientific and commercial information available, we conclude that
overutilization of the golden orb for commercial, recreational,
scientific, or educational purposes does not pose a significant threat
to the species rangewide.
Factor C. Disease and Predation.
Disease
Little is known about disease in freshwater mussels. However,
disease is believed to be a contributing factor in documented mussel
die-offs in other parts of the United States (Neves 1987, pp. 11-12).
Diseases have not been documented or observed during any studies of
golden orb.
Predation
Raccoons will prey on freshwater mussels stranded by low waters or
deposited in shallow water or on bars following flooding or low water
periods (Howells 2010c, p. 12). Predation of golden orb by raccoons may
be occurring occasionally but there is no indication it is a
significant threat to the status of the species.
Some species of fish feed on mussels, such as common carp,
freshwater drum, and redear sunfish, all of which are common throughout
the range of golden orb (Hubbs et al. 2008, pp. 19, 45, 53). Common
species of flatworms are voracious predators of newly metamorphosed
juvenile mussels of many species (Zimmerman et al. 2003, p. 30).
Predation is a normal factor influencing population dynamics of a
healthy mussel population; however, predation may amplify declines in
small populations primarily caused by other factors.
Summary of Factor C
Disease in freshwater mussels is poorly known, and we do not have
any information indicating it is a threat to the golden orb.
Additionally, predation is a natural ecological interaction and we have
no information indicating the extent of any predation is a threat to
populations of golden orb. Based upon the best scientific and
commercial information available, we conclude that disease or predation
is not a threat to the golden orb.
Factor D. The Inadequacy of Existing Regulatory Mechanisms.
Existing regulatory mechanisms that could have an effect on threats
to the golden orb include State and Federal laws such as Texas
Threatened and Endangered Species regulations and freshwater mussel
sanctuaries, State and Federal sand and gravel mining regulations, and
regulation of point and non-point source pollution. For more
information on the effects of these regulations on the threats to
freshwater mussels in central Texas, please refer to Factor D under
Five-Factor Evaluation for Texas Fatmucket.
Summary of Factor D
Despite State and Federal laws protecting the species and water
quality, the golden orb continues to decline due to the effects of
habitat destruction, poor water quality, contaminants, and other
factors. The regulatory measures described above have been insufficient
to significantly reduce or remove the threats to the golden orb. Based
upon our review of the best commercial and scientific data available,
we conclude that the lack of existing regulatory mechanisms is an
immediate threat of moderate magnitude to the golden orb.
Factor E. Other Natural or Manmade Factors Affecting Its Continued
Existence.
Natural and manmade factors that threaten the golden orb include
climate change, population fragmentation and isolation, and nonnative
species.
Climate Change
For more general information on the effects of climate change on
freshwater mussels in central Texas, please refer to ``Climate Change''
under Factor E in Five-Factor Evaluation for Texas Fatmucket. Because
the range of the golden orb has been reduced to isolated locations,
many with low population numbers in small rivers and streams, the
golden orb is vulnerable to climatic changes that could decrease the
availability of water.
The disjunct nature of the remaining golden orb populations,
coupled with the limited ability of mussels to migrate, makes it
unlikely that golden orb can adjust their range in response to changes
in climate (Strayer 2008, p. 30). Climate change could affect the
golden orb through the combined effects of global and regional climate
change, along with the increased probability of long-term drought.
Climate change exacerbates threats such as habitat degradation from
prolonged periods of drought, increased water temperature, and the
increased allocation of water for municipal, agricultural, and
industrial uses. Climate change may be a significant stressor that
exacerbates existing threats by increasing the likelihood of prolonged
drought. As such, climate change, in and of itself, may affect the
golden orb, but the magnitude and imminence of the effects remain
uncertain. Based upon our review of the best commercial and scientific
data available, we conclude that the effects of climate change in the
future will likely exacerbate the current and ongoing threats of
habitat loss and degradation caused by other factors, as discussed
above.
Population Fragmentation and Isolation
For general information on the effects of population fragmentation
and isolation on freshwater mussels in
[[Page 62191]]
central Texas, please refer to ``Population Fragmentation and
Isolation'' under Factor E in Five-Factor Evaluation for Texas
Fatmucket. As with many freshwater mussels, several of the remaining
populations of the golden orb are small and geographically isolated and
thus are more susceptible to genetic drift, inbreeding depression, and
random or chance changes to the environment, such as toxic chemical
spills (Watters and Dunn 1995, pp. 257-258) or dewatering.
Historically, the golden orb was widespread throughout much of the
Guadalupe River system and in portions of the Nueces-Frio River system
when few natural barriers existed to prevent migration (via host
species) among suitable habitats. The extensive impoundment of the
Nueces, Guadalupe, and San Antonio River basins by the construction of
dams has fragmented the few remaining golden orb populations throughout
these river systems.
Small golden orb populations, including those in Lake Corpus
Christi Reservoir, the upper Guadalupe River in Kerr County, and the
San Antonio River in Victoria County, may now be below the minimum
population size required to maintain population viability into the
future, since they are less likely to be able to recover through
recruitment from events that reduce but do not extirpate populations.
Additionally, these small populations are more vulnerable to
extirpation from stochastic events, as the lack of connectivity among
populations does not permit nearby populations to recolonize areas
affected by intense droughts, toxic spills, or other isolated events
that result in significant mussel dieoffs. While the small, isolated
populations do not represent an independent threat to the species, the
situation does substantially increase the risk of extirpation from the
effects of all other threats, including those addressed in this
analysis, and those that could occur in the future from unknown
sources.
Based upon our review of the best commercial and scientific data
available, we conclude that fragmentation and isolation of small
remaining populations of the golden orb are occurring and are ongoing
threats to the species throughout all of its range.
Nonnative Species
For general information on the effects of nonnative species on
freshwater mussels of central Texas, please refer to ``Nonnative
Species'' under Factor E in Five-Factor Evaluation for Texas Fatmucket.
Various nonnative aquatic species pose a threat to the golden orb,
including golden algae, zebra mussels, and black carp. Zebra mussels
and black carp are not currently found within the range of golden orb,
but they are likely to be introduced within its range in the future.
Based upon our review of the best commercial and scientific data
available, we conclude that golden algae is an ongoing threat to the
golden orb, and other nonnative species, such as zebra mussels and
black carp, are a potential threat to the golden orb that is likely to
increase as these exotic species expand their occupancy to include the
range of the golden orb.
Summary of Factor E
The effects of climate change, while difficult to quantify at this
time, are likely to exacerbate the current and ongoing threat of
habitat loss caused by other factors, and the small sizes and
fragmented nature of the remaining populations render them more
vulnerable to extirpation. In addition, nonnative species, such as
golden algae, currently threaten the golden orb, and the potential
introduction of zebra mussels and black carp are potential future
threats. Based upon our review of the best commercial and scientific
data available, we conclude that other natural or manmade factors are
immediate threats of moderate magnitude to the golden orb.
Finding for Golden Orb
As required by the Act, we considered the five factors in assessing
whether the golden orb is threatened or endangered throughout all of
its range. We examined the best scientific and commercial information
available regarding the past, present, and future threats faced by the
golden orb. We reviewed the petition, information available in our
files, and other available published and unpublished information, and
we consulted with recognized golden orb experts and other Federal and
State agencies.
This status review identifies threats to the golden orb
attributable to Factors A, D, and E. The primary threat to the species
is from habitat destruction and modification (Factor A) from
impoundments, which scour riverbeds, thereby removing mussel habitat,
decrease water quality, modify stream flows, and restrict fish host
migration and distribution of freshwater mussels. Additional threats
under Factor A include sedimentation, dewatering, sand and gravel
mining, and chemical contaminants. Also, most of these threats may be
exacerbated by the current and projected effects of climate change,
population fragmentation and isolation, and the anticipated threat of
nonnative species (discussed under Factor E). Threats to the golden orb
are not being adequately addressed through existing regulatory
mechanisms (Factor D). Because of the limited distribution of this
endemic species and its lack of mobility, these threats are likely to
lead to the extinction of the golden orb in the foreseeable future.
On the basis of the best scientific and commercial information
available, we find that the petitioned action to list the golden orb
under the Act is warranted. We will make a determination on the status
of the species as threatened or endangered when we complete a proposed
listing determination. When we complete a proposed listing
determination, we will examine whether the species may be endangered or
threatened throughout all of its range or whether the species may be
endangered or threatened in a significant portion of its range.
However, as explained in more detail below, an immediate proposal of a
regulation implementing this action is precluded by higher priority
listing actions, and progress is being made to add or remove qualified
species from the Lists of Endangered and Threatened Wildlife and
Plants.
We reviewed the available information to determine if the existing
and foreseeable threats render the golden orb at risk of extinction now
such that issuing an emergency regulation temporarily listing the
species under section 4(b)(7) of the Act is warranted. We determined
that issuing an emergency regulation temporarily listing the species is
not warranted for the golden orb at this time, because we have not
identified a threat or activity that poses a significant risk, such
that losses to the species during the normal listing process would
endanger the continued existence of the entire species. However, if at
any time we determine that issuing an emergency regulation temporarily
listing the golden orb is warranted, we will initiate this action at
that time.
Listing Priority Number for Golden Orb
The Service adopted guidelines on September 21, 1983 (48 FR 43098),
to establish a rational system for utilizing available resources for
the highest priority species when adding species to the Lists of
Endangered and Threatened Wildlife and Plants or reclassifying species
listed as threatened to endangered status. These guidelines, titled
``Endangered and Threatened Species Listing and Recovery Priority
Guidelines'' address the immediacy and magnitude of threats, and the
level of taxonomic distinctiveness by assigning
[[Page 62192]]
priority in descending order to monotypic genera (genus with one
species), full species, and subspecies (or equivalently, distinct
population segments of vertebrates).
As a result of our analysis of the best available scientific and
commercial information, we have assigned the golden orb a Listing
Priority Number (LPN) of 8, based on our finding that the species faces
threats that are of moderate magnitude and are imminent. These threats
include habitat loss and degradation from impoundments, sedimentation,
sand and gravel mining, and chemical contaminants; other natural or
manmade factors such as climate change, small, isolated populations,
and nonnative species; and the fact that the threats to the species are
not being adequately addressed by existing regulatory mechanisms. Our
rationale for assigning the golden orb an LPN of 8 is outlined below.
Under the Service's guidelines, the magnitude of threat is the
first criterion we look at when establishing a listing priority. The
guidance indicates that species with the highest magnitude of threat
are those species facing the greatest threats to their continued
existence. These species receive the highest listing priority. We
consider the threats that the golden orb faces to be moderate in
magnitude. Habitat loss and degradation from impoundments,
sedimentation, sand and gravel mining, and chemical contaminants are
widespread throughout the range of the golden orb, but several large
populations remain, including one that was recently discovered,
suggesting that the threats are not high in magnitude.
Under our LPN guidelines, the second criterion we consider in
assigning a listing priority is the immediacy of threats. This
criterion is intended to ensure that the species facing actual,
identifiable threats are given priority over those for which threats
are only potential or that are intrinsically vulnerable but are not
known to be presently facing such threats. We consider the threats to
the golden orb as described in Factors A, D, and E under the Five-
Factor Evaluation for Golden Orb to be imminent because these threats
are ongoing and will continue in the foreseeable future. Habitat loss
and destruction has already occurred and will continue as the human
population continues to grow in central Texas. Several golden orb
populations may already be below the minimum viable population
requirement, which would cause a reduction in the number of populations
and an increase in the species' vulnerability to extinction. These
threats are exacerbated by climate change, which will increase the
frequency and magnitude of droughts. Therefore, we consider these
threats to be imminent.
The third criterion in our Listing Priority Number guidance is
intended to devote resources to those species representing highly
distinctive or isolated gene pools as reflected by taxonomy. The golden
orb is a valid taxon at the species level and, therefore, receives a
higher priority than subspecies, but a lower priority than species in a
monotypic genus. Therefore, we assigned golden orb an LPN of 8.
We will continue to monitor the threats to the golden orb and the
species' status on an annual basis, and should the magnitude or
imminence of the threats change, we will revisit our assessment of the
LPN.
While we conclude that listing the golden orb is warranted, an
immediate proposal to list this species is precluded by other higher
priority listings, which we address in the Preclusion and Expeditious
Progress section below. Because we have assigned the golden orb an LPN
of 8, work on a proposed listing determination for the species is
precluded by work on higher priority listing actions with absolute
statutory, court-ordered, or court-approved deadlines and final listing
determinations for those species that were proposed for listing with
funds from Fiscal Year (FY) 2011. This work includes all the actions
listed in the tables below under Preclusion and Expeditious Progress.
Five-Factor Evaluation for Smooth Pimpleback
Information pertaining to the smooth pimpleback in relation to the
five factors provided in section 4(a)(1) of the Act is discussed below.
Factor A. The Present or Threatened Destruction, Modification, or
Curtailment of Its Habitat or Range.
As discussed above, the decline of mussels in Texas and across the
United States is primarily the result of habitat loss and degradation.
Chief among the causes of decline of the smooth pimpleback in Texas are
the effects of impoundments, sedimentation, dewatering, sand and gravel
mining, and chemical contaminants.
Impoundments
For general information on the effects of impoundments on
freshwater mussels, please refer to ``Impoundments'' under Factor A in
Five-Factor Evaluation for Texas Fatmucket. As with golden orb, smooth
pimpleback are able to tolerate some impoundment conditions. Smooth
pimpleback have been known to occur in three mainstem reservoirs on the
Colorado River, although all but one population is likely extirpated
(Howells 1997a, pp. 32-33; 1999, p. 16; 2005, p. 8; 2006, p. 67). Dams
continue to fragment smooth pimpleback populations, and the downstream
effects of dams are detrimental to smooth pimpleback habitat. There are
74 major reservoirs and numerous smaller impoundments within the
historical and current range of the smooth pimpleback. Thirty-one of
the 74 major reservoirs are located within the Colorado River basin and
the remaining 43 reservoirs are located within the Brazos River basin.
There are also eleven new reservoirs that have been recommended for
development as feasible alternatives to meet future water needs within
the Brazos River basin (Brazos G Regional Water Planning Group 2010, p.
4B.12-1). In addition, six new off-channel reservoirs are also being
considered for future development (Brazos G Regional Water Planning
Group 2010, p. 4B.13-2). At least one of the proposed reservoir sites
on the Little River in Milam County is in the vicinity of where a
single live smooth pimpleback was found in 2006 (Karatayev and
Burlakova 2008, p. 6).
Dam construction fragments the range of smooth pimpleback, leaving
remaining habitats and populations isolated by the structures as well
as by extensive areas of deep, uninhabitable, impounded waters. These
isolated populations are unable to naturally recolonize suitable
habitat that may be impacted by temporary but devastating events, such
as severe drought, chemical spills, or unauthorized discharges. Dams
impound river habitats throughout almost the entire range of the
species. These impoundments have left short and isolated patches of
remnant habitat, typically in between impounded reaches. Habitat
downstream of dams may be impaired for many miles; in the Brazos River
downstream of Possum Kingdom Reservoir, substrate was unstable for 150
km (240 mi) below the dam (Yeager 1993, p. 68).
For species such as smooth pimpleback that may be able to survive
the initial inundation of reservoirs, conditions within the reservoir
are likely to become uninhabitable. The deep water in reservoirs is
very cold and often devoid of oxygen and necessary nutrients (Watters
2000, p. 264). Cold water (less than 11 [deg]C (52 [deg]F)) has been
shown to stunt mussel growth (Hanson et al. 1988, p. 352). Because
mussel reproduction is temperature dependent (Watters and O'Dee 1999,
p. 455), it is
[[Page 62193]]
likely that individuals living in the constantly cold hypolimnion in
these channels may never reproduce, or reproduce less frequently
(Watters 2000, p. 264). Any smooth pimpleback that survived the initial
inundation may have been unable to reproduce, eventually eliminating
the species from large areas of the reservoir. The same would be true
for mussels living in cold-water discharges downstream of large
impoundments (Watters 2000, p. 264).
The widespread construction of dams throughout the range of smooth
pimpleback has significantly altered stream habitat both upstream and
downstream of the dams by changing fish assemblages, temperature,
dissolved oxygen, and substrate. The effects of dams are ongoing,
decades after construction. In addition, the construction of new
reservoirs is also being considered within the species' range that
could result in additional habitat loss. Because of this loss of
habitat and its effects on the populations, we conclude that the
effects of impoundments are a threat to the smooth pimpleback.
Sedimentation
For general information on the effects of sedimentation on
freshwater mussels, please refer to ``Sedimentation'' under Factor A in
Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussel species, the smooth pimpleback is
also threatened by sedimentation. The dominant land use in the Colorado
River basin is grazing (Hersh 2007, p. 11). Soil compaction from
intensive grazing may reduce infiltration rates and increase runoff,
and trampling of riparian vegetation increases the probability of
erosion (Armour et al. 1994, p. 10; Brim Box and Mossa 1999, p. 103).
Additionally, much of the Brazos River basin is grazed or farmed for
row crops, which often contributes large amounts of sediment to the
basin (Brazos River Authority 2007, p. 4). Reservoir construction in
the upper portion of the basin has been attributed with the erosion and
subsequent sedimentation of the lower river (USGS 2001, p. 30), as
sediment-poor tailwaters scour the riverbanks below the dam and deposit
sediment farther downstream. In 2004, sedimentation was high enough in
the Brazos River below Possum Kingdom Reservoir to cause residents to
raise concerns to the Brazos River Authority (Brazos River Authority
2006, p. 2), and elevated suspended sediment levels have been reported
throughout the basin (Brazos River Authority 2006, p. 8).
Sedimentation may become an increasing threat to the smooth
pimpleback in the Colorado and Brazos River basins as the Austin
metropolitan area continues to expand. Activities associated with
urbanization, such as road construction, increased impervious surfaces,
and road construction can be detrimental to stream habitats (Couch and
Hamilton 2002, p. 1). The City of Austin, population approximately
800,000 people (Austin City Connection 2011, p. 1) lies within the
Colorado River basin, and 3.9 million people live within the Brazos
River basin (Brazos River Authority 2007, p. 1). Both of these basins
have undergone substantial urbanization providing sources of increased
sediment runoff into habitats of the smooth pimpleback.
The range of the smooth pimpleback receives sediment from
increasing levels of sedimentation from agriculture, urbanization, and
sand and gravel mining; sedimentation is likely to continue to threaten
the smooth pimpleback.
Dewatering
River dewatering can occur in several ways: Anthropogenic
activities such as surface water diversions and groundwater pumping,
and natural events, such as drought, which can result in mussels
stranded in previously wetted areas. This is a particular concern for
smooth pimpleback within and below reservoirs, where water levels are
managed for various purposes that can cause water levels in the
reservoir or downstream to rise or fall in very short periods of time,
such as when hydropower facilities release water during peak energy
demand periods. The three impoundments on the Colorado River with
records of smooth pimpleback all experience periodic water level
drawdowns, which may have contributed to the species' apparent
extirpation from Inks Lake and Lake Marble Falls. In fact, smooth
pimpleback have been found stranded (which leads to death) after
drawdowns in both of these reservoirs (Howells 1996, p. 22; 1999, p.
16).
Drought can also severely impact smooth pimpleback populations. For
example, the Little Brazos River, which once contained a diverse and
numerous freshwater mussel community that included smooth pimpleback
(Gentner and Hopkins 1966, p. 458), experienced a severe drought from
about 1950 to 1956 that reduced the river to a series of small,
stagnant pools. The results of this habitat degradation from the low
water nearly eliminated the mussel community and killed many smooth
pimpleback (Gentner and Hopkins 1966, p. 458). Later, central Texas,
including the Colorado and Brazos River basins, experienced a major
drought in the late 1970s (Lewis and Oliveria 1979, p. 243). Near
record dry conditions in 2008 followed by a pattern of below-normal
rainfall during the winter and spring of 2009 led to one of the worst
droughts in recorded history for most of central Texas, including the
range of the smooth pimpleback (Nielsen-Gammon and McRoberts 2009, p.
2). This drought's severity was exacerbated by abnormally high air
temperatures, a likely effect of climate change, which has already
increased average air temperatures in Texas by at least 1 [deg]C (1.8
[deg]F) (Nielsen-Gammon and McRoberts 2009, p. 22). Instream flows
throughout the Brazos River basin during this drought were
significantly reduced (USGS 2011c, p. 1) and smooth pimpleback
populations in areas with reduced water levels, such as in the middle
Brazos River, may have been negatively affected. Central Texas is
currently experiencing another extreme drought, with rainfall between
October 2010 and July 2011 being the lowest on record during those
months (LCRA 2011c, p. 1); the effects of this drought are being
observed but are not yet fully known. Droughts result in a decrease in
water depth and flow velocity in streams inhabited by smooth
pimpleback, which reduces the availability of food and dissolved oxygen
and reduces survivability. As droughts persist, mussels face hypoxia,
elevated water temperature and, ultimately, death due to stranding
(Golladay et al. 2004, p. 501).
Sand and Gravel Mining
For general information on the effects of sand and gravel mining on
freshwater mussels, please refer to ``Sand and Gravel Mining'' under
Factor A in Five-Factor Evaluation for Texas Fatmucket.
The Brazos River has a long history of sand mining, particularly in
the lower river, and channel morphology changes have been attributed to
destabilization due to instream sand mining in the area (USGS 2001, p.
27). The removal of sand from within the river creates sediment traps
during periods of high flow, which causes scouring and erosion
downstream (USGS 2001, p. 27). One gravel dredging operation in the
Brazos River was documented depositing sediment as far as 1.6 km (1
mile) downstream (Forshage and Carter 1973, p. 697). Accelerated stream
bank erosion and downcutting of streambeds are common effects of
instream sand and gravel mining, as is the mobilization of fine
sediments during sand and gravel extraction (Roell 1999, p. 7).
[[Page 62194]]
Within the range of the smooth pimpleback, TPWD has issued permits
for four current sand mining activities within the Brazos River
(Austin, Bosque, and Fort Bend Counties) (TPWD 2004, p. 1; 2007b, p. 1,
2008b, p. 1; 2010b, p. 1). The permits allow for the repeated removal
of sand and gravel at various locations within the Brazos River. The
lower Brazos River, where these mining activities occur, contains one
of the more numerous populations of smooth pimpleback.
The smooth pimpleback population in the lower Brazos River may be
currently affected by sand and gravel mining. These activities occur
over a long period of time, destabilizing mussel habitat both upstream
and downstream, which decreases the likelihood of recolonization after
the activity has been completed. Therefore, the effects of sand and
gravel mining are an ongoing threat to the smooth pimpleback and are
expected to continue to occur throughout the range of the species.
Chemical Contaminants
For general information on the effects of chemical contaminants on
freshwater mussels, please refer to ``Chemical Contaminants'' under
Factor A in Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussels, the smooth pimpleback is also
threatened by chemical contaminants. TCEQ data for 2010 indicated that
26 of the 98 assessed water bodies within Colorado River basin and 81
of approximately 124 assessed water bodies within Brazos River basin
did not meet surface water quality standards and were classified as
impaired water bodies (Texas Clean Rivers Program 2010a, p. 5; TCEQ
2010c, pp. 1-106). These water bodies were impaired with dissolved
solids, nitrites, nitrates, bacteria, low dissolved oxygen, aluminum,
sulfates, selenium, chloride, orthophosphorus, phosphorus, Chlorophyll
a, and low pH associated with agricultural, urban, municipal, and
industrial runoff. Of these, nitrites and low dissolved oxygen are
known to be harmful to freshwater mussels. Agricultural pesticides and
emerging contaminants are likely also present in streams inhabited by
smooth pimpleback. There are 53 wastewater treatment plants permitted
to discharge more than one million gallons per day into the Brazos
River basin (Valenti and Brooks 2008, p. 12); the outfalls of these
treatment plants have not been tested to determine if they contain
contaminants of note.
Examples of the exposure of smooth pimpleback to chemical
contaminants include an event in 1993 when an unknown substance was
dumped into a segment of the Little Brazos River upstream from a smooth
pimpleback population. This site once supported an abundant and diverse
number of mussel species, including the smooth pimpleback, but when it
was revisited in 1993, a massive die-off of freshwater mussels had
occurred (Howells 2010b, p. 11). In another instance in 2010, crude oil
overflowed from a failed storage tank into Keechi Creek in Leon County,
a tributary to the Navasota River (National Response Center 2010, p.
2). This location is near a small population of smooth pimpleback and
upstream of one of the largest known populations of the species.
Numerous other spills have occurred within the range of the smooth
pimpleback. These occurred from on-site accidents (storage tank or
pipeline spills) or from tanker truck accidents within watersheds
occupied by smooth pimpleback. For example, oil has spilled into the
Brazos River a number of times. As much as 320,000 L (84,000 gal) of
crude oil was spilled in the Brazos River in Knox County in 1991
(Associated Press 1991, p. 1). In June 2010, flooding of holding ponds
adjacent to oil drilling operations leaked oil into Thompson Creek and
subsequently into the Brazos River (Lewis 2010, p. 1). Also, in July
2010, oil pipelines burst and released approximately 165 barrels of
crude oil into the upper Double Mountain Fork of the Brazos River in
Garza County (Joiner 2010, p. 1). Although no analyses were conducted
of the specific effects of these spills on smooth pimpleback, we expect
that if the mussels are exposed to even moderate levels of toxic
chemical contaminants, such as crude oil, adverse effects (both direct
mortality and indirect effects to food source availabity) are likely to
occur.
Releases of chemical contaminants, such as oil, ammonia, copper,
mercury, nutrients, pesticides, and other compounds into the habitat of
the smooth pimpleback are an ongoing threat to the smooth pimpleback.
The species is vulnerable to acute contamination from spills, as well
as chronic contaminant exposure, which has occurred and is expected to
continue to occur throughout the range of the smooth pimpleback.
Summary of Factor A
The reduction in numbers and range of the smooth pimpleback is
primarily the result of the long-lasting effects of habitat alterations
such as the effects of impoundments, sedimentation, dewatering, sand
and gravel mining, and chemical contaminants. Impoundments occur
throughout the range of the species and have far-reaching effects to
riverine habitat both upstream and downstream of the dams. Both the
Colorado and Brazos River systems have experienced a large amount of
sedimentation from agriculture, instream mining, and urban development.
Sand and gravel mining affects smooth pimpleback habitat by increasing
sedimentation and channel instability downstream and by causing
headcutting upstream. Chemical contaminants exceeding the standards
developed to support aquatic life have been documented throughout the
range of the species and may represent a significant threat to the
smooth pimpleback. However, the large populations in the San Saba
River, lower Brazos River, Navasota River, Leon River, and Yegua Creek
indicate that some smooth pimpleback populations are not currently as
vulnerable to habitat loss as others. Therefore, based upon our review
of the best commercial and scientific data available, we conclude that
the present or threatened destruction, modification, or curtailment of
its habitat or range is an immediate threat of moderate magnitude to
the smooth pimpleback.
Factor B. Overutilization for Commercial, Recreational, Scientific,
or Educational Purposes.
The smooth pimpleback is not a commercially valuable species and
has never been harvested in Texas as a commercial mussel species
(Howells 2010b, p.12). Some scientific collecting occurs but is not
likely to be a significant threat to the species because it occurs only
rarely. However, handling mussels can disturb gravid females and result
in glochidial loss and subsequent reproductive failure. Additionally,
handling has also been shown to reduce shell growth across mussel
species, including several species of Lampsilis (Haag and Commens-
Carson 2008, pp. 505-506). Repeated handling by researchers may
adversely affect smooth pimpleback individuals, but these activities
are occurring rarely and are not likely to be a threat to populations.
Handling for scientific purposes contributes to the long-term
conservation of the species.
We do not have any evidence of risks to the smooth pimpleback from
overutilization for commercial, recreational, scientific, or
educational purposes, and we have no reason to believe this factor will
become a threat to the species in the future. Based upon the best
scientific and commercial information available, we conclude that
overutilization for commercial, recreational, scientific, or
educational
[[Page 62195]]
purposes does not pose a threat to the smooth pimpleback rangewide.
Factor C. Disease and Predation.
Disease
Little is known about disease in freshwater mussels. However,
disease is believed to be a contributing factor in documented mussel
die-offs in other parts of the United States (Neves 1987, pp. 11-12).
Diseases have not been documented or observed during any studies of
smooth pimpleback.
Predation
Raccoons will prey on freshwater mussels stranded by low waters or
deposited in shallow water or on bars following flooding or low water
periods (Howells 2010c, p. 12). Predation of smooth pimpleback by
raccoons may be occurring occasionally, but there is no indication it
is a significant threat to the status of the species.
Some species of fish feed on mussels, such as common carp,
freshwater drum, and redear sunfish, all of which are common throughout
the range of smooth pimpleback (Hubbs et al. 2008, pp. 19, 45, 53).
Common species of flatworms are voracious predators of newly
metamorphosed juvenile mussels of many species (Zimmerman et al. 2003,
p. 30). Predation is a normal factor influencing the population
dynamics of a healthy mussel population; however, predation may amplify
declines in small populations primarily caused by other factors.
Summary of Factor C
Disease in freshwater mussels is poorly known, and we do not have
any information indicating it is a threat to the smooth pimpleback.
Additionally, predation is a natural ecological interaction and we have
no information indicating the extent of any predation is a threat to
populations of smooth pimpleback. Based upon the best scientific and
commercial information available, we conclude that disease or predation
is not a threat to the smooth pimpleback.
Factor D. The Inadequacy of Existing Regulatory Mechanisms.
Existing regulatory mechanisms that could have an effect on threats
to the smooth pimpleback include State and Federal laws such as Texas
Threatened and Endangered Species regulations and freshwater mussel
sanctuaries, State and Federal sand and gravel mining regulations, and
regulation of point and non-point source pollution. For more
information on the effects of State and Federal laws on the threats to
freshwater mussels in central Texas, please refer to Factor D under
Five-Factor Evaluation for Texas Fatmucket.
Summary of Factor D
Despite State and Federal laws protecting the species and water
quality, the smooth pimpleback continues to decline due to the effects
of habitat destruction, poor water quality, contaminants, and other
factors. The regulatory measures described under Factor D in the Five-
Factor Evaluation for Texas Fatmucket have been insufficient to
significantly reduce or remove the threats to the smooth pimpleback.
Based upon our review of the best commercial and scientific data
available, we conclude that the lack of existing regulatory mechanisms
is an immediate and ongoing threat of moderate magnitude to the smooth
pimpleback.
Factor E. Other Natural or Manmade Factors Affecting Its Continued
Existence.
Natural and manmade factors that threaten the smooth pimpleback
include climate change, population fragmentation and isolation, and
nonnative species.
Climate Change
For general information on the effects of climate change on
freshwater mussels of central Texas, please refer to ``Climate Change''
under Factor E in Five-Factor Evaluation for Texas Fatmucket. Because
the range of the smooth pimpleback has been reduced to isolated
locations, many with low population numbers, in small rivers and
streams, the smooth pimpleback is vulnerable to climatic changes that
could decrease the availability of water.
The disjunct nature of the remaining smooth pimpleback populations,
coupled with the limited ability of mussels to migrate, makes it
unlikely that smooth pimpleback can adjust their range in response to
changes in climate (Strayer 2008, p. 30). Climate change exacerbates
threats to the smooth pimpleback, such as habitat degradation from
prolonged periods of drought; increased water temperature; and the
increased allocation of water for municipal, agricultural, and
industrial uses The magnitude and imminence of these effects, however,
remain uncertain. Based upon our review of the best commercial and
scientific data available, we conclude that the effects of climate
change in the future will likely exacerbate the current and ongoing
threats of habitat loss and degradation caused by other factors, as
discussed in Factor A.
Population Fragmentation and Isolation
For general information on the effects of population fragmentation
and isolation on freshwater mussels of central Texas, please refer to
``Population Fragmentation and Isolation'' under Factor E in Five-
Factor Evaluation for Texas Fatmucket. As with many freshwater mussels,
several of the remaining populations of the smooth pimpleback are small
and geographically isolated and thus are susceptible to genetic drift,
inbreeding depression, and random or chance changes to the environment,
such as toxic chemical spills (Watters and Dunn 1995, pp. 257-258), or
dewatering. Historically, the smooth pimpleback was widespread
throughout much of the Colorado and Brazos River systems when few
natural barriers existed to prevent migration (via host species) among
suitable habitats. The extensive impoundment of the Brazos and Colorado
River basins has fragmented smooth pimpleback populations throughout
these river systems.
Small smooth pimpleback populations, including those in Lake LBJ
Reservoir and the middle Brazos, Little, and Little Brazos Rivers, may
be below the minimum population size required to maintain population
viability into the future, therefore making these populations more
vulnerable to extirpation since they are less likely to be able to
recover through recruitment from events that reduce but do not
extirpate populations. Additionally, these small populations are more
vulnerable to extirpation from stochastic events, as the lack of
connectivity among populations does not permit nearby populations to
recolonize areas affected by intense droughts, toxic spills, or other
isolated events that result in significant mussel die-offs. While the
small, isolated populations do not represent an independent threat to
the species, the situation does substantially increase the risk of
extirpation from the effects of all other threats, including those
addressed in this analysis, and those that could occur in the future
from unknown sources.
Based upon our review of the best commercial and scientific data
available, we conclude that fragmentation and isolation of small
remaining populations of the smooth pimpleback are occurring and are
ongoing threats to the species throughout all of its range. Further,
stochastic events may play a magnified role in extirpation of small,
isolated populations.
[[Page 62196]]
Nonnative Species
For general information on the effects of nonnative species on
freshwater mussels of central Texas, please refer to ``Nonnative
Species'' in Factor E under Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussels, the smooth pimpleback is threatened
by nonnative species. Various nonnative aquatic species pose a threat
to the smooth pimpleback, including golden algae, zebra mussels, and
black carp. Of these, golden algae has been responsible for killing
more than eight million fish in the Brazos River since 1981 and more
than two million fish in the Colorado River since 1989 (TPWD 2010a, p.
1). Although mussel kills due to golden algae have not been recorded,
we expect golden algae to negatively affect mussel populations through
loss of host fish and direct toxicity. Zebra mussels and black carp do
not currently occur within the range of the smooth pimpleback, although
both are found in Texas and could be introduced to the Brazos and
Colorado Rivers in the forseeable future. Based on population responses
of other mussel species that overlap with zebra mussels and black carp
in similar river conditions, we conclude that the introduction of zebra
mussels or black carp into the range of smooth pimpleback would be
devastating to the species.
Based upon our review of the best commercial and scientific data
available, we conclude that golden algae is an ongoing threat to the
smooth pimpleback, and other nonnative species, such as zebra mussels
and black carp, are a potential threat to the smooth pimpleback that is
likely to increase as these exotic species expand their occupancy to
include the range of the smooth pimpleback.
Summary of Factor E
The effects of climate change, while difficult to quantify at this
time, are likely to exacerbate the current and ongoing threat of
habitat loss caused by other factors, and the small sizes and
fragmented nature of the remaining populations render them more
vulnerable to extirpation. In addition, nonnative species, such as
golden algae, currently threaten the Texas fatmucket, and the potential
introduction of zebra mussels and black carp are potential future
threats. Based upon our review of the best commercial and scientific
data available, we conclude that other natural or manmade factors are
immediate and ongoing threats of moderate magnitude to the smooth
pimpleback.
Finding for Smooth Pimpleback
As required by the Act, we considered the five factors in assessing
whether the smooth pimpleback is threatened or endangered throughout
all of its range. We examined the best scientific and commercial
information available regarding the past, present, and future threats
faced by the smooth pimpleback. We reviewed the petition, information
available in our files, and other available published and unpublished
information, and we consulted with recognized smooth pimpleback experts
and other Federal and State agencies.
This status review identifies threats to the smooth pimpleback
attributable to Factors A, D, and E. The primary threat to the species
is from habitat destruction and modification (Factor A) from
impoundments, which scour riverbeds, thereby removing mussel habitat,
decreases water quality, modifies stream flows, and restricts fish host
migration and distribution of freshwater mussels. Additional threats
under Factor A include sedimentation, dewatering, sand and gravel
mining, and chemical contaminants. Also, most of these threats may be
exacerbated by the current and projected effects of climate change
(discussed under Factor E). Threats to the smooth pimpleback are not
being adequately addressed through existing regulatory mechanisms
(Factor D). Because of the limited distribution of this endemic species
and its lack of mobility, these threats are likely to lead to the
extinction of the smooth pimpleback in the foreseeable future.
On the basis of the best scientific and commercial information
available, we find that the petitioned action to list the smooth
pimpleback under the Act is warranted. We will make a determination on
the status of the species as threatened or endangered when we complete
a proposed listing determination. When we complete a proposed listing
determination, we will examine whether the species may be endangered or
threatened throughout all of its range; or whether the species may be
endangered or threatened in a significant portion of its range.
However, as explained in more detail below, an immediate proposal of a
regulation implementing this action is precluded by higher priority
listing actions, and progress is being made to add or remove qualified
species from the Lists of Endangered and Threatened Wildlife and
Plants.
We reviewed the available information to determine if the existing
and foreseeable threats render the smooth pimpleback at risk of
extinction now such that issuing an emergency regulation temporarily
listing the species under section 4(b)(7) of the Act is warranted. We
determined that issuing an emergency regulation temporarily listing the
species is not warranted for the smooth pimpleback at this time,
because we have not identified a threat or activity that poses a
significant risk, such that losses to the species during the normal
listing process would endanger the continued existence of the entire
species. However, if at any time we determine that issuing an emergency
regulation temporarily listing the smooth pimpleback is warranted, we
will initiate this action at that time.
Listing Priority Number for Smooth Pimpleback
The Service adopted guidelines on September 21, 1983 (48 FR 43098),
to establish a rational system for utilizing available resources for
the highest priority species when adding species to the Lists of
Endangered and Threatened Wildlife and Plants or reclassifying species
listed as threatened to endangered status. These guidelines, titled
``Endangered and Threatened Species Listing and Recovery Priority
Guidelines'' address the immediacy and magnitude of threats, and the
level of taxonomic distinctiveness by assigning priority in descending
order to monotypic genera (genus with one species), full species, and
subspecies (or equivalently, distinct population segments of
vertebrates).
As a result of our analysis of the best available scientific and
commercial information, we have assigned the smooth pimpleback an LPN
of 8, based on our finding that the species faces threats that are of
moderate magnitude and are imminent. These threats include habitat loss
and degradation from impoundments, sedimentation, sand and gravel
mining, and chemical contaminants; other natural or manmade factors
such as climate change, small, isolated populations, and nonnative
species; and the fact that the threats to the species are not being
adequately addressed by existing regulatory mechanisms. Our rationale
for assigning the smooth pimpleback an LPN of 8 is outlined below.
We consider the threats that the smooth pimpleback faces to be
moderate in magnitude. Habitat loss and degradation from impoundments,
sedimentation, sand and gravel mining, and chemical contaminants are
widespread throughout the range of the smooth pimpleback, but several
large populations remain, including one that was recently discovered,
indicating the threats are not high in magnitude.
[[Page 62197]]
Under our LPN guidelines, the second criterion we consider in
assigning a listing priority is the immediacy of threats. We consider
the threats to the smooth pimpleback as described under ``Factor A. The
Present or Threatened Destruction, Modification, or Curtailment of Its
Habitat or Range,'' ``Factor D. The Inadequacy of Existing Regulatory
Mechanisms,'' and ``Factor E. Other Natural Or Manmade Factors
Affecting Its Continued Existence'' under the Five-Factor Evaluation
for Smooth Pimpleback to be imminent because these threats are ongoing
and will continue in the foreseeable future. Habitat loss and
destruction has already occurred and will continue as the human
population continues to grow in central Texas. Several smooth
pimpleback populations may already be below the minimum viable
population requirement, which would cause a reduction in the number of
populations and an increase in the species' vulnerability to
extinction. These threats are exacerbated by climate change, which will
increase the frequency and magnitude of droughts. Therefore, we
consider these threats to be imminent.
Thirdly, the smooth pimpleback is a valid taxon at the species
level and, therefore, receives a higher priority than subspecies, but a
lower priority than species in a monotypic genus. Therefore, we
assigned smooth pimpleback an LPN of 8. We will continue to monitor the
threats to the smooth pimpleback and the species' status on an annual
basis, and should the magnitude or imminence of the threats change, we
will revisit our assessment of the LPN.
While we conclude that listing the smooth pimpleback is warranted,
an immediate proposal to list this species is precluded by other higher
priority listings, which we address in the Preclusion and Expeditious
Progress section below. Because we have assigned the smooth pimpleback
an LPN of 8, work on a proposed listing determination for the species
is precluded by work on higher priority listing actions with absolute
statutory, court-ordered, or court-approved deadlines and final listing
determinations for those species that were proposed for listing with
funds from Fiscal Year (FY) 2011. This work includes all the actions
listed in the tables below under Preclusion and Expeditious Progress.
Five-Factor Evaluation for Texas Pimpleback
Information pertaining to the Texas pimpleback in relation to the
five factors provided in section 4(a)(1) of the Act is discussed below.
Factor A. The Present or Threatened Destruction, Modification, or
Curtailment of Its Habitat or Range.
As discussed above, the decline of mussels in Texas and across the
United States is primarily the result of habitat loss and degradation.
Chief among the causes of decline of the Texas pimpleback are the
effects of impoundments, sedimentation, dewatering, sand and gravel
mining, and chemical contaminants. These threats are discussed below.
Impoundments
For general information on the effects of impoundments on
freshwater mussels, please refer to ``Impoundments'' in Factor A under
Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussel species, the Texas pimpleback is
also threatened by impoundments. There are 37 major reservoirs and
numerous smaller impoundments within the historical and current range
of the Texas pimpleback. There are 31 major reservoirs within the
Colorado River basin, with another reservoir (Goldthwaite Reservoir)
proposed for the Colorado River in San Saba County near a Texas
pimpleback population; this reservoir was the number one recommendation
in the water plan for the region (TWDB 2011, pp. 4-85). There are 29
reservoirs within the Guadalupe River basin and 34 within the San
Antonio River basin, each with a storage capacity of 3,000 acre-feet or
more, and many other smaller reservoirs (Exelon 2010, p. 2.3-4). The
majority of the large dams were constructed for power generation, flood
control, and water supply by the Lower Colorado River and Guadalupe-
Blanco River Authorities beginning as early as 1935 (Guadalupe-Blanco
River Authority 2011, p. 1; LCRA 2011a, p. 1). These and numerous
smaller dams occur throughout the Colorado and Guadalupe River basins,
fragmenting habitat and populations of Texas pimpleback.
There are no natural lakes within the range of the Texas
pimpleback, nor has it ever been found in reservoirs. Historically, the
Texas pimpleback could be found in areas of the Guadalupe River in
Comal County (Randklev et al. 2010c, p. 4), but it has not been found
in the area since the construction of Canyon Reservoir (Burlakova and
Karatayev 2009, p. 6). We presume the species is extirpated from this
reach because of the effects of the reservoir. Surveys of other
reservoirs on the Guadalupe and Colorado Rivers have been ongoing since
at least 1992, and no evidence of live or dead Texas pimpleback has
been found in any reservoir (Howells 1994, pp. 1-20; 1995, pp. 1-50;
1996, pp. 1-45; 1997a, pp. 1-58; 1998, pp. 1-30; 1999, pp. 1-34; 2000a,
pp. 1-56; 2001, pp. 1-50; 2002a, pp. 1-28; 2003, pp. 1-42; 2004, pp. 1-
48; 2005, pp. 1-23; 2006, pp. 1-106; Karatayev and Burlakova 2008, pp.
1-47; Burlakova and Karatayev 2010a, pp. 1-30; 2011, pp. 1-8), further
indicating that this species is not tolerant of impoundments.
Texas pimpleback populations downstream of dams are affected as
well. Cold water (less than 11 [deg]C (52 [deg]F)) has been shown to
stunt mussel growth (Hanson et al. 1988, p. 352) and reduce or inhibit
reproduction, because mussel reproduction is temperature dependent
(Watters and O'Dee 1999, pp. 455). Texas pimpleback living in cold-
water discharges downstream of large impoundments are unlikely to
reproduce (Watters 2000, p. 264).
Dam construction also fragments the range of Texas pimpleback,
leaving remaining habitats and populations isolated by the structures
as well as by extensive areas of deep, uninhabitable, impounded waters.
These isolated populations are unable to naturally recolonize suitable
habitat that may be impacted by temporary but devastating events, such
as severe drought, chemical spills, or unauthorized discharges. Dams
impound river habitats throughout almost the entire range of the
species. These impoundments have left short and isolated patches of
suitable habitat, typically in between impounded reaches.
The widespread construction of dams throughout the range of Texas
pimpleback has significantly altered stream habitat both upstream and
downstream of the dams by changing fish assemblages, temperature,
dissolved oxygen, and substrate. The effects of dams are ongoing
decades after construction. Because of this loss of habitat and its
effects on the populations, we conclude that the effects of dams are a
threat to the Texas pimpleback.
Sedimentation
For general information on the effects of sedimentation on
freshwater mussels, please refer to ``Sedimentation'' in Factor A under
Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussel species, the Texas pimpleback is
affected by sedimentation. The dominant land use in the Colorado River
basin is grazing (Hersh 2007, p. 11); soil compaction from intensive
[[Page 62198]]
grazing may reduce infiltration rates and increase runoff, and
trampling of riparian vegetation increases the probability of erosion
(Armour et al. 1994, p. 10; Brim Box and Mossa 1999, p. 103). Even in
1959, the Guadalupe River was noted as having high sedimentation rates
from agricultural activities (Soil Conservation Service 1959, p. 59).
Turbidity has also been recorded as high in the Guadalupe River near
Victoria (Exelon 2010, p. 2.3-186), indicating a large amount of
suspended sediment where a small Texas pimpleback population was
recently found.
Streams occupied by Texas pimpleback are subject to increasing
levels of sedimentation from agriculture, urbanization, and sand and
gravel mining. Agriculture is a common land use in the Guadalupe and
San Antonio River basins, and the city of San Antonio, the second
largest city in Texas, continues to grow (City of San Antonio 2010, p.
5). Sedimentation from agriculture, urbanization, and sand and gravel
mining will continue to threaten the Texas pimpleback in the
foreseeable future.
Dewatering
River dewatering can occur in several ways: Anthropogenic
activities such as surface water diversions and groundwater pumping,
and natural events, such as drought, which can result in mussels
stranded in previously wetted areas. This is a particular concern below
reservoirs, whose water levels are managed for various purposes that
can cause water levels in the reservoir or downstream to rise or fall
in very short periods of time, such as when hydropower facilities
release water during peak energy demand periods.
Drought can also severely impact Texas pimpleback populations.
Central Texas, including the Colorado and Guadalupe River basins,
experienced a major drought in the late 1970s (Lewis and Oliveria 1979,
p. 243). Near record dry conditions in 2008 followed by a pattern of
below-normal rainfall during the winter and spring of 2009 led to one
of the worst droughts in recorded history for most of central Texas,
including the range of the Texas pimpleback (Nielsen-Gammon and
McRoberts 2009, p. 2). This drought's severity was exacerbated by
abnormally high air temperatures, a likely effect of climate change,
which has already increased average air temperatures in Texas by at
least 1 [deg]C (1.8 [deg]F) (Nielsen-Gammon and McRoberts 2009, p. 22).
Instream flows throughout the Colorado River basin during this drought
were significantly reduced (USGS 2011c, p. 1) and Texas pimpleback
populations in areas with reduced water levels may have been negatively
affected. Central Texas is currently experiencing another extreme
drought, with rainfall between October 2010 and July 2011 being the
lowest on record during those months (LCRA 2011c, p. 1); the effects of
this drought are being observed but are not yet fully known. Droughts
result in a decrease in water depth and flow velocity, which reduces
food and oxygen delivery. As droughts persist, mussels face hypoxia,
elevated water temperature and, ultimately, stranding (Golladay et al.
2004, p. 501).
We do not know the extent of the impacts of stream dewatering on
the Texas pimpleback; however, because several populations are small
and isolated, the loss of numerous individuals at a site can have
dramatic consequences to the population. Hydropower facilities,
diversions associated with construction, and drought are occurring
throughout the range of the Texas pimpleback; therefore, the effects of
dewatering are ongoing and unlikely to decrease, resulting in
significant threats to the Texas pimpleback.
Sand and Gravel Mining
For general information on the effects of sand and gravel mining on
freshwater mussels, please refer to ``Sand and Gravel Mining'' in
Factor A under Five-Factor Evaluation for Texas Fatmucket.
In 1995, the reach of the Guadalupe River near Victoria, which
contains a Texas pimpleback population, was described as having
numerous current and abandoned sand and gravel mining areas (USACE
1995, p. 7). Currently, TPWD has permitted one sand mining activity
within the current range of Texas pimpleback, in the Guadalupe River
basin in Comal County (TPWD 2009b, p. 1); a small Texas pimpleback
population occurs downstream of this area in the Guadalupe River. The
permit allows for the repeated removal of sand and gravel at various
locations within the stream.
Headcuts from sand and gravel mining operations have been
documented in the San Antonio River basin in Karnes County from as
early as 1967, with downstream channels having steep, eroded banks
(Kennon et al. 1967, p. 22). There has been no evidence of Texas
pimpleback in Karnes County in recent years (Howells 1997a, pp. 41-42),
and the effects of sand mining may have been a factor in the species'
extirpation.
The Texas pimpleback population in the Guadalupe River may be
currently threatened by sand and gravel mining. These activities occur
over a long period of time, destabilizing habitat both upstream and
downstream, which decreases the likelihood of recolonization after the
activity has been completed. Therefore, the effects of sand and gravel
mining are an ongoing threat to the Texas pimpleback.
Chemical Contaminants
For general information on the effects of chemical contaminants on
freshwater mussels, please refer to ``Chemical Contaminants'' in Factor
A under Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussels, the Texas pimpleback is affected
by chemical contaminants. TCEQ data for 2010 indicated that 26 of the
98 assessed water bodies within the historical and current range of the
Texas pimpleback did not meet surface water quality standards and were
classified as impaired water bodies under the Clean Water Act (Texas
Clean Rivers Program 2010a, p. 5). These water bodies were impaired
with dissolved solids, nitrates, bacteria, low dissolved oxygen,
aluminum, sulfates, selenium, chloride, and low pH associated with
agricultural, urban, municipal, and industrial runoff. Additionally,
the Concho River near Paint Rock has been repeatedly documented as
having high nitrates (Texas Clean Rivers Program 2008, p. 2); a
significant Texas pimpleback population occurs just upstream of this
site. Nitrates and low dissolved oxygen pose the greatest threat to
Texas pimpleback.
Within the range of Texas pimpleback, several streams have been
listed as impaired due to high ammonia concentrations, including Elm
Creek in the Guadalupe River basin (TCEQ 2010a, p. 294). Additionally,
high copper concentrations have been recorded in the lower Guadalupe
and San Antonio Rivers (Lee and Schultz 1994, p. 8), and mercury has
been documented throughout the Guadalupe and San Antonio Rivers, with
particularly high concentrations in fish in the upper reaches of both
rivers (Lee and Schultz 1994, p. 8). Agricultural pesticides and
emerging contaminants are likely also present in streams inhabited by
Texas pimpleback.
Chemical contaminants, such as ammonia, copper, mercury, nutrients,
pesticides, and other compounds are currently a threat to the Texas
pimpleback. The species is vulnerable to acute contamination from
spills as well as chronic contaminant exposure, which is occurring
rangewide.
Summary of Factor A
The reduction in numbers and range of the Texas pimpleback is
primarily the
[[Page 62199]]
result of the long-lasting effects of habitat alterations such as the
effects of impoundments, sedimentation, sand and gravel mining, and
chemical contaminants. Impoundments occur throughout the range of the
species and have far-reaching effects both up and downstream. Both the
Colorado and Guadalupe River systems have experienced a large amount of
sedimentation from agriculture, instream mining, and urban development.
Sand and gravel mining affects Texas pimpleback habitat by increasing
sedimentation and channel instability downstream and causing
headcutting upstream. Chemical contaminants have been documented
throughout the range of the species and may represent a significant
threat to the Texas pimpleback. Based upon our review of the best
commercial and scientific data available, we conclude that the present
or threatened destruction, modification, or curtailment of its habitat
or range is an immediate threat of high magnitude to the Texas
pimpleback.
Factor B. Overutilization for Commercial, Recreational, Scientific,
or Educational Purposes.
The Texas pimpleback was historically harvested occasionally but
never experienced high levels of collecting pressure (Howells 2010e,
p.10). Although levels were light enough that commercial harvest was
likely not a threat to populations, all commercial collecting became
illegal when Texas pimpleback was listed as threatened by TPWD;
therefore, commercial harvest is not a current threat to Texas
pimpleback. Some scientific collecting occurs but is not likely to be a
significant threat to the species because it occurs only rarely.
However, handling mussels can disturb gravid females and result in
glochidial loss and subsequent reproductive failure. Additionally,
handling has been shown to reduce shell growth across mussel species,
including several species of Lampsilis (Haag and Commens-Carson 2008,
pp. 505-506). Repeated handling by researchers may adversely affect
Texas pimpleback individuals, but these activities are occurring rarely
and are not likely to be a threat to populations. Handling for
scientific purposes contributes to the long-term conservation of the
species.
We do not have any evidence of risks to the Texas pimpleback from
overutilization for commercial, recreational, scientific, or
educational purposes, and we have no reason to believe this factor will
become a threat to the species in the future. Based upon the best
scientific and commercial information available, we conclude that
overutilization for commercial, recreational, scientific, or
educational purposes does not pose a significant threat to the Texas
pimpleback rangewide.
Factor C. Disease and Predation.
Disease
Little is known about disease in freshwater mussels. However,
disease is believed to be a contributing factor in documented mussel
die-offs in other parts of the United States (Neves 1987, pp. 11-12).
Diseases have not been documented or observed during any studies of
Texas pimpleback.
Predation
Raccoons will prey on freshwater mussels stranded by low waters or
deposited in shallow water or on bars following flooding or low water
periods (Howells 2010c, p. 12). Predation of Texas pimpleback by
raccoons may be occurring occasionally but there is no indication it is
a significant threat to the status of the species.
Some species of fish feed on mussels, such as common carp,
freshwater drum, and redear sunfish, all of which are common throughout
the range of Texas pimpleback (Hubbs et al. 2008, pp. 19, 45, 53).
Common species of flatworms are voracious predators of newly
metamorphosed juvenile mussels of many species (Zimmerman et al. 2003,
p. 30). Predation is a normal factor influencing the population
dynamics of a healthy mussel population; however, predation may amplify
declines in small populations primarily caused by other factors.
Summary of Factor C
Disease in freshwater mussels is poorly known, and we do not have
any information indicating it is a threat to the Texas pimpleback.
Additionally, predation is a natural ecological interaction and we have
no information indicating the extent of any predation is a threat to
populations of Texas pimpleback. Based upon the best scientific and
commercial information available, we conclude that disease or predation
is not a threat to the Texas pimpleback.
Factor D. The Inadequacy of Existing Regulatory Mechanisms.
Existing regulatory mechanisms that could have an effect on threats
to the Texas pimpleback include State and Federal laws such as Texas
Threatened and Endangered Species regulations and freshwater mussel
sanctuaries, State and Federal sand and gravel mining regulations, and
regulation of point and non-point source pollution. For more
information on the effects of State and Federal laws on the threats to
freshwater mussels in central Texas, please refer to Factor D under
Five-Factor Evaluation for Texas
Fatmucket
Summary of Factor D
Despite State and Federal laws protecting the species and water
quality, the Texas pimpleback continues to decline due to the effects
of habitat destruction, poor water quality, contaminants, and other
factors. The regulatory measures described above have been insufficient
to significantly reduce or remove the threats to the Texas pimpleback.
Based upon our review of the best commercial and scientific data
available, we conclude that the lack of existing regulatory mechanisms
is an immediate threat of moderate magnitude to the Texas pimpleback.
Factor E. Other Natural or Manmade Factors Affecting Its Continued
Existence.
Natural and manmade factors that threaten the Texas pimpleback
include climate change, population fragmentation and isolation, and
nonnative species.
Climate Change
For general information on the effects of climate change on
freshwater mussels of central Texas, please refer to``Climate Change''
in Factor E under Five-Factor Evaluation for Texas Fatmucket. Because
the range of the Texas pimpleback has been reduced to isolated
locations with low population numbers in small rivers and streams, the
Texas pimpleback is vulnerable to climatic changes that could decrease
the availability of water.
The disjunct nature of the remaining Texas pimpleback populations,
coupled with the limited ability of mussels to migrate, makes it
unlikely that Texas pimpleback can adjust their range in response to
changes in climate (Strayer 2008, p. 30). Climate change could affect
the Texas pimpleback through the combined effects of global and
regional climate change, along with the increased probability of long-
term drought. Climate change exacerbates threats such as habitat
degradation from prolonged periods of drought, increased water
temperature, and the increased allocation of water for municipal,
agricultural, and industrial use. Climate change may be a significant
stressor that exacerbates existing threats by increasing the likelihood
of prolonged drought. As such, climate change, in and of itself, may
affect the Texas
[[Page 62200]]
pimpleback, but the magnitude and imminence of the effects remain
uncertain. Based upon our review of the best commercial and scientific
data available, we conclude that the effects of climate change in the
future will likely exacerbate the current and ongoing threats of
habitat loss and degradation caused by other factors, as discussed
above.
Population Fragmentation and Isolation
For more information on the effects of population fragmentation and
isolation on freshwater mussels of central Texas, please refer to
``Population Fragmentation and Isolation'' in Factor E under Five-
Factor Evaluation for Texas Fatmucket. As with many freshwater mussels,
most of the remaining populations of the Texas pimpleback are small and
geographically isolated and thus are susceptible to genetic drift,
inbreeding depression, and random or chance changes to the environment,
such as toxic chemical spills (Watters and Dunn 1995, pp. 257-258) or
dewatering. Historically, the Texas pimpleback was once widespread
throughout much of the Colorado and Guadalupe River systems when few
natural barriers existed to prevent migration (via host species) among
suitable habitats. The extensive impoundment of the Colorado and
Guadalupe River basins has fragmented Texas pimpleback populations
throughout these river systems.
Small Texas pimpleback populations, including those in the lower
Guadalupe River, mainstem Colorado River, and San Marcos River, may be
below the minimum population size required to maintain population
viability into the future. These populations are more vulnerable to
extirpation since they are less likely to be able to recover through
recruitment from events that reduce but do not extirpate populations.
Additionally, these small populations are more vulnerable to
extirpation from stochastic events, as the lack of connectivity among
populations does not permit nearby populations to recolonize areas
affected by intense droughts, toxic spills, or other isolated events
that result in significant mussel die-offs. While the small, isolated
populations do not represent an independent threat to the species, the
situation does substantially increase the risk of extirpation from the
effects of all other threats, including those addressed in this
analysis, and those that could occur in the future from unknown
sources.
Based upon our review of the best commercial and scientific data
available, we conclude that fragmentation and isolation of small
remaining populations of the Texas pimpleback are occurring and are
ongoing threats to the species throughout all of its range. Further,
stochastic events may play a magnified role in extirpation of small,
isolated populations.
Nonnative Species
For general information on the effects of nonnative species on
freshwater mussels of central Texas, please refer to ``Nonnative
Species'' in Factor E under Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussels, the Texas pimpleback is threatened by
nonnative species. Various nonnative aquatic species pose a threat to
the Texas pimpleback, including golden algae, zebra mussels, and black
carp. Of these, golden algae has been responsible for killing more than
two million fish in the Colorado River since 1989 (TPWD 2010a, p. 1).
Although mussel kills due to golden algae have not been recorded, we
expect golden algae to negatively affect mussel populations through
loss of host fish and direct toxicity. Zebra mussels and black carp do
not currently occur within the range of the Texas pimpleback, although
both are found in Texas and could be introduced to the Colorado and
Guadalupe Rivers in the forseeable future. Their introduction into the
range of Texas pimpleback would be devastating.
Based upon our review of the best commercial and scientific data
available, we conclude that golden algae is an ongoing threat to the
Texas pimpleback and other nonnative species, such as zebra mussels and
black carp, are a potential threat to the Texas pimpleback that is
likely to increase as these exotic species expand their occupancy
within the range of the Texas pimpleback.
Summary of Factor E
The effects of climate change, while difficult to quantify at this
time, are likely to exacerbate the current and ongoing threat of
habitat loss caused by other factors, and the small sizes and
fragmented nature of the remaining populations render them more
vulnerable to extirpation. In addition, nonnative species, such as
golden algae, currently threaten the Texas fatmucket, and the potential
introduction of zebra mussels and black carp are potential future
threats. Based upon our review of the best commercial and scientific
data available, we conclude that other natural or manmade factors are
immediate threats of moderate magnitude to the Texas pimpleback.
Finding for Texas Pimpleback
As required by the Act, we considered the five factors in assessing
whether the Texas pimpleback is threatened or endangered throughout all
of its range. We examined the best scientific and commercial
information available regarding the past, present, and future threats
faced by the Texas pimpleback. We reviewed the petition, information
available in our files, and other available published and unpublished
information, and we consulted with recognized Texas pimpleback experts
and other Federal and State agencies.
This status review identifies threats to the Texas pimpleback
attributable to Factors A, D, and E. The primary threat to the species
is from habitat destruction and modification (Factor A) from
impoundments, which scour riverbeds, thereby removing mussel habitat,
decrease water quality, modify stream flows, and restrict fish host
migration and distribution of freshwater mussels. Additional threats
under Factor A include sedimentation, dewatering, sand and gravel
mining, and chemical contaminants. Also, most of these threats may be
exacerbated by the current and projected effects of climate change
(discussed under Factor E). Threats to the Texas pimpleback are not
being adequately addressed through existing regulatory mechanisms
(Factor D). Because of the limited distribution of this endemic species
and its lack of mobility, these threats are likely to lead to the
extinction of the Texas pimpleback in the foreseeable future.
On the basis of the best scientific and commercial information
available, we find that the petitioned action to list the Texas
pimpleback under the Act is warranted. We will make a determination on
the status of the species as threatened or endangered when we complete
a proposed listing determination. When we complete a proposed listing
determination, we will examine whether the species may be endangered or
threatened throughout all of its range or whether the species may be
endangered or threatened in a significant portion of its range.
However, as explained in more detail below, an immediate proposal of a
regulation implementing this action is precluded by higher priority
listing actions, and progress is being made to add or remove qualified
species from the Lists of Endangered and Threatened Wildlife and
Plants.
We reviewed the available information to determine if the existing
and foreseeable threats render the Texas
[[Page 62201]]
pimpleback at risk of extinction now such that issuing an emergency
regulation temporarily listing the species under section 4(b)(7) of the
Act is warranted. We determined that issuing an emergency regulation
temporarily listing the species is not warranted for the Texas
pimpleback at this time, because we have not identified a threat or
activity that poses a significant risk, such that losses to the species
during the normal listing process would endanger the continued
existence of the entire species. However, if at any time we determine
that issuing an emergency regulation temporarily listing the Texas
pimpleback is warranted, we will initiate this action at that time.
Listing Priority Number for Texas Pimpleback
The Service adopted guidelines on September 21, 1983 (48 FR 43098),
to establish a rational system for utilizing available resources for
the highest priority species when adding species to the Lists of
Endangered and Threatened Wildlife and Plants or reclassifying species
listed as threatened to endangered status. These guidelines, titled
``Endangered and Threatened Species Listing and Recovery Priority
Guidelines'' address the immediacy and magnitude of threats, and the
level of taxonomic distinctiveness by assigning priority in descending
order to monotypic genera (genus with one species), full species, and
subspecies (or equivalently, distinct population segments of
vertebrates).
As a result of our analysis of the best available scientific and
commercial information, we have assigned the Texas pimpleback an LPN of
2, based on our finding that the species faces threats that are of high
magnitude and are imminent. These threats include habitat loss and
degradation from impoundments, sedimentation, sand and gravel mining,
and chemical contaminants; other natural or manmade factors such as
climate change, small, isolated populations, and nonnative species; and
the fact that the threats to the species are not being adequately
addressed by existing regulatory mechanisms. Our rationale for
assigning the Texas pimpleback an LPN of 2 is outlined below.
We consider the threats that the Texas pimpleback faces to be high
in magnitude. Habitat loss and degradation from impoundments,
sedimentation, sand and gravel mining, and chemical contaminants are
widespread throughout the range of the Texas pimpleback and profoundly
affect its habitat, and remaining populations are small, isolated, and
highly vulnerable to stochastic events.
Under our LPN guidelines, the second criterion we consider in
assigning a listing priority is the immediacy of threats. We consider
the threats to the Texas pimpleback as described under Factors A, D,
and E in the Five-Factor Evaluation for Texas Pimpleback section to be
imminent because these threats are ongoing and will continue in the
foreseeable future. Habitat loss and destruction has already occurred
and will continue as the human population continues to grow in central
Texas. The Texas pimpleback populations may already be below the
minimum viable population requirement, which would cause a reduction in
the number of populations and an increase in the species' vulnerability
to extinction. These threats are exacerbated by climate change, which
will increase the frequency and magnitude of droughts. Therefore, we
consider these threats to be imminent.
Thirdly, the Texas pimpleback is a valid taxon at the species level
and, therefore, receives a higher priority than subspecies, but a lower
priority than species in a monotypic genus. Therefore, we assigned
Texas pimpleback an LPN of 2. We will continue to monitor the threats
to the Texas pimpleback and the species' status on an annual basis, and
should the magnitude or imminence of the threats change, we will
revisit our assessment of the LPN.
While we conclude that listing the Texas pimpleback is warranted,
an immediate proposal to list this species is precluded by other higher
priority listings, which we address in the Preclusion and Expeditious
Progress section below. Because we have assigned the Texas pimpleback
an LPN of 2, work on a proposed listing determination for the species
is precluded by work on higher priority listing actions with absolute
statutory, court-ordered, or court-approved deadlines and final listing
determinations for those species that were proposed for listing with
funds from Fiscal Year (FY) 2010. This work includes all the actions
listed in the tables below under Preclusion and Expeditious Progress.
Five-Factor Evaluation for Texas Fawnsfoot
Information pertaining to the Texas fawnsfoot in relation to the
five factors provided in section 4(a)(1) of the Act is discussed below.
Factor A. The Present or Threatened Destruction, Modification, or
Curtailment of Its Habitat or Range.
As discussed above, the decline of mussels in Texas and across the
United States is primarily the result of habitat loss and degradation.
Chief among the causes of decline of the Texas fawnsfoot in Texas are
the effects of impoundments, sedimentation, dewatering, sand and gravel
mining, and chemical contaminants. These threats are discussed below.
Impoundments
For general information on the effects of impoundments on
freshwater mussels, please refer to ``Impoundments'' in Factor A under
Five-Factor Evaluation for Texas Fatmucket. Impoundments and numerous
smaller dams occur throughout the Colorado and Guadalupe River basins,
fragmenting habitat and populations of Texas fawnsfoot. There are 74
major reservoirs and numerous smaller impoundments within the
historical and current range of the smooth pimpleback. Thirty-one of
the 74 major reservoirs are located within the Colorado River basin and
the remaining 43 reservoirs are located within the Brazos River basin.
There are also eleven new reservoirs that have been recommended for
development as feasible alternatives to meet future water needs within
the Brazos River basin (Brazos G Regional Water Planning Group 2010, p.
4B.12-1). In addition, six new off-channel reservoirs are also being
considered for future development (Brazos G Regional Water Planning
Group 2010, p. 4B.13-2).
There are no natural lakes within the range of the Texas fawnsfoot,
nor has it ever been found in reservoirs. Surveys of the reservoirs on
the Brazos and Colorado Rivers have been ongoing since at least 1992,
and no evidence of live or dead Texas pimpleback has been found in any
reservoir (Howells 1994, pp. 1-20; 1995, pp. 1-50; 1996, pp. 1-45;
1997a, pp. 1-58; 1998, pp. 1-30; 1999, pp. 1-34; 2000a, pp. 1-56; 2001,
pp. 1-50; 2002a, pp. 1-28; 2003, pp. 1-42; 2004, pp. 1-48; 2005, pp. 1-
23; 2006, pp. 1-106; Karatayev and Burlakova 2008, pp. 1-47; Burlakova
and Karatayev 2010a, pp. 1-30; 2011, pp. 1-8), further indicating that
this species is not tolerant of impoundments.
Texas fawnsfoot populations downstream of dams are affected as
well. Cold water (less than 11 [deg]C (52 [deg]F)) has been shown to
stunt mussel growth (Hanson et al. 1988, p. 352) and reduce or inhibit
reproduction, because mussel reproduction is temperature dependent
(Watters and O'Dee 1999, pp. 455). Texas fawnsfoot living in cold-water
discharges downstream of large
[[Page 62202]]
impoundments are unlikely to reproduce (Watters 2000, p. 264).
Dam construction also fragments the range of Texas fawnsfoot,
leaving remaining habitats and populations isolated by the structures
as well as by extensive areas of deep, uninhabitable, impounded waters.
These isolated populations are unable to naturally recolonize suitable
habitat that may be impacted by temporary but devastating events, such
as severe drought, chemical spills, or unauthorized discharges. Dams
impound river habitats throughout almost the entire range of the
species. These impoundments have left short and isolated patches of
remnant habitat, typically in between impounded reaches. Habitat
downstream of dams may be impaired for many miles; in the Brazos River
downstream of Possum Kingdom Reservoir, substrate was unstable for 150
km (240 mi) below the dam (Yeager 1993, p. 68).
The widespread construction of dams throughout the range of Texas
fawnsfoot has significantly altered stream habitat both upstream and
downstream of the dams by changing fish assemblages, temperature,
dissolved oxygen, and substrate. The effects of dams are ongoing
decades after construction. Because of this loss of habitat and its
effects on the populations, we conclude that the effects of dams are a
threat to the Texas fawnsfoot.
Sedimentation
For general information on the effects of sedimentation on
freshwater mussels, please refer to ``Sedimentation'' in Factor A under
Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussel species, the Texas fawnsfoot is
also threatened by sedimentation. The dominant land use in the Colorado
River basin is grazing (Hersh 2007, p. 11); soil compaction from
intensive grazing may reduce infiltration rates and increase runoff,
and trampling of riparian vegetation increases the probability of
erosion (Armour et al. 1994, p. 10; Brim Box and Mossa 1999, p. 103).
Additionally, much of the Brazos River basin is grazed or farmed for
row crops, which can contribute large amounts of sediment to the basin
(Brazos River Authority 2007, p. 4). Reservoir construction in the
upper portion of the basin has been attributed with the erosion and
subsequent sedimentation of the lower river (USGS 2001, p. 30), as
sediment-poor tailwaters scour the riverbanks below the dam and deposit
sediment farther downstream. In 2004, sedimentation was high enough in
the Brazos River below Possum Kingdom Reservoir to cause residents to
raise concerns to the Brazos River Authority (Brazos River Authority
2006, p. 2). Elevated suspended sediment levels have been reported
throughout the basin (Brazos River Authority 2006, p. 8).
The LCRA TSC is proposing to construct two new 345-kV electric
transmission line facilities between Tom Green (in the Colorado River
basin near San Angelo) and Kendall Counties (in the Guadalupe River
basin north of San Antonio) to provide electrical power to accommodate
increased demand (Clary 2010, p. 1). One of the proposed project lines
would cross the San Saba River, which contains one of the more numerous
Texas fawnsfoot populations. The proposed project could negatively
affect Texas fawnsfoot habitat by clearing land within the riparian
zone and may increase sediment runoff into the San Saba River (Clary
2010, p. 9). Similar activities to accommodate Texas population growth
and demands are expected to be undertaken across the species' range and
will likely lead to additional sources of sediment in the streams
inhabited by the Texas fawnsfoot.
The City of Austin lies within the Colorado River basin, and 3.9
million people live within the Brazos River basin (Brazos River
Authority 2007, p. 1). The range of the Texas fawnsfoot receives
sediment from agriculture, urbanization, and sand and gravel mining.
Sedimentation will continue to threaten the Texas fawnsfoot in the
foreseeable future.
Dewatering
River dewatering can occur in several ways: anthropogenic
activities such as surface water diversions and groundwater pumping,
and natural events, such as drought, which can result in mussels
stranded in previously wetted areas. This is a particular concern below
reservoirs, whose water levels are managed for various purposes that
can cause water levels in the reservoir or downstream to rise or fall
in very short periods of time, such as when hydropower facilities
release water during peak energy demand periods.
Drought can also severely impact Texas fawnsfoot populations.
Central Texas, including the Colorado and Brazos River basins,
experienced a major drought in the late 1970s (Lewis and Oliveria 1979,
p. 243). Near record dry conditions in 2008 followed by a pattern of
below-normal rainfall during the winter and spring of 2009 led to one
of the worst droughts in recorded history for most of central Texas,
including the range of the Texas fawnsfoot (Nielsen-Gammon and
McRoberts 2009, p. 2). This drought's severity was exacerbated by
abnormally high air temperatures, a likely effect of climate change,
which has already increased average air temperatures in Texas by at
least 1 [deg]C (1.8 [deg]F) (Nielsen-Gammon and McRoberts 2009, p. 22).
Instream flows throughout the Colorado River basin during this drought
were significantly reduced (USGS 2011c, p. 1), and Texas fawnsfoot
populations in areas with reduced water levels may have been negatively
affected. Central Texas is currently experiencing another extreme
drought, with rainfall between October 2010 and July 2011 being the
lowest on record during those months (LCRA 2011c, p. 1); the effects of
this drought are being observed but are not yet fully known. Droughts
result in a decrease in water depth and flow velocity, which reduces
food and oxygen delivery. As droughts persist, mussels face hypoxia,
elevated water temperature and, ultimately, stranding (Golladay et al.
2004, p. 501).
We do not know the extent of the impacts of stream dewatering on
the Texas fawnsfoot; however, because several populations are small and
isolated, the loss of numerous individuals at a site can have dramatic
consequences to the population. Hydropower facilities, construction,
and drought are occurring throughout the range of the Texas fawnsfoot;
therefore, the effects of dewatering are ongoing and unlikely to
decrease, resulting in significant threats to the Texas fawnsfoot.
Sand and Gravel Mining
For general information on the effects of sand and gravel mining on
freshwater mussels, please refer to ``Sand and Gravel Mining'' in
Factor A under Five-Factor Evaluation for Texas Fatmucket.
The Brazos River has a long history of sand mining, particularly in
the lower river, and channel morphology changes have been attributed to
destabilization due to instream sand mining in the area (USGS 2001, p.
27). The removal of sand from within the river creates sediment traps
during periods of high flow, which causes scouring and erosion
downstream (USGS 2001, p. 27). A gravel dredging operation in the
Brazos River has been documented as depositing sediment as far as 1.6
km (1 mile) downstream (Forshage and Carter 1973, p. 697). Accelerated
stream bank erosion and downcutting of streambeds are common effects of
instream sand and gravel mining, as is the mobilization of fine
sediments during sand and gravel extraction (Roell 1999, p. 7).
[[Page 62203]]
Within the current range of Texas fawnsfoot, TPWD has issued
permits for four sand mining activities in the Brazos River basin
(Austin, Bosque, and Fort Bend Counties) (TPWD 2004, p. 1; 2007b, p. 1;
2008b, p. 1; 2010b, p. 1). All of the permits allow for the repeated
removal of sand and gravel at various locations within a stream. The
lower Brazos River, near where these mining activities are occurring,
contains a small Texas fawnsfoot population.
The Texas fawnsfoot population in the lower Brazos River is likely
threatened by sand and gravel mining. These activities occur over a
long period of time, destabilizing habitat both upstream and
downstream, which decreases the likelihood of recolonization after the
activity has been completed. Therefore, the effects of sand and gravel
mining are an ongoing threat to the Texas fawnsfoot.
Chemical Contaminants
For general information on the effects of chemical contaminants on
freshwater mussels, please refer to ``Chemical Contaminants'' under
Factor A under Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussels, the Texas fawnsfoot is also
affected by chemical contaminants. TCEQ data for 2010 indicated that 26
of the 98 assessed water bodies within Colorado River basin and 81 of
approximately 124 assessed water bodies within Brazos River basin did
not meet surface water quality standards and were classified as 303(d)
impaired Water Bodies (Texas Clean Rivers Program 2010a, p. 5; TCEQ
2010c, pp. 1-106). These water bodies were impaired with dissolved
solids, nitrites, nitrates, bacteria, low dissolved oxygen, aluminum,
sulfates, selenium, chloride, orthophosphorus, phosphorus, Chlorophyll
a, and low pH associated with agricultural, urban, municipal, and
industrial runoff. Of these, nitrates and low dissolved oxygen pose a
threat to Texas fawnsfoot, as discussed above.
In 2010, crude oil overflowed into Keechi Creek in Leon County, a
tributary to Navasota River (National Response Center 2010, p. 2). This
location is upstream of one of the few remaining Texas fawnsfoot
populations. Numerous other spills have occurred within the range of
the Texas fawnsfoot. These can occur from on site accidents (tank,
pipeline spills) or from tanker truck accidents within watersheds
occupied by Texas fawnsfoot. For example, oil has spilled into the
Brazos River a number of times. As much as 320,000 L (84,000 gal) of
crude oil was spilled in the Brazos River in 1991 (Associated Press
1991, p. 1). In June 2010, flooding of holding ponds adjacent to oil
drilling operations leaked oil into Thompson Creek and subsequently
into the Brazos River. Also, in July 2010, oil pipelines burst and
released approximately 165 barrels of crude oil into the upper Brazos
River (Joiner 2010, p. 1).
Agricultural pesticides and emerging contaminants are likely also
present in streams inhabited by Texas fawnsfoot. There are 53
wastewater treatment plants permitted to discharge into the Brazos
River basin (Valenti and Brooks 2008, p. 12); the outfalls from these
treatment plants have not been tested to determine if they contain
contaminants of note.
Chemical contaminants, such as oil, ammonia, copper, mercury,
nutrients, pesticides, and other compounds are currently a threat to
the Texas fawnsfoot. The species is vulnerable to acute contamination
from spills as well as chronic contaminant exposure, which is occurring
rangewide.
Summary of Factor A
The reduction in numbers and range of the Texas fawnsfoot is
primarily the result of the long-lasting effects of habitat alterations
such as the effects of impoundments, sedimentation, sand and gravel
mining, and chemical contaminants. Impoundments occur throughout the
range of the species and have far-reaching effects both up- and
downstream. Both the Colorado and Brazos River systems have experienced
a large amount of sedimentation from agriculture, sand and gravel
mining, and urban development. Sand and gravel mining affects Texas
fawnsfoot habitat by increasing sedimentation and channel instability
downstream and causing headcutting upstream. Chemical contaminants have
been documented throughout the range of the species and may represent a
significant threat to the Texas fawnsfoot. Based upon our review of the
best commercial and scientific data available, we conclude that the
present or threatened destruction, modification, or curtailment of its
habitat or range is an immediate and ongoing threat of high magnitude
to the Texas fawnsfoot.
Factor B. Overutilization for Commercial, Recreational, Scientific,
or Educational Purposes.
The Texas fawnsfoot is not a commercially valuable species and has
never been harvested in Texas as a commercial mussel species (Howells
2010d, pp. 9-10). Some scientific collecting occurs but is not likely
to be a significant threat to the species because it occurs only
rarely. However, handling mussels can disturb gravid females and result
in glochidial loss and subsequent reproductive failure. Additionally,
handling has been shown to reduce shell growth across mussel species,
including several species of Lampsilis (Haag and Commens-Carson 2008,
pp. 505-506). Repeated handling by researchers may adversely affect
Texas fawnsfoot individuals, but these activities are occurring rarely
and are not likely to be a threat to populations. Handling for
scientific purposes contributes to the long-term conservation of the
species.
We do not have any evidence of risks to the Texas fawnsfoot from
overutilization for commercial, recreational, scientific, or
educational purposes, and we have no reason to believe this factor will
become a threat to the species in the future. Based upon the best
scientific and commercial information available, we conclude that
overutilization for commercial, recreational, scientific, or
educational purposes does not pose a significant threat to the Texas
fawnsfoot rangewide.
Factor C. Disease and Predation.
Disease
Little is known about disease in freshwater mussels. However,
disease is believed to be a contributing factor in documented mussel
die-offs in other parts of the United States (Neves 1987, pp. 11-12).
Diseases have not been documented or observed during any studies of
Texas fawnsfoot.
Predation
Raccoons will prey on freshwater mussels stranded by low waters or
deposited in shallow water or on bars following flooding or low water
periods (Howells 2010c, p. 12). Predation of Texas fawnsfoot by
raccoons may be occurring occasionally but there is no indication it is
a significant threat to the status of the species.
Some species of fish feed on mussels, such as common carp,
freshwater drum, and redear sunfish, all of which are common throughout
the range of Texas fawnsfoot (Hubbs et al. 2008, pp. 19, 45, 53).
Common species of flatworms are voracious predators of newly
metamorphosed juvenile mussels of many species (Zimmerman et al. 2003,
p. 30). Predation is a normal factor influencing the population
dynamics of a healthy mussel population; however, predation may amplify
declines in small populations primarily caused by other factors.
Summary of Factor C
Disease in freshwater mussels is poorly known, and we do not have
any information indicating it is a threat to
[[Page 62204]]
the Texas fawnsfoot. Additionally, predation is a natural ecological
interaction and we have no information indicating the extent of any
predation is a threat to populations of Texas fawnsfoot. Based upon the
best scientific and commercial information available, we conclude that
disease or predation is not a threat to the Texas fawnsfoot.
Factor D. The Inadequacy of Existing Regulatory Mechanisms.
Existing regulatory mechanisms that could have an effect on threats
to the Texas fawnsfoot include State and Federal laws such as Texas
Threatened and Endangered Species regulations and freshwater mussel
sanctuaries, State and Federal sand and gravel mining regulations, and
regulation of point and non-point source pollution. For more
information on the effects of State and Federal laws on the threats to
freshwater mussels in central Texas, please refer to Factor D under
Five-Factor Evaluation for Texas Fatmucket.
Summary of Factor D
Despite State and Federal laws protecting the species and water
quality, the Texas fawnsfoot continues to decline due to the effects of
habitat destruction, poor water quality, contaminants, and other
factors. The regulatory measures described in Factor D under Five-
Factor Evaluation for Texas Fatmucket have been insufficient to
significantly reduce or remove the threats to the Texas fawnsfoot.
Based upon our review of the best commercial and scientific data
available, we conclude that the lack of existing regulatory mechanisms
is an immediate threat of moderate magnitude to the Texas fawnsfoot.
Factor E. Other Natural or Manmade Factors Affecting Its Continued
Existence.
Natural and manmade factors that threaten the Texas fawnsfoot
include climate change, population fragmentation and isolation, and
nonnative species.
Climate Change
For general information on the effects of climate change on
freshwater mussels in central Texas, please refer to ``Climate Change''
in Factor E under Five-Factor Evaluation for Texas Fatmucket. Because
the range of the Texas fawnsfoot has been reduced to isolated
locations, many with low population numbers, in small rivers and
streams, the Texas fawnsfoot is vulnerable to climatic changes that
could decrease the availability of water.
The disjunct nature of the remaining Texas fawnsfoot populations,
coupled with the limited ability of mussels to migrate, makes it
unlikely that Texas fawnsfoot can adjust their range in response to
changes in climate (Strayer 2008, p. 30). Climate change could affect
the Texas fawnsfoot through the combined effects of global and regional
climate change, along with the increased probability of long-term
drought. Climate change exacerbates threats such as habitat degradation
from prolonged periods of drought, increased water temperature, and the
increased allocation of water for municipal, agricultural, and
industrial use. Climate change may be a significant stressor that
exacerbates existing threats by increasing the likelihood of prolonged
drought. As such, climate change, in and of itself, may affect the
Texas fawnsfoot, but the magnitude and imminence of the effects remain
uncertain. Based upon our review of the best commercial and scientific
data available, we conclude that the effects of climate change in the
future will likely exacerbate the current and ongoing threats of
habitat loss and degradation caused by other factors, as discussed
above.
Population Fragmentation and Isolation
For general information on the effects of population fragmentation
and isolation on freshwater mussels in central Texas, please refer to
``Population Fragmentation and Isolation'' in Factor E under Five-
Factor Evaluation for Texas Fatmucket. As with many freshwater mussels,
most of the remaining populations of the Texas fawnsfoot are small and
geographically isolated and thus are susceptible to genetic drift,
inbreeding depression, and random or chance changes to the environment,
such as toxic chemical spills (Watters and Dunn 1995, pp. 257-258) or
dewatering. Historically, the Texas fawnsfoot was once widespread
throughout much of the Colorado and Brazos River systems when few
natural barriers existed to prevent migration (via host species) among
suitable habitats. The extensive impoundment of the Colorado and Brazos
River basins has fragmented Texas fawnsfoot populations throughout
these river systems.
Small Texas fawnsfoot populations, including those in the Brazos
River, Clear Fork Brazos River, Navasota River, and Deer Creek, may be
below the minimum population size required to maintain population
viability into the future. These populations are more vulnerable to
extirpation since they are less likely to be able to recover through
recruitment from events that reduce but do not extirpate populations.
Additionally, these small populations are more vulnerable to
extirpation from stochastic events, as the lack of connectivity among
populations does not permit nearby populations to recolonize areas
affected by intense droughts, toxic spills, or other isolated events
that result in significant mussel dieoffs. While the small, isolated
populations do not represent an independent threat to the species, the
situation does substantially increase the risk of extirpation from the
effects of all other threats, including those addressed in this
analysis, and those that could occur in the future from unknown
sources.
Based upon our review of the best commercial and scientific data
available, we conclude that fragmentation and isolation of small
remaining populations of the Texas fawnsfoot are occurring and are
ongoing threats to the species throughout all of its range; these
threats will continue. Further, stochastic events may play a magnified
role in extirpation of small, isolated populations.
Nonnative Species
For general information on the effects of nonnative species on
freshwater mussels in central Texas, please refer to ``Nonnative
Species'' in Factor E under Five-Factor Evaluation for Texas Fatmucket.
As with other freshwater mussels, the Texas fawnsfoot is threatened by
nonnative species. Various nonnative aquatic species pose a threat to
the Texas fawnsfoot, including golden algae, zebra mussels, and black
carp. Of these, golden algae has been responsible for killing more than
two million fish in the Colorado River since 1989 (TPWD 2010a, p. 1).
Although mussel kills due to golden algae have not been recorded, we
expect golden algae to negatively affect mussel populations through
loss of host fish and direct toxicity. Zebra mussels and black carp do
not currently occur within the range of the Texas fawnsfoot, although
both are found in Texas and could be introduced to the Brazos and
Colorado Rivers in the future. Based on population responses of other
mussel species that overlap with zebra mussels and black carp in
similar river conditions, we conclude that the introduction of zebra
mussels or black carp into the range of smooth pimpleback would be
devastating to the species.
Based upon our review of the best commercial and scientific data
available, we conclude that golden algae is an ongoing threat to the
Texas fawnsfoot, and other nonnative species, such as zebra mussels and
black carp,
[[Page 62205]]
are a potential threat to the Texas fawnsfoot that is likely to
increase as these exotic species expand their occupancy within the
range of the Texas fawnsfoot.
Summary of Factor E
The effects of climate change, while difficult to quantify at this
time, are likely to exacerbate the current and ongoing threat of
habitat loss caused by other factors, and the small sizes and
fragmented nature of the remaining populations render them more
vulnerable to extirpation. In addition, nonnative species, such as
golden algae, currently threaten the Texas fatmucket, and the potential
introduction of zebra mussels and black carp are potential future
threats. Based upon our review of the best commercial and scientific
data available, we conclude that other natural or manmade factors are
immediate threats of moderate magnitude to the Texas fawnsfoot.
Finding for Texas Fawnsfoot
As required by the Act, we considered the five factors in assessing
whether the Texas fawnsfoot is threatened or endangered throughout all
of its range. We examined the best scientific and commercial
information available regarding the past, present, and future threats
faced by the Texas fawnsfoot. We reviewed the petition, information
available in our files, and other available published and unpublished
information, and we consulted with recognized Texas fawnsfoot experts
and other Federal and State agencies.
This status review identifies threats to the Texas fawnsfoot
attributable to Factors A, D, and E. The primary threat to the species
is from habitat destruction and modification (Factor A) from
impoundments, which scour riverbeds, thereby removing mussel habitat,
decrease water quality, modify stream flows, and restrict fish host
migration and distribution of freshwater mussels. Additional threats
under Factor A include sedimentation, dewatering, sand and gravel
mining, and chemical contaminants. Also, most of these threats may be
exacerbated by the current and projected effects of climate change
(discussed under Factor E). Threats to the Texas fawnsfoot are not
being adequately addressed through existing regulatory mechanisms
(Factor D). Because of the limited distribution of this endemic species
and its lack of mobility, these threats are likely to lead to the
extinction of the Texas fawnsfoot in the foreseeable future.
On the basis of the best scientific and commercial information
available, we find that the petitioned action to list the Texas
fawnsfoot under the Act is warranted. We will make a determination on
the status of the species as threatened or endangered when we complete
a proposed listing determination. When we complete a proposed listing
determination, we will examine whether the species may be endangered or
threatened throughout all of its range or whether the species may be
endangered or threatened in a significant portion of its range.
However, as explained in more detail below, an immediate proposal of a
regulation implementing this action is precluded by higher priority
listing actions, and progress is being made to add or remove qualified
species from the Lists of Endangered and Threatened Wildlife and
Plants.
We reviewed the available information to determine if the existing
and foreseeable threats render the Texas fawnsfoot at risk of
extinction now such that issuing an emergency regulation temporarily
listing the species under section 4(b)(7) of the Act is warranted. We
determined that issuing an emergency regulation temporarily listing the
species is not warranted for the Texas fawnsfoot at this time, because
we have not identified a threat or activity that poses a significant
risk, such that losses to the species during the normal listing process
would endanger the continued existence of the entire species. However,
if at any time we determine that issuing an emergency regulation
temporarily listing the Texas fawnsfoot is warranted, we will initiate
this action at that time.
Listing Priority Number for Texas Fawnsfoot
The Service adopted guidelines on September 21, 1983 (48 FR 43098),
to establish a rational system for utilizing available resources for
the highest priority species when adding species to the Lists of
Endangered and Threatened Wildlife and Plants or reclassifying species
listed as threatened to endangered status. These guidelines, titled
``Endangered and Threatened Species Listing and Recovery Priority
Guidelines'' address the immediacy and magnitude of threats, and the
level of taxonomic distinctiveness by assigning priority in descending
order to monotypic genera (genus with one species), full species, and
subspecies (or equivalently, distinct population segments of
vertebrates).
As a result of our analysis of the best available scientific and
commercial information, we have assigned the Texas fawnsfoot an LPN of
2, based on our finding that the species faces threats that are of high
magnitude and are imminent. These threats include habitat loss and
degradation from impoundments, sedimentation, sand and gravel mining,
and chemical contaminants; other natural or manmade factors such as
climate change, small, isolated populations, and nonnative species; and
the fact that the threats to the species are not being adequately
addressed by existing regulatory mechanisms. Our rationale for
assigning the Texas fawnsfoot an LPN of 2 is outlined below.
We consider the threats that the Texas fawnsfoot faces to be high
in magnitude. Habitat loss and degradation from impoundments,
sedimentation, sand and gravel mining, and chemical contaminants are
widespread throughout the range of the Texas fawnsfoot and profoundly
affect its habitat. Remaining populations are small, isolated, and
highly vulnerable to stochastic events.
Under our LPN guidelines, the second criterion we consider in
assigning a listing priority is the immediacy of threats. We consider
the threats to the Texas fawnsfoot as described under Factors A, D, and
E in the Five-Factor Evaluation for Texas Fawnsfoot section to be
imminent because these threats are ongoing and will continue in the
foreseeable future. Habitat loss and destruction has already occurred
and will continue as the human population continues to grow in central
Texas. The Texas fawnsfoot populations may already be below the minimum
viable population requirement, which would cause a reduction in the
number of populations and an increase in the species' vulnerability to
extinction. These threats are exacerbated by climate change, which will
increase the frequency and magnitude of droughts. Therefore, we
consider these threats to be imminent.
Thirdly, the Texas fawnsfoot is a valid taxon at the species level
and, therefore, receives a higher priority than subspecies, but a lower
priority than species in a monotypic genus. Therefore, we assigned
Texas fawnsfoot an LPN of 2. We will continue to monitor the threats to
the Texas fawnsfoot and the species' status on an annual basis, and
should the magnitude or imminence of the threats change, we will
revisit our assessment of the LPN.
While we conclude that listing the Texas fawnsfoot is warranted, an
immediate proposal to list this species is precluded by other higher
priority listings, which we address in the Preclusion and Expeditious
Progress section below. Because we have assigned the Texas fawnsfoot an
LPN of 2, work on a proposed listing
[[Page 62206]]
determination for the species is precluded by work on higher priority
listing actions with absolute statutory, court-ordered, or court-
approved deadlines and final listing determinations for those species
that were proposed for listing with funds from Fiscal Year (FY) 2011.
This work includes all the actions listed in the tables below under
Preclusion and Expeditious Progress.
Preclusion and Expeditious Progress
Preclusion is a function of the listing priority of a species in
relation to the resources that are available and the cost and relative
priority of competing demands for those resources. Thus, in any given
fiscal year (FY), multiple factors dictate whether it will be possible
to undertake work on a listing proposal regulation or whether
promulgation of such a proposal is precluded by higher priority listing
actions.
The resources available for listing actions are determined through
the annual Congressional appropriations process. The appropriation for
the Listing Program is available to support work involving the
following listing actions: Proposed and final listing rules; 90-day and
12-month findings on petitions to add species to the Lists of
Endangered and Threatened Wildlife and Plants (Lists) or to change the
status of a species from threatened to endangered; annual
``resubmitted'' petition findings on prior warranted-but-precluded
petition findings as required under section 4(b)(3)(C)(i) of the Act;
critical habitat petition findings; proposed and final rules
designating critical habitat; and litigation-related, administrative,
and program-management functions (including preparing and allocating
budgets, responding to Congressional and public inquiries, and
conducting public outreach regarding listing and critical habitat). The
work involved in preparing various listing documents can be extensive
and may include, but is not limited to: Gathering and assessing the
best scientific and commercial data available and conducting analyses
used as the basis for our decisions; writing and publishing documents;
and obtaining, reviewing, and evaluating public comments and peer
review comments on proposed rules and incorporating relevant
information into final rules. The number of listing actions that we can
undertake in a given year also is influenced by the complexity of those
listing actions; that is, more complex actions generally are more
costly. The median cost for preparing and publishing a 90-day finding
is $39,276; for a 12-month finding, $100,690; for a proposed rule with
critical habitat, $345,000; and for a final listing rule with critical
habitat, $305,000.
We cannot spend more than is appropriated for the Listing Program
without violating the Anti-Deficiency Act (see 31 U.S.C.
1341(a)(1)(A)). In addition, in FY 1998 and for each fiscal year since
then, Congress has placed a statutory cap on funds that may be expended
for the Listing Program, equal to the amount expressly appropriated for
that purpose in that fiscal year. This cap was designed to prevent
funds appropriated for other functions under the Act (for example,
recovery funds for removing species from the Lists), or for other
Service programs, from being used for Listing Program actions (see
House Report 105-163, 105th Congress, 1st Session, July 1, 1997).
Since FY 2002, the Service's budget has included a critical habitat
subcap to ensure that some funds are available for other work in the
Listing Program (``The critical habitat designation subcap will ensure
that some funding is available to address other listing activities''
(House Report No. 107-103, 107th Congress, 1st Session, June 19,
2001)). In FY 2002 and each year until FY 2006, the Service has had to
use virtually the entire critical habitat subcap to address court-
mandated designations of critical habitat, and consequently none of the
critical habitat subcap funds have been available for other listing
activities. In some FYs since 2006, we have been able to use some of
the critical habitat subcap funds to fund proposed listing
determinations for high-priority candidate species. In other FYs, while
we were unable to use any of the critical habitat subcap funds to fund
proposed listing determinations, we did use some of this money to fund
the critical habitat portion of some proposed listing determinations so
that the proposed listing determination and proposed critical habitat
designation could be combined into one rule, thereby being more
efficient in our work. At this time, for FY 2011, we plan to use some
of the critical habitat subcap funds to fund proposed listing
determinations.
We make our determinations of preclusion on a nationwide basis to
ensure that the species most in need of listing will be addressed first
and also because we allocate our listing budget on a nationwide basis.
Through the listing cap, the critical habitat subcap, and the amount of
funds needed to address court-mandated critical habitat designations,
Congress and the courts have in effect determined the amount of money
available for other listing activities nationwide. Therefore, the funds
in the listing cap, other than those needed to address court-mandated
critical habitat for already listed species, set the limits on our
determinations of preclusion and expeditious progress.
Congress identified the availability of resources as the only basis
for deferring the initiation of a rulemaking that is warranted. The
Conference Report accompanying Public Law 97-304 (Endangered Species
Act Amendments of 1982), which established the current statutory
deadlines and the warranted-but-precluded finding, states that the
amendments were ``not intended to allow the Secretary to delay
commencing the rulemaking process for any reason other than that the
existence of pending or imminent proposals to list species subject to a
greater degree of threat would make allocation of resources to such a
petition [that is, for a lower-ranking species] unwise.'' Although that
statement appeared to refer specifically to the ``to the maximum extent
practicable'' limitation on the 90-day deadline for making a
``substantial information'' finding, that finding is made at the point
when the Service is deciding whether or not to commence a status review
that will determine the degree of threats facing the species, and
therefore the analysis underlying the statement is more relevant to the
use of the warranted-but-precluded finding, which is made when the
Service has already determined the degree of threats facing the species
and is deciding whether or not to commence a rulemaking.
In FY 2011, on April 15, 2011, Congress passed the Full-Year
Continuing Appropriations Act (Pub. L. 112-10), which provides funding
through September 30, 2011. The Service has $20,902,000 for the listing
program. Of that, $9,472,000 is being used for determinations of
critical habitat for already listed species. Also $500,000 is
appropriated for foreign species listings under the Act. The Service
thus has $10,930,000 available to fund work in the following
categories: Compliance with court orders and court-approved settlement
agreements requiring that petition findings or listing determinations
be completed by a specific date; section 4 (of the Act) listing actions
with absolute statutory deadlines; essential litigation-related,
administrative, and listing program-management functions; and high-
priority listing actions for some of our candidate species. In FY 2010,
the Service received many new petitions and a single petition to list
404 species. The receipt of petitions for a large number of species is
consuming the
[[Page 62207]]
Service's listing funding that is not dedicated to meeting court-
ordered commitments. Absent some ability to balance effort among
listing duties under existing funding levels, the Service is only able
to initiate a few new listing determinations for candidate species in
FY 2011.
In 2009, the responsibility for listing foreign species under the
Act was transferred from the Division of Scientific Authority,
International Affairs Program, to the Endangered Species Program.
Therefore, starting in FY 2010, we used a portion of our funding to
work on the actions described above for listing actions related to
foreign species. In FY 2011, we anticipate using $1,500,000 for work on
listing actions for foreign species, which reduces funding available
for domestic listing actions; however, currently only $500,000 has been
allocated for this function. Although there are no foreign species
issues included in our high-priority listing actions at this time, many
actions have statutory or court-approved settlement deadlines, thus
increasing their priority. The budget allocations for each specific
listing action are identified in the Service's FY 2011 Allocation Table
(part of our record).
For the above reasons, funding proposed listing determinations for
the Texas fatmucket, golden orb, smooth pimpleback, Texas pimpleback,
and Texas fawnsfoot is precluded by court-ordered and court-approved
settlement agreements, listing actions with absolute statutory
deadlines, and work on proposed listing determinations for those
candidate species with a higher listing priority (i.e., candidate
species with LPNs of 1).
Based on our September 21, 1983, guidelines for assigning an LPN
for each candidate species (48 FR 43098), we have a significant number
of species with a LPN of 2. Using these guidelines, we assign each
candidate an LPN of 1 to 12, depending on the magnitude of threats
(high or moderate to low), immediacy of threats (imminent or
nonimminent), and taxonomic status of the species (in order of
priority: monotypic genus (a species that is the sole member of a
genus); species; or part of a species (subspecies, or distinct
population segment)). The lower the listing priority number, the higher
the listing priority (that is, a species with an LPN of 1 would have
the highest listing priority).
Because of the large number of high-priority species, we have
further ranked the candidate species with an LPN of 2 by using the
following extinction-risk type criteria: International Union for the
Conservation of Nature and Natural Resources (IUCN) Red list status/
rank, Heritage rank (provided by NatureServe), Heritage threat rank
(provided by NatureServe), and species currently with fewer than 50
individuals, or 4 or fewer populations. Those species with the highest
IUCN rank (critically endangered), the highest Heritage rank (G1), the
highest Heritage threat rank (substantial, imminent threats), and
currently with fewer than 50 individuals, or fewer than 4 populations,
originally comprised a group of approximately 40 candidate species
(``Top 40''). These 40 candidate species have had the highest priority
to receive funding to work on a proposed listing determination. As we
work on proposed and final listing rules for those 40 candidates, we
apply the ranking criteria to the next group of candidates with an LPN
of 2 and 3 to determine the next set of highest priority candidate
species. Finally, proposed rules for reclassification of threatened
species to endangered species are lower priority, because as listed
species, they are already afforded the protections of the Act and
implementing regulations. However, for efficiency reasons, we may
choose to work on a proposed rule to reclassify a species to endangered
if we can combine this with work that is subject to a court-determined
deadline.
With our workload so much bigger than the amount of funds we have
to accomplish it, it is important that we be as efficient as possible
in our listing process. Therefore, as we work on proposed rules for the
highest priority species in the next several years, we are preparing
multi-species proposals when appropriate, and these may include species
with lower priority if they overlap geographically or have the same
threats as a species with an LPN of 2. In addition, we take into
consideration the availability of staff resources when we determine
which high-priority species will receive funding to minimize the amount
of time and resources required to complete each listing action.
As explained above, a determination that listing is warranted but
precluded must also demonstrate that expeditious progress is being made
to add and remove qualified species to and from the Lists of Endangered
and Threatened Wildlife and Plants. As with our ``precluded'' finding,
the evaluation of whether progress in adding qualified species to the
Lists has been expeditious is a function of the resources available for
listing and the competing demands for those funds. (Although we do not
discuss it in detail here, we are also making expeditious progress in
removing species from the list under the Recovery program in light of
the resource available for delisting, which is funded by a separate
line item in the budget of the Endangered Species Program. So far
during FY 2011, we have completed delisting rules for three species.)
Given the limited resources available for listing, we find that we are
making expeditious progress in FY 2011 in the Listing Program. This
progress included preparing and publishing the following
determinations:
FY 2011 Completed Listing Actions
----------------------------------------------------------------------------------------------------------------
Publication date Title Actions FR Pages
----------------------------------------------------------------------------------------------------------------
10/6/2010................... Endangered Status for Proposed Listing 75 FR 61664-61690
the Altamaha Endangered.
Spinymussel and
Designation of
Critical Habitat.
10/7/2010................... 12-Month Finding on a Notice of 12-month 75 FR 62070-62095
Petition to list the petition finding, Not
Sacramento Splittail warranted.
as Endangered or
Threatened.
10/28/2010.................. Endangered Status and Proposed Listing 75 FR 66481-66552
Designation of Endangered
Critical Habitat for (uplisting).
Spikedace and Loach
Minnow.
11/2/2010................... 90-Day Finding on a Notice of 90-day 75 FR 67341-67343
Petition to List the Petition Finding, Not
Bay Springs Salamander substantial.
as Endangered.
11/2/2010................... Determination of Final Listing 75 FR 67511-67550
Endangered Status for Endangered.
the Georgia Pigtoe
Mussel, Interrupted
Rocksnail, and Rough
Hornsnail and
Designation of
Critical Habitat.
11/2/2010................... Listing the Rayed Bean Proposed Listing 75 FR 67551-67583
and Snuffbox as Endangered.
Endangered.
[[Page 62208]]
11/4/2010................... 12-Month Finding on a Notice of 12-month 75 FR 67925-67944
Petition to List petition finding,
Cirsium wrightii Warranted but
(Wright's Marsh precluded.
Thistle) as Endangered
or Threatened.
12/14/2010.................. Endangered Status for Proposed Listing 75 FR 77801-77817
Dunes Sagebrush Lizard. Endangered.
12/14/2010.................. 12-Month Finding on a Notice of 12-month 75 FR 78029-78061
Petition to List the petition finding,
North American Warranted but
Wolverine as precluded.
Endangered or
Threatened.
12/14/2010.................. 12-Month Finding on a Notice of 12-month 75 FR 78093-78146
Petition to List the petition finding,
Sonoran Population of Warranted but
the Desert Tortoise as precluded.
Endangered or
Threatened.
12/15/2010.................. 12-Month Finding on a Notice of 12-month 75 FR 78513-78556
Petition to List petition finding,
Astragalus microcymbus Warranted but
and Astragalus precluded.
schmolliae as
Endangered or
Threatened.
12/28/2010.................. Listing Seven Brazilian Final Listing 75 FR 81793-81815
Bird Species as Endangered.
Endangered Throughout
Their Range.
1/4/2011.................... 90-Day Finding on a Notice of 90-day 76 FR 304-311
Petition to List the Petition Finding, Not
Red Knot subspecies substantial.
Calidris canutus
roselaari as
Endangered.
1/19/2011................... Endangered Status for Proposed Listing 76 FR 3392-3420
the Sheepnose and Endangered.
Spectaclecase Mussels.
2/10/2011................... 12-Month Finding on a Notice of 12-month 76 FR 7634-7679
Petition to List the petition finding,
Pacific Walrus as Warranted but
Endangered or precluded.
Threatened.
2/17/2011................... 90-Day Finding on a Notice of 90-day 76 FR 9309-9318
Petition to List the Petition Finding,
Sand Verbena Moth as Substantial.
Endangered or
Threatened.
2/22/2011................... Determination of Final Listing 76 FR 9681-9692
Threatened Status for Threatened.
the New Zealand-
Australia Distinct
Population Segment of
the Southern
Rockhopper Penguin.
2/22/2011................... 12-Month Finding on a Notice of 12-month 76 FR 9722-9733
Petition to List petition finding,
Solanum conocarpum Warranted but
(marron bacora) as precluded.
Endangered.
2/23/2011................... 12-Month Finding on a Notice of 12-month 76 FR 9991-10003
Petition to List petition finding, Not
Thorne's Hairstreak warranted.
Butterfly as
Endangered.
2/23/2011................... 12-Month Finding on a Notice of 12-month 76 FR 10166-10203
Petition to List petition finding,
Astragalus hamiltonii, Warranted but
Penstemon flowersii, precluded & Not
Eriogonum soredium, Warranted.
Lepidium ostleri, and
Trifolium friscanum as
Endangered or
Threatened.
2/24/2011................... 90-Day Finding on a Notice of 90-day 76 FR 10299-10310
Petition to List the Petition Finding, Not
Wild Plains Bison or substantial.
Each of Four Distinct
Population Segments as
Threatened.
2/24/2011................... 90-Day Finding on a Notice of 90-day 76 FR 10310-10319
Petition to List the Petition Finding, Not
Unsilvered Fritillary substantial.
Butterfly as
Threatened or
Endangered.
3/8/2011.................... 12-Month Finding on a Notice of 12-month 76 FR 12667-12683
Petition to List the petition finding,
Mt. Charleston Blue Warranted but
Butterfly as precluded.
Endangered or
Threatened.
3/8/2011.................... 90-Day Finding on a Notice of 90-day 76 FR 12683-12690
Petition to List the Petition Finding,
Texas Kangaroo Rat as Substantial.
Endangered or
Threatened.
3/10/2011................... Initiation of Status Notice of Status 76 FR 13121-13122
Review for Longfin Review.
Smelt.
3/15/2011................... Withdrawal of Proposed Proposed rule 76 FR 14210-14268
Rule to List the Flat- withdrawal.
tailed Horned Lizard
as Threatened.
3/15/2011................... Proposed Threatened Proposed Listing 76 FR 14126-14207
Status for the Threatened; Proposed
Chiricahua Leopard Designation of
Frog and Proposed Critical Habitat.
Designation of
Critical Habitat.
3/22/2011................... 12-Month Finding on a Notice of 12-month 76 FR 15919-15932
Petition to List the petition finding,
Berry Cave Salamander Warranted but
as Endangered. precluded.
4/1/2011.................... 90-Day Finding on a Notice of 90-day 76 FR 18138-18143
Petition to List the Petition Finding,
Spring Pygmy Sunfish Substantial.
as Endangered.
4/5/2011.................... 12-Month Finding on a Notice of 12-month 76 FR 18684-18701
Petition to List the petition finding, Not
Bearmouth Warranted and
Mountainsnail, Byrne Warranted but
Resort Mountainsnail, precluded.
and Meltwater Lednian
Stonefly as Endangered
or Threatened.
4/5/2011.................... 90-Day Finding on a Notice of 90-day 76 FR 18701-18706
Petition to List the Petition Finding,
Peary Caribou and Substantial.
Dolphin and Union
population of the
Barren-ground Caribou
as Endangered or
Threatened.
4/12/2011................... Proposed Endangered Proposed Listing 76 FR 20464-20488
Status for the Three Endangered; Proposed
Forks Springsnail and Designation of
San Bernardino Critical Habitat.
Springsnail, and
Proposed Designation
of Critical Habitat.
4/13/2011................... 90-Day Finding on a Notice of 90-day 76 FR 20613-20622
Petition to List Petition Finding,
Spring Mountains Substantial.
Acastus Checkerspot
Butterfly as
Endangered.
4/14/2011................... 90-Day Finding on a Notice of 90-day 76 FR 20911-20918
Petition to List the Petition Finding,
Prairie Chub as Substantial.
Threatened or
Endangered.
4/14/2011................... 12-Month Finding on a Notice of 12-month 76 FR 20918-20939
Petition to List petition finding,
Hermes Copper Warranted but
Butterfly as precluded.
Endangered or
Threatened.
4/26/2011................... 90-Day Finding on a Notice of 90-day 76 FR 23256-23265
Petition to List the Petition Finding,
Arapahoe Snowfly as Substantial.
Endangered or
Threatened.
[[Page 62209]]
4/26/2011................... 90-Day Finding on a Notice of 90-day 76 FR 23265-23271
Petition to List the Petition Finding, Not
Smooth-Billed Ani as substantial.
Threatened or
Endangered.
5/12/2011................... Withdrawal of the Proposed Rule, 76 FR 27756-27799
Proposed Rule to List Withdrawal.
the Mountain Plover as
Threatened.
5/25/2011................... 90-Day Finding on a Notice of 90-day 76 FR 30082-30087
Petition to List the Petition Finding,
Spot-tailed Earless Substantial.
Lizard as Endangered
or Threatened.
5/26/2011................... Listing the Salmon- Final Listing 76 FR 30758-30780
Crested Cockatoo as Threatened.
Threatened Throughout
its Range with Special
Rule.
5/31/2011................... 12-Month Finding on a Notice of 12-month 76 FR 31282-31294
Petition to List petition finding,
Puerto Rican Harlequin Warranted but
Butterfly as precluded.
Endangered.
6/2/2011.................... 90-Day Finding on a Notice of 90-day 76 FR 31903-31906
Petition to Reclassify Petition Finding,
the Straight-Horned Substantial.
Markhor (Capra
falconeri jerdoni) of
Torghar Hills as
Threatened.
6/2/2011.................... 90-Day Finding on a Notice of 90-day 76 FR 31920-31926
Petition to List the Petition Finding,
Golden-winged Warbler Substantial.
as Endangered or
Threatened.
6/7/2011.................... 12-Month Finding on a Notice of 12-month 76 FR 32911-32929
Petition to List the petition finding,
Striped Newt as Warranted but
Threatened. precluded.
6/9/2011.................... 12-Month Finding on a Notice of 12-month 76 FR 33924-33965
Petition to List petition finding, Not
Abronia ammophila, Warranted and
Agrostis rossiae, Warranted but
Astragalus precluded.
proimanthus, Boechera
(Arabis) pusilla, and
Penstemon gibbensii as
Threatened or
Endangered.
6/21/2011................... 90-Day Finding on a Notice of 90-day 76 FR 36049-36053
Petition to List the Petition Finding, Not
Utah Population of the substantial.
Gila Monster as an
Endangered or a
Threatened Distinct
Population Segment.
6/21/2011................... Revised 90-Day Finding Notice of 90-day 76 FR 36053-36068
on a Petition to Petition Finding, Not
Reclassify the Utah substantial.
Prairie Dog From
Threatened to
Endangered.
6/28/2011................... 12-Month Finding on a Notice of 12-month 76 FR 37706-37716
Petition to List petition finding, Not
Castanea pumila var. warranted.
ozarkensis as
Threatened or
Endangered.
6/29/2011................... 90-Day Finding on a Notice of 90-day 76 FR 38095-38106
Petition to List the Petition Finding,
Eastern Small-Footed Substantial.
Bat and the Northern
Long-Eared Bat as
Threatened or
Endangered.
6/30/2011................... 12-Month Finding on a Notice of 12-month 76 FR 38504-38532
Petition to List a petition finding, Not
Distinct Population warranted.
Segment of the Fisher
in Its United States
Northern Rocky
Mountain Range as
Endangered or
Threatened with
Critical Habitat.
7/12/2011................... 90-Day Finding on a Notice of 90-day 76 FR 40868-40871
Petition to List the Petition Finding,
Bay Skipper as Substantial.
Threatened or
Endangered.
7/19/2011................... 12-Month Finding on a Notice of 12-month 76 FR 42631-42654
Petition to List Pinus petition finding,
albicaulis as Warranted but
Endangered or precluded.
Threatened with
Critical Habitat.
7/19/2011................... Petition to List Grand Notice of 12-month 76 FR 42654-42658
Canyon Cave petition finding, Not
Pseudoscorpion. warranted.
7/26/2011................... 12-Month Finding on a Notice of 12-month 76 FR 44547-44564
Petition to List the petition finding, Not
Giant Palouse warranted.
Earthworm (Drilolerius
americanus) as
Threatened or
Endangered.
7/26/2011................... 12-Month Finding on a Notice of 12-month 76 FR 44566-44569
Petition to List the petition finding, Not
Frigid Ambersnail as warranted.
Endangered.
7/27/2011................... Determination of Final Listing 76 FR 45054-45075
Endangered Status for Endangered,
Ipomopsis polyantha Threatened.
(Pagosa Skyrocket) and
Threatened Status for
Penstemon debilis
(Parachute
Beardtongue) and
Phacelia submutica
(DeBeque Phacelia).
7/27/2011................... 12-Month Finding on a Notice of 12-month 76 FR 45130-45162
Petition to List the petition finding,
Gopher Tortoise as Warranted but
Threatened in the precluded.
Eastern Portion of its
Range.
8/2/2011.................... Proposed Endangered Proposed Listing 76 FR 46218-46234
Status for the Endangered.
Chupadera Springsnail
(Pyrgulopsis
chupaderae) and
Proposed Designation
of Critical Habitat.
8/2/2011.................... 90-Day Finding on a Notice of 90-day 76 FR 46238-46251
Petition to List the Petition Finding, Not
Straight Snowfly and substantial.
Idaho Snowfly as
Endangered.
8/2/2011.................... 12-Month Finding on a Notice of 12-month 76 FR 46251-46266
Petition to List the petition finding, Not
Redrock Stonefly as warranted.
Endangered or
Threatened.
8/2/2011.................... Listing 23 Species on Proposed Listing 76 FR 46362-46594
Oahu as Endangered and Endangered.
Designating Critical
Habitat for 124
Species.
8/4/2011.................... 90-Day Finding on a Notice of 90-day 76 FR 47123-47133
Petition to List Six Petition Finding, Not
Sand Dune Beetles as substantial and
Endangered or substantial.
Threatened.
8/9/2011.................... Endangered Status for Final Listing 76 FR 48722-48741
the Cumberland Darter, Endangered.
Rush Darter,
Yellowcheek Darter,
Chucky Madtom, and
Laurel Dace.
8/9/2011.................... 12-Month Finding on a Notice of 12-month 76 FR 48777-48788
Petition to List the petition finding, Not
Nueces River and warranted.
Plateau Shiners as
Threatened or
Endangered.
[[Page 62210]]
8/9/2011.................... Four Foreign Parrot Proposed Listing 76 FR 49202-49236
Species [crimson Endangered and
shining parrot, white Threatened; Notice of
cockatoo, Philippine 12-month petition
cockatoo, yellow- finding, Not
crested cockatoo]. warranted.
8/10/2011................... Proposed Listing of the Proposed Listing 76 FR 49408-49412
Miami Blue Butterfly Endangered Similarity
as Endangered, and of Appearance.
Proposed Listing of
the Cassius Blue,
Ceraunus Blue, and
Nickerbean Blue
Butterflies as
Threatened Due to
Similarity of
Appearance to the
Miami Blue Butterfly.
8/10/2011................... 90-Day Finding on a Notice of 90-day 76 FR 49412-49417
Petition to List the Petition Finding,
Saltmarsh Topminnow as Substantial.
Threatened or
Endangered Under the
Endangered Species Act.
8/10/2011................... Proposed Listing of the Proposed Listing 76 FR 49408-49412
Miami Blue Butterfly Endangered and
as Endangered, and Similarity of
Proposed Listing of Appearance.
the Cassius Blue,
Ceraunus Blue, and
Nickerbean Blue
Butterflies as
Threatened Due to
Similarity of
Appearance to the
Miami Blue Butterfly.
8/10/2011................... Emergency Listing of Emergency Listing 76 FR 49542-49567
the Miami Blue Endangered and
Butterfly as Similarity of
Endangered, and Appearance.
Emergency Listing of
the Cassius Blue,
Ceraunus Blue, and
Nickerbean Blue
Butterflies as
Threatened Due to
Similarity of
Appearance to the
Miami Blue Butterfly.
8/11/2011................... Listing Six Foreign Final Listing 76 FR 50052-50080
Birds as Endangered Endangered.
Throughout Their Range.
8/17/2011................... 90-Day Finding on a Notice of 90-day 76 FR 50971-50979
Petition to List the Petition Finding,
Leona's Little Blue Substantial.
Butterfly as
Endangered or
Threatened.
9/01/2011................... 90-Day Finding on a Notice of 90-day 76 FR 54423-54425
Petition to List All Petition Finding,
Chimpanzees (Pan Substantial.
troglodytes) as
Endangered.
9/6/2011.................... 12-Month Finding on Notice of 12-month 76 FR 55170-55203
Five Petitions to List petition finding,
Seven Species of Warranted but
Hawaiian Yellow-faced precluded.
Bees as Endangered.
9/8/2011.................... 12-Month Petition Notice of 12-month 76 FR 55623-55638
Finding and Proposed petition finding,
Listing of Warranted; Proposed
Arctostaphylos Listing Endangered.
franciscana as
Endangered.
9/8/2011.................... 90-Day Finding on a Notice of 90-day 76 FR 55638-55641
Petition to List the Petition Finding, Not
Snowy Plover and substantial.
Reclassify the
Wintering Population
of Piping Plover.
9/13/2011................... 90-Day Finding on a Notice of 90-day 76 FR
Petition to List the Petition Finding,
Franklin's Bumble Bee Substantial.
as Endangered.
9/13/2011................... 90-Day Finding on a Notice of 90-day 76 FR
Petition to List 42 Petition Finding,
Great Basin and Mojave Substantial and Not
Desert Springsnails as substantial.
Threatened or
Endangered with
Critical Habitat.
----------------------------------------------------------------------------------------------------------------
Our expeditious progress also includes work on listing actions that
we funded in FY 2010 and FY 2011 but have not yet been completed to
date. These actions are listed below. Actions in the top section of the
table are being conducted under a deadline set by a court. Actions in
the middle section of the table are being conducted to meet statutory
timelines, that is, timelines required under the Act. Actions in the
bottom section of the table are high-priority listing actions. These
actions include work primarily on species with an LPN of 2, and, as
discussed above, selection of these species is partially based on
available staff resources, and when appropriate, include species with a
lower priority if they overlap geographically or have the same threats
as the species with the high priority. Including these species together
in the same proposed rule results in considerable savings in time and
funding, when compared to preparing separate proposed rules for each of
them in the future.
Actions Funded in FY 2010 and FY 2011 But Not Yet Completed
------------------------------------------------------------------------
Species Action
------------------------------------------------------------------------
Actions Subject to Court Order/Settlement Agreement
------------------------------------------------------------------------
4 parrot species (military macaw, yellow- 12-month petition finding.
billed parrot, red-crowned parrot,
scarlet macaw) \5\.
4 parrot species (blue-headed macaw, great 12-month petition finding.
green macaw, grey-cheeked parakeet,
hyacinth macaw) \5\.
Longfin smelt............................. 12-month petition finding.
------------------------------------------------------------------------
Actions with Statutory Deadlines
------------------------------------------------------------------------
Casey's june beetle....................... Final listing determination.
5 Bird species from Colombia and Ecuador.. Final listing determination.
Queen Charlotte goshawk................... Final listing determination.
Ozark hellbender \4\...................... Final listing determination.
Altamaha spinymussel \3\.................. Final listing determination.
6 Birds from Peru & Bolivia............... Final listing determination.
[[Page 62211]]
Loggerhead sea turtle (assist National Final listing determination.
Marine Fisheries Service) \5\.
2 mussels (rayed bean (LPN = 2), snuffbox Final listing determination.
No LPN) \5\.
CA golden trout \4\....................... 12-month petition finding.
Black-footed albatross.................... 12-month petition finding.
Mojave fringe-toed lizard \1\............. 12-month petition finding.
Kokanee--Lake Sammamish population \1\.... 12-month petition finding.
Cactus ferruginous pygmy-owl \1\.......... 12-month petition finding.
Northern leopard frog..................... 12-month petition finding.
Tehachapi slender salamander.............. 12-month petition finding.
Coqui Llanero............................. 12-month petition finding/
Proposed listing.
Dusky tree vole........................... 12-month petition finding.
Leatherside chub (from 206 species 12-month petition finding.
petition).
Platte River caddisfly (from 206 species 12-month petition finding.
petition) \5\.
3 Texas moths (Ursia furtiva, Sphingicampa 12-month petition finding.
blanchardi, Agapema galbina) (from 475
species petition).
3 South Arizona plants (Erigeron 12-month petition finding.
piscaticus, Astragalus hypoxylus,
Amoreuxia gonzalezii) (from 475 species
petition).
14 parrots (foreign species).............. 12-month petition finding.
Mohave Ground Squirrel \1\................ 12-month petition finding.
Western gull-billed tern.................. 12-month petition finding.
OK grass pink (Calopogon oklahomensis) \1\ 12-month petition finding.
Ashy storm-petrel \5\..................... 12-month petition finding.
Honduran emerald.......................... 12-month petition finding.
Eagle Lake trout \1\...................... 90-day petition finding.
32 Pacific Northwest mollusks species 90-day petition finding.
(snails and slugs) \1\.
Spring Mountains checkerspot butterfly.... 90-day petition finding.
10 species of Great Basin butterfly....... 90-day petition finding.
404 Southeast species..................... 90-day petition finding.
American eel \4\.......................... 90-day petition finding.
Aztec gilia \5\........................... 90-day petition finding.
White-tailed ptarmigan \5\................ 90-day petition finding.
San Bernardino flying squirrel \5\........ 90-day petition finding.
Bicknell's thrush \5\..................... 90-day petition finding.
Sonoran talussnail \5\.................... 90-day petition finding.
2 AZ Sky Island plants (Graptopetalum 90-day petition finding.
bartrami & Pectis imberbis) \5\.
I'iwi \5\................................. 90-day petition finding.
Humboldt marten........................... 90-day petition finding.
Desert massasauga......................... 90-day petition finding.
Western glacier stonefly (Zapada glacier). 90-day petition finding.
Thermophilic ostracod (Potamocypris 90-day petition finding.
hunteri).
Sierra Nevada red fox \5\................. 90-day petition finding.
Boreal toad (eastern or southern Rocky Mtn 90-day petition finding.
population) \5\.
Alexander Archipelago wolf \5\............ 90-day petition finding.
------------------------------------------------------------------------
High-Priority Listing Actions
------------------------------------------------------------------------
20 Maui-Nui candidate species \2\ (17 Proposed listing.
plants, 3 tree snails) (14 with LPN = 2,
2 with LPN = 3, 3 with LPN = 8).
8 Gulf Coast mussels (southern kidneyshell Proposed listing.
(LPN = 2), round ebonyshell (LPN = 2),
Alabama pearlshell (LPN = 2), southern
sandshell (LPN = 5), fuzzy pigtoe (LPN =
5), Choctaw bean (LPN = 5), narrow pigtoe
(LPN = 5), and tapered pigtoe (LPN = 11))
\4\.
Umtanum buckwheat (LPN = 2) and white Proposed listing.
bluffs bladderpod (LPN = 9) \4\.
Grotto sculpin (LPN = 2) \4\.............. Proposed listing.
2 Arkansas mussels (Neosho mucket (LPN = Proposed listing.
2) & Rabbitsfoot (LPN = 9)) \4\.
Diamond darter (LPN = 2) \4\.............. Proposed listing.
Gunnison sage-grouse (LPN = 2) \4\........ Proposed listing.
Coral Pink Sand Dunes Tiger Beetle (LPN = Proposed listing.
2) \5\.
Lesser prairie chicken (LPN = 2).......... Proposed listing.
4 Texas salamanders (Austin blind Proposed listing.
salamander (LPN = 2), Salado salamander
(LPN = 2), Georgetown salamander (LPN =
8), Jollyville Plateau (LPN = 8)) \3\.
5 SW aquatics (Gonzales Spring Snail (LPN Proposed listing.
= 2), Diamond Y springsnail (LPN = 2),
Phantom springsnail (LPN = 2), Phantom
Cave snail (LPN = 2), Diminutive amphipod
(LPN = 2)) \3\.
2 Texas plants (Texas golden gladecress Proposed listing.
(Leavenworthia texana) (LPN = 2), Neches
River rose-mallow (Hibiscus dasycalyx)
(LPN = 2)) \3\.
4 AZ plants (Acuna cactus (Echinomastus Proposed listing.
erectocentrus var. acunensis) (LPN = 3),
Fickeisen plains cactus (Pediocactus
peeblesianus fickeiseniae) (LPN = 3),
Lemmon fleabane (Erigeron lemmonii) (LPN
= 8), Gierisch mallow (Sphaeralcea
gierischii) (LPN = 2)) \5\.
FL bonneted bat (LPN = 2) \3\............. Proposed listing.
3 Southern FL plants (Florida semaphore Proposed listing.
cactus (Consolea corallicola) (LPN = 2),
shellmound applecactus (Harrisia
(=Cereus) aboriginum (=gracilis)) (LPN =
2), Cape Sable thoroughwort (Chromolaena
frustrata) (LPN = 2)) \5\.
[[Page 62212]]
21 Big Island (HI) species \5\ (includes 8 Proposed listing.
candidate species--6 plants & 2 animals;
4 with LPN = 2, 1 with LPN = 3, 1 with
LPN = 4, 2 with LPN = 8).
12 Puget Sound prairie species (9 Proposed listing.
subspecies of pocket gopher (Thomomys
mazama ssp.) (LPN = 3), streaked horned
lark (LPN = 3), Taylor's checkerspot (LPN
= 3), Mardon skipper (LPN = 8)) \3\.
2 TN River mussels (fluted kidneyshell Proposed listing.
(LPN = 2), slabside pearlymussel (LPN =
2)) \5\.
Jemez Mountain salamander (LPN = 2) \5\... Proposed listing.
------------------------------------------------------------------------
\1\ Funds for listing actions for these species were provided in
previous FYs.
\2\ Although funds for these high-priority listing actions were
provided in FY 2008 or 2009, due to the complexity of these actions
and competing priorities, these actions are still being developed.
\3\ Partially funded with FY 2010 funds and FY 2011 funds.
\4\ Funded with FY 2010 funds.
\5\ Funded with FY 2011 funds.
We have endeavored to make our listing actions as efficient and
timely as possible, given the requirements of the relevant law and
regulations, and constraints relating to workload and personnel. We are
continually considering ways to streamline processes or achieve
economies of scale, such as by batching related actions together. Given
our limited budget for implementing section 4 of the Act, these actions
described above collectively constitute expeditious progress.
Texas fatmucket, golden orb, smooth pimpleback, Texas pimpleback,
and Texas fawnsfoot will be added to the list of candidate species upon
publication of this 12-month finding. We will continue to evaluate
these species as new information becomes available. Continuing review
will determine if a change in status is warranted, including the need
to make prompt use of emergency listing procedures.
We intend that any proposed listing determination for Texas
fatmucket, golden orb, smooth pimpleback, Texas pimpleback, and Texas
fawnsfoot will be as accurate as possible. Therefore, we will continue
to accept additional information and comments from all concerned
governmental agencies, the scientific community, industry, or any other
interested party concerning this finding.
References Cited
A complete list of references cited is available on the Internet at
http://www.regulations.gov and upon request from the Clear Lake
Ecological Services Field Office (see ADDRESSES).
Authors
The primary authors of this notice are the staff members from the
Southwest Region of the U.S. Fish and Wildlife Service.
Authority
The authority for this section is section 4 of the Endangered
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).
Dated: September 26, 2011.
Rowan W. Gould,
Acting Director, Fish and Wildlife Service.
[FR Doc. 2011-25471 Filed 10-5-11; 8:45 am]
BILLING CODE 4310-55-P