[Federal Register: June 11, 2002 (Volume 67, Number 112)]
[Proposed Rules]
[Page 39936-39947]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr11jn02-38]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
Endangered and Threatened Wildlife and Plants; Candidate Status
Review for Rio Grande Cutthroat Trout
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of candidate status review.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service) announce the
results of the candidate status review for the Rio Grande cutthroat
trout (Onchorhynchus clarki virginalis) under the Endangered Species
Act of 1973, as amended. After a review of all available scientific and
commercial information, we have determined that listing of the Rio
Grande cutthroat trout is not warranted at this time.
DATES: The finding announced in this document was made on June 3, 2002.
ADDRESSES: You may submit comments regarding this notice to the
Supervisor, U.S. Fish and Wildlife Service, New Mexico Ecological
Services Field Office, 2105 Osuna Road NE, Albuquerque, New Mexico
87113. Written comments and materials received in response to this
notice will be available for public inspection, by appointment, during
normal business hours at the New Mexico Field Office.
FOR FURTHER INFORMATION CONTACT: Joy E. Nicholopoulos, Field
Supervisor, U.S. Fish and Wildlife Service, 2105 Osuna Road NE,
Albuquerque, New Mexico 87113. (505) 346-2525 ext 106.
SUPPLEMENTARY INFORMATION:
Background
On February 25, 1998, we received a petition from Kieran Suckling,
of the Southwest Center for Biological Diversity requesting that the
Service add the Rio Grande cutthroat trout (Oncorhynchus clarki
virginalis) to the list of threatened and endangered species. The
petition addressed the range-wide distribution of the Rio Grande
cutthroat trout that includes populations in Colorado and New Mexico.
Section 4(b)(3)(B) of the Endangered Species Act (Act) requires that we
make a finding on whether a petition to list, delist or reclassify a
species presents substantial scientific or commercial information
indicating that the petitioned action is--(a) not warranted; (b)
warranted; or (c) warranted but precluded by listing proposals of
higher priority. We subsequently published a notice of a 90-day finding
in the Federal Register (63 FR 49062) on September 14, 1998. In the 90-
day finding we concluded that the petition did not present substantial
information indicating that listing of the Rio Grande cutthroat trout
may be warranted.
On June 9, 1999, a complaint was filed by the Southwest Center for
Biological Diversity challenging the September 14, 1998, 90-day
petition finding as violating the Act and the Administrative Procedures
Act. While the litigation was pending, we received information
(particularly related to the presence of whirling disease in hatchery
fish in the wild) that led us to believe that further review of the
status of the species was warranted. On November 8, 2001, a settlement
agreement executed by both parties (the Service and the Southwest
Center for Biological Diversity) was filed with the court. The
settlement stipulates that we will initiate a candidate status review
for the Rio Grande cutthroat trout. The settlement also stipulates that
on or before June 3, 2002, we will make a determination concerning the
results of this review and, shortly thereafter, we will publish our
determination in the Federal Register. The agreement also states that
we will not vacate our previous determination in the interim.
Biogeography and Taxonomy
The Rio Grande cutthroat trout (RGCT) is a subspecies of cutthroat
trout, endemic to the Rio Grande, Pecos, and possibly the Canadian
River Basins in New Mexico and Colorado. The first specimens that were
collected for scientific purposes came from Ute Creek in Costilla
County, Colorado. Girard described these fish as Salar virginalis in
1856 (Behnke 1967). Cutthroat trout are distinguished by the red to
orange slashes in the throat folds beneath the lower jaw. Rio Grande
cutthroat trout have irregular shaped spots that are concentrated
behind the dorsal fin (largest fin on the back), smaller less numerous
spots located primarily above the lateral line anterior to the dorsal
fin, and basibranchial (located on the floor of the gill chamber) teeth
that are minute or absent. Rio Grande cutthroat trout are light rose to
red-orange on the sides and pink or yellow-orange on the belly.
The historical distribution of RGCT is not known with certainty. In
general, it is assumed that RGCT occupied all streams capable of
supporting trout in the Rio Grande and Pecos basins (Stumpff and Cooper
1996). It is unclear if RGCT were also present in the Canadian River
Basin. The Pecos River is a tributary of the Rio Grande, so a historic
connection between RGCT in the two basins is possible. The Canadian
River, tributary to the Mississippi River, has no connection with the
Rio Grande. It is possible that through headwater capture (a tributary
from one watershed joins with a tributary from another), there may have
been natural migration of fish between the Pecos and Canadian headwater
streams. However, because trout were moved and stocked frequently
beginning in the 1800s, the difficulties in correctly identifying fish,
and errors in locality records make it difficult to know if early
reports of trout from the Canadian River headwaters were indeed RGCT.
Genetic testing of RGCT from the three basins using
[[Page 39937]]
molecular methods has not yet clarified the situation, but research
continues on this subject (pers. comm., Yvette Paroz, New Mexico
Department of Game and Fish (NMDGF), 2002). Biologists have suggested
that RGCT may have occurred in Texas (Garrett and Matlock 1991) and
Mexico (Behnke 1967). Currently, the southern most distribution of RGCT
occurs in Animas Creek, Sierra County, New Mexico, and Indian Creek on
the Mescalero Apache Indian Reservation in Otero County, New Mexico.
Life History
Because the RGCT has not been studied intensively, less is known
specifically about their habitat requirements or life history
characteristics than is known for several other subspecies of cutthroat
trout. As is true of other subspecies of cutthroat trout, it is found
in clear, cold streams. Unlike some subspecies of cutthroat trout, such
as the Bonneville (O. c. utah) and Yellowstone (O. c. bouvieri), RGCT
did not originally inhabit large lake systems. However, they have been
introduced into coldwater lakes and reservoirs. They spawn as high
flows from snowmelt recede, typically from the middle of May to the
middle of June in New Mexico (NMDGF 2002). Spawning is probably keyed
to day length, water temperature, elevation, and runoff (Stumpff 1998,
Sublette et al. 1990). The size of mature females ranges from 10.7-26
centimeters (4.21-10.27 inches (in)) (Stumpff 1998). Number of eggs per
female varies greatly depending on the size and age of the fish.
Stumpff (1998) reported that average egg production from 93 females
spawned from Rio Puerco, New Mexico, was less than 100 eggs per female;
however, these fish may have been collected after the peak of the
spawn. From efforts to develop RGCT broodstock, fish from several
streams were collected and spawned from 1994 to 1997. The average
number of eggs per female from these collections was 175 (Stumpff
1998). The mean number of eggs taken from 12 RGCT from Indian Creek
(Tularosa Basin) was 311 with the range between 232-454 (Cowley 1993).
Sublette et al. (1990) state that females produce between 200-4,500
eggs; however, this figure applies to all cutthroat subspecies and is
not specific to RGCT.
It is unknown if RGCT spawn every year or if some portion of the
population spawns every other year as has been recorded for westslope
cutthroat trout (O. c. lewisi) (McIntyre and Rieman 1995). Likewise,
while it is assumed that females mature at age 3, they may not spawn
until age 4 or 5 as seen in westslope cutthroat trout (McIntyre and
Rieman 1995). Sex ratio is also unknown, but a ratio skewed towards
more females might be expected (Cowley 1993). Although Yellowstone
(Gresswell 1995), Colorado River (O. c. pleuriticus) (Young 1995),
Bonneville (Service 2001), and westslope (Bjornn and Mallet 1964,
McIntyre and Riemand 1995) cutthroat subspecies are known to have a
migratory life history phase, it is not known if RGCT currently have,
or once had, a migratory form when there were fluvial (flowing water)
connections among watersheds.
Most cutthroat trout are opportunistic feeders, eating both aquatic
invertebrates and terrestrial insects that fall into the water
(Sublette et al. 1990). RGCT evolved with Rio Grande chub (Gila
pandora), longnose dace (Rhinichthys cataractae) (all basins); Rio
Grande sucker (Catastomus plebius) (Rio Grande Basin); white sucker (C.
commersoni) and creek chub (Semotilus atromaculatus) (Pecos and
Canadian Basins), and the southern redbelly dace (Phoxinus
erythrogaster) (Canadian River Basin) (Rinne 1995). Many of these fish
have either been extirpated from streams with RGCT or are greatly
reduced in number. It is not known if they once were an important
component of RGCT diet. Other species of cutthroat trout become more
piscivorous (fish eating) as they mature (Sublette et al. 1990, Moyle
1976), and cutthroat trout living in lakes will prey heavily on other
species of fish (Echo 1954). It is possible that native cyprinids
(i.e., chubs, minnows, and dace) and catastomids may have once been
important prey items for RGCT.
Growth of cutthroat trout varies with water temperature and
availability of food. Slowest growth is seen in high-elevation streams
where temperatures are cold and productivity is typically low. Most
populations of RGCT are found in high-elevation streams and under these
conditions growth may be relatively slow, and time to maturity may take
longer than is seen in subspecies that inhabit lower elevation streams.
Based on 471 fish from 3 streams, Cowley (1993) estimated the following
age/size classes: age 0, 30-64 millimeters (mm), (1.0-2.5 in); age 1,
65-114 mm (2.5-4.5 in); age 2, 115-149 mm (4.5-5.9 in); age 3, 150-174
mm (5.9-6.9 in); age 4, 175-205 mm (6.9-8.0 in); and age 5, over 205 mm
(8.0 in). At Seven Springs Hatchery, eggs hatched in 32 days at 10
degrees Celcius ( deg.C), 50 degrees Fahrenheit ( deg.F) (NMDGF 2002).
Typical of trout, RGCT require four types of habitat for survival:
spawning habitat, nursery or rearing habitat, adult habitat, and
overwintering habitat. Spawning habitat consists of clean gravel
(little or no fine sediment present) that ranges between 6 to 40 mm
(0.24-1.6 in) (NMDGF 2002). Nursery habitat is usually at the stream
margins where water velocity is low and water temperature is slightly
warmer. Harig and Fausch (in press) have found that water temperature
may play a critical role in the life history of the young of the year
cutthroat. Streams with cold temperatures (less than 7.8 deg.C
(46 deg.F) mean daily temperature for July) may not have successful
recruitment or reproduction in most years. The cold temperatures can
delay spawning and prolong egg incubation. Fry (recently hatched fish)
emerge later in the summer and may not have sufficient time to grow and
gain metabolic reserves to be able to overwinter. Overwintering habitat
in the form of large deep pools that do not freeze is also necessary
for survival. Lack of large pools may be a limiting factor in headwater
streams (Harig and Fausch in press).
Analysis
It has been estimated that there are 106 populations of RGCT in New
Mexico (NMDGF 2002) and 161 in Colorado (Alves et al. 2002) in both
streams and lakes. All of these populations contribute in some way to
the overall security of the range-wide population. However, many of
these populations are hybrids, some populations have an extremely low
number of individuals, and some have been invaded by nonnative
salmonids that either hybridize or compete with RGCT. These factors can
make individual RGCT populations more vulnerable to extinction and
limit the likelihood of their long-term persistence. Conservation
actions can remove or reduce these threats. Because ecological factors
affecting persistence vary among populations, we decided to use
criteria to categorize populations based on vulnerability to threats
that affect long-term persistence. The populations deemed most likely
to persist are considered ``core'' populations. Criteria were
established for purity, population stability, and security from
invasion by nonnative salmonids. We recognize that our criteria are
conservative, and that population estimates are not precise. For these
reasons we also evaluate non-core populations (discussed in the
conclusion) that do not meet all of the core criteria but are important
components of the range-wide population.
[[Page 39938]]
Genetic Purity
For the purposes of this review we considered ``pure'' to mean that
there was less than 1 percent introgression (genetic mixing) with
either rainbow or another subspecies of cutthroat trout. Allendorf et
al. (2001) suggest that conservation efforts should focus on
maintaining and expanding remaining pure populations, and we have
decided to follow this guidance for RGCT. To meet our criteria, testing
for purity had to include either allozymes (forms of an enzyme) or
nuclear DNA (genetic coding molecule in cell nucleus). We did not
include populations that were tested only with meristics (counts of
body parts). Although a meristic evaluation is a good first step to
determine purity, individuals can look pure and still have a
significant level of introgression. We also did not include the results
from mitochondrial DNA (mtDNA). Because mtDNA is passed on only from
the mother to her offspring, it can only detect hybridization when the
mother is a rainbow trout or another subspecies of cutthroat trout and
the father is RGCT; however, it cannot detect hybridization when the
mother was RGCT and the father was another species. For this reason we
have not included populations that were only tested with meristics and
mtDNA or mtDNA only.
The exclusion of populations with evidence of greater than 1
percent introgression does not imply that these populations may not be
important to the species conservation or that they should be eliminated
from stream systems. They provide recreational opportunities for
anglers; in some watersheds they may act as a buffer between pure
populations and downstream areas where nonnatives are present, and in
some streams hybrids may still contain genes unique to a watershed.
There is a minimum of 30 pure, remnant populations of RGCT widely
distributed range-wide. It is likely that the gene pool of the hybrid
populations is represented in one of the many pure, remnant
populations. In terms of restoration, only pure populations are used
for translocation into renovated streams or for use as broodstock in
hatcheries. For these reasons we view pure populations as particularly
important to the status of the RGCT.
We identified a total of 82 populations (remnant and transplants)
in New Mexico and Colorado that are genetically pure. An additional 13
populations have been identified as pure by NMDGF and Colorado
Department of Wildlife (CDOW) based on meristics or a combination of
meristics and mtDNA. Genetics testing is in progress on 12 populations
in New Mexico, and 31 more populations are scheduled for testing
through 2005 (NMDGF 2002). Once additional genetic testing is
completed, it is likely that several more pure populations will be
identified.
Population Stability
For the long-term persistence of a population, sufficient
population size is needed to prevent inbreeding depression (genetic
defects caused by mating of closely related family members) and
maintain genetic variation (Franklin 1980). Large populations also have
been suggested to be less susceptible to both demographic events
(random changes in the population structure, e.g., uneven male/female
ratios), and environmental random events (random changes in the fishes'
surroundings) that can eliminate small populations. The expected time
to extinction decreases as population size decreases (Rieman et al.
1993). Habitat size (length of stream) and habitat quality affect the
potential size of the population: the larger the fragment, the more
likely the population will be large and able to resist chance
extinctions (Gilpin and Soul 1986). Smaller stream fragments can have
less diverse habitats and a lack of refugia (areas where individuals
can survive through environmentally challenging periods) that can lead
to greater population fluctuations through time (Rieman and McIntyre
1995). As long as birth rate equals or exceeds death rate, small
populations may persist; however, smaller isolated populations may be
more vulnerable to detrimental effects of genetic change and
detrimental effects of demographic and environmental change.
Dr. David Cowley (New Mexico State University) developed a model to
determine population viability for RGCT in New Mexico (NMDGF 2002). The
model incorporates habitat size, population size, reproductive success,
a probability of extinction of less than 10 percent over 100 years, and
a probability that long-term net effective population size
(Ne) of 500 is greater than 90 percent. For the purposes of
this review, we consider elements in the model and work done on other
populations of salmonids to evaluate the likelihood of long-term
population persistence. Three factors were considered: population
number, biomass (weight of fish per unit area), and stream length. Of
these factors, population number is considered to be the most important
for viability and has been discussed most often in the literature.
Franklin (1980) proposed some general rules for effective
population sizes to maintain a genetically viable population.
Franklin's ``50/500'' rule is still used as a starting point by which
to judge the viability of populations. This rule suggests that a short-
term Ne size of 50 will prevent an unacceptable rate of
inbreeding, and a long-term Ne size of 500 will maintain
overall genetic variability. The Ne size refers to an ideal
population of breeding adults produced by the random union of an equal
number of male and female gametes randomly drawn from the previous
generation. The population size (N) needed to meet the effective
population varies according the percent of individuals that are capable
of breeding, the number of animals that actually breed, sex ratio, and
other factors. Typically, Ne/N ratios vary from 10 to 33
percent giving long term population sizes of 2,000 to 5,000 (Thompson
1991). Population sizes between 2,000 and 5,000 have been suggested as
appropriate for the long-term persistence of other fish populations
(Nelson and Soul 1987, Reiman and McIntyre 1993, Hilderbrand and
Kershner 2000), based on both genetic and demographic consideration.
For this analysis we consider 2,500 total fish in a population to
be a number that will ensure long-term persistence (i.e., reduce the
risks associated with small population size alone). Although larger
populations are most likely incrementally ``safer,'' in the absence of
specific work on RGCT, we determined that 2,500 individuals is a
reasonable number that falls within the range suggested for other
salmonids. Although there are examples of persistence of much smaller
populations of RGCT (100-500 individuals), these fish evolved in
connected systems and we have no assurance at this time that they can
persist (i.e., survive as a species for 100-500 years). We do not know
if isolated populations of RGCT can be sustained for long periods (100
years) in small stream fragments; however, managers have documented the
persistence of small RGCT populations for at least 30 years
(Interagency meeting on RGCT, pers. comm. 2002). There are 11 pure
populations in New Mexico and 10 in Colorado that have more than 500
and less than 2,500 individuals and 15 populations in both States with
less than 500 individuals.
Biomass of fish and stream length are related to population size.
Both of these factors have been used as alternative methods to judge
the viability of inland trout populations (Service 1998, Hilderbrand
and Kershner 2000). In the greenback cutthroat recovery plan, one
[[Page 39939]]
recovery goal is that populations have a biomass of 22 kilograms/
hectare (kg/ha), 20 pounds/acre (ac) (lb/ac) (Service 1998). All the
RGCT populations with 2,500 fish or more have a biomass greater than 22
kg/ha (20 lb/ac). The lowest biomass in the populations with 2,500 or
more individuals is 29 kg/ha (26 lb/ac). Seventeen of 22 populations of
RGCT with 2,500 fish or more have a biomass of 50 kg/ha (44.6 lb/ac) or
more. Biomass is not considered a limiting factor in these pure
populations.
Having sufficient stream length is another factor that can play a
role in the survival of cutthroat trout populations (Hilderbrand and
Kershner 2000, Harig and Fausch in press). Fish density is high for
RGCT populations with over 2,500 individuals, suggesting that the
stream length of 8 kilometers (km) (4.9 miles (mi)) suggested by
Hilderbrand and Kershner (2000) is probably sufficient for most of the
streams. Only one stream reach with a population of more than 2,500
fish is of a length shorter than is recommended. However, fish density
is high (0.7 fish/meter, 0.21 fish/foot), and we deduce from this that
the habitat is of high quality and sufficient to support a strong
population.
We identified 22 pure populations with 2,500 or more fish, but
there may be slightly more or slightly fewer. An inherent problem with
using population size as a criterion for the status review is that
populations fluctuate naturally from year to year. Survey sites might
not represent the entire stream; a limited number of surveys have been
conducted on each stream (0-4); survey methods vary; survey efficiency
varies with crew experience and stream conditions (deep water, complex
habitats such as beaver ponds, and low water conductivity decrease
electrofishing efficiency); and surveys have not been conducted
recently on some streams. Around every population estimate are upper
and lower confidence intervals that may be large or small. It is
possible that more populations should be included in the pure, secure,
and stable category because they have slightly less than the 2,500 fish
criterion employed here. Riley and Fausch (1992) found that two- and
three-pass removal methods underestimate total abundance because of
decreasing catchability of fish with each pass (electrofishing a set
length of stream). Nearly all the survey results are from two- or
three-pass methods, so it is possible that of the populations that did
not meet the 2,500 fish criterion, some actually have 2,500 fish or
more. It is possible that with new survey data the streams in the
stable group could change with some dropping down below 2,500 fish and
with others being added. Twelve populations in New Mexico that have
tested pure have no population information available. It is possible
that five of these, which are in longer stream segments (8 to 18 km
[5.0 to 11.2 mi] long), would meet the 2,500 fish criterion.
Population Security
A population of RGCT is not considered secure if nonnative
salmonids are present. The presence of rainbow trout in RGCT
populations is unacceptable because of hybridization. Because brook
trout (Salvelinus fontinalis) and brown trout (Salmo trutta) are fall
spawners (RGCT spawn in spring), they do not hybridize with RGCT.
However, they are competitors for food and space, and there have been
both historic and recent examples of population extirpation due to
nonnative introductions. In some limited situations, co-existence of
RGCT and brook or brown trout may occur, especially in high-gradient or
high-elevation streams that may favor cutthroat trout. However, not
enough is known about the competitive interactions between these fish
to know what factors tip the scale in favor of the nonnatives over
RGCT. Preliminary evidence from Peterson and Fausch (2001) indicate
that brook trout have the most impact on young of the year Colorado
River cutthroat trout. Competitive interactions between RGCT and brook
or brown trout have not yet been studied. Where nonnatives are present,
active management must occur to remove them on a regular basis or the
nonnative trout will gradually replace RGCT. For the purposes of this
review, the emphasis is on self-sustaining pure populations of RGCT.
Brook and brown trout are present in several pure populations of RGCT.
While these populations are less secure than the populations without
nonnatives, removal of the nonnatives by State agency personnel on a
regular basis can lead to stable RGCT populations. These populations
are important to the overall status of the subspecies.
Inextricably linked to the presence of nonnatives is the presence
of a barrier. Barriers prevent nonnatives from migrating into habitat
occupied by RGCT. They also prevent the upstream migration of RGCT,
limiting gene flow among populations. Until more watersheds with
connecting tributaries are restored, having secure barriers to prevent
invasion of nonnatives is essential for protecting existing
populations. Once large watersheds are restored, upstream barriers
could be breached to allow for free passage of RGCT upstream and
downstream. For this status review, populations had to be protected by
a barrier to be considered secure with no nonnative trout above the
barrier. We identified 13 populations that are pure (confirmed by
appropriate genetic testing), have over 2,500 fish, are secured by a
barrier, and do not coexist with nonnatives (see Table 1 below).
Table 1.--Streams With Pure, Stable, and Secure Populations of Rio
Grande Cutthroat Trout, Their Watersheds, and Land Status
------------------------------------------------------------------------
Watershed Stream Ownership
------------------------------------------------------------------------
Colorado
------------------------------------------------------------------------
Saguache........................ Cross............. Rio Grande NF/
private.
San Luis........................ Medano Cr......... Rio Grande NF/NPS.
Alamosa/Trinchera............... San Francisco Cr.. private/Rio Grande
NF.
------------------------------------------------------------------------
New Mexico
------------------------------------------------------------------------
Canones Cr...................... Canones Cr........ Santa Fe NF.
El Rito Cr...................... El Rito Cr........ Carson NF.
Red River....................... Bitter Cr......... Carson NF.
Red River....................... Columbine Cr...... Carson NF.
Rio Cebolla..................... Rio Cebolla....... Santa Fe NF.
Rio Puerco West................. Rio Puerco (west). Santa Fe NF.
[[Page 39940]]
San Cristobal................... San Cristobal..... Carson NF.
Pecos River..................... Jacks............. Santa Fe NF.
Rio Chamita..................... Powderhouse....... Carson NF.
------------------------------------------------------------------------
Rio Pueblo...................... Policarpio........ Carson NF.
------------------------------------------------------------------------
Tested pure with meristics and mtDNA or meristics only..................
------------------------------------------------------------------------
Colorado
------------------------------------------------------------------------
Alamosa/Trinchera............... Cat Cr............ Rio Grande NF.
Alamosa/Trinchera............... Jaroso Cr......... private.
Alamosa/Trinchera............... Torcido........... private.
Conejos......................... Osier............. Rio Grande NF.
Conejos......................... Cascade Cr........ Rio Grande NF.
------------------------------------------------------------------------
NF = National Forest, NPS = National Park Service. Five streams have not
been tested using allozymes or nuclear DNA, however, it is highly
likely that they will test pure based on their isolation from
nonnative trout.
Analysis of Factors Affecting the Populations
Section 4 of the Act and regulations (50 CFR 424) promulgated to
implement the listing provisions of the Act set forth the procedures
for adding species to the Federal lists. A species may be determined to
be threatened or endangered due to one or more of the five factors
discussed below.
A. The Present or Threatened Destruction, Modification, or Curtailment
of its Habitat or Range
The historic range of RGCT has been greatly reduced over the last
150 years. Many populations have been lost or impacted by water
diversions, dams, habitat degradation, changes in hydrology,
hybridization with rainbow trout, or competition with brown or brook
trout. Quantifying the exact magnitude of loss in either number of fish
or habitat is difficult because there are no baseline data. Stumpff and
Cooper (1996) estimated the loss in habitat (stream miles) to be about
91 percent in New Mexico. Harig and Fausch (1998) suggest that native
cutthroat (greenback and RGCT) have been reduced to less than one
percent of their historic habitat. Because RGCT are now restricted to
headwater and first and second order streams that are narrow and small
compared to larger second, third, and fourth order streams they once
occupied, the absolute loss of habitat is greater than stream miles
might indicate and includes the loss of diversity of habitat found in
larger stream systems. As a consequence of the habitat loss, RGCT
populations that were once connected are now fragmented.
The constriction and fragmentation of RGCT habitat most likely
began gradually about 1350 A.D. and accelerated in the late 1800s.
Agriculture in the Rio Grande Valley began about 1350 A.D. and water
diversions for the irrigation of crops started at that time (Crawford
et al. 1993). Diversion of water from tributaries of the Rio Grande
probably represents the first interruptions in RGCT habitat. Following
Spanish colonization in 1598, human influence increased as more land
was cleared and more acequias (irrigation canals) were built to divert
water into fields. The greatest contraction in RGCT habitat most likely
occurred between 1880 and 1973. In 1880, the maximum number of acres in
the middle Rio Grande Valley were under cultivation, and grazing
pressure was intense with over 2 million sheep and 200,000 cattle,
horses, and mules (Crawford et al. 1993). In addition, it is likely
that RGCT were sought for subsistence during this time. In the early
1900s, numerous water supply and flood control dams were built in the
Rio Grande headwaters (Crawford et al. 1993). Rainbow, brook, and brown
trout were introduced at the turn of the century (Sublette et al.
1990). The livestock industry grew through the mid-1930s and livestock
numbers increased far beyond the carrying capacity of the range and had
a widespread negative impact on riparian systems (Meehan and Platts
1978). In addition, timber harvest and an associated increase in roads
led to increased levels of sedimentation in the streams. As a result of
these multiple impacts, reduction of RGCT habitat occurred range-wide,
affecting essentially every watershed.
Habitat fragmentation reduces the total area of habitat available,
reduces habitat complexity, and isolates the fragments (Saunders et al.
1991, Rieman and McIntyre 1993, Rieman and McIntyre 1995, Burkey 1995).
Originally, many watersheds supporting RGCT would have been connected
creating an interconnected network. For example, in Colorado, the
Trinchera, Conejos, Culebra, Costilla, and Alamosa Rivers would all
have been connected through the upper Rio Grande, forming a vast
network of streams. Each of these watersheds is now isolated from one
another, and RGCT are restricted to fragments of streams. Compared to
the lower elevation, larger order streams, the high-elevation streams
that RGCT are now restricted to may represent relatively poor habitat.
Water temperatures are colder, productivity is lower, length of time
for young-of-the-year development is shorter, and amount of habitat
available is less. For some isolated populations, fragmentation may
lead to a negative growth rate and extinction over time (Terborgh and
Winter 1980).
Burkey (1995) suggests that fragmentation accelerates extinction,
especially when dispersal among fragments is not possible, as is the
case with some RGCT populations. Isolated populations are vulnerable to
extinction through demographic change (random changes in the population
structure, e.g., uneven male/female ratios), environmental change
(random changes in the fishes' surroundings) and catastrophes (e.g.,
fires and massive flooding), loss of genetic heterozygosity (genetic
diversity) and fixation of rare detrimental alleles (inherited forms of
a genetic trait), and human disturbance (Burkey 1995). It has been
suggested that spatial and temporal complexity is needed so that the
expression of complex life histories (i.e., migratory and sedentary
forms) can be maintained (Rieman et al. 1993, Dunham et al. 1997, Harig
and Fausch in press). In
[[Page 39941]]
fragmented habitats, fish are unable to migrate or if they do migrate
downstream past a barrier, they are lost from the population. It is
possible that migratory behavior is a hedge against catastrophes.
Individuals that have migrated away from a stream segment escape death
during the catastrophic event and are then available to recolonize the
open habitat once it becomes suitable again (Rieman and McIntyre 1993).
In streams subject to a variety of natural extreme events (drought,
fire, flooding) such as the streams in New Mexico, having a variety of
life histories may have been an evolutionarily advantageous adaptation.
Currently, fish migrating from isolated streams are lost from the
population, and, if a population is extirpated, recolonization is not
possible except through specific management activities such as
stocking. Over time, this can lead to the loss of migratory behavior as
the genes responsible for the behavior are non-advantageous and are
essentially selected against.
Watershed scale projects have been initiated on both private and
National Forest lands and are in various phases of implementation.
Three projects are briefly summarized. A joint project between Vermejo
Park Ranch and the States of Colorado and New Mexico to restore the
Costilla Creek watershed is in progress. A Memorandum of Understanding
was signed by all parties in 2001 and an Environmental Assessment was
completed. Restoration is scheduled for July 2002. The restoration will
remove brook trout, brown trout, and introgressed cutthroat trout and
reintroduce pure RGCT into 4 tributaries and 4 small lakes, totaling 22
km (13.6 miles) of stream and 9.5 ha (23.5 acres) of lake. A draft
environmental assessment has been completed on Animas Creek on the
Ladder Ranch, Sierra County, New Mexico, in cooperation with the Gila
National Forest. The restoration portion of the project is scheduled to
occur in October 2002. Approximately 48 km (29.8 miles) of stream will
be restored. A Watershed Restoration Action Strategy for the Comanche
Creek watershed has been written, and a work plan has been submitted
and approved by the New Mexico Environment Department. Six partners
will work together to improve habitat conditions on Comanche Creek, a
watershed with over 70 km of streams and pure RGCT in the upper
tributaries. Recovery of this watershed will be a substantial gain for
RGCT, especially if the pure populations expand downstream.
The recent establishment of the Valles Caldera National Preserve
presents the opportunity to restore the headwaters of the East Fork
Jemez and San Antonia Rivers with RGCT. With the Santa Fe National
Forest managing the land downstream of the Valles Caldera, there is the
opportunity to connect the two river systems together and restore over
112 km (69.6 miles) of stream. Initial contacts have been made and both
parties are interested in pursuing this large-scale restoration
project. The Rio Santa Barbara watershed (Camino Real Ranger District,
Carson National Forest) is another site with excellent potential to
reconnect multiple populations (West Fork, Middle Fork, and East Forks
of Rio Santa Barbara, Jicarita, and Indian Creeks). In 1999, a barrier
was built on East Fork and the barrier on the Middle Fork Rio Santa
Barbara was improved. Brown trout were removed from above the barriers
from 1998 to 2000. While some progress has been made, we note that a
significant amount of planning and on the ground activities remain to
be done. We recognize that these projects may not come to fruition, and
we are not relying on them as part of this status review. However, we
mentioned them here to recognize that the States and Federal agencies
are looking for opportunities to conserve the RGCT in areas where it
historically occurred.
Habitat fragmentation is a threat that can be alleviated by
management activities. Currently there are five pure, stable, and
secure populations that are connected to at least one other tributary.
Six other large, pure, connected populations exist but nonnatives are
present. State and Forest Service personnel remove nonnatives from
these streams during population surveys and as part of ongoing
management actions.
The Service determines that fragmentation is not a threat to the
persistence of these 13 populations now or in the foreseeable future.
All the 13 pure, stable, and secure populations have over 2,500 fish,
which provide sufficient numbers to prevent an unacceptable rate of
inbreeding and to maintain genetic variability in these populations.
Recognizing this, population sizes between 2,000 and 5,000 have been
suggested as appropriate for the long-term persistence of other fish
populations (Nelson and Soul 1987, Reiman and McIntyre 1993,
Hilderbrand and Kershner 2000), based on both genetic and demographic
consideration. Additionally, the length of these streams (mean equals
12.4 km (7.7 mi)) is sufficient to provide diverse habitats to meet all
the life history requirements of the fish. This statement is supported
by the high fish density (mean equals 0.5 fish/m (0.15 fish/ft))
present in these core streams. Another potential threat from
fragmentation is related to catastrophic events. However, if a
catastrophic event (e.g., fire, drought) results in the extirpation of
one or more of these 13 populations, the States and Federal agencies
have the capability to replace the population with hatchery fish or
fish transplanted from another pure population.
Habitat Condition
Rio Grande cutthroat habitat has been degraded by many activities.
Impacts have been caused by livestock grazing and timber harvest (with
associated roads). Mining has impacted specific sites. Livestock
grazing practices on public land in New Mexico have improved. Changing
livestock stocking levels and improved management practices have
occurred and will continue to occur following current management
direction (James Webb, Rio Grande National Forest, in litt. 1994).
Restoration of riparian areas and maintaining healthy habitat is a
priority for the Forest Supervisors and Regional Foresters (Leonard
Atencio, Santa Fe National Forest, in litt. 2002, Peter Clark, Rio
Grande National Forest in litt. 2002). Although recovery of these
habitats can be slow, the continued commitment of managers to restore
watersheds will continue to improve RGCT habitat over time.
Timber harvest and associated road building have also led to the
deterioration of RGCT habitat. However, timber harvest in the National
Forests has declined appreciably in the last 15 years. As an example,
in New Mexico, from 1987 to 1990 the amount of timber cut averaged
146,722 million board feet (MBF). From 1991 to 2001 the average has
been 35,740 (MBF) (Paul Fink, USDA Forest Service, in litt. 2002). Few
new roads are built in conjunction with timber harvest as the existing
infrastructure can be used (Paul Fink, USDA Forest Service, pers. comm.
2002). Roads are being decommissioned and obliterated on all the
forests, reducing their contribution to sedimentation of streams. For
example in Region 3 of the USDA Forest Service, in 1999, 2000, and
2001, 528, 375, and 332 miles of roads, respectively, were
decommissioned (Mike Noland, USDA Forest Service, in litt. 2002). Many
of the current pure, stable, and secure populations occur at elevations
where timber harvest has not occurred and therefore, have not been
affected. As management activities proceed to expand populations to
lower elevations, restoration will continue to improve habitat
condition in those areas, such as
[[Page 39942]]
is planned on Comanche Creek (discussed above).
Habitat condition in streams with pure, stable, and secure
populations was assessed by CDOW, NMDGF, or Forest Service biologists
depending on which agency was most familiar with a particular stream.
Condition was rated either as 0, no habitat problems; 0-1 which usually
indicated that headwater reaches were in good condition and lower
reaches had problems in discrete areas; 1, some problems identified
(sedimentation, lack of pools, warm water temperature, heavy metals,
etc.); and 2, pervasive problems related to RGCT habitat were
identified. In most instances, sedimentation and problems related to
livestock grazing were identified as primary sources of habitat
degradation. While streams that are rated with a ``1'' have some level
of habitat degradation that probably prevents populations from reaching
maximum reproductive capability, the degradation is not judged to be a
threat to the existence of any of the populations. In most instances,
stream habitat condition was rated between the range of 0 to 1, with
very few streams rated as 2. Based on the outcome of these assessments
for each stream, it is the opinion of the agencies responsible that
habitat problems are typically localized and can be or are being
addressed through management practices (Interagency meeting on RGCT,
pers. comm. 2002).
Based on the information provided to us by agency personnel
(Interagency meeting on RGCT, pers. comm. 2002), discussed in the
paragraph above, as well as the information stated above on timber
harvest and livestock grazing, the Service determines that habitat
condition is not a threat to the 13 pure, stable, and secure
populations or to the populations with 500 to 2,500 fish. Although
habitat condition may prevent maximum reproductive potential in some
populations, habitat condition is not judged a threat to the existence
of any of the populations. In addition, as evidenced by the number of
roads being decommissioned, lower levels of timber harvest and
associated road building, and changes in livestock management
practices, sedimentation from these sources is most likely declining.
Over time we expect RGCT trout habitat to improve.
Fish Barriers
Barriers are essential to separate RGCT from nonnative salmonids.
However, to be effective barriers must be checked frequently and be
maintained. Flood events can either blow a man-made barrier out, change
the channel morphology permanently, or provide a temporary channel
around the barrier that fish can use for upstream migration. Older
gabion barriers (rocks in a wire basket) and culverts appear to be the
most vulnerable structures. Changes in water velocity (either an
increase or decrease depending on the situation) can change an
impassable barrier into one that can be passed. These structures should
be checked on a regular basis. Regardless of the structure, reaches
above barriers need to be checked regularly because nonnatives are
sometimes found upstream of barriers with no evidence of impairment to
the barrier. This can be caused by an incomplete removal of nonnatives
during stream restoration or illegal transplantation of nonnative
trout. The only solution to the latter situation is the education of
the public and gaining their widespread support for RGCT. Education and
outreach efforts are discussed below under ``Public sentiment.''
Both Colorado and New Mexico have conducted barrier inventories
(see factor D. for further information on past activities). New Mexico
will assess the status of 8 barriers in 2003, 13 in 2004, and 13 in
2005 (NMDFG 2002). The Forest Service also assesses barriers as part of
its stream surveys. With the increase in numbers of Forest Service
fisheries biologists and technicians that has occurred in the last few
years, miles of stream inventory have increased. For example, on the
Carson National Forest a full time Fisheries Biologist and two
technicians have been added to the staff (Fact sheet received from
Carson National Forest, in litt. 2002). They completed 50 miles of
stream surveys in 2001. In 2000, the Santa Fe National Forest hired a
full time fisheries biologist. In 2001, they employed 2 temporary
fisheries biologists, 8 fisheries technicians, and 7 interns. In 2001,
105 miles of stream were surveyed (Ferrel 2001). A similar level of
staffing is expected for the field season of 2002, and it is
anticipated that approximately 150 miles of streams will be surveyed
(James Simino, Santa Fe National Forest, pers. comm. 2002). For these
reasons, the Service determines that barrier failure is not a threat to
the 13 pure, stable, and secure populations.
B. Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
There is no commercial fishing for RGCT. Because of fishing
regulations in New Mexico and Colorado, recreational angling is not
considered a threat to the species. Many of the streams with RGCT are
``catch and release.'' Those that are not have a 2 (New Mexico) or 4
(Colorado) fish limit. Many of the streams with pure populations of
RGCT are remote and angling pressure is light (Interagency meeting on
RGCT, pers. comm. 2002).
Overutilization for scientific purposes is not considered a threat
to RGCT. Because of advancements in molecular technology, a small
clipping from a fin provides sufficient material to perform molecular
analysis of genetic purity. To test for whirling disease, usually 60
fish are collected and these fish must be sacrificed. To minimize the
collection of RGCT, nonnative salmonids are collected preferentially
over RGCT or sample sites are selected below a barrier that protects a
population of RGCT. In some situations fewer RGCT will be collected and
sacrificed for testing.
Overutilization of a population can occur when it is used
repeatedly as a source of fish for translocations. Managers must
carefully assess the status of a population before it is used as a
source of fish or eggs for broodstock or transplantation of adults to
other streams. Reducing a population to low levels can make it very
susceptible to other impacts, such as the introduction of nonnatives as
has occurred on West Indian Creek in Colorado (Alves et al. 2002). When
collecting fish for translocation, care must be taken in deciding how
many, of what age class, and from where fish are taken. The broodstock
management plan developed by Cowley (1993) for NMDGF addresses these
issues and provides criteria regarding the selection of founder
populations. With proper management, depletion of the 13 core
populations is not a threat.
The Service determines that overutilization for recreational and
scientific purposes is not a threat to the 13 pure, stable, and secure
populations for the reasons stated above. Overutilization for
commercial or educational reasons has not been identified as a threat.
C. Disease or Predation
Whirling disease (WD) was first detected in Pennsylvania in 1956,
being transmitted here from fish brought from Europe (Thompson et al.
1995). Myxobolus cerebralis is a parasite that penetrates through the
skin or digestive tract of young fish and migrates to the spinal
cartilage where it multiplies very rapidly, putting pressure on the
organ of equilibrium. This causes the fish to swim erratically (whirl),
and have difficulty feeding and avoiding predators. In severe
infections, the disease can cause high rates of mortality in young-of-
the-year fish. Water
[[Page 39943]]
temperature, fish species and age, and dose of exposure are critical
factors influencing whether infection will occur and its severity
(Hedrick et al. 1999). Fish that survive until the cartilage hardens to
bone can live a normal life span, but have skeletal deformities. Once a
fish reaches three to four inches in length, cartilage forms into bone
and the fish is no longer susceptible to effects from whirling disease.
Fish can reproduce without passing the parasite to their offspring;
however, when an infected fish dies, many thousands to millions of the
parasite spores are released to the water.
The spores can withstand freezing, desiccation, passage through the
gut of mallard ducks, and can survive in a stream for many years (El-
Matbouli and Hoffmann 1991). Eventually, the spore must be ingested by
its alternate host, the common aquatic worm, Tubifex tubifex. After
about 3.5 months in the gut of the worms, the spores transform into a
Triactinomyon (TAM). The TAM's leave the worm and attach to the fish or
they are ingested when the fish eats the worm. Either method can lead
to infection. It is likely that the parasite will continue to spread to
more and more streams because the spores are easily transported by
animals and humans.
Salmonids native to the United States did not evolve with WD.
Consequently, most native species have little or no natural resistance.
Colorado River cutthroat trout and rainbow trout are very susceptible
to the disease with 85 percent mortality within 4 months of exposure to
ambient levels of infectivity in the Colorado River (Thompson et al.
1999). Percent survival of RGCT in this research was less than one
percent (Thompson et al. 1999). Even though the cutthroat trout had
lower spore concentrations than did the rainbow trout, they often
showed more overt signs of the disease and died at a faster rate. Brown
trout, native to Europe, become infected by M. cerebralis, but rarely
suffer clinical disease. At the study site on the Colorado River, brown
trout thrive whereas there has been little recruitment to age 1 of
rainbow trout since 1992 (Thompson et al. 1999). Yellowstone cutthroat
trout have also been shown to be very susceptible to WD (Hiner and
Moffitt 2001).
Whirling disease was first detected in New Mexico in 1988 in
rainbow trout imported into private ponds in the Moreno Valley in
northern New Mexico. The first case of WD in wild trout that could not
be directly linked to importation or transportation of fish was
detected in autumn of 1999 in the Pecos River. The Cebolla, San Juan,
Cimarron, Red and Canones Rivers are also infected. Three of seven
State hatcheries also tested positive (Seven Springs, Lisboa Springs,
and Parkview). The M. cerebralis was accidentally introduced in
Colorado in the 1980s through imported trout from a private hatchery.
The parasite has been confirmed in three drainages that support RGCT:
South Fork Rio Grande, Rio Grande, and the Conejos. Eight of Colorado's
State hatcheries have tested positive for WD.
In New Mexico all WD positive fish are destroyed. Seven Springs
fish hatchery has been renovated and is no longer WD positive. There is
an ongoing program to test more drainages for WD. In Colorado, a policy
implemented in spring 1995 prevents the stocking of trout from
hatcheries testing positive into waters where WD has not been found,
including wilderness areas and streams where native trout may be
restored, and no WD positive fish are to be stocked in habitats that
are capable of supporting self-reproducing salmonid populations in
Colorado after 2003. Trout from positive hatcheries will be stocked
into waters where the parasite has been found to minimize the risk of
contaminating other watersheds. Only trout from hatcheries testing
negative can be stocked into waters where the parasite has not been
found.
Although WD is a potential threat to RGCT, high infection rates
will probably only occur where water temperatures are relatively warm
and where T. tubifex is abundant. T. tubifex is the secondary host for
the parasite; when T. tubifex numbers are low, the number of TAMs
produced will be low, and consequently, the infection rate of RGCT will
be low. T. tubifiex is a ubiquitous aquatic oligochaete (worm);
however, it is most abundant in degraded aquatic habitats, particularly
in areas with high sedimentation, warm water temperatures, and low
dissolved oxygen. In clear coldwater streams, as is typical of RGCT
habitat, it is present but seldom abundant. T. tubifex is likely to be
most abundant in beaver ponds, and populations of RGCT below beaver
ponds may be at risk (Hiner and Moffitt 2001). In addition, infection
rate is low at temperatures less than 10 deg.C (50 deg.F) (Thompson et
al. 1999). At the time when the young fish are most susceptible (spring
and early summer), the populations in high-elevation streams are
probably partially protected by low water temperatures.
One threat to the RGCT is the introduction of WD infected fish into
waters inhabited by the RGCT. Both States currently have web sites,
brochures, and information in their fishing regulations regarding WD
and what anglers can do to prevent its spread. In addition, both States
have regulations regarding the stocking of fish by private landowners
that are designed to eliminate the importation of WD positive fish. It
states clearly in the fishing regulations that it is illegal to stock
fish in public waters without prior permission from a State agency.
Public education and compliance are two important elements in keeping
imported fish disease free and not having nonnatives stocked in
locations where they can enter RGCT streams.
The Service determines that WD is not a threat to the 13 pure,
stable, and secure populations because these populations are located in
high-elevation, headwater streams that typically have cold water and
low levels of sedimentation limiting T. tubifex populations and
infection rates from TAMs. Although RGCT is susceptible to infection
there has not been a documented loss or decline in population number
due to WD in a wild RGCT population. The States are testing all their
hatchery fish before stocking, are in the process of documenting which
streams in their States are WD positive, and are educating the public
about how to prevent the spread of WD. With these efforts the spread of
WD should be slowed and any problems in wild populations should be
quickly detected.
D. The Inadequacy of Existing Regulatory Mechanisms
The NMDGF and the CDOW have authority and responsibility for the
management of RGCT on all Federal, State, and private land within their
respective States. The State agencies' capabilities include the
regulation of fishing, law enforcement, research, and conservation and
educational activities relating to RGCT. Policies regarding the
stocking of nonnative fish (no nonnatives are stocked in RGCT
populations) and minimization of exposure to WD and other diseases are
in place in both Colorado and New Mexico. Additionally, New Mexico has
a broodstock management plan in place.
New Mexico has an approved management plan currently being
implemented that will ``facilitate long range cooperative, interagency
conservation of Rio Grande cutthroat trout.'' From 1999 to 2001,
population inventory was completed on 18 streams, barrier evaluations
were completed on 14 streams, and genetic samples were taken from fish
in 17 streams. The plan has schedules for fiscal years 2003 to 2005 for
population inventory and monitoring, collection and analysis of genetic
material, assessing barriers,
[[Page 39944]]
habitat inventory, inventory of unexplored streams, testing for and
mapping WD, and maintaining a database of all the information. For
example, 17 streams are scheduled for inventory and monitoring in 2003,
the genetic purity of 8 populations will be analyzed, and barriers on 8
streams will be surveyed. A budget for all activities from 2003-2005 is
also developed.
Rio Grande cutthroat trout is designated as a species of special
concern by the State of Colorado. Colorado is both implementing and
revising a previous management plan. Consistent with their direction to
monitor populations, protect habitat and populations, and detect
genetic contamination, 58 populations were monitored and 20 populations
were analyzed using molecular techniques from 1998 to 2001. From 1999
to 2001, nonnative trout were removed from 3 streams and one lake, two
barriers were maintained and one new barrier was installed. An
inventory of barriers on RGCT streams in Colorado has been developed.
Approximately 10,000 brochures on RGCT conservation have been
distributed.
A range-wide conservation agreement that will facilitate
cooperation and coordination among State and Federal agencies and other
interested parties is in final draft and is expected to be finalized
before the end of 2002. The agreement's goal is to assure the long-term
persistence of the subspecies, preserve its genetic integrity, and to
provide adequate numbers and populations. We applaud the efforts of the
States to establish this multi-party agreement, and we believe that it
will serve to better the status of the RGCT overall. We mentioned the
draft plan in this finding to recognize that the States and Federal
agencies have taken steps to draft such a plan. However, we are not
relying on it as part of this status review because it is not finalized
and would require us to speculate as to the final outcome of the plan.
The Forest Service, the landowner with the majority of pure RGCT
populations, is also implementing special management for the RGCT. RGCT
is a Management Indicator Species (MIS, species which have been
identified as a representative for a group of species with special
habitat requirements) on the Santa Fe and Carson National Forests, and
is proposed as an MIS on the Rio Grande National Forest. All resident
trout are MISs on the Gila National Forest. Management Indicator
Species act as proxies for fulfilling the National Forest Management
Act viability requirement. Habitat objectives are established for
maintaining the viability of the MIS. The RGCT is also listed on the
Regional Forester's Sensitive Species List. Sensitive species must
receive special management emphasis to ensure their viability and to
preclude trends towards endangerment. Forest Service objectives for
sensitive species are to develop and implement management practices to
ensure that the species does not become threatened or endangered,
maintain viable populations, and develop and implement management
objectives. The Forest Service also assesses barriers as part of its
stream surveys (see discussion above in factor A. ``Fish Barriers''
above).
Based on the discussion above, both the States and the National
Forests have adequate regulatory mechanisms to protect and enhance RGCT
populations and habitat.
E. Other Natural or Manmade Factors Affecting Its Continued Existence
Fire
Wildfires are a natural disturbance in forested watersheds.
Historically, fires occurred every 4-5 years (Swetman 1990), and burned
the understory leaving open stands of older trees. Fire suppression has
resulted in large increases in fuel loads and understory density. As a
result, under the proper conditions, wildfires today can spread rapidly
and burn intensely. In the Southwest, the fire season (May to June) is
followed by the monsoon season (July to August). Consequently, denuded
watersheds can be hit by heavy precipitation leading to floods and ash
flows in streams. Although fish often survive the fire, the ash/slurry
floods that occur after a fire can eliminate populations of fish from a
stream (Rinne, 1996, Brown et al. 2001). In addition to ash, fire
retardant slurry deposited on the fire may wash into streams and kill
fish (Buhl and Hamilton 2000). Although the return interval for stand
replacing fire is much greater in the Rocky Mountains (200 + years)
(Ruediger et al. 2000), a fire of this magnitude could affect fish
populations in several watersheds as it did in the greater Yellowstone
ecosystem (Bozek and Young 1994). Because the return interval is
shorter, fire is a more frequent threat to populations in New Mexico.
There appears to be an association between severe droughts and large
fire years (Swetnam and Baisan 1994). Because fire is unpredictable, it
is hard to assess how great the risk of fire is to individual RGCT
populations. Because several trout populations in New Mexico have been
impacted in the last 10 years by fire, it is logical to assume that a
few isolated RGCT populations could be lost to the effects of fire in
the foreseeable future.
Catastrophic fire can also provide the opportunity to reclaim
streams that were invaded by nonnatives. This situation has occurred on
the Santa Fe National Forest where fish populations were eliminated
from the Cow Creek watershed by the Viveash Fire in 2000. Once the
habitat recovers, approximately 25 stream miles will be repatriated
with RGCT (Ferrel 2002). The Dome Fire in the Jemez Mountains
extirpated the fish residing in Capulin Canyon. In partnership with
Bandalier National Monument, the Santa Fe National Forest is developing
plans to repatriate RGCT in approximately 10 miles of perennial stream
(Ferrel 2002). Fire risk can be reduced through fuels reduction and
prescribed burns. The National Forests in New Mexico have active
programs to improve forest health. As an example, 69,965 ac have been
treated, improving watershed conditions associated with 62 stream
miles, and an additional 145,575 ac are planned for treatment to
improve conditions associated with an additional 79.5 stream miles
(Ferrel 2002). Over the next 10 to 20 years it is possible that a small
number of RGCT populations will be lost to fire; however, we do not
believe that such a loss will affect the long-term persistence of the
RGCT because the populations are widely distributed and loss of RGCT
populations that contain nonnatives provides an opportunity to
reestablish pure RGCT populations.
The Service cannot determine if fire is a threat to the 13 pure,
stable, and secure populations. Fire is unpredictable and we have no
way of determining where or with what intensity a fire may burn because
so many variables are involved. New Mexico is in the midst of a drought
and fire can be a threat. Because the populations are spread out across
the landscape and are not grouped together, the chances of more than
one population being affected is reduced. As mentioned above, if
catastrophic fire does occur, it provides an opportunity to reintroduce
pure RGCT trout into streams that had been dominated by nonnative trout
and expand the range of RGCT.
Electrofishing
The standard method to collect population information on stream
trout is electrofishing. In addition, short of complete stream
renovation, electrofishing is the primary method used to remove brook
and brown trout
[[Page 39945]]
from RGCT streams. Although there is a continuing need for additional
data on the existing RGCT populations, it should also be recognized
that electrofishing could have a negative effect on fish. Kocovsky et
al. (1997) found that 44 percent of X-rayed fish showed evidence of
spinal injury in a stream that had been electrofished for 8 years even
though the fish showed no external sign of injury. It has also been
shown that in a laboratory setting electroshocking can have a negative
impact on salmonid eggs (Cho et al. 2001). Nielsen (1998) warns that
the accumulated effects of electrofishing may be significant especially
in small populations. Although some fish may be killed or injured by
electrofishing, it is not known if these impacts affect RGCT
populations over time. However, managers need to be aware of the
potential dangers of electrofishing and begin exploring alternative
methods such as trapping or visual observation as a means by which to
evaluate populations.
Currently electrofishing is the primary tool to conduct population
surveys, and to detect and remove nonnative trout in RGCT streams. It
is expected that electrofishing in RGCT streams will continue until
alternative census methods are adopted. Electrofishing will also
continue to be the primary method for removing nonnatives, as no other
expedient method exists. Snorkeling surveys are being used by the
Forest Service as part of their stream inventories. While these
inventories can detect nonnative adults, it is very difficult to
distinguish between young trout species.
The Service determines that electrofishing is not a threat to the
13 pure, stable, and secure populations. Although individual fish may
be injured, no research indicates that electrofishing is detrimental to
populations as a whole. Electrofishing is a necessary tool at this time
to control nonnative trout and to monitor population size.
Hatcheries
It is likely that future management of RGCT will depend in part on
the use of hatchery-reared fish. Although hatcheries can produce many
fish in a short period of time, the use of hatchery fish is not without
risks (Busack and Currens 1995). Transmission of disease has been
discussed (see above discussion on WD) and is a threat that must be
managed. Maintenance of a ``wild'' broodstock is difficult, but if
hatchery-reared RGCT are to survive in the wild, care must be taken so
that broodstock does not become domesticated. Inbreeding can also pose
a problem (Cowley 1993). Planning is essential in the selection of fish
used as broodstock. Fish used as broodstock must be genetically pure.
Streams that are used as sources for broodstock should be rotated so
that the source population is not depleted and also so that the
hatchery broodstock is infused with new genes. However, stocks from the
Rio Grande, Pecos, and Canadian Basins should not be mixed until the
population genetics of the fish has been clarified. New Mexico has a
broodstock management plan designed specifically for RGCT that
addresses these issues (Cowley 1993). Having been implemented in the
field over the last several years, the feasibility and difficulties of
various aspects of the plan have been tested. The Plan is currently
under revision, and it could serve as a range-wide protocol.
Currently New Mexico has about 16,500 captive RGCT. Although Seven
Springs Hatchery was to be in full RGCT production by 1998, infection
by WD, subsequent disinfection and renovation of the hatchery, and
difficulties in rearing RGCT have delayed full production. However,
production from Seven Springs should increase over the next few years.
In Colorado, Haypress Lake contains wild broodstock, and captive
populations are reared at Poudre Rearing Unit and at the Fishery
Research Hatchery in Fort Collins. Colorado planted 33,400 RGCT into 6
waters in 1999, 66,600 into 40 waters in 2000, and 152,700 into 77
waters in 2001.
The Service determines that hatchery management is not a threat to
the 13 pure, stable, and secure populations. Hatchery-reared fish are
not planted into pure, stable RGCT populations so there is no risk of
disease transmission into these populations. Hatchery equipment is
sterilized before being used in the field to prevent disease
transmission. If the criteria suggested by Cowley (1993) are
implemented, a wild population would be used for spawning purposes only
once, insuring that the source population is not depleted or
compromised.
Public Sentiment
Several stream renovation projects are planned in the upcoming
years. One obstacle that must be recognized is public resistance to the
use of piscicides such as antimycin. Antimycin is an antibiotic that is
an effective fish toxicant. It can be neutralized at stations outside
the treatment area. The public must be educated and support range
expansion of RGCT, or restoration efforts could be undermined. The
``Respect the Rio'' program on the Santa Fe National Forest is a
particularly good example of an outreach effort to educate the public
and gain support for stream restoration. In 2000, the Santa Fe National
Forest was awarded a grant to begin this program, and an education
coordinator was hired in 2002. Nearly 1,000 students and over 200
adults have heard presentations relating to native fish and respect for
the land. The Respect the Rio program has three mascots: RGCT, Rio
Grande chub, and Rio Grande sucker (Ferrel 2002). The Carson and Rio
Grande National Forests also sponsor activities (e.g., Fish Fiesta) to
educate and raise public awareness about RGCT. Both State management
plans include education and outreach elements. Public support is
essential for the success of future projects, and the States of New
Mexico and Colorado recognize the importance of education and outreach
in achieving their conservation goals for the RGCT. For this reason,
the Service determines that public sentiment is not a threat to the 13
pure, stable, and secure populations.
Finding
There are 13 confirmed pure populations of RGCT with populations
over 2,500 fish, that are secured by barriers and do not have nonnative
competitors. There are an additional five populations in Colorado that
are considered pure by CDOW based on meristics and/or mtDNA that have
over 2,500 fish, are protected by a barrier, and have no nonnatives but
have not yet been tested by allozymes or nuclear DNA (Torcido, Jaroso,
Osier, Cat, and Cascade Creeks) (Table 1). Once these populations have
been tested using allozymes or nuclear DNA, it is very likely that some
or all will be part of the core group of secure populations, bringing
the total to as many as 18. Biomass values for these populations range
from 37 to 160 kg/ha (33 to 142 lb/acre). Stream length on Osier and
Cascade Creeks is less than ideal; however, as in the case of
Policarpio Creek, New Mexico, fish density in the two streams is high
(0.89 and 0.5 fish/m (0.27 and 0.15 fish/foot), respectively),
indicating suitable habitat conditions. In New Mexico, there are 12
populations that are in the process of being tested and an additional
12 populations that have tested pure but for which there is inadequate
information to judge the status of the populations. Five of these
creeks (Rio Frijoles, Chihuahuenos, Polvadera, Rio de Truchas, and
Tienditas) are between 8 and 18 km (5.0 and 11.2 miles) long
[[Page 39946]]
and have the potential to be secure populations (see Table 2 below).
Table 2.--Streams That Did Not Meet All The Core Criteria But Are Important Components of Range-Wide RGCT Status
and Are Likely To Persist Into The Foreseeable Future.
----------------------------------------------------------------------------------------------------------------
Watershed Stream name Ownership
----------------------------------------------------------------------------------------------------------------
Tested pure, large populations (5,000-15,000), brook or brown trout present:
----------------------------------------------------------------------------------------------------------------
Colorado
----------------------------------------------------------------------------------------------------------------
Alamosa/Trinchera...................... Sangre de Cristo.......... private.
Alamosa/Trinchera...................... Placer.................... private.
----------------------------------------------------------------------------------------------------------------
New Mexico
----------------------------------------------------------------------------------------------------------------
Rio de las Vacas....................... Rio de las Vacas.......... Santa Fe NF.
Rio de las Vacas....................... Rito Caf.................. Santa Fe NF.
Comanche Creek......................... Comanche Creek............ Carson NF.
----------------------------------------------------------------------------------------------------------------
Tested pure, no population information, stream length 8-18 km:
----------------------------------------------------------------------------------------------------------------
New Mexico
----------------------------------------------------------------------------------------------------------------
Rio Frijoles........................... Rio Frijoles.............. Santa Fe NF.
Canones................................ Chihuahuenos.............. Santa Fe NF.
Rio Quemado............................ Rio de Truchas............ Carson NF.
Rio de Fernando de Taos................ Tienditas................. Carson NF.
Canones................................ SF Polvadera.............. Santa Fe NF.
----------------------------------------------------------------------------------------------------------------
NF = National Forest. Not shown are the 21 streams with pure populations with between 500-2,500 RGCT (discussed
below).
Additionally, some large populations of pure RGCT have recently
been invaded by nonnatives, either because of barrier failure or
illegal transplantation. In Colorado, low numbers of brook trout have
been found in Sangre de Cristo Creek (with tributary Wagon Creek);
however, population size (over 9,000 RGCT), biomass, and stream length
are excellent. The same situation exists in the Placer Creek watershed
where there are four linked tributaries (total of over 11,000 RGCT). In
New Mexico, Rio de las Vacas and its tributaries, Rio de las Perchas
and Rio Anastacio (total of over 15,000 RGCT); Rito Caf (5,000 RGCT);
and Comanche Creek (5,000 RGCT) are all strong RGCT populations that
have either brook trout or brown trout present (Table 2). Brown trout
were found in Rio de las Vacas in 2001. Electrofishing removal and
surveys are scheduled for 2002 and the existing barrier will be
improved by the Forest Service. These populations are important
components of the range-wide population. Agency personnel are aware of
the undesirability of nonnatives in RGCT streams and remove nonnatives
both during the course of regular stream surveys and as on-going
programs in selected streams.
In addition, there are 11 pure populations in New Mexico and 10 in
Colorado (21 total) that have more than 500 and less than 2,500 fish
and 15 pure populations in both States with less than 500 individuals.
While these populations may be at greater long-term risk of extinction
compared to large populations, they continue to persist. In the future
these populations may be expanded downstream, and they may serve as
repositories of unique genetic material. As such they also are
important components of the range-wide population and provide
additional security for the overall status of the subspecies.
In the context of the Act, the term ``threatened species'' means
any species that is likely to become an endangered species within the
foreseeable future throughout all or a significant portion of its
range. The term ``endangered species'' means any species that is in
danger of extinction throughout all or a significant portion of its
range. The Act does not indicate threshold levels of historic
population size at which (as the population of a species declines)
listing as either ``threatened or endangered'' becomes warranted.
Instead, the principal considerations in the determination of whether
or not a species warrants listing as a threatened or endangered species
under the Act are the threats that currently confront the species and
the likelihood that the species will persist in the ``foreseeable
future.'' Specific threats discussed in detail above in our five factor
analysis include nonnative salmonids that either hybridize or compete
with RGCT, habitat fragmentation, livestock grazing, timber harvest,
overutilization, disease (e.g., whirling disease), inadequacy of
existing regulatory mechanisms, fire, electrofishing, and opposition to
the use of fish poisons (e.g., piscicides). We have determined that the
13 core populations are not threatened by any of the identified threats
alone or in combination.
Our finding is also based upon the other large populations of RGCT
identified in Tables 1 and 2, as well as the 21 other populations
discussed above. We find that these populations are likely to persist
into the future because of the large numbers of individuals within
these populations and the threats are adequately addressed by the
ongoing management actions of the States and Federal agencies to remove
nonnatives (brook and brown trout), test for genetic purity, conduct
stream surveys, maintain barriers, conduct public education and
outreach, and test for WD.
At different times in discussing the ongoing management actions by
the State or Federal government we have included a discussion of
actions that are projected to occur over the next few years. We
described the future conservation actions that agencies indicate they
will be undertaking, but we have not relied on these future actions for
purposes of determining the current status of the species or the
adequacy of current management actions to alleviate threats to the
RGCT.
[[Page 39947]]
After reviewing the best scientific and commercial information
available (1998 status review, available literature, information
supplied to us by State and Federal agencies, and other unpublished
documents and maps), for all of the reasons discussed herein, we find
that the RGCT is not endangered and is not likely to become endangered
within the foreseeable future throughout all or a significant portion
of its range and that listing as threatened or endangered is not
warranted at this time.
References Cited
A complete list of all references cited in this notice is available
from the New Mexico Ecological Services Field Office (see ADDRESSES
section).
Authority
The authority for this action is the Endangered Species Act (16
U.S.C. 1531 et seq.).
Dated: June 3, 2002.
Steve Williams,
Director, Fish and Wildlife Service.
[FR Doc. 02-14569 Filed 6-10-02; 8:45 am]
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