[Federal Register: November 25, 2008 (Volume 73, Number 228)]
[Proposed Rules]
[Page 71787-71826]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr25no08-34]
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Part III
Department of the Interior
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Fish and Wildlife Service
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50 CFR 17
Endangered and Threatened Wildlife and Plants; 12-Month Finding on a
Petition To List the Northern Mexican Gartersnake (Thamnophis eques
megalops) as Threatened or Endangered With Critical Habitat; Proposed
Rule
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[FWS-R2-ES-2008-0065; MO 9221050083-B2]
Endangered and Threatened Wildlife and Plants; 12-Month Finding
on a Petition To List the Northern Mexican Gartersnake (Thamnophis
eques megalops) as Threatened or Endangered with Critical Habitat
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 the northern Mexican gartersnake
(Thamnophis eques megalops) as threatened or endangered with critical
habitat under the Endangered Species Act of 1973, as amended (Act). The
petitioners provided three listing options for consideration by the
Service: (1) Listing the U.S. population as a Distinct Population
Segment (DPS); (2) listing Thamnophis eques megalops throughout its
range in the United States and Mexico based on its rangewide status; or
(3) listing Thamnophis eques megalops throughout its range in the
United States and Mexico based on its status in the United States. On
the basis of the best scientific and commercial information available,
we find that listing the northern Mexican gartersnake as threatened or
endangered throughout its range in the United States and Mexico, based
on its rangewide status, is warranted under the Act, due to the present
or threatened destruction, modification or curtailment of its habitat;
predation; and the inadequacy of existing regulatory mechanisms.
Currently, listing is precluded by higher priority actions to amend the
Lists of Endangered and Threatened Wildlife and Plants. Upon
publication of this 12-month petition finding, the northern Mexican
gartersnake will be added to our candidate species list. We will
develop a proposed rule to list the northern Mexican gartersnake as our
priorities allow. Any determination on critical habitat will be made
during development of the proposed rule.
DATES: The finding announced in this document was made on November 25,
2008.
ADDRESSES: This finding is available on the Internet at http://
www.regulations.gov at Docket Number FWS-R2-ES-2008-0065. 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, Arizona Ecological Services Office, 2321
West Royal Palm Road, Suite 103, Phoenix, AZ 85021-4951. Please submit
any new information, materials, comments, or questions concerning this
finding to the above address.
FOR FURTHER INFORMATION CONTACT: Steve Spangle, Field Supervisor,
Arizona Ecological Services Office (see ADDRESSES), telephone 602-242-
0210. 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 containing substantial scientific and commercial
information indicating that listing may be warranted, we make a finding
within 12 months of the date of receipt of the petition on whether the
petitioned action is: (a) Not warranted, (b) warranted, or (c)
warranted, but 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 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.
On December 19, 2003, we received a petition dated December 15,
2003, requesting that we list the northern Mexican gartersnake as
threatened or endangered, and that we designate critical habitat
concurrently with the listing. The petition, submitted by the Center
for Biological Diversity, was clearly identified as a petition for a
listing rule and contained the names, signatures, and addresses of the
requesting parties. Included in the petition was supporting information
regarding the species' taxonomy and ecology, historical and current
distribution, present status, and actual and potential causes of
decline. We acknowledged the receipt of the petition in a letter to Mr.
Noah Greenwald, dated March 1, 2004. In that letter, we also advised
the petitioners that, due to funding constraints in fiscal year (FY)
2004, we would not be able to begin processing the petition at that
time.
Previous Federal Actions
The Mexican gartersnake (Thamnophis eques) (which included the
subspecies megalops) was placed on the list of candidate species as a
Category 2 species in 1985 (50 FR 37958). Category 2 species were those
for which existing information indicated that listing was possibly
appropriate, but for which substantial supporting biological data to
prepare a proposed rule were lacking. In the 1996 Candidate Notice of
Review (February 28, 1996; 61 FR 7596), the use of Category 2
candidates was discontinued, and the northern Mexican gartersnake was
no longer recognized as a candidate.
On May 17, 2005, the petitioners filed a complaint for declaratory
and injunctive relief, challenging our failure to issue a 90-day
finding in response to the petition as required by 16 U.S.C.
1533(b)(3)(A) and (B). In a stipulated settlement agreement, we agreed
to submit a 90-day finding to the Federal Register by December 16,
2005, and if substantial, submit a 12-month finding to the Federal
Register by September 15, 2006 (Center for Biological Diversity v.
Norton, CV-05-341-TUC-CKJ (D. Az)). The settlement agreement was signed
and adopted by the District Court of Arizona on August 2, 2005.
On December 13, 2005, we made our 90-day finding that the petition
presented substantial scientific information indicating that listing
the northern Mexican gartersnake (Thamnophis eques megalops) may be
warranted, but we did not discuss the applicability of any of the three
listing scenarios that were provided in the petition. The finding and
our initiation of a status review was published in the Federal Register
on January 4, 2006 (71 FR 315).
On September 26, 2006, we published a 12-month finding that listing
of the northern Mexican gartersnake was not warranted because we
determined that not enough information on the subspecies' status and
threats in Mexico was known at that time (71 FR 56227). On November 17,
2007, the petitioners filed a complaint for declaratory and injunctive
relief pursuant to section 11 of the Act (16 U.S.C. 1540), seeking to
set aside the 12-month finding. Additionally, a formal opinion was
issued by the Solicitor of the Department of the Interior, ``The
Meaning of In Danger of Extinction Throughout All or a Significant
Portion
[[Page 71789]]
of Its Range'' (U.S. DOI 2007), which provides further guidance on how
to conduct a detailed analysis of whether a species is in danger of
extinction throughout a significant portion of its range. In December
2007, the Service withdrew the September 26, 2006, 12-month finding to
consider the new ``Significant Portion of the Range'' policy. In a
stipulated settlement agreement with the petitioners, we agreed to
submit a new 12-month finding to the Federal Register by November 17,
2008 (Center for Biological Diversity v. Kempthorne, CV-07-596-TUC-RCCJ
(D. Az)). The settlement agreement was signed and adopted by the
District Court of Arizona on June 18, 2008.
This notice constitutes a new 12-month finding for the petition to
list the northern Mexican gartersnake as threatened or endangered. The
petitioners described three potentially listable entities of
gartersnake for consideration by the Service: (1) Listing the U.S.
population as a Distinct Population Segment (DPS); (2) listing
Thamnophis eques megalops throughout its range in the United States and
Mexico based on its rangewide status; or (3) listing Thamnophis eques
megalops throughout its range in the United States and Mexico based on
its status in the United States. Because we found that listing the
northern Mexican gartersnake rangewide was warranted, there was no need
to conduct any further analysis of the remaining two options, which are
smaller geographic entities and are subsumed by the rangewide listing.
Biology
Species Description. The northern Mexican gartersnake ranges in
color from olive to olive-brown or olive-gray with three stripes that
run the length of the body, the middle of which darkens towards the
tail. It may occur with other native gartersnake species and can be
difficult for people without herpetological expertise to identify. The
snake may reach a maximum known length of 44 inches (in) [(112
centimeters (cm)]. The pale yellow to light-tan lateral stripes
distinguish the northern Mexican gartersnake from other sympatric (co-
occurring) gartersnake species because a portion of the lateral stripe
is found on the fourth scale row, while it is confined to lower scale
rows for other species. Paired black spots extend along the olive
dorsolateral fields (region adjacent to the top of the snake's back)
and the olive-gray ventrolateral fields (region adjacent to the area of
the snake's body in contact with the ground). A more detailed species
description can be found in our 2006 12-month finding for this species
(71 FR 56227), or by reviewing Rosen and Schwalbe (1988, p.4), Rossman
et al. (1996, pp. 171-172), or Manjarrez and Garcia (1993, pp. 1-5).
Taxonomy. The northern Mexican gartersnake is a member of the
family Colubridae and subfamily Natricinae (harmless live-bearing
snakes) (Lawson et al. 2005, p. 596). The taxonomy of the genus
Thamnophis has a complex history, partly because many of the species
are similar in appearance and scutelation (arrangement of scales), but
also because many of the early museum specimens were in such poor and
faded condition that it was difficult to study them (Conant 2003, p.
6).
In recent history and prior to 2003, Thamnophis eques was
considered to have three subspecies, T. e. eques, T. e. megalops, and
T. e. virgatenuis (Rossman et al. 1996, p. 175). In 2003, an additional
seven new subspecies were identified under T. eques: (1) T. e.
cuitzeoensis; (2) T. e. patzcuaroensis; (3) T. e. inspiratus; (4) T. e.
obscurus; (5) T. e. diluvialis; (6) T. e. carmenensis; and (7) T. e.
scotti (Conant 2003, p. 3). Common names were not provided, so in this
finding, we use the scientific name for all subspecies of Mexican
gartersnake other than the northern Mexican gartersnake. These seven
new subspecies were described based on morphological differences in
coloration and pattern; have highly restricted distributions; and occur
in isolated wetland habitats within the mountainous Transvolcanic Belt
region of southern Mexico, which contains the highest elevations in the
country (Conant 2003, pp. 7-8). There are no known challenges within
the scientific literature of the validity of current taxonomy of any of
the 10 subspecies of T. eques. A more detailed description of the
taxonomy of the northern Mexican gartersnake is found in our September
26, 2006 12-month finding for this species (71 FR 56227). Additional
information regarding this species' taxonomy can be found in De Queiroz
et al. (2002, P. 323), De Queiroz and Lawson (1994, p. 217), Rossman et
al. (1996, pp. xvii-xviii, pp. 171-175), Rosen and Schwalbe (1988, pp.
2-3), Liner (1994, p. 107), and Crother (2008, p. 63).
On many occasions throughout this finding, we discuss the status of
and threats to several prey species of the northern Mexican
gartersnake, including anuran (frog and toad) species of the genera
historically known as Rana and Bufo (true frogs and true toads,
respectively). Frost et al. (2006, pp. 9-11) proposed several taxonomic
name changes, including many species under the genus Rana to
Lithobates, and many species under the genus Bufo to Anaxyrus. Crother
(2008, pp. 2-12), Committee Chair for the Standard English and
Scientific Names Committee, adopted these scientific name changes.
However, these taxonomic revisions have not escaped significant
scrutiny in the scientific literature. Weins (2007, pp. 55-56)
criticized the methodologies and analysis of Frost et al. (2006, pp. 9-
11). Subsequently, Frost et al. (2008, pp. 385-395) rebutted these
criticisms. Throughout this finding, we continue to use the genera Rana
and Bufo to maintain taxonomic familiarity among the interested
parties, retain consistency in the Federal Register with respect to
notices regarding the northern Mexican gartersnake, and allow ample
opportunity for peer review and deliberation in the scientific
community with respect to the findings of Frost et al. (2006, pp. 9-
11).
Habitat. Throughout its rangewide distribution, the northern
Mexican gartersnake occurs at elevations from 130 to 8,497 feet (ft)
(40 to 2,590 meters (m)) (Rossman et al. 1996, p. 172). The northern
Mexican gartersnake is a riparian obligate (restricted to riparian
areas when not engaged in dispersal behavior) and occurs chiefly in the
following general habitat types: (1) Source-area wetlands (e.g.,
cienegas (mid-elevation wetlands with highly organic, reducing (basic
or alkaline) soils), stock tanks (small earthen impoundment), etc.);
(2) large-river riparian woodlands and forests; and (3) streamside
gallery forests (as defined by well-developed broadleaf deciduous
riparian forests with limited, if any, herbaceous ground cover or dense
grass) (Hendrickson and Minckley 1984, p. 131; Rosen and Schwalbe 1988,
pp. 14-16; Arizona Game and Fish Department 2001). Additional
information on the habitat requirements of the northern Mexican
gartersnake within the United States and Mexico can be found in our
2006 12-month finding for this species (71 FR 56227) and in Rosen and
Schwalbe (1988, pp. 14-16), Rossman et al. (1996, p. 176), McCranie and
Wilson (1987, pp. 11-17), and Cirett-Galan (1996, p. 156).
Behavior, Prey Base, and Reproduction. The northern Mexican
gartersnake is surface active at ambient temperatures ranging from 71
degrees Fahrenheit ([deg]F) to 91 [deg]F (22 degrees Celsius ([deg]C)
to 33 [deg]C) and forages along the banks of waterbodies. Rosen (1991,
pp. 308-309) found that northern Mexican gartersnakes spent
approximately 60 percent of their time
[[Page 71790]]
moving, 13 percent of their time basking on vegetation, 18 percent of
their time basking on the ground, and 9 percent of their time under
surface cover; body temperatures ranged from 24-33 [deg]C (75-91
[deg]F) and averaged 28 [deg]C (82 [deg]F), which is lower than other,
similar species with comparable habitat and prey preferences. Rosen
(1991, p. 310) suggested that lower preferred body temperatures
exhibited by northern Mexican gartersnakes may be due to both (1) their
tendency to occupy cienega-like habitat where warm ambient temperatures
are relatively unavailable; and, (2) their tendency to remain in dense
cover.
The northern Mexican gartersnake is an active predator and is
believed to heavily depend upon a native prey base (Rosen and Schwalbe
1988, pp. 18, 20). Northern Mexican gartersnakes forage generally along
vegetated banklines, searching for prey in water and on land, using
different strategies (Alfaro 2002, p. 209). Generally, its diet
consists predominantly of amphibians and fishes, such as adult and
larval native leopard frogs (e.g., lowland leopard frog (Rana
yavapaiensis) and Chiricahua leopard frog (Rana chiricahuensis)), as
well as juvenile and adult native fish species (e.g., Gila topminnow
(Poeciliopsis occidentalis occidentalis), desert pupfish (Cyprinodon
macularius), Gila chub (Gila intermedia), and roundtail chub (Gila
robusta)) (Rosen and Schwalbe 1988, p. 18). Auxiliary prey items may
also include young Woodhouse's toads (Bufo woodhousei), treefrogs
(Family Hylidae), earthworms, deermice (Peromyscus spp.), lizards of
the genera Aspidoscelis and Sceloporus, larval tiger salamanders
(Ambystoma tigrinum), and leeches (Gregory et al. 1980, pp. 87, 90-92;
Rosen and Schwalbe 1988, p. 20; Holm and Lowe 1995, pp. 30-31;
Degenhardt et al. 1996, p. 318; Rossman et al. 1996, p. 176; Manjarrez
1998). To a much lesser extent, this snake's diet may include nonnative
species, including larval and juvenile bullfrogs, and mosquitofish
(Gambusia affinis) (Holycross et al. 2006, p. 23). Venegas-Barrera and
Manjarrez (2001, p. 187) reported the first observation of a snake in
the natural diet of any species of Thamnophis after documenting the
consumption by a Mexican gartersnake of a Mexican alpine blotched
gartersnake (Thamnophis scalaris).
Marc[iacute]as-Garc[iacute]a and Drummond (1988, pp. 129-134)
sampled the stomach contents of Mexican gartersnakes and the prey
populations at (ephemeral) Lake Tecocomulco, Hidalgo, Mexico. Field
observations indicated with high statistical significance that larger
snakes fed primarily upon aquatic vertebrates (fishes, frogs, and
larval salamanders) and leeches, whereas smaller snakes fed primarily
upon earthworms and leeches (Marc[iacute]as-Garc[iacute]a and Drummond
1988, p. 131). Marc[iacute]as-Garc[iacute]a and Drummond (1988, p. 130)
also found that parturition (birth) of neonatal T. eques tended to
coincide with the annual peak density of annelids (earthworms and
leeches). Positive correlations were also made with respect to capture
rates (which are correlated with population size) of T. eques to lake
levels and to prey scarcity; that is, when lake levels were low and/or
prey species scarce, Mexican gartersnake capture rates declined
(Marc[iacute]as-Garc[iacute]a and Drummond 1988, p. 132). This
indicates the importance of available water and an adequate prey base
to maintaining viable populations of Mexican gartersnakes.
Marc[iacute]as-Garc[iacute]a and Drummond (1988, p. 133) found that
while certain prey items were positively associated with size classes
of snakes, the largest of specimens consume any prey available.
Sexual maturity in northern Mexican gartersnakes occurs at 2 years
of age in males and at 2 to 3 years of age in females (Rosen and
Schwalbe 1988, pp. 16-17). Northern Mexican gartersnakes are
ovoviviparous (eggs develop and hatch within the oviduct of the
female). Mating occurs in April and May followed by the live birth of
between 7 and 26 newborns (newly born individuals) (average is 13.6) in
July and August (Rosen and Schwalbe 1988, p. 16). Unlike other
gartersnake species, which typically breed annually, approximately half
of the sexually mature females within a population of northern Mexican
gartersnake reproduce in any one season (Rosen and Schwalbe 1988, p.
17). This may have negative implications for the species' ability to
rebound in isolated populations facing threats such as nonnative
species, habitat modification or destruction, and other perturbations.
Low birth rates will impede recovery of such populations by
accentuating the effects of these threats.
Distribution
Historical Distribution. Within the United States, the northern
Mexican gartersnake historically occurred predominantly in Arizona at
elevations ranging from 130 to 6,150 ft (40 to 1,875 m) in elevation.
It was generally found where water was relatively permanent and
supported suitable habitat. The northern Mexican gartersnake
historically occurred in every county within Arizona, within several
perennial or intermittent drainages and disassociated wetlands (Woodin
1950, p. 40; Nickerson and Mays 1970, p. 503; Bradley 1986, p. 67;
Rosen and Schwalbe 1988, Appendix I; 1995, p. 452; 1997, pp. 16-17;
Holm and Lowe 1995, pp. 27-35; Sredl et al. 1995b, p. 2; 2000, p. 9;
Rosen et al. 2001, Appendix I; Holycross et al. 2006, pp. 1-2, 15-51;
Brennan and Holycross 2006, p. 123; Radke 2006; Rosen 2006; Holycross
2006).
Historically, the northern Mexican gartersnake had a limited
distribution in New Mexico that consisted of scattered locations
throughout the Gila and San Francisco headwater drainages in Grant and
western Hidalgo Counties (Price 1980, p. 39; Fitzgerald 1986, Table 2;
Degenhardt et al. 1996, p. 317; Holycross et al. 2006, pp. 1-2).
One record for the northern Mexican gartersnake exists for the
State of Nevada, opposite Fort Mohave, in Clark County along the shore
of the Colorado River (De Queiroz and Smith 1996, p. 155). The species
may have occurred historically in the lower Colorado River region of
California, although we were unable to verify any museum records for
California. Any populations of northern Mexican gartersnakes that may
have historically occurred in either Nevada or California likely
pertained directly to the Colorado River and are extirpated.
Within Mexico, northern Mexican gartersnakes historically occurred
within the Sierra Madre Occidental and the Mexican Plateau in the
Mexican states of Sonora, Chihuahua, Durango, Coahila, Zacatecas,
Guanajuato, Nayarit, Hidalgo, Jalisco, San Luis Potos[iacute],
Aguascalientes, Tlaxacala, Puebla, M[eacute]xico, Veracruz, and
Quer[eacute]taro, comprising approximately 85 percent of the total
rangewide distribution of the species (Conant 1963, p. 473; 1974, pp.
469-470; Van Devender and Lowe 1977, p. 47; McCranie and Wilson 1987,
p. 15; Rossman et al. 1996, p. 173; Lemos-Espinal et al. 2004, p. 83).
Status in the United States. Variability in survey design and
effort makes it difficult to compare population trends among sites and
between sampling periods. Thus, for each of the sites considered in our
analysis, we have attempted to translate and quantify search and
capture efforts into comparable units (i.e., person-search hours and
trap-hours) and have cautiously interpreted those results. Given the
data provided, it is not possible to determine population densities at
the sites.
A detailed status of the northern Mexico gartersnake in the United
States and Mexico can be found in our 2006 12-month finding (71 FR
56227) and in Holycross et al. (2006, p. 12); Rosen and Schwalbe (1988,
Appendix 1); Rosen et
[[Page 71791]]
al. (2001, pp. 21-22, Appendix 1); d'Orgeix (2008); Holm and Lowe
(1995, pp. 27-35). Subsequent to our 2006 12-month finding, we have
obtained and analyzed additional information pertinent to the status of
the northern Mexico gartersnake and present it below.
Scotia Canyon was the last area intensively resurveyed by Rosen et
al. (2001, pp. 15-16). In comparing capture rates from Holm and Lowe
(1995, pp. 27-35), northern Mexican gartersnake populations in this
area appear to have declined from 1980-1982, to low capture rates in
1993, and even lower capture rates in 2000 (Boyarski 2008c, p. 1). In
2008, a multi-party effort was initiated within Scotia Canyon,
including the Peterson Ranch Pond and vicinity, to eradicate bullfrogs
as well as record observations of Chiricahua leopard frogs or northern
Mexican gartersnakes (Frederick 2008, 2008b). These efforts occurred in
the same area investigated by Holm and Lowe (1995, pp. 27-35) and Rosen
et al. (2001, pp. 15-16). After many surveys of herpetofauna (reptiles
and amphibians) in this area to identify the presence of bullfrogs for
eradication, a single, large adult northern Mexican gartersnake was
observed, the first in over 8 years of informal surveys at this site
(Frederick 2008b), which is frequently visited by biologists. This
observation suggests that the species continues to occur in the upper
Scotia Canyon area, but, given the extensive survey effort, it occurs
in exceptionally low densities and no longer represents a stable
population because of problems with reproduction and survivorship that
exist with populations comprised of very low numbers of individuals.
A significant amount of survey effort for northern Mexican
gartersnakes was conducted at the Las Cienegas National Conservation
Area (Cienega Creek and Empire Cienega) from 2002-2008. During the 2002
and 2003 field seasons, Rosen and Caldwell (2004, pp. 1-52) conducted
an in-depth assessment of the riparian herpetofaunal community of this
area and in 11,784 trap-hours captured by hand and trap, 29 northern
Mexican gartersnakes that were marked and released. Twenty-one northern
Mexican gartersnakes were trapped, which equates to 561 trap-hours per
snake. In 2004, Rosen and Caldwell (2004, p. 21) considered the species
to be ``widely distributed, though perhaps reduced in abundance'' in
this area.
In 2007 and 2008, significant effort to collect northern Mexican
gartersnakes was given to this same area using similar techniques as
Rosen and Caldwell (2004) (Gartersnake Conservation Working Group
(GCWG) 2008, pp. 1-10). Servoss et al. (2007, p. 4) captured one
juvenile northern Mexican gartersnake by hand after 27 person search-
hours and 1,000 trap-hours of effort.
Due to limited success in collecting the species in 2007, in 2008,
the Arizona Game and Fish Department contracted with a recognized
reptile and amphibian researcher familiar with the area to collect
specimens for captive propagation (GCWG 2008, pp. 1-10). The
herpetologist trapped a single juvenile northern Mexican gartersnake in
3,612 trap-hours and 104 person search-hours of effort (Caldwell 2008a,
2008b).
The wildlife biologist for the Bureau of Land Management (BLM)
Tucson Field Office (who has conducted fish sampling at the Las
Cienegas National Conservation Area since 1998) expressed concerns for
the apparent population decline of northern Mexican gartersnakes in
this area. Several fish sampling techniques he employs are also used
specifically to sample aquatic snake species such as the northern
Mexican gartersnake. Simms (2008) stated that seining and hoop netting
at 40 locations, as well as visual surveys of this area performed in
2008, have yielded no observations of Mexican gartersnakes.
The data from 2007 and 2008 confirm that this formerly stable
population at the Las Cienegas National Conservation Area is
experiencing significant declines, may no longer be viable, and could
become extirpated in the near-term. In 2007 and 2008, more than 2,300
trap-hours were required per snake captured (Caldwell 2008a, 2008b;
Servoss et al. 2007, p. 1-12), compared with Rosen and Caldwell's
(2004, p. 21 Table 2) capture rates of 561 trap-hours per snake in 2002
and 2003. This is a more than four-fold increase in the effort needed
to capture northern Mexican gartersnakes.
The recently documented population of northern Mexican gartersnakes
within Tonto Creek is the only known population that remains from the
Salt River Basin (the status of the species in the basin on the White
Mountain Apache and San Carlos Apache reservations remains unknown).
Wallace et al. (2008, pp. 243-244) documented the first record of
northern Mexican gartersnakes from the Tonto Creek watershed in Gila
County, from a specimen that was observed in the road (killed by a
vehicle) on State Route 188 in 1995. Seventeen individual northern
Mexican gartersnakes were subsequently captured in Tonto Creek with
20,444 trap-hours of effort (1,202 trap-hours per snake) in 2004 and
2005 (Holycross et al. 2006, pp. 41-44; Wallace et al. 2008, pp. 243-
244). Wallace et al. (2008, pp. 243-244) suggest northern Mexican
gartersnakes in Tonto Creek persist in low densities and raise the
possibility that recruitment (the process by which individuals within a
population achieve reproductive maturity) may be in decline because
only adult and newborn specimens were captured, with no intermediate
age classes observed.
The population of northern Mexican gartersnakes along the Verde
River within the Verde Valley of Yavapai County is presumed to remain
as a low-density population. Approximately 15 individuals, including
agency personnel and private citizens, surveyed the Verde River within
the Verde Valley (including Dead Horse Ranch State Park) for the
purpose of collecting 5 Mexican gartersnakes for captive propagation in
2007 (GCWG 2007, p. 2). Approximately 120 person-search hours resulted
in no observations of northern Mexican gartersnakes (GCWG 2007, p. 2).
Haney et al. (2008, p. 61) declared the northern Mexican gartersnake
nearly lost from the Verde River.
A population of northern Mexican gartersnakes that remains at the
Arizona Game and Fish Department's Page Springs and Bubbling Ponds fish
hatcheries (hatcheries), located adjacent to Oak Creek, upstream of its
confluence with the Verde River, represents the highest density
population in Arizona and potentially the last remaining viable
population in the United States. Boyarski (2008b, pp. 1-10) summarizes
the first (2007) field season of a northern Mexican gartersnake
monitoring project at the hatcheries, which had the objective of
establishing the baseline population demographics from which to launch
future investigations (Boyarski 2008b, p. 4). Although several capture
techniques were employed, trapping was the most effective by far. In
total, 52 individual northern Mexican gartersnakes were captured in
2007; 42 from Bubbling Ponds, 8 from Page Springs, and 2 from the
adjacent Oak Creek (Boyarski 2008b, p. 5). In total, 19,457 trap-hours
captured 56 northern Mexican gartersnakes (including 7 recaptures),
which equates to 347 trap-hours per capture (Boyarski 2008b, p. 6). As
this was the first year to acquire population data for northern Mexican
gartersnakes within the hatcheries, population trends at these sites
cannot be determined. However, hatchery personnel stated that northern
Mexican gartersnakes are not observed as frequently and do not appear
to be as common as they once were at these sites
[[Page 71792]]
(Boyarski 2008b, p. 8). While not associated with a scientific study,
this statement by hatchery personnel, who spend most of their time in
the immediate vicinity of occupied habitat, is of special concern
because it illustrates the potential that long-term declines may have
been occurring at the hatchery although potential declines can not be
quantified.
Sonoita Creek in Santa Cruz County in southern Arizona was a
historical location for northern Mexican gartersnakes. Turner (2006,
pp. 1-21) found no northern Mexican gartersnakes in a herpetological
inventory conducted from April through September 2006, in the Sonoita
Creek State Natural Area. The last record of a northern Mexican
gartersnake in this area was in 1974 and the subspecies was not found
during Turner's 204-person-search-hour, 5,472-trap-hour survey effort
(Turner 2006, pp. 3, 9). Crayfish, bullfrogs, and nonnative fish were
observed by Turner (2006, p. 10) throughout the riparian area of the
study area, as was evidence of improper livestock grazing.
In our 2006 12-month finding for this species, we specified that
the last known observation of the northern Mexican gartersnake in New
Mexico occurred in 1994 on private land (Painter 2000, p. 36, Painter
2005). In 2007, we became aware of a single photo-vouchered record of a
northern Mexican gartersnake in New Mexico. The specimen was discovered
and photo-vouchered in August 2002, observed in a debris pile along the
Gila River off Highway 180 in Grant County, New Mexico (Hill 2007).
Subsequent searches for northern Mexican gartersnakes were conducted in
the same vicinity in 2006 and 2007, but no individuals were observed
(Hill 2007). In our 2006 finding (71 FR 56227), we considered the
northern Mexican gartersnake as extirpated from New Mexico. In
consideration of: (1) A single observation of the species in New Mexico
within the last 14 years that occurred in 2002; (2) 2 years of survey
effort in 2006 and 2007 within the Gila River in the area of the 2002
observation by Hill (2007); and (3) additional survey effort of
historical habitat for the species in New Mexico in 2007, we consider
the status of the northern Mexican gartersnake in the Gila River at the
Highway 180 crossing in New Mexico as unknown at this time (Painter
2008; Cotton 2008; Kindscher In Prep., pp. 1-26). All other historical
locations of the northern Mexican gartersnake in New Mexico are
considered extirpated (Painter 2005).
General concerns within the scientific community exist for age
class structure within northern Mexican gartersnake populations that
have been affected by nonnative species. It is widely believed that
recruitment of northern Mexican gartersnakes may be significantly
impeded by nonnative predation on the neonate and juvenile age classes.
Individuals that survive past these age classes are likely to have
increased survivorship, in part by foraging on the nonnative species
that preyed upon them during their younger age classes. These
population-level observations have been made in several populations
including Scotia Canyon (Holm and Lowe 1995, p. 34), Tonto Creek
(Wallace et al. 2008, pp. 243-244), and the San Bernardino National
Wildlife Refuge (Rosen and Schwalbe 1988, p. 18).
Our analysis of the best available data on the status of the
northern Mexican gartersnake distribution in the United States
indicates that its distribution has been significantly reduced, and it
is likely extirpated from a large portion of its historical
distribution within the United States. We define a population as
``likely extirpated'' when there have been no northern Mexican
gartersnakes reported for a decade or longer at a site within the
historical distribution of the species, despite survey efforts, and
there is no expectation of natural recovery at the site due to the
presence of known or strongly suspected causes of extirpation. The
perennial or intermittent stream reaches and disassociated wetlands
(i.e., stock tanks, ponds, cienegas, etc.) where the northern Mexican
gartersnake has likely been extirpated in Arizona include: (1) The Gila
River; (2) the Lower Colorado River from Davis Dam to the International
Border; (3) the San Pedro River; (4) the Santa Cruz River downstream
from the International Border at Nogales; (5) the Salt River; (6) the
Rio San Bernardino from International Border to headwaters at Astin
Spring (San Bernardino National Wildlife Refuge); (7) the Agua Fria
River; (8) the Verde River upstream of Clarkdale; (9) the Verde River
from the confluence with Fossil Creek downstream to its confluence with
the Salt River; (10) Tanque Verde Creek in Tucson; (11) Rillito Creek
in Tucson; (12) Agua Caliente Spring in Tucson; (13) Potrero Canyon/
Springs; (14) Babocamari Cienega; (15) Barchas Ranch, Huachuca Mountain
bajada; (16) Parker Canyon Lake and tributaries in the Canelo Hills;
and (17) Oak Creek at Midgley Bridge (Rosen and Schwalbe 1988, pp. 25-
26, Appendix I; 1997, pp. 16-17; Rosen et al. 2001, Appendix I; Brennan
and Holycross 2006, p. 123; Holycross 2006; Holycross et al. 2006, pp.
15-51, 66; Radke 2006; Rosen 2006).
In New Mexico, the following historical populations are considered
extirpated: (1) Mule Creek; (2) the Gila River, 5 miles (mi) (8
kilometers (km)) east of Virden; (3) Spring Canyon; (4) the West Fork
Gila River at Cliff Dwellings National Monument; (5) the Tularosa River
at its confluence with the San Francisco River; (6) the San Francisco
River at Tub Spring Canyon; (7) Little Creek at Highway 15; (8) the
Middle Box of Gila River at Ira Ridge; (9) Turkey Creek; (10) Negrito
Creek; and (11) the Rio Mimbres (Fitzgerald 1986, Table 2; Painter
2005, 2006; 2008; Cotton 2008; Kindscher In Prep., pp. 1-26).
Conversely, our review of the best available information indicates
the northern Mexican gartersnake likely occurs in a fraction of its
former range in Arizona. We define populations as ``likely occurring''
when the species is expected to reliably occur in appropriate habitat
as supported by recent museum records and/or recent (i.e., less than 10
years) reliable observations. The perennial or intermittent stream
reaches and disassociated wetlands where we conclude northern Mexican
gartersnakes remain include: (1) The Santa Cruz River/Lower San Rafael
Valley (headwaters downstream to the International Border); (2) the
Verde River from the confluence with Fossil Creek upstream to
Clarkdale; (3) Oak Creek at Page Springs; (4) Tonto Creek from the
mouth of Houston Creek downstream to Roosevelt Lake; (5) Cienega Creek
from the headwaters downstream to the ``Narrows'' just downstream of
Apache Canyon; (6) Pantano Wash (Cienega Creek) from Pantano downstream
to Vail; (7) Appleton-Whittell Research Ranch and vicinity near Elgin;
and (8) Red Rock Canyon east of Patagonia (Rosen et al. 2001, Appendix
I; Caldwell 2005; Brennan and Holycross 2006, p. 123; Holycross 2006;
Holycross et al. 2006, pp. 15-51, 66; Rosen 2006; Jones 2008a).
The current status of the northern Mexican gartersnake is unknown
in several areas within Arizona and New Mexico where the species is
known to have historically occurred. We base this determination
primarily on historical museum records for locations where survey
access is restricted, survey data are unavailable or insufficient, and/
or current threats could preclude occupancy. The perennial or
intermittent stream reaches and disassociated wetlands where the status
of the northern Mexican gartersnake remains uncertain include: (1) The
downstream portion of the Black River drainage from the Paddy Creek
[[Page 71793]]
confluence; (2) the downstream portion of the White River drainage from
the confluence of the East and North forks; (3) Big Bonito Creek; (4)
Lake O'Woods near Lakeside; (5) Spring Creek above the confluence with
Oak Creek; (6) Bog Hole Wildlife Area; (7) Upper 13 Tank, Patagonia
Mountain bajada; (8) Babocamari River; (9) Upper Scotia Canyon in the
Huachuca Mountains; (10) Arivaca Cienega; and, (11) Gila River at
Highway 180 (in New Mexico) (Rosen and Schwalbe 1988, Appendix I; Rosen
et al. 2001, Appendix I; Brennan and Holycross 2006, p. 123; Holycross
2006; Holycross et al. 2006, pp. 15-51; Rosen 2006).
In summary, based upon our analysis of the best available
scientific and commercial data, we conclude that the northern Mexican
gartersnake has been extirpated from approximately 90 percent of its
historical distribution in the United States.
Status in Mexico. Determining the status and current distribution
of the northern Mexican gartersnake in Mexico is difficult because of
the lack of large-scale surveys, research, and other pertinent
information. We can determine that there have been important large-
scale losses of northern Mexican gartersnake habitat, and that, at
least locally, northern Mexican gartersnake populations have been
extirpated or are declining. We relied, in part, on information that
addresses the status of both riparian and aquatic biological
communities that are habitat for the northern Mexican gartersnake and
the status of native freshwater fish species that are documented prey
species for the northern Mexican gartersnake from areas within its
historical distribution in Mexico. From the status of those communities
or fish species, we inferred a similar status for the northern Mexican
gartersnake as we have no reason to conclude these particular predator-
prey relationships respond any differently to biological community-
level perturbations in Mexico as has been observed reliably in the
United States. See Factors A and C for analysis of threats to the
habitat and prey base.
A large number of springs have dried up in several Mexican states
within the distribution of the northern Mexican gartersnake,
particularly from the years 1974-1994 in states including Chihuahua,
Durango, Coahila, and San Luis Potos[iacute] (Contreras Balderas and
Lozano 1994, p. 381). Because this has eliminated the habitat and
aquatic prey base of the snake, we conclude that the northern Mexican
gartersnake has also been lost from these sites. Contreras Balderas and
Lozano (1994, p. 381) stated that several streams and rivers throughout
Mexico and within the distribution of the northern Mexican gartersnake
have also dried up or become intermittent due to overuse of surface and
groundwater supplies. Ramirez Bautista and Arizmendi (2004, p. 3)
stated that the principal threats to northern Mexican gartersnake
habitat in Mexico include the drying of wetlands. Because this has
decreased the amount of habitat and the aquatic prey base of the snake,
we conclude that the northern Mexican gartersnake has likely declined
at these sites.
Burger (2008) provides a preliminary data set of survey effort for
Mexican gartersnakes (Thamnophis eques), southern Durango spotted
gartersnakes (T. nigronuchalis), and narrow-headed gartersnakes (T.
rufipunctatus) from the United States and Mexico through 2007 (T.
nigronuchalis only occurs in Mexico). The Burger (2008) data set
provides information from surveys of 17 stream systems in the Mexican
states of Durango and southern Chihuahua along the Sierra Madre
Occidental during June 2007. Mexican gartersnakes were observed at 5 of
the 17 sites visited; however, specimens were not identified to
subspecies, and some sites visited may not have been within the
historical distribution of the northern Mexican gartersnake.
Individuals observed from locations in southern Durango were likely T.
e. virgatenuis, rather than the northern Mexican gartersnake. This
sampling effort in Mexico geographically constitutes a small portion of
the range of the northern Mexican gartersnake in that country, but it
provides limited regional insight into the species' status. Population
trends at locations visited cannot be assessed because these sites have
only been visited once.
A research biologist with the Universidad Autonoma del Estado de
M[eacute]xico, who has been doing field research on Mexican
gartersnakes in central Mexico (within the distribution of northern
Mexican gartersnakes) for approximately two decades, has documented the
decline or disappearance of populations from drying of water bodies,
water contamination, and other human impacts where, 20 years ago, the
species was abundant (Manjarrez 2008).
Determining the status of the northern Mexican gartersnake in
Mexico is hampered by the lack of large-scale surveys, research, and
other pertinent information for that country. We can determine that
there have been important large-scale losses of northern Mexican
gartersnake habitat, including surface waters such as rivers, streams,
wetlands, and springs, that certainly have affected gartersnake
populations. We can also determine that, where local surveys have been
conducted, northern Mexican gartersnakes have been extirpated or are
declining (Manjarrez 2008).
Summary of Factors Affecting the Northern Mexican Gartersnake
Section 4 of the Act (16 U.S.C. 1533), and implementing regulations
at 50 CFR 424, set forth procedures for adding species to the Federal
Lists of Endangered and Threatened Wildlife and Plants. Under section
4(a)(1) of the Act, we may list a species on the basis of any of five
factors, as follows: (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 this finding, information
regarding the status of, and threats to, the northern Mexican
gartersnake in relation to the five factors provided in section 4(a)(1)
of the Act is discussed below and summarized in Table 1 below.
Table 1--Summary of northern Mexican gartersnake status and threats
by population in the United States. (Note: ``Extirpated'' means that
there have been no northern Mexican gartersnakes reported for a decade
or longer at a site within the historical distribution of the species,
despite survey efforts, and there is no expectation of natural recovery
at the site due to the presence of known or strongly suspected causes
of extirpation. ``Extant'' means areas where the species is expected to
reliably occur in appropriate habitat as supported by museum records or
recent, reliable observations. ``Unknown'' means areas where the
species is known to have occurred based on museum records (mostly
historical) but access is restricted, or survey data is unavailable or
insufficient, or where threats could preclude occupancy.)
[[Page 71794]]
----------------------------------------------------------------------------------------------------------------
Population locality Current status Regional historical or current threats
----------------------------------------------------------------------------------------------------------------
Gila River (outside of Highway 180 Extirpated............. Factor A: Improper grazing, recreation,
crossing) (Arizona, New Mexico). development, groundwater pumping, water
diversions, channelization, dewatering, road
construction/use, wildfire, intentional harm,
dams.
Factor C: Nonnative species, prey base
reduction.
Gila and San Francisco Headwaters Extirpated............. Factor A: Improper grazing, recreation.
(New Mexico).
Factor C: Nonnative species, prey base
reduction.
Lower Colorado River from Davis Dam Extirpated............. Factor A: Recreation, development, road
to International Border (Arizona). construction and use, borderland security and
undocumented immigration, intentional harm,
dams.
Factor C: Nonnative species, prey base
reduction.
San Pedro River in United States Extirpated............. Factor A: Improper grazing, groundwater pumping,
(Arizona). road construction and use, borderland security
and undocumented immigration, intentional harm.
Factor C: Nonnative species, prey base
reduction.
Santa Cruz River downstream of the Extirpated............. Factor A: Improper grazing, development,
Nogales area of the International groundwater pumping, water diversions,
Border (Arizona). channelization, road construction and use,
borderland security and undocumented
immigration, intentional harm, contaminants.
Factor C: Nonnative species, prey base
reduction.
Salt River (Arizona)................. Extirpated............. Factor A: Improper grazing, recreation,
development, water diversions, wildfire,
channelization, road construction/use,
intentional harm, dams.
Factor C: Nonnative species, prey base
reduction.
Rio San Bernardino from International Extirpated............. Factor A: Borderland security and undocumented
Border to headwaters at Astin Spring immigration, intentional harm.
(San Bernardino National Wildlife Factor C: Nonnative species, prey base
Refuge, Arizona). reduction.
Factor E: Competition with Marcy's checkered
gartersnake.
Agua Fria River (Arizona)............ Extirpated............. Factor A: Improper grazing, development,
recreation, dams, road construction and use,
wildfire, intentional harm.
Factor C: Nonnative species, prey base
reduction.
Verde River upstream of Clarkdale Extirpated............. Factor A: Improper grazing, recreation,
(Arizona). development, groundwater pumping, water
diversions, channelization, road construction
and use, intentional harm.
Factor C: Nonnative species, prey base
reduction.
Verde River from the confluence with Extirpated............. Factor A: Improper grazing, recreation,
the Salt upstream to Fossil Creek groundwater pumping, water diversions,
(Arizona). channelization, road construction and use,
wildfire, development, intentional harm, dams.
Factor C: Nonnative species, prey base
reduction.
Potrero Canyon/Springs (Arizona)..... Extirpated............. Factor A: Improper grazing.
Factor C: Nonnative species, prey base
reduction.
Tanque Verde Creek in Tucson Extirpated............. Factor A: Improper grazing, recreation,
(Arizona). development, groundwater pumping, road
construction and use, intentional harm.
Factor C: Nonnative species, prey base
reduction.
Rillito Creek in Tucson (Arizona).... Extirpated............. Factor A: Improper grazing, recreation,
development, groundwater pumping, road
construction and use, intentional harm.
Factor C: Nonnative species, prey base
reduction.
Agua Caliente Spring in Tucson Extirpated............. Factor A: Improper grazing, recreation,
(Arizona). development, groundwater pumping, road
construction and use, intentional harm.
Factor C: Nonnative species, prey base
reduction.
Babocamari Cienega (Arizona)......... Extirpated............. Factor A: Improper grazing.
Factor C: Nonnative species, prey base
reduction.
Barchas Ranch, Huachuca Mountain Extirpated............. Factor A: Improper grazing, borderland security
bajada (Arizona). and undocumented immigration, intentional harm.
Factor C: Nonnative species, prey base
reduction.
Parker Canyon Lake and tributaries in Extirpated............. Factor A: Improper grazing, recreation, road
the Canelo Hills (Arizona). construction and use, borderland security and
undocumented immigration, intentional harm,
dams.
Factor C: Nonnative species, prey base
reduction.
Oak Creek at Midgley Bridge (Arizona) Extirpated............. Factor A: Improper grazing, recreation,
development, intentional harm.
Factor C: Nonnative species, prey base
reduction.
Santa Cruz River/Lower San Rafael Extant................. Factor A: Improper grazing, borderland security
Valley (headwaters downstream to and undocumented immigration, intentional harm.
International Border) (Arizona). Factor C: Nonnative species, prey base
reduction.
Verde River from the confluence with Extant................. Factor A: Improper grazing, recreation,
Fossil Creek upstream to Clarkdale development, groundwater pumping, water
(Arizona). diversions, channelization, road construction
and use, intentional harm, dams.
Factor C: Nonnative species, prey base
reduction.
Oak Creek at Page Springs (Arizona).. Extant................. Factor A: Development, construction, vehicle
mortality.
Factor C: Nonnative species, prey base
reduction, domestic cat predation, parasites.
Tonto Creek from mouth of Houston Extant................. Factor A: Improper grazing, recreation,
Creek downstream to Roosevelt Lake development, water diversions, channelization,
(Arizona). road construction and use, wildfire,
intentional harm, dams, flood control.
Factor C: Nonnative species, prey base
reduction.
Cienega Creek from headwaters Extant................. Factor A: Improper grazing.
downstream to the ``Narrows'' just Factor C: Nonnative species, prey base
downstream of Apache Canyon reduction.
(Arizona).
[[Page 71795]]
Pantano Wash (Cienega Creek) from Extant................. Factor A: Improper grazing, development,
Pantano downstream to Vail (Arizona). wildfire.
Factor C: Nonnative species, prey base
reduction.
Appleton-Whittell Research Ranch and Extant................. Factor A: Improper grazing.
vicinity near Elgin (Arizona). Factor C: Nonnative species, prey base
reduction.
Upper Scotia Canyon in the Huachuca Unknown................ Factor A: Wildfire.
Mountains (Arizona).
Factor C: Nonnative species, prey base
reduction.
Downstream portion of the Black River Unknown................ Factor A: Improper grazing, recreation,
drainage from the Paddy Creek intentional harm.
confluence (Arizona). Factor C: Nonnative species, prey base
reduction.
Downstream portion of the White River Unknown................ Factor A: Improper grazing, recreation, road
drainage from the confluence of the construction and use, intentional harm.
East/North (Arizona). Factor C: Nonnative species, prey base
reduction.
Big Bonito Creek (Arizona)........... Unknown................ Factor A: Improper grazing.
Factor C: Nonnative species, prey base
reductions.
Lake O' Woods (Lakeside, Arizona).... Unknown................ Factor A: recreation, development, road
construction/use, intentional harm.
Factor C: Nonnative species, prey base
reduction.
Spring Creek above confluence with Unknown................ Factor A: Development.
Oak Creek (Arizona). Factor C: Nonnative species, prey base
reduction.
Bog Hole Wildlife Area (Arizona)..... Unknown................ Factor C: Nonnative species, prey base
reduction.
Upper 13 Tank, Patagonia Mountains Unknown................ Factor A: Improper grazing.
bajada (Arizona).
Factor C: Nonnative species, prey base
reduction.
Babocamari River (Arizona)........... Unknown................ Factor A: Improper grazing.
Factor C: Nonnative species, prey base
reduction.
Arivaca Cienega (Arizona)............ Unknown................ Factor A: Improper grazing, borderland security
and undocumented immigration, intentional harm.
Factor C: Nonnative species, prey base
reduction.
Gila River at Highway 180 (New Unknown................ Factor A: Improper grazing, recreation,
Mexico). development, groundwater pumping, water
diversions, channelization, dewatering, road
construction/use, wildfire, intentional harm,
dams.
Factor C: Nonnative species, prey base
reduction.
----------------------------------------------------------------------------------------------------------------
References: For each of the population localities discussed in Table 1,
a detailed textual discussion of the identified threats, including
applicable reference citations, is found in subsequent sections of this
finding related to each of the five listing factors. Site-specific
information from locations in Mexico is limited and, therefore,
locations in Mexico are not included in this table. Where available,
the information from Mexico is presented and cited in our discussion of
the five listing factors below.
In the discussions of Factors A through E below, we describe the
known factors that have contributed to the current status of the
northern Mexican gartersnake. For populations within the United States,
our analysis benefitted from the availability of specific research,
monitoring, and other studies. The discussion of these factors that
pertain to the status and threats to the northern Mexican gartersnake
in Mexico are mainly regional, or statewide, in scope because, in many
cases, there was limited specific information available. In some
instances, we do include discussion on more refined geographic areas of
Mexico when supported by the literature. It is important to understand,
however, that many of the threats that affect the northern Mexican
gartersnake in the United States are also likely present in Mexico, as
further discussed below, despite the lack of formal documentation.
Thus, we expect impacts to the habitat and the species to be similar in
the United States and Mexico.
A. The Present or Threatened Destruction, Modification, or Curtailment
of Its Habitat or Range
Various threats that have affected and continue to affect riparian
and aquatic communities that provide habitat for the northern Mexican
garter snake include dams, water diversions, groundwater pumping,
introduction of nonnative species (vertebrates, plants, and crayfish),
woodcutting, recreation, mining, contaminants, urban and agricultural
development, road construction, improper livestock grazing, wildfires,
and undocumented immigration (Hendrickson and Minckley 1984, p. 161;
Ohmart et al. 1988, p. 150; Bahre 1995, pp. 240-252; Medina 1990, p.
351; Sullivan and Richardson 1993, pp. 35-42; Fleischner 1994, pp. 630-
631; Hadley and Sheridan 1995; Hale et al. 1995, pp. 138-140; DeBano
and Neary 1996, pp. 73-75; Rinne and Neary 1996, p. 135; Stromberg et
al. 1996, pp. 124-127; Girmendock and Young 1997, pp. 45-52; Rinne et
al. 1998, pp. 7-11; Belsky et al. 1999, pp. 8-12; Esque and Schwalbe
2002, pp. 165, 190; Hancock 2002, p. 765; Voeltz 2002, pp. 87-88; Webb
and Leake 2005, pp. 305-308; Holycross et al. 2006, pp. 52-61; McKinnon
2006a, 2006b, 2006c, 2006d, 2006e; Paradzick et al. 2006, pp. 88-93;
Segee and Neeley 1996, Executive Summary, pp. 10-12, 21-23; Burger
2008, USFS 2008; USFWS 2007, pp. 25, 35-39; Gila County Board of
Supervisors 2008, pp. 1-2; Kimmel 2008; Trammell 2008; Sanchez 2008;
Lyons and Navarro-Perez 1990, p. 37; Minckley et al. 2002, pp. 696;
Nijhuis 2007, pp. 1-7; Ouren et al. 2007, pp. 16-22; Rorabaugh 2008,
pp. 25-26). Threats to northern Mexican gartersnake habitat in Mexico
include the intentional and unintentional introductions of nonnative
species, improper livestock grazing, urbanization and development,
water diversions and groundwater pumping, loss of vegetation cover and
deforestation, erosion, and pollution, as well as impoundments and dams
that have modified or destroyed riparian and aquatic communities within
Mexico in areas where the species occurred historically (Conant 1974,
p. 471; Lyons and Navarro-Perez 1990, p. 37; Contreras Balderas and
Lozano 1994, p.
[[Page 71796]]
384; va Landa et al. 1997, p. 316; Jim[eacute]nez-Ruiz et al. 2002, p.
458; Minckley et al. 2002, pp. 696; Miller et al. 2005, pp. 60-61;
Abarca 2006; Burger 2008; Luja and Rodr[iacute]guez-Estrella 2008, pp.
17-22; Rorabaugh 2008, pp. 25-26; Manjarrez 2008).
Rorabaugh (2008, pp. 25-26) noted threats to northern Mexican
gartersnakes and their native amphibian prey base in Sonora, which
included disease, pollution, improper livestock grazing, conversion of
land for agriculture, nonnative plant invasions, and logging. Ramirez
Bautista and Arizmendi (2004, p. 3) stated that the principal threats
to northern Mexican gartersnake habitat in Mexico include the drying of
wetlands, improper livestock grazing, deforestation, wildfires, and
urbanization. In addition, nonnative species, such as bullfrogs and
sport and bait fish, have been introduced throughout Mexico and
continue to disperse naturally, broadening their distributions (Conant
1974, pp. 487-489; Miller et al. 2005, pp. 60-61; Luja and
Rodr[iacute]guez-Estrella 2008, pp. 17-22).
The activities outlined above for both the United States and Mexico
and their effects on the northern Mexican gartersnake are discussed in
further detail below. It is important to recognize that in most areas
where northern Mexican gartersnakes historically or currently occur,
two or more threats may be acting in combination in their influence on
the suitability of those habitats or on the northern Mexican
gartersnake itself. In our assessment of the status of these habitats,
discussion of the role that nonnative species introductions have had on
habitat suitability is critical. However, we provide that discussion
under ``Factor C. Disease and Predation'' due to the intricate and
complex relationship nonnative species have with respect to direct and
indirect pressures applied to the northern Mexican gartersnake and to
its native prey base.
Destruction and Modification of Riparian and Aquatic Biological
Communities
The modification and destruction of aquatic and riparian
communities in the post-settlement arid southwestern United States is
well documented (Medina 1990, p. 351; Sullivan and Richardson 1993, pp.
35-42; Fleischner 1994, pp. 630-631; Stromberg et al. 1996, pp. 113,
123-128; Girmendock and Young 1997, pp. 45-52; Belsky et al. 1999, pp.
8-12; Webb and Leake 2005, pp. 305-310; Holycross et al. 2006, pp. 52-
61; Nijhuis 2007, pp. 1-7; Ouren et al. 2007, pp. 16-22). Several
threats have been identified in the decline of many native riparian
flora and fauna species through habitat modification and destruction,
as well as nonnative species introductions. Researchers agree that the
period from 1850 to 1940 marked the greatest loss and degradation of
riparian and aquatic communities in Arizona, which were caused by
anthropogenic (human-caused) land uses and the primary and secondary
effects of those uses (Stromberg et al. 1996, p. 114; Webb and Leake
2005, pp. 305-310). Many of these land activities continue today and
are discussed in detail below. An estimated one-third of Arizona's pre-
settlement wetlands have dried or have been rendered ecologically
dysfunctional (Yuhas 1996).
Modification and Loss of Cienegas. Cienegas are particularly
important habitat for the northern Mexican gartersnake and are
considered ideal for the species (Rosen and Schwalbe 1988, p. 14).
Hendrickson and Minckley (1984, p. 131) defined cienegas as ``mid-
elevation (3,281-6,562 ft (1,000-2000 m)) wetlands characterized by
permanently saturated, highly organic, reducing [lowering of oxygen
level] soils.'' Many of these unique communities of the southwestern
United States, Arizona in particular, and Mexico have been lost in the
past century to streambed modification, improper livestock grazing,
woodcutting, artificial drainage structures, stream flow stabilization
by upstream dams, channelization, and stream flow reduction from
groundwater pumping and water diversions (Hendrickson and Minckley
1984, p. 161). Stromberg et al. (1996, p. 114) state that cienegas were
formerly extensive along streams of the Southwest; however, most were
destroyed during the late 1800s, when groundwater tables declined
several meters and stream channels became incised.
Nonnative shrub species in the genus Tamarix, such as salt cedar,
have been widely introduced throughout the western States and appear to
thrive in regulated river systems (Stromberg and Chew 2002, pp. 210-
213). Tamarix invasions may result in habitat alteration from potential
effects to water tables, changes to canopy and ground vegetation
structures, and increased fire risk, which hasten the loss of native
cottonwood and willow communities and affect the suitability of the
vegetation component to northern Mexican gartersnake habitat (Stromberg
and Chew 2002, pp. 211-212; USFWS 2002b, p. H-9).
Many sub-basins, where cienegas have been severely modified or lost
entirely, wholly or partially overlap the historical distribution of
the northern Mexican gartersnake, including the San Simon, Sulphur
Springs, San Pedro, and Santa Cruz valleys of southeastern and south-
central Arizona. The San Simon Valley in Arizona possessed several
natural cienegas with luxuriant vegetation prior to 1885, and was used
as a watering stop for pioneers, military, and surveying expeditions
(Hendrickson and Minckley 1984, pp. 139-140). In the subsequent
decades, the disappearance of grasses and commencement of severe
erosion were the result of heavy grazing pressure by large herds of
cattle, as well as the effects from wagon trails that paralleled
arroyos, occasionally crossed them, and often required stream bank
modification (Hendrickson and Minckley 1984, p. 140). Today, only the
artificially maintained San Simon Cienega exists in this valley.
Similar accounts of past conditions, adverse effects from historical
anthropogenic activities, and subsequent reduction in the extent and
quality of cienega habitats in the remaining valleys are also provided
in Hendrickson and Minckley (1984, pp. 138-160).
Urban and Rural Development. Development within and adjacent to
riparian areas has proven to be a significant threat to riparian
biological communities and their suitability for native species (Medina
1990, p. 351). Riparian communities are sensitive to even low levels
(less than 10 percent) of urban development within a watershed (Wheeler
et al. 2005, p. 142). Development along or within proximity to riparian
zones can alter the nature of stream flow dramatically, changing once-
perennial streams into ephemeral streams, which has direct consequences
on the riparian community (Medina 1990, pp. 358-359) and, within
occupied habitat, the northern Mexican gartersnake. Medina (1990, pp.
358-359) concluded that perennial streams had greater tree densities in
all diameter size classes of Alnus oblongifolius (Arizona alder) and
Acer negundo (box elder) as compared to ephemeral reaches where small-
diameter trees were absent. Small-diameter trees assist the northern
Mexican gartersnake by providing additional habitat complexity and
cover needed to reduce predation risk and enhance the usefulness of
areas for maintaining optimal body temperature.
Obvious examples of the influence of urbanization and development
can be observed within the areas of greater Tucson and Phoenix,
Arizona, where impacts have modified riparian vegetation, structurally
altered stream
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channels, facilitated nonnative species introductions, and dewatered
large reaches of formerly perennial rivers where the northern Mexican
gartersnake historically occurred (Santa Cruz, Gila, and Salt rivers,
respectively). Urbanization and development of these areas, along with
the introduction of nonnative species, are largely responsible for the
likely extirpation of the northern Mexican gartersnake from these
areas.
Urbanization on smaller scales can also impact habitat suitability
and the prey base for the northern Mexican gartersnake. Regional
development and subsequent land use changes, spurred by increasing
populations, along lower Tonto Creek and within the Verde Valley where
northern Mexican gartersnakes occur, continue to threaten this snake's
habitat and affect the habitat's suitability for the northern Mexican
gartersnake and its prey species (Girmendock and Young 1997, pp. 45-52;
Voeltz 2002, pp. 58-59, 69-71; Paradzick et al. 2006, pp. 89-90).
Holycross et al. (2006, pp. 53, 56) recently documented the damage and
removal of northern Mexican gartersnake streamside habitat from
development in the vicinity of Rock Springs along the Agua Fria River
and also within the Verde Valley along the Verde River.
Ongoing small-scale development projects within the Page Springs
and Bubbling Ponds fish hatcheries along Oak Creek, upstream of its
confluence with the Verde River, occur within potentially the most
robust remaining population of northern Mexican gartersnakes in the
United States (AGFD 1997a, pp. 1-13; 1997b, pp. 1-12). The Page Springs
trout hatchery is an 82-acre (ac) (33-hectare (ha)) facility located
within a semi-desert grassland vegetative community (AGFD 1997a, p. 3).
It is the largest State-run hatchery and was renovated in 1993,
resulting in construction-related impacts such as the removal of
riparian vegetation and other earth-moving activities to occupied snake
habitat (AGFD 1997a, p.1). Current and future management and
maintenance of Page Springs include a variety of activities that would
potentially affect occupied snake habitat, such as the maintenance of
roads, buildings, fences, equipment, as well as development
(residences, storage facilities, asphalt, resurfacing, etc.) and both
human- and habitat-based enhancement projects (AGFD 1997a, p. 8).
Implementation of such projects is expected to result in the damage or
removal of habitat or potentially the contamination of habitat from the
use of industrial products and chemicals. These projects may adversely
affect the northern Mexican gartersnake directly through physical harm
or injury or indirectly from effects to its habitat or prey base.
The Bubbling Ponds hatchery, which raises nonnative and native fish
(largemouth bass, smallmouth bass, and bluegill, Colorado River
pikeminnow, razorback sucker), is located on Oak Creek, just north of
the Page Springs hatchery, and comprises 2 parcels approximately 117 ac
(47 ha) in size (AGFD 1997b, p. 2). The hatchery consists of 11 earthen
ponds and 6 lined ponds totaling 10 surface acres (4 surface hectares),
3 residential structures, and the hatchery building (AGFD 1997b, p. 2).
Hatchery operations are confined to 17 of the 117 ac (7 of 47 ha) and
have been modified extensively (AGFD 1997b, p. 4). The remaining 100 ac
(40 ha) support riparian woodland and forest along Oak Creek (AGFD
1997b, p. 4). Northern Mexican gartersnakes are presumed to occur
throughout this property; using the earthen ponds for foraging on young
bullfrogs, their tadpoles, and fish, and using areas near or adjacent
to structures on the property. Current and future management and
maintenance of Bubbling Ponds include a variety of activities that
would potentially affect snake habitat, such as the maintenance of
roads, buildings, fences, equipment, as well as development
(residences, storage facilities, asphalt, resurfacing, etc.) and both
human- and habitat-based enhancement projects (AGFD 1997b, pp. 8-9;
Wilson and Company 1991, pp. 1-40; 1992, pp. 1-99). Implementation of
such projects is expected to result in the damage or removal of habitat
or potentially the contamination of habitat from the use of industrial
products and chemicals. The small-scale development projects at these
hatcheries may injure or kill northern Mexican gartersnakes or their
prey base, and may also temporarily damage or remove occupied habitat.
The Arizona Game and Fish Department is a long-standing partner in
research and survey efforts related to the northern Mexican
gartersnake, and there is an ongoing population study at the
hatcheries. Adaptive management in relation to activities at the
hatcheries, as informed by the population study, will help reduce the
overall effects to gartersnakes and their habitat at the hatcheries.
The effects of urban and rural development are expected to increase
as human populations increase. Consumer interest in second home and/or
retirement real estate investments has increased significantly in
recent times within the southwestern United States. Medina (1990, p.
351) points out that many real estate investors are looking for
aesthetically scenic, mild climes to enjoy seasonally or year-round and
hence choose to develop pre- or post-retirement properties that are
within or adjacent to riparian areas due to their aesthetic appeal and
available water, especially in the southwestern United States. Arizona
increased its population by 394 percent from 1960 to 2000, and is
second only to Nevada as the fastest growing State in terms of human
population (Social Science Data Analysis Network (SSDAR) 2000, p.1).
Over the same time period, population growth rates in Arizona counties
where the northern Mexican gartersnake historically occurred or may
still occur have varied by county but are no less remarkable, and all
are increasing: Maricopa (463 percent); Pima (318 percent); Santa Cruz
(355 percent); Cochise (214 percent); Yavapai (579 percent); Gila (199
percent); Graham (238 percent); Apache (228 percent); Navajo (257
percent); Yuma (346 percent); LaPaz (142 percent); and Mohave (2004
percent) (SSDAR 2000).
Population growth trends in Arizona, Maricopa County in particular,
are expected to continue into the future. The Phoenix metropolitan
area, founded in part due to its location at the junction of the Salt
and Gila rivers, is a population center of 3.63 million people. The
Phoenix metropolitan area is the sixth largest in the United States and
resides in the fastest growing county in the United States since the
2000 census (Arizona Republic 2006). Given the large amount of
perennial habitat at the confluence of two large, flowing rivers that
was historically present in this area prior to settlement, northern
Mexican gartersnakes likely maintained dense populations in this region
of Arizona. However, with the burgeoning population growth and
associated urbanization and development that have occurred since, any
remaining habitat for the northern Mexican gartersnake has been
rendered unsuitable and the subspecies is now likely extirpated from
this area and its recovery is unlikely.
Massive growth predictions have been made for traditionally rural
portions of Arizona. The populations of developing cities and towns of
the Verde watershed are expected to more than double in the next 50
years, which may pose exceptional threats to riparian and aquatic
communities of the Verde Valley where northern Mexican gartersnakes
occur (Girmendock and Young 1993, p. 47; American Rivers 2006;
Paradzick et al. 2006, p. 89). Communities in Yavapai and Gila
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counties such as the Prescott-Chino Valley, Strawberry, Pine, and
Payson have all seen rapid population growth in recent years. For
example, the population in the town of Chino Valley, at the headwaters
of the Verde River, has grown by 22 percent between 2000 and 2004; Gila
County, which includes reaches of the Salt, White, and Black rivers and
Tonto Creek, grew by 20 percent between 2000 and 2003 (http://
www.census.gov). The upper San Pedro River is also the location of
rapid population growth in the Sierra Vista-Huachuca City-Tombstone-
Benson area (http://www.census.gov). All of these communities are near
or within the vicinity of historical or current northern Mexican
gartersnake populations.
In Mexico, the magnitude and significance of adverse effects to
riparian communities related to development lags somewhat behind that
experienced in the United States due to slower population and economic
growth, but it is reported that threats to riparian and aquatic
communities that have been observed in Arizona are currently occurring
with increasing significance in Mexico (Conant 1974, pp. 471, 487-489;
Contreras Balderas and Lozano 1994, pp. 379-381; va Landa et al. 1997,
p. 316; Miller et al. 2005, p. 60-61; Abarca 2006; Rosen 2006).
Ortega-Huerta and Kral (2007, p. 1) found that land legislation
within Mexico has changed considerably over recent years to integrate
free market policies into local agricultural production methods that
may result in the loss of land management practices that protect the
natural environment. Community-based lands generally presented higher
instance of habitat conservation in terms of natural vegetation, higher
species aggregations, more evenly distributed cover types, and greater
species richness (Ortega-Huerta and Kral 2007, p. 1). These
correlations between land ownership and bird and mammal species
richness can be generally extrapolated to other aspects of biotic
communities, including the aquatic and semi-aquatic communities within
areas. A shift away from traditional land management in Mexico presents
threats to riparian and aquatic habitats occupied by the northern
Mexican gartersnake.
Collectively, development impacts of all types in Mexico are
expected to continue as a result of Mexico's expanding role as an
economical labor force for international manufacturing under the North
American Free Trade Agreement (NAFTA) and the subsequent increase in
population size, economic growth and development, and infrastructure.
The threats to northern Mexican gartersnake habitat in riparian and
aquatic communities in Mexico vary in their significance, based on
geographical distribution of land management activities and urban
centers, but are expected to continue into the future.
Mexico's human population grew 700 percent from 1910 to 2000
(Miller et al. 2005, p. 60). Mexico's population increased by 245
percent from 1950 to 2002, and is projected to grow by another 28
percent by 2025 (EarthTrends 2005). As of 1992, Mexico had the second
highest gross domestic product in Latin America at 5.8 percent,
following Brazil (DeGregorio 1992, p. 60). As a result of NAFTA, the
number of maquiladoras (export assembly plants) is expected to increase
by as many as 3,000 to 4,000 (Contreras Balderas and Lozano 1994, p.
384). To accommodate Mexico's increasing human population, rural areas
are largely devoted to food production based on traditional methods,
which has led to serious losses in vegetative cover and soil erosion
(va Landa et al. 1997, p. 316).
Road Construction, Use, and Maintenance. Roads cover approximately
1 percent of the land area in the United States, but negatively affect
20 percent of the habitat and biota in the United States (Angermeier et
al. 2004, p. 19). Roads pose unique threats to herpetofauna and
specifically to species like the northern Mexican gartersnake, its prey
base, and the habitat where it occurs through: (1) Fragmentation,
modification, and destruction of habitat; (2) increase in genetic
isolation; (3) alteration of movement patterns and behaviors; (4)
facilitation of the spread of nonnative species via human vectors; (5)
an increase in recreational access and the likelihood of subsequent,
decentralized urbanization; (6) interference with or inhibition of
reproduction; (7) contributions of pollutants to riparian and aquatic
communities; and (8) population sinks (a factor resulting in
unnaturally high death rates that exceed birth rates within a
population) through direct mortality (Rosen and Lowe 1994, pp. 146-148;
Waters 1995, p. 42; Carr and Fahrig 2001, pp. 1074-1076; Hels and
Buchwald 2001, p. 331; Smith and Dodd 2003, pp. 134-138; Angermeier et
al. 2004, pp. 19-24; Shine et al. 2004, pp. 9, 17-19; Andrews and
Gibbons 2005, pp. 777-781; Wheeler et al. 2005, pp. 145, 148-149; Roe
et al. 2006, p. 161).
Construction and maintenance of roads and highways near riparian
areas can be a source of sediment and pollutants (Waters 1995, p. 42;
Wheeler et al. 2005, pp. 145, 148-149). Sediment can adversely affect
fish populations used as prey by the northern Mexican gartersnake by
(1) interfering with respiration; (2) reducing the effectiveness of
fish's visually-based hunting behaviors; and (3) filling in
interstitial spaces of the substrate, which reduces reproduction and
foraging success of fish (Wheeler et al. 2005, p. 145). Excessive
sediment also fills in intermittent pools required for amphibian prey
reproduction and foraging. Fine sediment pollution in streams impacted
by highway construction without the use of sediment control structures
was 5 to 12 times greater than control streams (Wheeler et al. 2005, p.
144). As stated above, sediment can lead to several effects in resident
fish species used by northern Mexican gartersnakes as prey, which can
ultimately cause increased direct mortality, reduced reproductive
success, lower overall abundance of the northern Mexican gartersnake,
lower species diversity of prey, and reductions in food base as
documented by Wheeler et al. (2005, p. 145). The underwater foraging
ability of northern Mexican gartersnakes is also directly compromised
by excessive turbidity caused by sedimentation of water bodies, because
this snake locates its prey visually.
Metal contaminants, including iron, zinc, lead, cadmium, nickel,
copper, and chromium, are associated with highway construction and use
(Foreman and Alexander 1998, p. 220; Hopkins et al. 1999, p. 1260;
Campbell et al. 2005, p. 241; Wheeler et al. 2005, pp. 146-149) and are
bioaccumulative. A bioaccumulative substance increases in concentration
in an organism or in the food chain over time. A mid- to higher-order
predator, such as a gartersnake, may therefore accumulate these types
of contaminants over time in their fatty tissues, which may lead to
adverse health effects. Several studies have addressed the effects of
bioaccumulative substances on watersnakes. We find these studies
relevant because watersnakes and gartersnakes have very similar life
histories and prey bases and, therefore, the effects from contamination
of their habitat from bioaccumulative agents are expected to be
similar. Campbell et al. (2005, pp. 241-243) found that metal
concentrations accumulated in the northern watersnake (Nerodia sipedon)
at levels six times that of their primary food item, the central
stoneroller (fish) (Campostoma anomalum). Metals, in trace amounts,
affect the structure and
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function of the liver and kidneys of vertebrates and may also act as
neurotoxins, affecting nervous system function (Rainwater et al. 2005,
p. 670). Metals may also be sequestered in the skin of reptiles, but
this effect is tempered somewhat by ecdysis (the regular shedding or
molting of the skin) (Burger 1999, p. 212). Hopkins et al. (1999, p.
1261) found that metals may even interfere with metabolic rates of
banded watersnakes (Nerodia fasciata), altering the allocation of
energy between maintenance and reproduction, reducing the efficiency of
energy stores, and forcing individuals to forage more often, which
increases activity costs (the energy expended in hunting, which affects
the net nutritional intake of an organism) and predation risk.
Snakes of all species are particularly vulnerable to mortality when
they attempt to cross roads. Snakes are animals that derive heat from
warm surfaces, which often compels them to slow down or even stop and
rest on road surfaces that have been warmed by the sun as they attempt
to cross (Rosen and Lowe 1994, p. 143). Gartersnakes are generally
diurnal (active during daylight hours) and are often active when
traffic densities are greatest (Rosen and Lowe 1994, p. 147). Mortality
data have been collected at the Bubbling Ponds Hatchery since 2006. Of
the eight dead specimens, half were struck by vehicles on roads
adjacent to the hatchery ponds that are crossed by northern Mexican
gartersnakes in traveling between ponds to forage (Boyarski 2008a). Van
Devender and Lowe (1977, p. 47), however, observed several northern
Mexican gartersnakes crossing the road at night after the commencement
of the summer monsoon (rainy season), which highlights the seasonal
variability in surface activity of this snake. Perhaps the most common
factor in road mortality of snakes is the propensity for drivers to
intentionally run over snakes, which generally make easy targets
because they usually cross roads at a perpendicular angle (Klauber
1956, p. 1026; Langley et al. 1989, p. 47; Shine et al. 2004, p. 11).
This driving behavior is exacerbated by the general animosity that
humans have toward snakes (Ernst and Zug 1996, p. 75; Green 1997 pp.
285-286). In fact, Langley et al. (1989, p. 47) conducted an experiment
on the propensity for drivers to hit reptiles on the road using turtle
and snake models and found that many people have a greater desire to
hit a snake on the road than any other animal; several drivers actually
stopped and backed-over the snake mimic to ensure it was dead. Roe et
al. (2006, p. 161) conclude that mortality rates due to roads are
higher in vagile (mobile) species, such as gartersnakes (active
hunters), than those of more sedentary species, which more commonly
employ sit-and-wait foraging strategies. Roads that bisect wetland
communities also act as mortality sinks in the dispersal or migratory
movements of snakes (Roe et al. 2006, p. 161). The effect of road
mortality of snakes becomes most significant in the case of small,
highly fragmented populations where the chance removal of mature
females from the population may appreciably degrade the viability of a
population.
Even lightly used roads may also lead to mortality of northern
Mexican gartersnakes. For example, gravel roads that surround the
hatchery ponds that are traveled by hatchery, research lab, and
resident vehicles at the Bubbling Ponds fish hatchery have resulted in
four documented northern Mexican gartersnake mortalities since
mortality data began being collected in 2006 (Boyarski 2008a, pp. 1-4).
These vehicle mortalities represent 50 percent of the mortalities
documented at the hatcheries. Of note is the fact that these vehicles
are likely traveling at slow speeds, which indicates that even slow-
moving vehicles pose a hazard to crossing and basking snakes. Wallace
et al. (2008, pp. 243-244) documented a vehicle-related mortality of a
northern Mexican gartersnake on Arizona State Route 188 near Tonto
Creek that occurred in 1995. As shown in the above examples, vehicle-
related mortalities of northern Mexican gartersnakes likely occur
routinely along roads or trails adjacent to occupied habitat throughout
the range of the subspecies but are generally difficult to document.
Off-highway vehicle (OHV) use has grown considerably in Arizona.
For example, as of 2007, 385,000 OHVs were registered in Arizona (a 350
percent increase since 1998) and 1.7 million people (29 percent of the
Arizona's public) engaged in off-road activity from 2005-2007 (Sacco
2007). Over half of OHV users reported that merely driving off-road was
their primary activity, versus using the OHV for the purpose of
hunting, fishing, or hiking (Sacco 2007). Given the pervasive use of
OHV's on the landscape, OHV-related mortalities are likely a threat to
northern Mexican gartersnakes. Ouren et al. (2007, pp. 16-22) provide
additional data on the effects of OHV use on wildlife. Specifically,
OHV use may cause mortality or injury to species, such as northern
Mexican gartersnakes, that attempt to cross trails created through
occupied habitat and may even lead to depressed populations of snakes
depending on the rate of use and number of trails within a given area
(Ouren et al. 2007, pp. 20-21). This threat may be even more extensive
from OHVs than from conventional vehicles because OHV trails often
travel through undeveloped habitat and often cross directly through
waterbodies. OHV use may also affect northern Mexican gartersnake
habitat by reducing vegetation cover and plant species diversity,
reducing infiltration rates, increasing erosion, and reducing habitat
connectivity (Ouren et al. 2007, pp. 6-7, 11, 16).
Roads create access to areas that were previously visited only
infrequently or were inaccessible to humans, increasing the frequency
and significance of anthropogenic threats to riparian areas and
fragmenting the landscape, which in addition to direct effects to
snakes and habitat, may genetically isolate herpetofaunal populations
(Rosen and Lowe 1994, pp. 146-148; Andrews and Gibbons 2005, p. 772).
McCranie and Wilson (1987, p. 2) discuss threats to the pine-oak
communities of higher elevation habitats within the distribution of the
northern Mexican gartersnake in the Sierra Madre Occidental in Mexico,
specifically noting that ``* * * the relative pristine character of the
pine-oak woodlands is threatened * * * every time a new road is
bulldozed up the slopes in search of new madera or pasturage. Once the
road is built, further development follows; pueblos begin to pop up
along its length * * *.'' Several drainages that possess suitable
habitat for the species occur in the area referenced above by McCranie
and Wilson (1987, p. 2) including the Rio de la Cuidad, Rio Quebrada El
Salto, Rio Chico, Rio Las Bayas, Rio El Cigarrero, Rio Galindo, Rio
Santa Barbara, and the Rio Chavaria.
While snakes of all species may suffer direct mortality as a result
of attempting to cross roads, Andrews and Gibbons (2005, pp. 777-779)
found that many individuals of small, diurnal snake species avoid open
areas (e.g., roads) instinctively in order to lower predation rates,
which represents a different type of threat from roads. Shine et al.
(2004, p. 9) found that the common gartersnake typically changed
direction when encountering a road. These avoidance behaviors by
individuals aversive to crossing roads affect movement patterns and may
ultimately affect reproductive output within populations (Shine et al.
2004, pp. 9, 17-19). Not crossing roads can reduce the amount of
habitat available for individual snakes to find
[[Page 71800]]
prey, mates, etc. This avoidance behavior has been observed in the
common gartersnake (Thamnophis sirtalis), a sister taxon to the Mexican
gartersnake with similar life histories and behavior (Shine et al.
2004, p. 9). In our discussion and as evidenced by the literature we
reviewed on the effect of roads on snake movements, we acknowledge the
individuality of snakes in their behaviors towards road crossings.
In addition to altering the movement patterns of some snakes, roads
interfere with the male gartersnake's olfactory-driven ability to
follow the pheromone trails left by receptive females (Shine et al.
2004, pp. 17-18). This effect to the male's ability to efficiently
trail females may exacerbate the effects of low population density and
fragmentation that affect several species of snakes, including the
northern Mexican gartersnake. Because the male gartersnake's ability to
trail females is hampered by roads, the extra time and distance
traveled by male snakes seeking receptive females increases exposure to
predation and subsequently increases mortality rates (Shine et al.
2004, pp. 18-19). Although the northern Mexican gartersnake was not the
subject of the 2004 Shine et al. study, similar responses can be
expected in the northern Mexican gartersnake because its life history
is similar to the study's subject species (i.e., the common
gartersnake).
Roads also affect prey availability for northern Mexican garter
snakes. Roads tend to adversely affect aquatic breeding anuran
populations more so than other species due to their activity patterns
(mass movements of individuals), population structures (large cohorts
of similarly aged individuals within a population), and preferred
habitats which are often adjacent to roads and usually constrained to
aquatic or semiaquatic areas (Hels and Buchwald 2001, p. 331). Carr and
Fahrig (2001, pp. 1074-1076) found that populations of highly mobile
anuran species such as leopard frogs (Rana pipiens) were run over more
frequently than more sedentary species and that population persistence
can be at risk depending on traffic densities, which may adversely
affect the prey base for northern Mexican gartersnakes because leopard
frogs are a primary prey species.
Recreation. As discussed above, population growth trends are
expected to continue into the future. Expanding population growth leads
to higher recreational use of riparian areas, as evidenced along
reaches of the Salt and Verde rivers in proximity to the Phoenix
metropolitan area. Riparian areas located near urban areas are
vulnerable to the effects of increased recreation with predictable
changes in the type and intensity of land use following residential
development. An example of such an area within the existing
distribution of the northern Mexican gartersnake is the Verde Valley.
The reach of the Verde River that winds through the Verde Valley
receives a high amount of recreational use from people living in
central Arizona (Paradzick et al. 2006, pp. 107-108). Increased human
use results in the trampling of near-shore vegetation, which reduces
cover for gartersnakes, especially newborns. Increased human visitation
in occupied habitat also increases the potential for human-gartersnake
interactions, which frequently leads to the capture, injury, or death
of the snake (Rosen and Schwalbe 1988, p. 43; Ernst and Zug 1996, p.
75; Green 1997, pp. 285-286; Nowak and Santana-Bendix 2002, p. 39).
Recreational activities in the Southwest are often tied to water bodies
and riparian areas. Increased recreational impacts on the quantity and
quality of water, as well as the adjacent vegetation, are threats to
local populations of the northern Mexican gartersnake.
Groundwater Pumping, Surface Water Diversions, and Flood Control.
Increased urbanization and population growth results in an increase in
the demand for water and, therefore, water development projects.
Collier et al. (1996, p. 16) mention that water development projects
are one of two main causes of decline of native fish in the Salt and
Gila rivers of Arizona. Municipal water use in central Arizona has
increased by 39 percent in the last 8 years (American Rivers 2006).
Water for development and urbanization is often supplied by groundwater
pumping and surface water diversions from sources that include
reservoirs and Central Arizona Project's allocations from the Colorado
River. The hydrologic connection between groundwater and surface flow
of intermittent and perennial streams is becoming better understood.
Groundwater pumping creates a cone of depression within the affected
aquifer that slowly radiates outward from the well site. When the cone
of depression intersects the hyporheic zone of a stream (the active
transition zone between two adjacent ecological communities under or
beside a stream channel or floodplain between the surface water and
groundwater that contributes water to the stream itself), the surface
water flow may decrease, and the subsequent drying of riparian and
wetland vegetative communities can follow. This situation has been
created by groundwater use by the community of Sierra Vista in Cochise
County, which continues to threaten the riparian community along the
upper San Pedro River where the northern Mexican gartersnake
historically occurred. Continued groundwater pumping at such levels
draws down the aquifer sufficiently to create a water-level gradient
away from the stream and floodplain (Webb and Leake 2005, p. 309).
Finally, complete disconnection of the aquifer and the stream results
in strong negative effects to riparian vegetation (Webb and Leake 2005,
p. 309). If complete disconnection occurs, the hyporheic zone could be
adversely affected. The hyporheic zone can promote ``hot spots'' of
productivity where groundwater upwelling produces nitrates that can
enhance the growth of vegetation, but its significance is contingent
upon its activity and extent of connection with the groundwater
(Boulton et al. 1998, p. 67; Boulton and Hancock 2006, pp. 135, 138).
Such ``hot spots'' can enhance the quality of northern Mexican
gartersnake habitat. Conversely, changes to the duration and timing of
upwelling can potentially lead to localized extinctions in biota
(Boulton and Hancock 2006, p. 139), reducing gartersnake habitat
suitability.
The effects of groundwater pumping on surface water flow and
riparian communities have been observed in the Santa Cruz, San Pedro,
and Verde rivers as a result of groundwater demands of Tucson, Sierra
Vista, and the rapidly growing Prescott Valley, respectively (Stromberg
et al. 1996, pp. 113, 124-128; Rinne et al. 1998, p. 9; Voeltz 2002,
pp. 45-47, 69-71). Along the upper San Pedro River, Stromberg et al.
(1996, pp. 124-127) found that wetland herbaceous species, important as
cover for northern Mexican gartersnakes, are the most sensitive to the
effects of a declining groundwater level. Webb and Leake (2005, pp.
302, 318-320) described a correlative trend regarding vegetation along
southwestern streams from historically being dominated by marshy
grasslands preferable to northern Mexican gartersnakes, to currently
being dominated by woody species more tolerant of declining water
tables due to their associated deeper rooting depths.
The full effects of large-scale groundwater pumping associated with
the proposed Big Chino Water Ranch Project and its associated 30-mile
(48-km), 36-in (91-cm) diameter pipeline have yet to be realized in the
Verde River (McKinnon 2006c). This groundwater pumping and inter-basin
transfer project is projected to deliver
[[Page 71801]]
2.8 billion gallons of groundwater annually from the Big Chino sub-
basin aquifer to the rapidly growing area of Prescott Valley for
municipal use (McKinnon 2006c). The Big Chino sub-basin provides 86
percent of the baseflow to the upper Verde River (American Rivers 2006;
McKinnon 2006a). The potential for this project to obtain funding and
approval for implementation has placed the Verde River on American
River's 2006 ``Ten Most Endangered Rivers List'' (American Rivers
2006). This potential reduction or loss of baseflow in the Verde River
could seasonally dry up large reaches or adversely affect the riparian
community and the suitability of the habitat for remaining populations
of the northern Mexican gartersnake and its prey species in that area.
Within the Verde River watershed, and particularly within the Verde
Valley where the northern Mexican gartersnake is believed to currently
remain, several other activities continue to threaten surface flows
(Rinne et al. 1998, p. 9; Paradzick et al. 2006, pp. 104-110). The
demands for surface water allocations from rapidly growing communities
and agricultural and mining interests have altered flows or dewatered
significant reaches during the spring and summer months in some of the
Verde River's larger, formerly perennial tributaries such as Wet Beaver
Creek, West Clear Creek, and the East Verde River, which may have
supported the northern Mexican gartersnake (Girmendock and Young 1993,
pp. 45-47; Sullivan and Richardson 1993, pp. 38-39; Paradzick et al.
2006, pp. 104-110). Groundwater pumping in the Tonto Creek drainage
regularly eliminates surface flows during parts of the year (Abarca and
Weedman 1993, p. 2). The upper Gila River is also threatened by water
diversions and water allocations. In New Mexico, a proposed water
project that resulted from a landmark Gila River water settlement in
2004 allows New Mexico the right to withhold 4.5 billion gallons of
surface water every year (McKinnon 2006d). If this proposed water
diversion project is implemented, in dry years, currently perennial
reaches of the upper Gila River will dry completely, which removes all
suitability of this habitat for the northern Mexican gartersnakes and a
host of other riparian and aquatic species (McKinnon 2006d).
The Arizona Department of Water Resources (ADWR) manages water
supplies in Arizona and has established five Active Management Areas
(AMA) across the State (ADWR 2006). An AMA is established by ADWR when
an area's water demand has exceeded the groundwater supply and an
overdraft has occurred. In these areas, groundwater use has exceeded
the rate that precipitation can recharge the aquifer, which leads to
conditions described above. Geographically, all five AMAs overlap the
historical distribution of the northern Mexican gartersnake in Arizona.
The declaration of these AMAs further illustrates the condition and
future threats to riparian habitat in these areas and are a cause of
concern for the long-term maintenance of historical and occupied
northern Mexican gartersnake habitat. Such overdrafts reduce surface
water flow of streams that are hydrologically connected to the aquifer
under stress, which can be further exacerbated by the surface water
diversions.
To accommodate the needs of rapidly growing rural and urban
populations, surface water is commonly diverted to serve many
industrial and municipal uses. These water diversions have dewatered
large reaches of once perennial or intermittent streams, adversely
affecting northern Mexican gartersnake habitat throughout its range in
Arizona and New Mexico. Many tributaries of the Verde River are
permanently or seasonally dewatered by water diversions for agriculture
(Paradzick et al. 2006, pp. 104-110).
Effects from flood control projects threaten riparian and aquatic
habitat, as well as threaten the northern Mexican gartersnake directly.
Kimmell (2008), Gila County Board of Supervisors (2008), Trammell
(2008), and Sanchez (2008) all discuss a growing concern of residents
that live within or adjacent to the floodplain of Tonto Creek in Gila
County, Arizona, both upstream and downstream of the town of Gisela,
Arizona. Specifically, there is growing concern to address threats to
private property and associated infrastructure posed by flooding of
Tonto Creek (Sanchez 2008). The only known remaining population of
northern Mexican gartersnakes within the large Salt River watershed
occurs on Tonto Creek. The status of the northern Mexican gartersnake
on tribal lands within the Salt River watershed remains unknown. In
Resolution No. 08-06-02, the Gila County Board of Supervisors has
proactively declared a state of emergency within Gila County as a
result of the expectation for heavy rain and snowfall causing
repetitive flooding conditions (Gila County Board of Supervisors 2008).
In response, the Arizona Division of Emergency Management called
meetings and initiated discussions among stakeholders in an attempt to
mitigate these flooding concerns (Kimmell 2008, Trammell 2008).
Mitigation measures that have been discussed include removal of
riparian vegetation, removal of debris piles, potential channelization
of Tonto Creek, improvements to existing flood control structures or
addition of new structures, and the construction of new bridges.
Adverse effects of these types of activities to aquatic and riparian
habitat and to the northern Mexican gartersnake or its prey species
will result from the physical alteration or destruction of habitat,
significant increases to flow velocity, and removal of key foraging
habitat and areas to hibernate, such as debris jams. Specifically,
flood control projects permanently alter stream flow characteristics
and have the potential to make the stream unsuitable as habitat for the
northern Mexican gartersnake by reducing or eliminating stream
sinuosity and associated pool and backwater habitats that are critical
to northern Mexican gartersnakes and their prey species. Threats
presented by these flood control planning efforts are considered
imminent.
In Mexico, Conant (2003, p. 4) noted human-caused threats to seven
fragmented, highly localized subspecies of Mexican gartersnake in the
Transvolcanic Belt Region of southern Mexico, which extends from
southern Jalisco eastward through the State of Mexico to central
Veracruz. Although this is a relatively small area, rural land uses are
widespread in the region and these threats can be extrapolated to other
areas of that region within the distribution of the northern Mexican
gartersnake in Mexico. Some of these threats included water diversions,
pollution (e.g., discharge of raw sewage), sedimentation of aquatic
habitats, and increased dissolved nutrients, resulting in decreased
dissolved oxygen, in still-water habitats. Conant (2003, p. 4) stated
that many of these threats were evident during his field work in the
1960s, but that they are ``continuing with increased velocity.''
Water pollution, dams, groundwater pumping, and impoundments were
identified by Miller et al. (2005, pp. 60-61) as significant threats to
aquatic biota in Mexico. Miller et al. (2005, p. 60) stated that
``During the time we have collectively studied fishes in M[eacute]xico
and southwestern United States, the entire biotas of long reaches of
major streams where the northern Mexican gartersnake is distributed,
such as the R[iacute]o Grande de Santiago below Guadalajara (Jalisco)
and R[iacute]o Colorado (lower Colorado River in Mexico) downstream of
Hoover (Boulder) Dam (in the United States), have simply been destroyed
by pollution and river
[[Page 71802]]
alteration.'' Near Torre[oacute]n, Coahuila, where the northern Mexican
gartersnake occurs, groundwater pumping has resulted in flow reversal,
which has dried up many local springs, drawn arsenic-laden water to the
surface, and resulted in adverse human health effects in that area.
Severe water pollution from untreated domestic waste is evident
downstream of large Mexican cities, such as Mexico City, and inorganic
pollution from nearby industrialized areas and agricultural irrigation
return flow has dramatically affected aquatic communities through
contamination (Miller et al. 2005, p. 60). Miller et al. (2005, p. 61)
provides an excerpt from Soto Galera et al. (1999) addressing the
threats to the R[iacute]o Lerma, Mexico's longest river, and which is
occupied by the northern Mexican gartersnake: ``The basin has
experienced a staggering amount of degradation during the 20th Century.
By 1985-1993, over half of our study sites had disappeared or become so
polluted that they could no longer support fishes. Only 15 percent of
the sites were still capable of supporting sensitive species. Forty
percent (17 different species) of the native fishes of the basin had
suffered major declines in distribution, and three species may be
extinct. The extent and magnitude of degradation in the R[iacute]o
Lerma basin matches or exceeds the worst cases reported for comparably
sized basins elsewhere in the world.''
Several rivers within the historical range of the northern Mexican
gartersnake have been impounded and dammed throughout Mexico, resulting
in habitat modification and the dispersal and establishment of
nonnative species. The damming and modification of the lower Colorado
River in Mexico, where the northern Mexican gartersnake occurred, has
facilitated the replacement of the entire native fishery with nonnative
species (Miller et al. 2005, p. 61). Nonnative species continue to pose
significant threats in the decline of native, often highly localized,
prey species of the northern Mexican gartersnake, as discussed further
in Factor C below (Miller et al. 2005, p. 60).
Miller et al. (2005) provide information on threats to freshwater
fishes, and riparian and aquatic communities in specific waterbodies
throughout Mexico that are within the historical range of the northern
Mexican gartersnake: The R[iacute]o Grande (dam construction, p. 78 and
extirpations of freshwater fish species, pp. 82, 112); headwaters of
the R[iacute]o Lerma (extirpation of freshwater fish species, nonnative
species, pollution, dewatering, pp. 60, 105, 197); Lago de Chapala and
its outlet to the R[iacute]o Grande de Santiago (major declines in
freshwater fish species, p. 106); medium-sized streams throughout the
Sierra Madre Occidental (localized extirpations, logging, dewatering,
pp. 109, 177, 247); the Rio Conchos (extirpations of freshwater fish
species, p. 112); the r[iacute]os Casas Grandes, Santa Mar[iacute]a,
del Carmen, and Laguna Bustillos (water diversions, groundwater
pumping, channelization, flood control practices, pollution, and
introduction of nonnative species, pp. 124, 197); the R[iacute]o Santa
Cruz (extirpations, p. 140); the R[iacute]o Yaqui (nonnative species,
pp. 148, Plate 61); the R[iacute]o Colorado (nonnative species, p.
153); the r[iacute]os Fuerte and Culiac[aacute]n (logging, p. 177);
canals, ponds, lakes in the Valle de M[eacute]xico (nonnative species,
extirpations, pollution, pp. 197, 281); the R[iacute]o Verde Basin
(dewatering, nonnative species, extirpations, Plate 88); the R[iacute]o
Mayo (dewatering, nonnative species, p. 247); the R[iacute]o Papaloapan
(pollution, p. 252); lagos de Zacapu and Yuriria (habitat destruction,
p. 282); and the R[iacute]o P[aacute]nuco Basin (nonnative species, p.
295).
Conant (1974, pp. 486-489) described significant threats to
northern Mexican gartersnake habitat within its distribution in western
Chihuahua, Mexico, and within the Rio Concho system where it occurs.
These threats included impoundments, water diversions, and purposeful
introductions of largemouth bass, common carp, and bullfrogs. We
discuss the threats from nonnative species introductions below in our
discussion of Factor C.
Clearly, water quality and quantity are being affected by ongoing
activities in the United States and Mexico. Due to the reliance of the
northern Mexican gartersnake on ecosystems and communities supported by
permanent water sources, these threats are significant to the survival
and viability of existing and future northern Mexican gartersnake
populations.
Improper Livestock Grazing and Agricultural Uses. In a number of
ways described below, poorly managed livestock grazing has damaged
approximately 80 percent of stream, cienega, and riparian ecosystems in
the western United States (Kauffman and Krueger 1984, pp. 433-435;
Weltz and Wood 1986, pp. 367-368; Waters 1995, pp. 22-24; Pearce et al.
1998, p. 307; Belsky et al. 1999, p. 1). Fleischner (1994, p. 629)
found that ``Because livestock congregate in riparian ecosystems, which
are among the most biologically rich habitats in arid and semiarid
regions, the ecological costs of grazing are magnified at these
sites.'' Stromberg and Chew (2002, p. 198) and Trimble and Mendel
(1995, p. 243) also discussed the propensity for poorly managed cattle
to remain within or adjacent to riparian communities. Trimble and
Mendel (1995, p. 243) stated that ``Cows, unlike sheep, appear to love
water and spend an inordinate amount of time together lounging in
streams and ponds, especially in summer (surface-active season for
reptiles and amphibians), sometimes going in and coming out several
times in the course of a day.'' Expectedly, this behavior is more
pronounced in more arid regions (Trimble and Mendel 1995, p. 243). In
one rangeland study, it was concluded that 81 percent of the vegetation
that was consumed, trampled, or otherwise removed was from a riparian
area, which amounted to only 2 percent of the total grazing space
(Trimble and Mendel 1995, p. 243). Another study reported that grazing
rates were 5 to 30 times higher in riparian areas than on the uplands,
which may be due in part to several factors: (1) Higher forage volume
and palatability of species in riparian areas; (2) water availability;
(3) the close proximity of riparian areas to the best upland grazing
sites; and (4) microclimatic features such as cooler temperatures and
shade (Trimble and Mendel 1995, p. 244).
Effects of improper livestock management on riparian and aquatic
communities have spanned from early settlement to modern day. Some
historical accounts of riparian area conditions in Arizona clarify
early effects of poor livestock management. Cheney et al. (1990, pp. 5,
10) provide historical accounts of the early adverse effects of
improper livestock management in the riparian zones and adjacent
uplands of the Tonto National Forest and in south-central Arizona.
These accounts describe the removal of riparian trees for preparation
of livestock use and substantial changes to flow regimes accentuated by
observed increases in runoff and erosion rates. Such accounts of
riparian conditions within the historical distribution of the northern
Mexican gartersnake in Arizona contribute to the understanding of when
declines in abundance and distribution may have occurred and the
contributions of this factor to the subsequent fragmentation of
populations and widespread extirpations.
Poor livestock management causes a decline in diversity, abundance,
and species composition of riparian herpetofauna communities from
direct or indirect threats to the prey base, the habitat, or to the
northern Mexican
[[Page 71803]]
gartersnake. These effects include: (1) Declines in the structural
richness of the vegetative community; (2) losses or reductions of the
prey base; (3) increased aridity of habitat; (4) loss of thermal cover
and protection from predators; and (5) a rise in water temperatures to
levels lethal to larval stages of amphibian and fish development (Szaro
et al. 1985, p. 362; Schulz and Leininger 1990, p. 295; Belsky et al.
1999, pp. 8-11). Improper livestock grazing may also lead to
desertification (the process of becoming arid land or desert as a
result of land mismanagement or climate change) due to a loss in soil
fertility from erosion and gaseous emissions spurred by a reduction in
vegetative ground cover (Schlesinger et al. 1990, p. 1043).
Szaro et al. (1985, p. 360) assessed the effects of improper
livestock management on a sister taxon. They found that western
(terrestrial) gartersnake (Thamnophis elegans vagrans) populations were
significantly higher (versus controls) in terms of abundance and
biomass in areas that were excluded from grazing, where the streamside
vegetation remained lush, than where uncontrolled access to grazing was
permitted. This effect was complemented by higher amounts of cover from
organic debris from ungrazed shrubs that accumulate as the debris moves
downstream during flood events. Specifically, results indicated that
snake abundance and biomass were significantly higher in ungrazed
habitat, with a five-fold difference in number of snakes captured,
despite the difficulty of making observations in areas of increased
habitat complexity (Szaro et al. 1985, p. 360). Szaro et al. (1985, p.
362) also noted the importance of riparian vegetation for the
maintenance of an adequate prey base and as cover in thermoregulation
and predation avoidance behaviors, as well as for foraging success.
Watersheds where improper grazing has been documented as a
contributing factor of northern Mexican gartersnake declines include
the Verde, Salt, Agua Fria, San Pedro, Gila, and Santa Cruz
(Hendrickson and Minckley 1984, pp. 140, 152, 160-162; Rosen and
Schwalbe 1988, pp. 32-33; Girmendock and Young 1997, p. 47; Voeltz
2002, pp. 45-81; Krueper et al. 2003, pp. 607, 613-614; Holycross et
al. 2006, pp. 52-61; McKinnon 2006d, 2006e; Paradzick et al. 2006, pp.
90-92; USFS 2008). Holycross et al. (2006, pp. 53-55, 58) recently
documented adverse effects from improper livestock grazing on northern
Mexican gartersnake habitat along the Agua Fria from EZ Ranch to Bloody
Basin Road, along Dry Creek from Dugas Road to Little Ash Creek, along
Little Ash Creek from Brown Spring to Dry Creek, along Sycamore Creek
in the vicinity of its confluence with the Verde River, and on
potential northern Mexican gartersnake habitat along Pinto Creek at the
confluence with the West Fork of Pinto Creek. In southeastern Arizona,
there have been observations of effects to the vegetative community
suggesting that livestock grazing activities continue to adversely
affect remaining populations of northern Mexican gartersnakes by
reducing or eliminating cover required by the northern Mexican
gartersnake for thermoregulation, protection from predation, and
foraging (Hale 2001, pp. 32-34, 50, 56).
To increase forage and stocking rates for livestock production in
the arid lowlands of northern Mexico, African buffelgrass was widely
introduced in Mexico and has subsequently spread via its own natural
means of dispersal (B[uacute]rquez-Montijo et al. 2002, p. 131; Nijhuis
2007, pp. 1-7). Buffelgrass invasions pose a serious threat to native
arid ecosystems because buffelgrass prevents germination of native
plant species, competes for water, crowds out native vegetation, and
creates fine fuels in vegetation communities not adapted to fire. In
such native arid ecosystems, buffelgrass has caused many changes,
including severe soil erosion resulting from an increase in the number
and severity of fires (B[uacute]rquez-Montijo et al. 2002, pp. 135,
138). Erosion affects the suitability of habitat for northern Mexican
gartersnakes and their prey species by increasing the turbidity of
streams and filling in important pool habitat, which increases the
water temperature of pools, lowers the dissolved oxygen content of the
water, and reduces their permanency. Recent estimates indicate that 80
percent of Mexico is affected by soil erosion caused by vegetation
removal related to grazing, fires, agriculture, deforestation, etc. The
most serious erosion is occurring in the States of Guanajuato (43
percent of the State's land area), Jalisco (25 percent of the State's
land area), and M[eacute]xico (25 percent of the State's land area) (va
Landa et al. 1997, p. 317), the states in which the northern Mexican
gartersnake occurs.
The effects of stock tanks associated with livestock grazing on
northern Mexican gartersnakes depend on how they are managed. Dense
bank and aquatic vegetation is an important habitat characteristic for
the northern Mexican gartersnake that can be affected if the
impoundment is poorly managed, which may lead to trampling or
overgrazing of the bankside vegetation. Alternatively, well-managed
stock tanks can provide habitat suitable for northern Mexican
gartersnakes both structurally and in terms of prey base, especially
when the tank remains devoid of nonnative species while supporting
native prey species; provides adequate vegetation cover; and provides
reliable water sources in periods of prolonged drought. Given these
benefits of well-managed stock tanks, we believe well-managed stock
tanks may be an important component to northern Mexican gartersnake
conservation.
Direct mortality of amphibian species, in all life stages, from
being trampled by livestock has been documented in the literature
(Bartelt 1998, p. 96; Ross et al. 1999, p. 163). The resultant
extirpation risk of amphibian populations as a prey base for northern
Mexican gartersnakes by direct mortality is governed by the relative
isolation of the amphibian population, the viability of that
population, and the propensity for stochastic events such as wildfires.
Livestock grazing within habitat occupied by northern Mexican
gartersnakes can result in direct mortality of individual gartersnakes
as observed in a closely related taxon on the Apache-Sitgreaves
National Forest. In that instance, a black-necked gartersnake
(Thamnophis cyrtopsis cyrtopsis) had apparently been killed by
trampling by cattle along the shore of a stock tank within an actively
grazed allotment (Chapman 2005). This event was not observed first-
hand, but was supported by postmortem photographic documentation of the
physical injuries to the specimen and the location of the carcass among
a dense cluster of hoof tracks along the shoreline of the stock tank.
It is also unlikely that a predator would kill the snake and leave it
uneaten. While this type of direct mortality of gartersnakes has long
been suspected by agency biologists and academia, this may be the first
recorded observation of direct mortality of a gartersnake due to
livestock trampling. We expect this type of direct mortality to be
uncommon but significant in the instance of a fragmented population
with a skewed age-class distribution (large adults), without a
neighboring source population to assist with recolonization, and low to
no recruitment as currently observed in many northern Mexican
gartersnake populations in the United States. In these circumstances,
the loss of one or more adults, most notably reproductive females, may
lead directly to extirpation of the species from a given site with no
expectation of recolonization.
Poor forestry and agricultural practices were cited as the largest
and
[[Page 71804]]
most widespread threats to the native fisheries of the Jalisco and
Colima area in Mexico investigated by Lyons and Navarro-Perez (1990, p.
37), affecting prey availability for northern Mexican gartersnakes in
areas where they occur. Lyons and Navarro-Perez (1990, p. 37) indicated
that in high-elevation areas, clear-cutting of trees and unrestricted
livestock grazing have increased erosion and sedimentation. They
suspected impacts on fish and invertebrate populations had occurred. In
lowland areas, Lyons and Navarro-Perez (1990, p. 37) cited diversion of
water for irrigation, runoff from cultivated fields, and runoff from
small towns and villages as causing additional environmental
degradation. Lyons and Navarro-Perez (1990, p. 37) found that the
tolerance of several fish species to degradation depended on the form
of degradation.
Minckley et al. (2002, pp. 687-705) described three new species of
pupfish and provided a summary of threats (p. 696) to these species and
their habitat in Chihuahua, Mexico, within the distribution of the
northern Mexican gartersnake. Initial settlement and agricultural
development of the area resulted in significant channel cutting through
soil layers protecting the alluvial plain above them, which resulted in
reductions in the base level of each basin in succession (Minckley et
al. 2002, p. 696). Related to these activities, the building of dams
and diversion structures dried entire reaches of some regional streams
and altered flow patterns of others (Minckley et al. 2002, p. 696).
This was followed by groundwater pumping (enhanced by the invention of
the electric pump) which lowered groundwater levels and dried-up
springs and small channels and reduced the reliability of baseflow in
``essentially all systems'' (Minckley et al. 2002, p. 696).
Subsequently, the introduction and expansion of nonnative species in
the area successfully displaced or extirpated many native species
(Minckley et al. 2002, p. 696).
Our analysis of the best available scientific and commercial
information available indicates that adverse effects from improper
livestock management on the northern Mexican gartersnake, its habitat,
and its prey base can be significant, especially when combined with
other threats, most notably nonnative species (discussed below under
Factor C). Preliminary gartersnake survey data from Burger (2008) from
the States of Durango and southern Chihuahua, Mexico, indicate that the
northern Mexican gartersnake is less susceptible to population impacts
associated with physical disturbances to its habitat, such as livestock
grazing, when the biotic community is comprised of wholly native
species. However, even modest alterations in the physical habitat of
the northern Mexican gartersnake may lead to population declines, or
even extirpations, when these adverse effects act in combination with
the adverse effects of nonnative species. In Mexico, livestock grazing,
often in association with deforestation and crop cultivation, are also
having adverse affects on the northern Mexican gartersnake. We
recognize that well-managed grazing can occur with limited effects to
this species when the presence or absence of nonnative species is
considered, and management emphasis is directed towards limiting some
access to riparian and aquatic habitats within occupied habitat. These
actions, combined with management that disperses livestock away from
riparian areas, reduce the threats of livestock grazing on northern
Mexican gartersnakes and their habitats. As previously stated, we also
recognize well-managed stock tanks as a valuable tool in the
conservation of northern Mexican gartersnakes.
Additional information on the effects of improper livestock grazing
to the northern Mexican gartersnake and its habitat can be found in our
2006, 12-month finding for this species (71 FR 56227) and in Sartz and
Tolsted (1974, p. 354); Szaro et al. (1985, pp. 360, 362, 364); Weltz
and Wood (1986, pp. 367-368); Rosen and Schwalbe (1988, pp. 32-33, 47);
Clary and Webster (1989, p. 1); Clary and Medin (1990, p. 1); Schulz
and Leininger (1990, p. 295); Schlesinger et al. (1990, p. 1043);
Orodho et al. (1990, p. 9); Fleischner (1994, pp. 629, 631-632);
Trimble and Mendel (1995, pp. 235-236, 243-244); Pearce et al. (1998,
p. 302); Belsky et al. (1999, pp. 8-11); Stromberg and Chew (2002, p.
198); and Krueper et al. (2003, pp. 607, 613-614).
High-Intensity Wildfires. Low-intensity fire has been a natural
disturbance factor in forested landscapes for centuries, and low-
intensity fires were common in southwestern forests prior to European
settlement (Rinne and Neary 1996, pp. 135-136). Rinne and Neary (1996,
p. 143) discuss the current effects of fire management policies on
aquatic communities in Madrean Oak Woodland biotic communities in the
southwestern United States. They concluded that existing wildfire
suppression policies intended to protect the expanding number of human
structures on forested public lands have altered the fuel loads in
these ecosystems and increased the probability of devastating
wildfires. The effects of these catastrophic wildfires include the
removal of vegetation, the degradation of watershed condition, altered
stream behavior, and increased sedimentation of streams. These effects
can harm fish communities, as observed in the 1990 Dude Fire, when
corresponding ash flows decimated some fish populations in Dude Creek
and the East Verde River (Voeltz 2002, p. 77), which, ultimately,
affects habitat suitability for the gartersnake. These effects can
significantly reduce the prey base for northern Mexican gartersnakes
and could lead to direct mortality in the case of high-intensity fires
that are within occupied habitat. The Chiricahua leopard frog recovery
plan cites altered fire regimes as a serious threat to Chiricahua
leopard frogs, a prey species for northern Mexican gartersnakes (USFWS
2008, pp. 38-39).
Fire has also become an increasingly significant threat in lower
elevation communities as well. Esque and Schwalbe (2002, pp. 180-190)
discuss the effect of wildfires in the upper and lower subdivisions of
Sonoran desertscrub where the northern Mexican gartersnake historically
occurred. The widespread invasion of nonnative annual grasses, such as
brome species (Bromus sp.) and Mediterranean grasses (Schismus sp.),
appear to be largely responsible for altered fire regimes that have
been observed in these communities, which are not adapted to fire
(Esque and Schwalbe 2002, p. 165). African buffelgrass (Pennisetum
ciliare) is recognized as another invading nonnative plant species
throughout the lower elevations of northern Mexico and Arizona. Nijhuis
(2007, pp. 1-7) discuss the spread of nonnative buffelgrass within the
Sonoran Desert of Arizona and adjoining Mexico, citing the grass'
ability to out compete native vegetation and present significant risks
of fire in an ecosystem that is not adapted to fire. In areas comprised
entirely of native species, ground vegetation density is mediated by
barren spaces that do not allow fire to carry itself across the
landscape. However, in areas where nonnative grasses have become
established, the fine fuel load is continuous, and fire is capable of
spreading quickly and efficiently (Esque and Schwalbe 2002, p. 175).
After disturbances such as fire, nonnative grasses may exhibit
dramatic population explosions, which hasten their effect on native
vegetative communities. Additionally, with increased fire frequency,
these population explosions ultimately lead to a type-conversion of the
vegetative
[[Page 71805]]
community from desertscrub to grassland (Esque and Schwalbe 2002, pp.
175-176). Fires carried by the fine fuel loads created by nonnative
grasses often burn at unnaturally high temperatures, which may result
in soils becoming hydrophobic (water repelling), exacerbate sheet
erosion, and contribute large amounts of sediment to receiving water
bodies, thereby affecting the health of the riparian community (Esque
and Schwalbe 2002, pp. 177-178). The siltation of isolated, remnant
pools in intermittent streams significantly affects lower elevation
species by increasing the water temperature, reducing dissolved oxygen,
and reducing or eliminating the permanency of pools, as observed in
pools occupied by lowland leopard frogs and native fish, important prey
species for northern Mexican gartersnakes (Esque and Schwalbe 2002, p.
190).
Undocumented Immigration and International Border Enforcement and
Management. Undocumented immigrants and smugglers attempt to cross the
International border from Mexico into the United States in areas
historically and currently occupied by the northern Mexican
gartersnake. These illegal border crossings and the corresponding
efforts to enforce U.S. border laws and policies have been occurring
for many decades with increasing intensity and have resulted in
unintended adverse effects to biotic communities in the border region.
During the warmest months of the year, many attempted border crossings
occur in riparian areas that serve to provide shade, water, and cover.
Increased U.S. border enforcement efforts that began in the early 1990s
in California and Texas have resulted in a shift in crossing patterns
and increasingly concentrated levels of attempted illegal border
crossings into Arizona (Segee and Neeley 2006, p. 6).
Riparian habitats that historically supported or may currently
support northern Mexican gartersnakes in the San Bernardino National
Wildlife Refuge, the San Pedro River corridor, the Santa Cruz River
corridor, the lower Colorado River corridor, and along many smaller
streamside and canyon bottom areas within Cochise, Santa Cruz, and Pima
counties have high levels of undocumented immigrant traffic (Segee and
Neeley 2006, Executive Summary, pp. 10-12, 21-23).
Traffic on new roads and trails from illegal border crossing and
enforcement activities, as well as the construction, use, and
maintenance of enforcement infrastructure (i.e., fences, walls, and
lighting systems), leads to compaction of streamside soils, and the
destruction and removal of riparian vegetation necessary as cover for
the northern Mexican gartersnake. Current border infrastructure
projects, including vehicle barriers and pedestrian fences, are located
specifically in valley bottoms and have resulted in direct impacts to
water courses and altered drainage patterns affecting northern Mexican
gartersnake habitat (USFWS 2008, p. 4). These activities also produce
sediment in streams, which affects their suitability as habitat for
prey species of the northern Mexican gartersnake by reducing their
permanency and altering their physical and chemical parameters.
Riparian areas along the upper San Pedro River have been impacted by
abandoned fires that undocumented immigrants started to keep warm or
prepare food (Segee and Neeley 2006, p. 23). There is also the threat
of pursuit, capture, and death of northern Mexican gartersnakes when
they are encountered by illegal border crossers and border enforcement
personnel in high-use areas due to the snake's stigma in society (Rosen
and Schwalbe 1988, p. 43; Ernst and Zug 1996, p. 75; Green 1997, pp.
285-286; Nowak and Santana-Bendix 2002, p. 39).
The wetland habitat within the San Bernardino National Wildlife
Refuge provides habitat for the northern Mexican gartersnake, where it
is now likely extirpated, and has been adversely affected by
undocumented immigration. It is estimated that approximately 1,000
undocumented immigrants per month use these important wetlands for
bathing, drinking, and other uses during their journey northward (Segee
and Neeley 2006, pp. 21-22). These activities occur in other border
areas, such as the Santa Cruz River, where the northern Mexican
gartersnake occurs, although they have not been quantified (Segee and
Neeley 2006, pp. 21-22). They can contaminate the water quality of the
wetlands and lead to reductions in the prey base for the northern
Mexican gartersnake, as well as increase exposure of the snake to
humans, and thereby increase direct mortality rates (Rosen and Schwalbe
1988, p. 43; Ernst and Zug 1996, p. 75; Green 1997, pp. 285-286; Nowak
and Santana-Bendix 2002, p. 39; Segee and Neeley 2006, pp. 21-22). In
addition, numerous observations of littering and destruction of
vegetation and wildlife occur annually throughout the San Bernardino
National Wildlife Refuge, which adversely affect the quality and
quantity of vegetation as habitat for the northern Mexican gartersnake
(USFWS 2006, p. 95). Due to the immediate proximity of the upper Santa
Cruz River to the international border and the effect of border control
operations that funnel undocumented immigrants into rural environments,
we conclude that these adverse effects likely occur in this area, which
is occupied by the northern Mexican gartersnake.
Threats from illegal border crossers appear to have increased in
recent years within the Coronado National Forest of southern Arizona
(USFS 2008). Reports of significant water pollution from bathing
activities by undocumented immigrants in habitat occupied by northern
Mexican gartersnakes have been received (USFS 2008). Of particular
concern to USFS (2008), was the concentrated use of pools by
undocumented immigrants during the warmest months before summer rains
commence, when the habitat is also critical to the northern Mexican
gartersnake and its prey. The amount of surface water is generally
considered the lowest during the early summer, pre-monsoon months in
Arizona, which compounds the effects of the use of pools for bathing by
concentrating water contamination in the limited habitat available to
northern Mexican gartersnakes and their prey species. Because of the
limited amount of alternative habitat, illegal border crossers and
gartersnakes are concentrated in the same areas, increasing encounter
rates and the potential threats to northern Mexican gartersnakes.
Summary of Factor A. Riparian and aquatic habitats that are
essential for the survival of the northern Mexican gartersnake are
being negatively impacted throughout the subspecies' range. Threats
including water diversions, groundwater pumping, dams, channelization,
and erosion-related effects are occurring in both the United States and
Mexico that affect the amount of water within occupied northern Mexican
gartersnake habitat, directly affecting its suitability for northern
Mexican gartersnakes. Threats from development, roads, flood control
and water diversion, improper livestock grazing, high-intensity
wildfire, and undocumented immigration that alter the vegetation of
occupied northern Mexican gartersnake habitat are documented throughout
its range and reduce the habitat's suitability as cover for protection
from predators, as a foraging area, and as an effective
thermoregulatory site. However, Rorabaugh (2008, p. 26) suggests that
an increased awareness of the potential for ecotourism to provide rural
economic growth is occurring in many areas
[[Page 71806]]
within Sonora, Mexico, which may provide enhanced opportunities for
conservation of biologically rich ecosystems in the future.
Nonnative plant species, in particular shrubs (genus Tamarix) and
buffelgrass, are increasing their distribution in both the United
States and Mexico and adversely affect habitat suitability and
availability for the northern Mexican gartersnake.
B. Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
The northern Mexican gartersnake may not be collected in the United
States without special authorization by the Arizona Game and Fish
Department or the New Mexico Department of Game and Fish. We have found
no evidence that current or historical levels of lawful or unlawful
field collecting of northern Mexican gartersnakes has played a
significant role in the decline of this species. The Arizona Game and
Fish Department recently produced identification cards for distribution
that provide information to assist with the field identification of
each of Arizona's five native gartersnake species, as well as guidance
on submitting photographic vouchers for university museum collections.
Additionally, Arizona State University and the University of Arizona
recently began to accept photographic vouchers, versus physical
specimens, in their respective museum collections, which will reduce
the amount of collection. We believe these measures reduce the
necessity for field biologists to collect physical specimens (unless
discovered postmortem) for locality voucher purposes and, therefore,
further reduce impacts to vulnerable populations of the northern
Mexican gartersnake. We were unable to obtain information about the
effect of overutilization for commercial, recreational, scientific, or
educational purposes in Mexico. Specific discussion of the regulatory
protections for the northern Mexican gartersnake is provided under
Factor D ``Inadequacy of Existing Regulatory Mechanisms'' below.
C. Disease or Predation
Disease. Disease in northern Mexican gartersnakes has not yet been
documented as a specific threat in the United States or Mexico.
However, because little is known about disease in wild snakes, it is
premature to conclude that there is no disease threat that could
directly affect remaining northern Mexican gartersnake populations
(Rosen 2006).
Disease and nonnative parasites have been implicated in the decline
in the prey base of the northern Mexican gartersnake. Particularly, the
outbreak of chytridiomycosis or ``Bd,'' a skin fungus (Batrachochytrium
dendrobatidis), has been identified as a chief causative agent in the
significant declines of many of the native ranid frogs and other
amphibian species, and regional concerns exist for the native fish
community due to nonnative parasites such as the Asian tapeworm
(Bothriocephalus achelognathi) in southeastern Arizona (Rosen and
Schwalbe 1997, pp. 14-15; 2002c, pp. 1-19; Morell 1999, pp. 728-732;
Sredl and Caldwell 2000, p. 1; Hale 2001, pp. 32-37; Bradley et al.
2002, p. 206). Bd has been implicated in both large-scale declines and
local extirpations of many amphibians, chiefly anuran species, around
the world (Johnson 2006, p. 3011). Lips et al. (2006, pp. 3166-3169)
suggest that the high virulence and large number of potential hosts
make Bd a serious threat to amphibian diversity. In Arizona, Bd
infections have been reported in several northern Mexican gartersnake
native prey species within the distribution of the snake (Morell 1999,
pp. 731-732; Sredl and Caldwell 2000, p. 1; Hale 2001, pp. 32-37;
Bradley et al. 2002, p. 207; USFWS 2002a, pp. 40802-40804; USFWS 2007,
pp. 26, 29-32). Declines of native prey species of the northern Mexican
gartersnake from Bd infections have contributed to the decline of this
species in the United States and likely in Mexico (Morell 1999, pp.
731-732; Sredl and Caldwell 2000, p. 1; Hale 2001, pp. 32-37; Bradley
et al. 2002, p. 207; USFWS 2002a, pp. 40802-40804; USFWS 2007, pp. 26,
29-32).
Research shows that, in a pure culture, the fungus Batrachochytrium
can grow on boiled snakeskin (keratin), which indicates the potential
for the fungus to live on gartersnake skin in the wild, if other
components of the ecosystem are favorable (Longcore et al. 1999, p.
227). Despite the demonstrated potential, no reports of the organism on
reptilian hosts in the wild have been documented. We, as well as other
researchers, will monitor the incidence of this disease in gartersnakes
in the wild for early detection purposes and to determine the status of
this potential threat.
Parasites have been observed in northern Mexican gartersnakes.
Boyarski (2008b, pp. 5-6) recorded several snakes within the population
at the Page Springs and Bubbling Ponds fish hatcheries with interior
bumps or bulges along the anterior one-third of the body although the
cause of these bumps was not identified or speculated upon, nor were
there any signs of trauma to their body in these areas. Dr. Jim
Jarchow, a veterinarian with herpetological expertise, reviewed
photographs of affected specimens and suggested the bumps may likely
contain plerocercoid larvae of a pseudophyllidean tapeworm (possibly
Spirometra spp.), which are common in fish- and frog-eating
gartersnakes. This may not be detrimental to their health provided the
bumps do not grow large enough to impair movement or other bodily
functions (Boyarski 2008b, p. 8). However, G[uacute]zman (2008, p. 102)
documented the first observation of mortality of a Mexican gartersnake
from a larval Eustrongylides sp. (endoparasitic nematode) which
``raises the possibility that infection of Mexican gartersnakes by
Eustrongylides sp. larvae might cause mortality in some wild
populations,'' especially in the presence of other threats.
Nonnative Species Interactions. A host of native predators prey
upon northern Mexican gartersnakes including birds of prey, other
snakes [kingsnakes (Lampropeltis sp.), whipsnakes (Masticophis sp.),
etc.], wading birds, raccoons (Procyon lotor), skunks (Mephitis sp.),
and coyotes (Canis latrans) (Rosen and Schwalbe 1988, p. 18).
Historically, large, highly predatory native fish species such as
Colorado pikeminnow may have preyed upon northern Mexican gartersnakes
where the two species co-occurred. However, nonnative species represent
the most serious threat to the northern Mexican gartersnake through
direct predation and predation on northern Mexican gartersnake prey
(competition). Nonnative species, such as the bullfrog, the northern
(virile) crayfish (Orconectes virilis) and red swamp (Procambarus
clarki) crayfish, and numerous species of nonnative sport and bait fish
species continue to be the most significant threat to the northern
Mexican gartersnake and to its prey base from direct predation,
competition, and modification of habitat (Meffe 1985, pp. 179-185;
Rosen and Schwalbe 1988, pp. 28, 32; 1997, p. 1; Bestgen and Propst
1989, pp. 409-410; Clarkson and Rorabaugh 1989, pp. 531, 535; Marsh and
Minckley 1990, p. 265; Stefferud and Stefferud 1994, p. 364; Douglas et
al. 1994, pp. 9-19; Rosen et al. 1995, pp. 257-258; 1996b, pp. 2, 11-
13; 2001, p. 2; Degenhardt et al. 1996, p. 319; Fernandez and Rosen
1996, pp. 8, 23-27; Richter et al. 1997, pp. 1089, 1092; Weedman and
Young 1997, p. 1, Appendices B, C; Inman et al. 1998, p. 17; Rinne et
al. 1998, pp. 4-6; Minckley
[[Page 71807]]
et al. 2002, p. 696; DFT 2003, p. 1; Clarkson et al. 2005, p. 20; Fagan
et al. 2005, pp. 34, 34-41; Olden and Poff 2005, pp. 82-87; Turner
2006, p. 10; Holycross et al. 2006, pp. 13-15; Brennan and Holycross
2006, p. 123; USFWS 2007, pp. 22-23; Caldwell 2008a, 2008b; Jones
2008b; d'Orgeix 2008; Haney et al. 2008, p. 59; Luja and
Rodr[iacute]guez-Estrella 2008, pp.. 17-22; Rorabaugh 2008, p. 25; USFS
2008; Wallace et al. 2008, pp. 243-244; Witte et al. 2008, p. 1).
Riparian and aquatic communities in both the United States and
Mexico have been dramatically impacted by a shift in species'
composition, from being historically dominated by native fauna to being
increasingly occupied by an expanding assemblage of nonnative animal
species that have been intentionally or accidentally introduced, such
as crayfish, bullfrogs, sportfish, and domestic pets. For example, in
two of eight cases of northern Mexican gartersnake mortality collected
at Bubbling Ponds Hatchery since 2006, the cause of death was
considered to be from domestic cats (Boyarski 2008a).
The population of northern Mexican gartersnakes at the hatcheries
occurs with potential and known nonnative predators including rainbow
and brown trout, largemouth and smallmouth bass, bluegill, crayfish (in
Oak Creek), and bullfrogs (Boyarski 2008b, pp. 3-4, 8). Seven snakes
(11 percent of those captured) were observed as having some level of
tail damage, presumably from bullfrog predation attempts and were noted
as having a lower body condition index (an indicator of overall health
based on a set of pre-determined variables) (Boyarski 2008b, pp. 5, 8).
The relatively low occurrence of tail damage, as compared to the 78
percent of snakes with tail damage found by Rosen and Schwalbe (1988,
pp. 28-31), may indicate (1) adequate vegetation density was used by
gartersnakes to avoid bullfrog predation attempts; (2) a relatively low
density population of bullfrogs occurs at the site (bullfrog population
density data were not collected); (3) gartersnakes may not need to move
significant distances to achieve foraging success, which might have
reduced the potential for encounters with bullfrogs; or, (4) that
gartersnakes infrequently escape bullfrog predation attempts, were
removed from the population, and were consequently not detected by
surveys. Additional information on tail damage as an indicator of
predation is found in our discussion of Factor C below.
Stock tanks associated with livestock grazing may facilitate the
spread of nonnative species when nonnative species of fish, amphibians,
and crayfish are intentionally or unintentionally stocked by anglers
and private landowners (Rosen et al. 2001, p. 24). The management of
stock tanks is an important consideration for northern Mexican
gartersnakes. Stock tanks associated with livestock grazing can be
intermediary ``stepping stones'' in the dispersal of nonnative species
from larger source populations to new areas (Rosen et al. 2001, p. 24).
The northern Mexican gartersnake appears to be particularly
vulnerable to a loss in native prey species (Rosen and Schwalbe 1988,
p. 20). Rosen et al. (2001, pp. 10, 13, 19) examined this issue in
detail and proposed two reasons for the decline in northern Mexican
gartersnakes following the loss or decline in the native prey base: (1)
The species is unlikely to increase foraging efforts at the risk of
increased predation; and (2) the species needs substantial food
regularly to maintain its weight and health. If forced to forage more
often for smaller prey items, a reduction in growth and reproductive
rates can result (Rosen et al. 2001, pp. 10, 13). Rosen et al. (2001,
p. 22) concluded that the presence and expansion of nonnative predators
(mainly bullfrogs, crayfish, and green sunfish) are the primary causes
of decline in northern Mexican gartersnakes and their prey in
southeastern Arizona.
The decline of the northern Mexican gartersnake within its
historical and currently occurring distribution was subsequent to the
declines in its prey base (native amphibian and fish populations) from
predation following introductions of nonnative bullfrogs, crayfish, and
numerous species of exotic sport and bait fish as documented in an
extensive body of literature (Nickerson and Mays 1970, p. 495; Hulse
1973, p. 278; Vitt and Ohmart 1978, p. 44; Meffe 1985, pp. 179-185;
Ohmart et al. 1988, pp. 143-147; Rosen and Schwalbe 1988, pp. 28-31;
1997, pp. 8-16; Bestgen and Propst 1989, pp. 409-410; Clarkson and
Rorabaugh 1989, pp. 531-538; Marsh and Minckley 1990, p. 265; Sublette
et al. 1990, pp. 112, 243, 246, 304, 313, 318; Stefferud and Stefferud
1994, p. 364; Holm and Lowe 1995, p. 5; Rosen et al. 1995, pp. 251,
257-258; 1996a, pp. 2-3; 1996b, p. 2; 2001, p. 2; Sredl et al. 1995a,
pp. 7-8; 1995b, pp. 8-9; 1995c, pp. 7-8; 2000, p. 10; Degenhardt et al.
1996, p. 319; Fernandez and Rosen 1996, pp. 8-27; Drost and Nowak 1997,
p. 11; Weedman and Young 1997, p. 1, Appendices B, C; Inman et al.
1998, p. 17; Rinne et al. 1998, pp. 4-6; Turner et al. 1999, p. 11;
Nowak and Spille 2001, p. 11; Bonar et al. 2004, p. 3; Fagan et al.
2005, pp. 34, 34-41; Olden and Poff 2005, pp. 82-87; Holycross et al.
2006, pp. 13-15, 52-61; Brennan and Holycross 2006, p. 123; USFWS 2007,
pp. 22-23; Caldwell 2008a, 2008b; Jones 2008b; d'Orgeix 2008; Haney et
al. 2008, p. 59; Luja and Rodr[iacute]guez-Estrella 2008, pp. 17-22;
Rorabaugh 2008, p. 25; USFS 2008; Wallace et al. 2008, pp. 243-244;
Witte et al. 2008, p. 1).
Declines in the Northern Mexican Gartersnake Anuran Prey Base.
Declines in the native leopard frog populations in Arizona have
contributed to declines in the northern Mexican gartersnake as a
primary native predator. Native ranid frog species such as lowland
leopard frogs, northern leopard frogs, and federally threatened
Chiricahua leopard frogs have all experienced significant declines
throughout their distribution in the Southwest, partially due to
predation and competition with nonnative species (Clarkson and
Rorabaugh 1989, pp. 531, 535; Hayes and Jennings 1986, p. 490). Rosen
et al. (1995, pp. 257-258) found that Chiricahua leopard frog
distribution in the Chiricahua Mountain region of Arizona was inversely
related to nonnative species distribution and without corrective
action, predicted that the Chiricahua leopard frog will be extirpated
from this region. Along the Mogollon Rim, Holycross et al. (2006, p.
13) found that only 8 sites of 57 surveyed (15 percent) consisted of an
entirely native anuran community and that native frog populations in
another 19 sites (33 percent) had been completely displaced by invading
bullfrogs.
Scotia Canyon in the Huachuca Mountains of southeastern Arizona is
a location where corresponding declines of leopard frog and northern
Mexican gartersnake populations have been documented through repeated
survey efforts over time (Holm and Lowe 1995, p. 33). Surveys of Scotia
Canyon occurred during the early 1980s and again during the early
1990s. Leopard frogs in Scotia Canyon were infrequently observed during
the early 1980s and were apparently extirpated by the early 1990s (Holm
and Lowe 1995, pp. 45-46). Northern Mexican gartersnakes were observed
in decline during the early 1980s with low capture rates remaining
through the early 1990s (Holm and Lowe 1995, pp. 27-35). Surveys
documented further decline in 2000 (Rosen et al. 2001, pp. 15-16). A
former large, local population of northern Mexican gartersnakes at the
San Bernardino National Wildlife Refuge has also experienced a
correlative decline of leopard frog and northern Mexican gartersnake
[[Page 71808]]
populations, at least in part related to illegal immigration and
smuggling activities in riparian and aquatic habitats as discussed in
Factor A above (Rosen and Schwalbe 1988, p. 28; 1995, p. 452; 1996, pp.
1-3; 1997, p. 1; 2002b, pp. 223-227; 2002c, pp. 31, 70; Rosen et al.
1996b, pp. 8-9; 2001, pp. 6-10). Survey data indicate that declines of
leopard frog populations, often correlated with nonnative species
introductions, the spread of chytridiomycosis disease, and habitat
modification and destruction, have occurred throughout much of the U.S.
distribution of the northern Mexican gartersnake (Nickerson and Mays
1970, p. 495; Vitt and Ohmart 1978, p. 44; Ohmart et al. 1988, p. 150;
Rosen and Schwalbe 1988, Appendix I; 1995, p. 452; 1996, pp. 1-3; 1997,
p. 1; 2002b, pp. 232-238; 2002c, pp. 1, 31; Clarkson and Rorabaugh
1989, pp. 531-538; Sredl et al. 1995a, pp. 7-8; 1995b, pp. 8-9; 1995c,
pp. 7-8; 2000, p. 10; Holm and Lowe 1995, pp. 45-46; Rosen et al.
1996b, p. 2; 2001, pp. 2, 22; Degenhardt et al. 1996, p. 319; Fernandez
and Rosen 1996, pp. 6-20; Drost and Nowak 1997, p. 11; Turner et al.
1999, p. 11; Nowak and Spille 2001, p. 32; Holycross et al. 2006, pp.
13-14, 52-61). Specifically, Holycross et al. (2006, pp. 53-57, 59)
recently documented extirpations of the northern Mexican gartersnake's
native leopard frog prey base at several currently, historically, or
potentially occupied locations including the Agua Fria River in the
vicinity of Table Mesa Road and Little Grand Canyon Ranch and at Rock
Springs, Dry Creek from Dugas Road to Little Ash Creek, Little Ash
Creek from Brown Spring to Dry Creek, Sycamore Creek (Agua Fria
watershed) in the vicinity of the Forest Service Cabin, at the Page
Springs and Bubbling Ponds fish hatchery along Oak Creek, Sycamore
Creek (Verde River watershed) in the vicinity of the confluence with
the Verde River north of Clarkdale, along several reaches of the Verde
River mainstem, Cherry Creek on the east side of the Sierra Ancha
Mountains, and Tonto Creek from Gisela to ``the Box,'' near its
confluence with Rye Creek.
Rosen et al. (2001, p. 22) identified the expansion of bullfrogs
into the Sonoita grasslands, which border occupied northern Mexican
gartersnake habitat, and the introduction of crayfish into Lewis
Springs as being of particular concern in terms of future recovery
efforts for the northern Mexican gartersnake. Rosen et al. (1995, pp.
252-253) sampled 103 sites in the Chiricahua Mountains region, which
included the Chiricahua, Dragoon, and Peloncillo mountains, and the
Sulphur Springs, San Bernardino, and San Simon valleys. They found that
43 percent of all cold-blooded aquatic and semi-aquatic vertebrate
species detected were nonnative. The most commonly encountered
nonnative species was the bullfrog (Rosen et al. 1995, p. 254).
Native ranid frogs (particularly lowland and Chiricahua leopard
frogs), which are a primary prey species for northern Mexican
gartersnakes, are one of the most imperiled taxa of Sonora, Mexico, due
primarily to threats from nonnative species (bullfrogs, crayfish, and
sport fish) (Rorabaugh 2008, p. 25).
Witte et al. (2008, p. 1) found that the disappearance of ranid
frog populations in Arizona were 2.6 times more likely in the presence
of crayfish. Witte et al. (2008, p. 7) emphasized the significant
influence of nonnative species on the disappearance of ranid frogs in
Arizona.
Declines in the Northern Mexican Gartersnake Native Fish Prey Base.
Native fish species such as the federally endangered Gila chub,
roundtail chub (a species petitioned for Federal listing), and
federally endangered Gila topminnow historically were among the primary
prey species for the northern Mexican gartersnake (Rosen and Schwalbe
1988, p. 18). Northern Mexican gartersnakes depend on native fish as a
principle part of their prey base, although nonnative mosquitofish may
also be taken as prey (Holycross et al. 2006, p. 23). Both nonnative
sport and bait fish compete with the northern Mexican gartersnake in
terms of its native fish and native anuran prey base. Collier et al.
(1996, p. 16) note that interactions between native and nonnative fish
have significantly contributed to the decline of many native fish
species from direct predation and indirectly from competition (which
has adversely affected the prey base for northern Mexican
gartersnakes). Holycross et al. (2006, pp. 53-55) recently documented
significantly depressed or extirpated native fish prey bases for the
northern Mexican gartersnake along the Agua Fria in the vicinity of
Table Mesa Road and the Little Grand Canyon Ranch, along Dry Creek from
Dugas Road to Little Ash Creek, along Little Ash Creek from Brown
Spring to Dry Creek, along Sycamore Creek (Agua Fria watershed) in the
vicinity of the Forest Service Cabin, and along Sycamore Creek (Verde
River watershed) in the vicinity of its confluence with the Verde River
north of Clarkdale. Rosen et al. (2001, Appendix I) documented the
decline of several native fish species in several locations visited in
southeastern Arizona, further affecting the prey base of northern
Mexican gartersnakes in that area.
The widespread decline of native fish species from the arid
southwestern United States and Mexico has resulted largely from
interactions with nonnative species and has been captured in the
listing rules of 13 native species listed under the Act whose
historical ranges overlap with the historical distribution of the
northern Mexican gartersnake. Native fish species that were likely prey
species for the northern Mexican gartersnake, including bonytail chub
(Gila elegans, 45 FR 27710, April 23, 1980), Yaqui catfish (Ictalurus
pricei, 49 FR 34490, August 31, 1984), Yaqui chub (Gila purpurea, 49 FR
34490, August 31, 1984), Yaqui topminnow (Poeciliopsis occidentalis
sonoriensis, 32 FR 4001, March 11, 1967), beautiful shiner (Cyprinella
formosa, 49 FR 34490, August 31, 1984), humpback chub (Gila cypha, 32
FR 4001, March 11, 1967), Gila chub (Gila intermedia, 70 FR 66663,
November 2, 2005), Colorado pikeminnow (Ptychocheilus lucius, 32 FR
4001, March 11, 1967), spikedace (Meda fulgida, 51 FR 23769, July 1,
1986) loach minnow (Tiaroga cobitis, 51 FR 39468, October 28, 1986),
razorback sucker (Xyrauchen texanus, 56 FR 54957, October 23, 1991),
desert pupfish (Cyprinodon macularius, 51 FR 10842, March 31, 1986),
and Gila topminnow (Poeciliopsis occidentalis occidentalis, 32 FR 4001,
March 11, 1967). In total within Arizona, 19 of 31 (61 percent) of
native fish species are listed under the Act. Arizona ranks the highest
of all 50 States in the percentage of native fish species with
declining trends (85.7 percent, Stein 2002, p. 21; Warren and Burr
1994, pp. 6-18).
There are significant ongoing threats from nonnative species to the
snake in Mexico. Lyons and Navarro-Perez (1990, pp. 32-46) investigated
the fish communities of 17 streams in and adjacent to the Sierra de
Manantl[aacute]n Biosphere Reserve in Jalisco and Colima, Mexico. They
noted the exceptionally high number of native fish species with small,
localized distributions, which makes them more susceptible to threats
and subsequent extirpation, stating that degradation of just a few
streams could result in the elimination of many species of fish and,
thus, prey availability for the northern Mexican gartersnake.
In an evolutionary context, native fishes co-evolved with very few
predatory fish species, whereas many of the nonnative species co-
evolved with many predatory species (Clarkson et al. 2005, p. 21). A
contributing factor to the decline of native fish species cited by
Clarkson et al. (2005, p. 21) is that most
[[Page 71809]]
of the nonnative species evolved behaviors, such as nest guarding, to
protect their offspring from these many predators, while native species
are generally broadcast spawners that provide no parental care. In the
presence of nonnative species, the reproductive behaviors of native
fish fail to allow them to compete effectively with the nonnative
species and, as a result, the viability of native fish populations is
reduced.
Olden and Poff (2005, p. 75) stated that environmental degradation
and the proliferation of nonnative fish species threaten the highly
localized and unique fish faunas of the American Southwest. The fastest
expanding nonnative species are red shiner (Cyprinella lutrensis),
fathead minnow (Pimephales promelas), green sunfish (Lepomis
cyanellus), largemouth bass (Micropterus salmoides), western
mosquitofish, and channel catfish (Ictalurus punctatus). These species
are considered to be the most invasive in terms of their negative
impacts on native fish communities (Olden and Poff 2005, p. 75). Many
nonnative fishes in addition to those listed immediately above,
including yellow and black bullheads (Ameiurus sp.), flathead catfish
(Pylodictis olivaris), and smallmouth bass (Micropterus dolomieue),
have been introduced into formerly and currently occupied northern
Mexican gartersnake habitat and are predators on northern Mexican
gartersnakes and their prey (Bestgen and Propst 1989, pp. 409-410;
Marsh and Minckley 1990, p. 265; Sublette et al. 1990, pp. 112, 243,
246, 304, 313, 318; Abarca and Weedman 1993, pp. 6-12; Stefferud and
Stefferud 1994, p. 364; Weedman and Young 1997, pp. 1, Appendices B, C;
Rinne et al. 1998, pp. 3-6; Voeltz 2002, p. 88; Bonar et al. 2004, pp.
1-108; Fagan et al. 2005, pp. 34, 38-39, 41).
Several authors have identified both the presence of nonnative fish
as well as their deleterious effects on native species within Arizona.
Abarca and Weedman (1993, pp. 6-12) found that the number of nonnative
fish species was twice the number of native fish species in Tonto Creek
in the early 1990s, with a stronger nonnative species influence in the
lower reaches where the northern Mexican gartersnake is considered to
still occur. Surveys in the Salt River above Lake Roosevelt indicate a
decline of roundtail chub and other natives with an increase in
flathead and channel catfish numbers (Voeltz 2002, p. 49). In New
Mexico, nonnative fish have been identified as the main cause for
declines observed in roundtail chub populations (Voeltz 2002, p. 40).
Douglas et al. (1994, pp. 9-19) provide data indicating that the
nonnative red shiner may be competitively displacing spikedace (a
potential prey item of the northern Mexican gartersnake) in Arizona and
New Mexico within the historical or current distribution of the
northern Mexican gartersnake.
In a comprehensive and thorough assessment of the Verde River,
Bonar et al. (2004, p. 57) found that in the Verde River mainstem,
nonnative fishes were approximately 2.6 times more dense per unit
volume of river than native fishes, and their populations were
approximately 2.8 times that of native fishes per unit volume of river.
Haney et al. (2008, p. 61) declared the northern Mexican
gartersnake as nearly lost from the Verde River and suggested that
diminished river flow may be an important factor. Differing river flows
may provide both advantages and disadvantages to aquatic species. The
timing, duration, intensity, and frequency of flood events has been
altered to varying degrees by the presence of dams along the Verde
River, which has an effect on fish communities. Specifically, Haney et
al. (2008, p. 61) suggested that flood pulses may help to reduce
populations of nonnative species (see discussion below) and efforts to
increase the baseflows may assist in sustaining native prey species for
the northern Mexican gartersnake. However, the investigators also
suggest that, because the northern Mexican gartersnake preys on both
fish and frogs, it may be less affected by reductions in baseflow but
might incur greater risks from concentrating nonnative predators and
higher water-borne disease rates (Haney et al. 2008, pp. 82, 93).
The Desert Fishes Team (DFT) is an ``independent group of
biologists and parties interested in protecting and conserving native
fishes of the Colorado River basin'' and includes personnel from the
U.S. Forest Service, U.S. Bureau of Reclamation, U.S. Bureau of Land
Management, University of Arizona, Arizona State University, the Nature
Conservancy, and independent experts (DFT 2003, p. 1). DFT (2003, p. 1)
declared the native fish fauna of the Gila River basin to be critically
imperiled, cite habitat destruction and nonnative species as the
primary factors for the declines, and call for the control and removal
of nonnative fish as an overriding need to prevent the decline and
ultimate extinction of native fish species within the basin.
Northern Mexican gartersnakes can successfully use some nonnative
species, such as mosquitofish and red shiner, as prey species. However,
all other nonnative species, most notably the spiny-rayed fish, are not
considered prey species for the northern Mexican gartersnake. These
nonnative species can be difficult to swallow due to their body shape
and spiny dorsal fins. They are predatory on juvenile gartersnakes and
reduce the abundance of or completely eliminate native fish
populations. This is particularly important in the wake of random,
high-intensity events, such as flooding, extreme water temperatures, or
excessive turbidity. Native fish are adapted to the dramatic
fluctuations in water conditions and flow regimes, and generally
persist in the wake of stochastic events and continue to provide a prey
base for the northern Mexican gartersnake. Nonnative fish, even species
that may be used as prey by the northern Mexican gartersnake, generally
are ill-adapted to these conditions and may be removed from the area
temporarily or permanently, depending on the hydrologic connectivity to
current populations. If an area is solely comprised of nonnative fish,
the northern Mexican gartersnake may be faced with nutritional stress
or starvation because only a few small-bodied, soft-rayed fish species
are taken as prey and significant effort may be required to obtain
these species.
Clarkson et al. (2005) discuss management conflicts as a primary
factor in the decline of native fish species in the southwestern United
States and declare the entire native fauna as imperiled. The
investigators cite nonnative species as the most consequential factor
that has led to rangewide declines that prevents or negates species'
recovery efforts from being implemented or being successful (Clarkson
et al. 2005, p. 20). Clarkson et al. (2005, p. 20) note that over 50
nonnative species have been introduced into the Southwest as either
sportfish or baitfish and are still being actively stocked, managed
for, and promoted by both Federal and State agencies as nonnative
recreational fisheries. To help resolve the conflicting management
mandates of native fish recovery and the promotion of recreational
fisheries, Clarkson et al. (2005, pp. 22-25) propose the designation of
entire watersheds as having either native or nonnative fisheries and
manage for these goals aggressively. While some discussion within
Arizona has taken place to designate portions of watersheds as either
native or nonnative fisheries, the geographic areas under consideration
for native fishery development do not currently coincide with current
populations of northern Mexican gartersnakes and no immediate
[[Page 71810]]
benefit is provided to the subspecies from their implementation.
Clarkson et al. (2005, p. 25) suggest that current management of
fisheries within the southwestern United States as status quo will have
serious adverse effects to native fish species and affect the long-term
viability of the northern Mexican gartersnake and to its potential
recovery.
We are not aware of any studies that have addressed the direct
relationship between prey base diversity and northern Mexican
gartersnake recruitment and survivorship. However, Krause and Burghardt
(2001, pp. 100-123) discuss the benefits and costs that may be
associated with diet variability in the common gartersnake (Thamnophis
sirtalis), an ecologically similar species to the northern Mexican
gartersnake. Foraging for mixed-prey species may impede predator
learning, as compared to specialization, on a certain prey species, but
may also provide long-term benefits (Krause and Burghardt 2001, p.
101). Krause and Burghardt (2001, p. 112) stated that varied predatory
experience played an important role in the feeding abilities of
gartersnakes through the first 8 months of age. These data suggest that
a varied prey base might also be important for neonatal and juvenile
northern Mexican gartersnakes (also a species with a varied diet) and
that decreases in the diversity of the prey base during the young age
classes might adversely affect the ability of individuals to capture
prey throughout their lifespan, in addition to the more obvious effects
of reduced prey availability.
The most conclusive evidence for the northern Mexican gartersnake's
intolerance for nonnative fish invasions remains the fact that, in most
incidences, nonnative fish species generally do not occur in the same
locations as the northern Mexican gartersnake and its native prey
species. Additional information on the decline of the northern Mexican
gartersnake's native fish prey species can be found in Bonar et al.
(2004, pp. 4, 79-87); DFT (2003, pp. 1-3, 5-6, 19; 2004, pp. 1-2, 4-5,
10, Table 1; 2006, pp. iii, 25); Richter et al. (1997, pp. 1081-1093);
and Haney et al. (2008, pp. 54-61, 82, 93).
Bullfrog Diet and Distribution. Bullfrogs are widely considered one
of the most serious threats to the northern Mexican gartersnake
throughout its range (Conant 1974, pp. 471, 487-489; Rosen and Schwalbe
1988, pp. 28-30; Rosen et al. 2001, pp. 21-22). Bullfrogs adversely
affect northern Mexican gartersnakes through direct predation of
juveniles and sub-adults and from competition with native prey species.
Bullfrogs first appeared in Arizona in 1926, as a result of a
systematic introduction effort by the State Game Department (now, the
Arizona Game and Fish Department) for the purposes of sport hunting and
as a food source. (Tellman 2002, p. 43). Bullfrogs are extremely
prolific, adept at colonizing new areas, and may disperse to distances
of 6.8 miles (10.9 km) and likely further within drainages (Bautista
2002, p. 131; Rosen and Schwalbe 2002a, p. 7; Casper and Hendricks
2005, p. 582). In Arizona, using mark and recapture methods, bullfrogs
have been documented to make overland movements of up to 7 miles (11
kilometers) across semi-desert grassland habitat on the Buenos Aires
National Wildlife Refuge (BANWR) (Suhre 2008). Investigators on the
BANWR also observed two bullfrogs at an overland distance of 10 miles
(16 kilometers) from the nearest source population although the origin
of the bullfrogs could not be confirmed. Batista (2002, p. 131)
confirmed ``the strong colonizing skills of the bullfrog and that the
introduction of this exotic species can disturb local anuran
communities.''
Bullfrogs are voracious, opportunistic, even cannibalistic
predators that readily attempt to consume any animal smaller than
themselves, including other species within the same genus, which can
comprise 80 percent of their diet (Casper and Hendricks 2005, p. 543).
Bullfrogs have a varied diet, which has been documented to include
vegetation, numerous invertebrate and vertebrate species which include
numerous species of snakes [eight genera; including six different
species of gartersnakes, two species of rattlesnakes, and Sonoran
gophersnakes (Pituophis catenifer affinis)] (Bury and Whelan 1984, p.
5; Clarkson and DeVos 1986, p. 45; Holm and Lowe 1995, pp. 37-38;
Carpenter et al. 2002, p. 130; King et al. 2002; Hovey and Bergen 2003,
pp. 360-361; Casper and Hendricks 2005, p. 544; Combs et al. 2005, p.
439; Wilcox 2005, p. 306; DaSilva et al. 2007, p. 443; Neils and Bugbee
2007, p. 443).
Bullfrogs have been documented throughout the State of Arizona.
Holycross et al. (2006, pp. 13-14, 52-61) found bullfrogs at 55 percent
of sample sites in the Agua Fria watershed, 62 percent of sites in the
Verde River watershed, 25 percent of sites in the Salt River watershed,
and 22 percent of sites in the Gila River watershed. In total,
bullfrogs were observed at 22 of the 57 sites surveyed (39 percent)
across the Mogollon Rim (Holycross et al. 2006, p. 13). A number of
authors have also documented the presence of bullfrogs through their
survey efforts throughout Arizona in specific regional areas,
drainages, and disassociated wetlands within or adjacent to the
historical distribution of the northern Mexican gartersnake, including
the Kaibab National Forest (Sredl et al. 1995a, p. 7); the Coconino
National Forest (Sredl et al. 1995c, p. 7); the White Mountain Apache
Reservation (Hulse 1973, p. 278); Beaver Creek (tributary to the Verde
River) (Drost and Nowak 1997, p. 11); the Watson Woods Riparian
Preserve near Prescott (Nowak and Spille 2001, p. 11); the Tonto
National Forest (Sredl et al. 1995b, p. 9); the Lower Colorado River
(Vitt and Ohmart 1978, p. 44; Clarkson and DeVos 1986, pp. 42-49;
Ohmart et al. 1988, p. 143); the Huachuca Mountains (Rosen and Schwalbe
1988, Appendix I; Holm and Lowe 1995, pp. 27-35; Sredl et al. 2000, p.
10; Rosen et al. 2001, Appendix I); the Pinaleno Mountains region
(Nickerson and Mays 1970, p. 495); the San Bernardino National Wildlife
Refuge (Rosen and Schwalbe 1988, Appendix I; 1995, p. 452; 1996, pp. 1-
3; 1997, p. 1; 2002b, pp. 223-227; 2002c, pp. 31, 70; Rosen et al.
1995, p. 254; 1996b, pp. 8-9; 2001, Appendix I); the Buenos Aires
National Wildlife Refuge (Rosen and Schwalbe 1988, Appendix I); the
Arivaca Area (Rosen and Schwalbe 1988, Appendix I; Rosen et al. 2001,
Appendix I); Cienega Creek drainage (Rosen et al. 2001, Appendix I);
Babocamari River drainage (Rosen et al. 2001, Appendix I); Turkey Creek
drainage (Rosen et al. 2001, Appendix I); O'Donnell Creek drainage
(Rosen et al. 2001, Appendix I); Appleton-Whittell Research Ranch near
Elgin (Rosen et al. 2001, Appendix I); Santa Cruz River drainage (Rosen
and Schwalbe 1988, Appendix I; Rosen et al. 2001, Appendix I); San
Rafael Valley (Rosen et al. 2001, Appendix I); San Pedro River drainage
(Rosen and Schwalbe 1988, Appendix I; Rosen et al. 2001, Appendix I);
Bingham Cienega (Rosen et al. 2001, Appendix I); Sulfur Springs Valley
(Rosen et al. 1996a, pp. 16-17); Whetstone Mountains region (Turner et
al. 1999, p. 11); Aqua Fria River drainage (Rosen and Schwalbe 1988,
Appendix I; Holycross et al. 2006, pp. 13, 15-18, 52-53); Verde River
drainage (Rosen and Schwalbe 1988, Appendix I; Holycross et al. 2006,
pp. 13, 26-28, 55-56); greater metropolitan Phoenix area (Rosen and
Schwalbe 1988, Appendix I); greater metropolitan Tucson area (Rosen and
Schwalbe 1988, Appendix I); Sonoita Creek drainage (Rosen and Schwalbe
1988, Appendix I); Sonoita Grasslands (Rosen and Schwalbe 1988,
Appendix I); Canelo Hills (Rosen and Schwalbe 1988,
[[Page 71811]]
Appendix I); Pajarito Mountains (pers. observation, J. Servoss, Fish
and Wildlife Biologist, U.S. Fish and Wildlife Service); Picacho
Reservoir (Rosen and Schwalbe 1988, Appendix I); Dry Creek drainage
(Holycross et al. 2006, pp. 19, 53); Little Ash Creek drainage
(Holycross et al. 2006, pp. 19, 54); Oak Creek drainage (Holycross et
al. 2006, pp. 23, 54); Sycamore Creek drainages (Holycross et al. 2006,
pp. 20, 25, 54-55); Rye Creek drainage (Holycross et al. 2006, pp. 37,
58); Spring Creek drainage (Holycross et al. 2006, pp. 25, 59); Tonto
Creek drainage (Holycross et al. 2006, pp. 40-44, 59; Wallace et al.
2008, pp. 243-244); San Francisco River drainage (Holycross et al.
2006, pp. 49-50, 61); Sonoita Creek (Tuner 2006; p. 10); and the upper
Gila River drainage (Holycross et al. 2006, pp. 45-50, 60-61).
Perhaps one of the most serious consequences of bullfrog
introductions is their persistence in an area once they have become
established, and the subsequent difficulty in eliminating bullfrog
populations. Rosen and Schwalbe (1995, p. 452) experimented with
bullfrog removal at various sites on the San Bernardino National
Wildlife Refuge in addition to a control site with no bullfrog removal
in similar habitat on the BANWR. Removal of adult bullfrogs, without
removal of eggs and tadpoles, resulted in a substantial increase in
younger age-class bullfrogs where removal efforts were the most
intensive (Rosen and Schwalbe 1997, p. 6). Contradictory to the goals
of bullfrog eradication, evidence from dissection samples from young
adult and sub-adult bullfrogs indicated these age-classes readily prey
upon juvenile bullfrogs (up to the average adult leopard frog size) as
well as juvenile gartersnakes, which suggests that the selective
removal of only the large adult bullfrogs (presumed to be the most
dangerous size class to leopard frogs and gartersnakes), favoring the
young adult and sub-adult age classes, could indirectly lead to
increased predation of leopard frogs and juvenile gartersnakes (Rosen
and Schwalbe 1997, p. 6). These findings illustrate that in addition to
large adults, bullfrogs in the young adult and subadult age classes
also negatively impact northern Mexican gartersnakes and their prey
species.
Bullfrog Effects on the Native Anuran Prey Base for the Northern
Mexican Gartersnake. As documented above and in the following studies,
bullfrogs significantly reduce native anuran prey availability for the
northern Mexican gartersnake (Conant (1974, pp. 471, 487-489); Hayes
and Jennings (1986, pp. 491-492); Rosen and Schwalbe (1988, pp. 28-30;
2002b, pp. 232-238); Rosen et al. (1995, pp. 257-258; 2001, pp. 2,
Appendix I); Wu et al. (2005, p. 668); Pearl et al. (2004, p. 18);
Kupferberg (1994, p. 95) Kupferburg (1997, pp. 1736-1751); Lawler et
al. (1999); Bury and Whelan (1986, pp. 9-10); Hayes and Jennings (1986,
pp. 500-501); Moyle (1973, pp. 18-22)). Different age classes of
bullfrogs within a community can affect native ranid populations via
different mechanisms. Juvenile bullfrogs affect native ranids through
competition, male bullfrogs affect native ranids through predation, and
female bullfrogs affect native ranids through both mechanisms depending
on body size and microhabitat (Wu et al. 2005, p. 668). Pearl et al.
(2004, p. 18) also suggested that the effect of bullfrog introductions
on native ranids may be different based on specific habitat conditions,
but also suggested that an individual ranid frog species' physical
ability to escape influences the effect of bullfrogs on each native
ranid community.
Bullfrog Predation on Northern Mexican Gartersnakes. Sub-adult and
adult bullfrogs not only compete with the northern Mexican gartersnake
for prey items, but directly prey upon juvenile and occasionally sub-
adult northern Mexican gartersnakes (Rosen and Schwalbe 1988, pp. 28-
31; 1995, p. 452; 2002b, pp. 223-227; Holm and Lowe 1995, pp. 29-29;
Rossman et al. 1996, p. 177; AGFD In Prep, p. 12; 2001, p. 3; Rosen et
al. 2001, pp. 10, 21-22; Carpenter et al. 2002, p. 130; Wallace 2002,
p. 116). A well-circulated photograph of an adult bullfrog in the
process of consuming a northern Mexican gartersnake at Parker Canyon
Lake, Cochise County, Arizona, taken by John Carr of the Arizona Game
and Fish Department in 1964, provides photographic documentation of
bullfrog predation (Rosen and Schwalbe 1988, p. 29; 1995, p. 452). A
common observation in northern Mexican gartersnake populations that co-
occur with bullfrogs is a preponderance of large, mature adult snakes
with conspicuously low numbers of individuals in the newborn and
juvenile age size classes due to bullfrogs preying on young small
snakes, which ultimately leads to low reproductive rates and survival
of young (Rosen and Schwalbe 1988, p. 18; Holm and Lowe 1995, p. 34).
Potential recruitment problems for northern Mexican gartersnakes due to
effects from nonnative species are also suspected at Tonto Creek
(Wallace et al. 2008, pp. 243-244).
The tails of gartersnakes broken off through predation attempts may
also lead to infection or compromise an individual's physical ability
to escape future predation attempts or successfully forage. Tails of
gartersnakes do not regenerate. The incidence of tail breaks in
gartersnakes can often be used to assess predation pressures within
gartersnake populations. Rosen and Schwalbe (1988, p. 22) found the
incidence of tail breaks to be statistically higher in females than in
males. Fitch (2003, p. 212) also found that tail breaks in the common
gartersnake occurred more frequently in females than males and in
adults more than in juveniles. Fitch (2003, p. 212) also commented
that, while tail breakage in gartersnakes can save the life of an
individual snake, it also leads to permanent handicapping of the snake,
resulting in slower swimming and crawling speeds, which could leave the
snake more vulnerable to predation or affect its foraging ability.
Furthermore, Mushinsky and Miller (1993, pp. 662-664) found that the
incidence of tail injury in water snakes in the genera Nerodia and
Regina (which have similar life histories to northern Mexican
gartersnakes) was higher in females than in males and in adults more
than juveniles. This can be explained by higher basking rates
associated with pregnant females that increase their visibility to
predators. Additionally, predation on juvenile snakes generally results
in complete consumption of the animal, which would limit observations
of tail injury in their age class. Rosen and Schwalbe (1988, p. 22)
suggested that the indication that female northern Mexican gartersnakes
bear more injuries is consistent with the inference that they employ a
riskier foraging strategy. Willis et al. (1982, p. 98) discussed the
incidence of tail injury in three species in the genus Thamnophis
(common gartersnake, Butler's gartersnake (T. butleri), and the eastern
ribbon snake (T. sauritus)) and concluded that individuals that
suffered nonfatal injuries prior to reaching a length of 12 in (30 cm)
are not likely to survive and that physiological stress during post-
injury hibernation may play an important role in subsequent mortality.
Ecologically significant observations on tail injuries were made by
Rosen and Schwalbe (1988, pp. 28-31) on the formerly occurring
population of northern Mexican gartersnakes on the San Bernardino
National Wildlife Refuge. Seventy-eight percent of specimens had broken
tails with a ``soft and club-like'' terminus, which suggests repeated
injury from multiple predation attempts by bullfrogs. While medically
[[Page 71812]]
examining pregnant female northern Mexican gartersnakes, Rosen and
Schwalbe (1988, p. 28) noted bleeding from the posterior region which,
suggested to the investigators the snakes suffered from ``squeeze-
type'' injuries inflicted by adult bullfrogs. While a sub-adult or
adult northern Mexican gartersnake may survive an individual predation
attempt from a bullfrog while only incurring tail damage, secondary
effects from infection of the wound can significantly contribute to
mortality of individuals.
Research on the effects of attempted predation performed by
Mushinsky and Miller (1993, pp. 661-664) and Willis et al. (1982, pp.
100-101) supports the observations made by Holm and Lowe (1995, p. 34)
on the northern Mexican gartersnake population age class structure in
Scotia Canyon in the Huachuca Mountains of southeastern Arizona in the
early 1990s. Specifically, Holm and Lowe (1995, pp. 33-34) observed a
conspicuously greater number of adult snakes in that population than
sub-adult snakes, as well as a higher incidence of tail injury (89
percent) in all snakes captured. Bullfrogs have been identified as the
primary cause for both the collapse of the native leopard frog (prey
base for the northern Mexican gartersnake) and northern Mexican
gartersnake populations on the San Bernardino National Wildlife Refuge
(Rosen and Schwalbe 1988, p. 28; 1995, p. 452; 1996, pp. 1-3; 1997, p.
1; 2002b, pp. 223-227; 2002c, pp. 31, 70; Rosen et al. 1996b, pp. 8-9).
Rosen and Schwalbe (1988, p. 18) stated that the low survivorship of
newborns, and possibly yearlings, due to bullfrog predation is an
important proximate cause of population declines of this snake at the
San Bernardino National Wildlife Refuge and throughout its distribution
in Arizona.
Crayfish. Nonnative crayfish are a primary threat to many prey
species of the northern Mexican gartersnake and may also prey upon
juvenile gartersnakes (Fernandez and Rosen 1996, p. 25; Voeltz 2002,
pp. 87-88; USFWS 2007, p. 22). Fernandez and Rosen (1996, p. 3) studied
the effects of crayfish introductions on two stream communities in
Arizona, a low-elevation semi-desert stream and a high mountain stream,
and concluded that crayfish can noticeably reduce species diversity and
destabilize food chains in riparian and aquatic ecosystems through
their effect on vegetative structure, stream substrate (stream bottom;
i.e., silt, sand, cobble, boulder) composition, and predation on eggs,
larval, and adult forms of native invertebrate and vertebrate species.
Crayfish fed on embryos, tadpoles, newly metamorphosed frogs, and adult
leopard frogs, but they did not feed on egg masses (Fernandez and Rosen
1996, p. 25). However, Gamradt and Kats (1996, p. 1155) found that
crayfish readily consumed the egg masses of California newts (Taricha
torosa). Fernandez and Rosen (1996, pp. 6-19, 52-56) and Rosen (1987,
p. 5) discussed observations of inverse relationships between crayfish
abundance and native reptile and amphibian populations including
narrow-headed gartersnakes, northern leopard frogs, and Chiricahua
leopard frogs. Crayfish may also affect native fish populations.
Carpenter (2005, pp. 338-340) documented that crayfish may reduce the
growth rates of native fish through competition for food and noted that
the significance of this impact may vary between species. Crayfish also
prey on fish eggs and larvae (Inman et al. 1998, p. 17).
Crayfish alter the abundance and structure of aquatic vegetation by
grazing on aquatic and semiaquatic vegetation, which reduces the cover
needed by frogs and gartersnakes as well as the food supply for prey
species such as tadpoles (Fernandez and Rosen 1996, pp. 10-12).
Fernandez and Rosen (1996, pp. 10-12) also found that crayfish
frequently burrow into stream banks, which leads to increased bank
erosion, stream turbidity, and siltation of substrates. Creed (1994, p.
2098) found that filamentous alga (Cladophora glomerata) was at least
10-fold greater in aquatic habitat absent crayfish. Filamentous alga is
an important component of aquatic vegetation that provides cover for
foraging gartersnakes as well as microhabitat for prey species.
Inman et al. (1998, p. 3) documented nonnative crayfish as widely
distributed and locally abundant in a broad array of natural and
artificial free-flowing and still-water habitats throughout Arizona,
many of which overlapped the historical and current distribution of the
northern Mexican gartersnake. Hyatt (undated, p. 71) concluded that the
majority of waters in Arizona contained at least one species of
crayfish. In surveying for northern Mexican and narrow-headed
gartersnakes, Holycross et al. (2006, p. 14) found crayfish in 64
percent of the sample sites in the Agua Fria watershed; in 85 percent
of the sites in the Verde River watershed; in 46 percent of the sites
in the Salt River watershed; and in 67 percent of the sites in the Gila
River watershed. In total, crayfish were observed at 35 (61 percent) of
the 57 sites surveyed across the Mogollon Rim (Holycross et al. 2006,
p. 14), most of which were sites historically occupied by northern
Mexican gartersnakes, or sites the investigators believed possessed
suitable habitat and may be occupied based upon the known historical
distribution of the subspecies.
Several other authors have specifically documented the presence of
crayfish in many areas and drainages throughout Arizona, which is
testament to their ubiquitous distribution in Arizona and their strong
colonizing abilities. These areas all fall within the range of the
northern Mexican gartersnake and include the Kaibab National Forest
(Sredl et al. 1995a, p. 7); the Coconino National Forest (Sredl et al.
1995c, p. 7); the Watson Woods Riparian Preserve near Prescott (Nowak
and Spille 2001, p. 33); the Tonto National Forest (Sredl et al. 1995b,
p. 9); the Lower Colorado River (Ohmart et al. 1988, p. 150; Inman et
al. 1998, Appendix B); the Huachuca Mountains (Sredl et al. 2000, p.
10); the Arivaca Area (Rosen et al. 2001, Appendix I); Babocamari River
drainage (Rosen et al. 2001, Appendix I); O'Donnell Creek drainage
(Rosen et al. 2001, Appendix I); Santa Cruz River drainage (Rosen and
Schwalbe 1988, Appendix I; Rosen et al. 2001, Appendix I); San Pedro
River drainage (Inman et al. 1998, Appendix B; Rosen et al. 2001,
Appendix I); Aqua Fria River drainage (Inman et al. 1998, Appendix B;
Holycross et al. 2006, pp. 14, 15-18, 52-54); Verde River drainage
(Inman et al. 1998, Appendix B; Holycross et al. 2006, pp. 14, 20-28,
54-56); Salt River drainage (Inman et al. 1998, Appendix B; Holycross
et al. 2006, pp. 15, 29-44, 56-60); Black River drainage (Inman et al.
1998, Appendix B); San Francisco River drainage (Inman et al. 1998,
Appendix B; Holycross et al. 2006, pp. 14, 49-50, 61); Nutrioso Creek
drainage (Inman et al. 1998, Appendix B); Little Colorado River
drainage (Inman et al. 1998, Appendix B); Leonard Canyon Drainage
(Inman et al. 1998, Appendix B); East Clear Creek drainage (Inman et
al. 1998, Appendix B); Chevelon Creek drainage (Inman et al. 1998,
Appendix B); Eagle Creek drainage (Inman et al. 1998, Appendix B;
Holycross et al. 2006, pp. 47-48, 60); Bill Williams drainage (Inman et
al. 1998, Appendix B); Sabino Canyon drainage (Inman et al. 1998,
Appendix B); Dry Creek drainage (Holycross et al. 2006, pp. 19, 53);
Little Ash Creek drainage (Holycross et al. 2006, pp. 19, 54); Sycamore
Creek drainage (Holycross et al. 2006, pp. 25, 54-55); East Verde River
drainage (Holycross et al. 2006, pp. 21-22, 54); Oak Creek drainage
(Holycross et al. 2006, pp. 23, 54); Pine Creek drainage (Holycross et
al. 2006, pp. 24, 55); Spring Creek
[[Page 71813]]
drainage (Holycross et al. 2006, pp. 25, 55); Big Bonito Creek drainage
(Holycross et al. 2006, pp. 29, 56); Cherry Creek drainage (Holycross
et al. 2006, pp. 33, 57); East Fork Black River drainage (Holycross et
al. 2006, pp. 34, 57); Haigler Creek drainage (Holycross et al. 2006,
pp. 35, 58); Houston Creek drainage (Holycross et al. 2006, pp. 35-36,
58); Rye Creek drainage (Holycross et al. 2006, pp. 37, 58); Tonto
Creek drainage (Holycross et al. 2006, pp. 40-44, 59; Wallace et al.
2008; pp. 243-244); Blue River drainage (Holycross et al. 2006, pp. 45,
60); Campbell Blue River drainage (Holycross et al. 2006, pp. 46, 60);
and the Gila River drainage (Inman et al. 1998, Appendix B; Holycross
et al. 2006, pp. 45-50, 61). Like bullfrogs, crayfish can be very
difficult, if not impossible, to eradicate once they have become
established in an area (Rosen and Schwalbe 1996a, pp. 5-8; 2002a, p. 7;
Hyatt undated, pp. 63-71).
Nonnative Fish Distribution and Community Interactions. As
indicated earlier in this document, nonnative fish are a threat to
northern Mexican gartersnakes and their native anuran and fish prey.
Similar to bullfrogs, predatory nonnative fish species, such as
largemouth bass, also prey upon juvenile northern Mexican gartersnakes.
Rosen et al. (2001, Appendix I) and Holycross et al. (2006, pp. 15-51)
conducted large-scale surveys for northern Mexican gartersnakes in
southeastern and central Arizona and narrow-headed gartersnakes in
central and east-central Arizona and documented the presence of
nonnative fish at many locations. Rosen et al. (2001, Appendix I) found
nonnative fish in the following survey locations: The Arivaca Area;
Babocamari River drainage; O'Donnell Creek drainage; Appleton-Whittell
Research Ranch (Post Canyon) near Elgin; Santa Cruz River drainage;
Agua Caliente Canyon; Santa Catalina Mountains; and the San Pedro River
drainage. Holycross et al. (2006, pp. 14-15, 52-61) found nonnative
fish in the Aqua Fria River drainage; the Verde River drainage; the Dry
Creek drainage; the Little Ash Creek drainage; the Sycamore Creek
drainage; the East Verde River drainage; the Oak Creek drainage; the
Pine Creek drainage; the Big Bonito Creek drainage; the Black River
drainage; the Canyon Creek drainage; the Cherry Creek drainage; the
Christopher Creek drainage; the East Fork Black River drainage; the
Haigler Creek drainage; the Houston Creek drainage; the Rye Creek
drainage; the Salt River drainage; the Spring Creek drainage; the Tonto
Creek drainage; the Blue River drainage; the Campbell Blue River
drainage; the Eagle Creek drainage; and the San Francisco River
drainage. Other authors have documented the presence of nonnative fish
through their survey efforts in specific regions that include the Tonto
National Forest (Sredl et al. 1995b, p. 8) and the Huachuca Mountains
(Sredl et al. 2000, p. 10).
Holycross et al. (2006, pp. 14-15) found nonnative fish species in
64 percent of the sample sites in the Agua Fria watershed, 85 percent
of the sample sites in the Verde River watershed, 75 percent of the
sample sites in the Salt River watershed, and 56 percent of the sample
sites in the Gila River watershed. In total, nonnative fish were
observed at 41 of the 57 sites surveyed (72 percent) across the
Mogollon Rim (Holycross et al. 2006, p. 14). Entirely native fish
communities were detected in only 8 of 57 sites surveyed (14 percent)
(Holycross et al. 2006, p. 14). While the locations and drainages
identified above that are known to support populations of nonnative
fish do not provide a thorough representation of the status of
nonnative fish distribution Statewide in Arizona, it is well documented
that nonnative fish have infiltrated the majority of aquatic
communities in Arizona.
Nonnative fish can also affect native amphibian populations.
Matthews et al. (2002, p. 16) examined the relationship of gartersnake
distributions, amphibian population declines, and nonnative fish
introductions in high-elevation aquatic ecosystems in California.
Matthews et al. (2002, p. 16) specifically examined the effect of
nonnative trout introductions on populations of amphibians and mountain
gartersnakes (Thamnophis elegans elegans). Their results indicated the
probability of observing gartersnakes was 30 times greater in lakes
containing amphibians than in lakes where amphibians have been
extirpated by nonnative fish. These results supported prediction by
Jennings et al. (1992, p. 503) that native amphibian declines will lead
directly to gartersnake declines. Matthews et al. (2002, p. 20) noted
that in addition to nonnative fish species adversely impacting
amphibian populations that are part of the gartersnake's prey base,
direct predation on gartersnakes by nonnative fish also occurs.
Inversely, gartersnake predation on nonnative species, such as
centrarchids, may physically harm the snake. Choking injuries to
northern Mexican gartersnakes may occur from attempting to ingest
nonnative spiny-rayed fish species (such as green sunfish and bass)
because the spines located in the dorsal fins of these species can
become lodged in, or cut into the gut tissue, of the snake, as observed
in narrow-headed gartersnakes (Nowak and Santana-Bendix 2002, p. 25).
Nonnative fish invasions can indirectly affect the health,
maintenance, and reproduction of the northern Mexican gartersnake by
altering its foraging strategy and foraging success. The more energy
expended in foraging, coupled by the reduced number of small to medium-
sized prey fish available in lower densities, may lead to deficiencies
in nutrition affecting growth and reproduction because energy is
instead allocated to maintenance and the increased energy costs of
intense foraging activity (Rosen et al. 2001, p. 19). In contrast, a
northern Mexican gartersnake diet that includes both fish and
amphibians such as leopard frogs provides larger prey items which
reduce the necessity to forage at a higher frequency allowing metabolic
energy gained from larger prey items to be allocated instead to growth
and reproductive development. Myer and Kowell (1973, p. 225)
experimented with food deprivation in common gartersnakes and found
significant reductions in lengths and weights in juvenile snakes that
were deprived of regular feedings versus the control group that were
fed regularly at natural frequencies. Reduced foraging success means
that individuals will become vulnerable to effects from starvation,
which may, therefore, increase mortality rates in the juvenile size
class and consequently affect recruitment of northern Mexican
gartersnakes where their prey base has been compromised by nonnative
species.
Nonnative Species in Mexico. As in the United States, the native
fish prey base for northern Mexican gartersnakes in Mexico has been
dramatically affected by the introduction of nonnative species (Conant
1974, pp. 471, 487-489; Miller et al. 2005, pp. 60-61; Abarca 2006). In
the lower elevations of Mexico where northern Mexican gartersnakes
occurred historically or are still found, there are approximately 200
species of native freshwater fish documented with 120 native species
under some form of threat and an additional 15 that have become extinct
due to human activities, which include the introduction of nonnative
species (Contreras Balderas and Lozano 1994, pp. 383-384). In 1979, The
American Fisheries Society listed 69 species of native fish in Mexico
as threatened or in danger of becoming extinct. Ten years later that
number rose to 123 species, an increase of 78 percent
[[Page 71814]]
(Contreras Balderas and Lozano 1994, pp. 383-384). Miller et al. (2005,
p. 60) concludes that some 20 percent of Mexico's native fish are
threatened or in danger of becoming extinct. Nonnative species are
increasing everywhere throughout Mexico, and this trend will have
adverse impacts on native fish, according to Miller et al. (2005, p.
61). A number of freshwater fish populations have been adversely
affected by nonnative species in many locations, several of which were
previously noted in the discussion under Factor A.
At the time of our 2006 12-month finding, we had less information
on the status and distribution of bullfrogs within Mexico. However,
since that time, Luja and Rodr[iacute]guez-Estrella (2008, pp 17-22)
examined the invasion of the bullfrog in Mexico. The earliest records
of bullfrogs in Mexico were Nuevo Leon (1853), Tamaulipas (1898),
Morelos (1968), and Sinaloa (1969) (Luja and Rodr[iacute]guez-Estrella
2008, p 20). By 1976, the bullfrog was documented in 7 more States:
Aguacalientes, Baja California Sur, Chihuahua, Distrito Federal,
Puebla, San Luis Potosi, and Sonora (Luja and Rodr[iacute]guez-Estrella
2008, p. 20). To date, Luja and Rodr[iacute]guez-Estrella (2008, p. 20)
have recorded bullfrogs in 20 of the 31 Mexican States (65 percent of
the states in Mexico) and suspect that they have invaded other States,
but were unable to find documentation.
Sponsored by the then Mexican Secretary of Aquaculture Support,
bullfrogs have been commercially produced for food in Mexico in
Yucatan, Nayarit, Morelos, Estado de Mexico, Michoac[aacute]n,
Guadalajara, San Luis Potosi, Tamaulipas, and Sonora (Luja and
Rodr[iacute]guez-Estrella 2008, p. 20). However, frog legs ultimately
never gained popularity in Mexican culinary culture (Conant 1974, pp.
487-489) and Luja and Rodr[iacute]guez-Estrella (2008, p. 22) point out
that only 10 percent of these farms remain in production. Luja and
Rodr[iacute]guez-Estrella (2008, p. 20 and 22) document instances where
bullfrogs have escaped production farms and suspect the majority of the
frogs that were produced commercially in farms that have since ceased
operation have assimilated into surrounding habitat.
Luja and Rodr[iacute]guez-Estrella (2008, p. 20) also state that
Mexican people deliberately introduce bullfrogs for ornamental
purposes, or ``for the simple pleasure of having them in ponds.'' The
act of deliberately releasing bullfrogs into the wild in Mexico was
cited by Luja and Rodr[iacute]guez-Estrella (2008, p. 21) as being
``more common than we can imagine.'' To further compound these
introductions, bullfrogs are available for purchase at Mexican pet
stores (Luja and Rodr[iacute]guez-Estrella 2008, p. 22).
Adverse effects such as predation upon, and competition with,
northern Mexican gartersnakes and their prey base from bullfrog
invasions in Mexico have been specifically documented with respect to
Chiricahua leopard frogs, a primary prey item for northern Mexican
gartersnakes (Luja and Rodr[iacute]guez-Estrella 2008, p. 21). Luja and
Rodr[iacute]guez-Estrella (2008, p. 21) also stated that bullfrog
eradication efforts in Mexico are often thwarted by their being favored
by local communities. Currently, no regulation exists in Mexico to
address the threat of bullfrog invasions (Luja and Rodr[iacute]guez-
Estrella 2008, p. 22).
Rosen and Melendez (2006, p. 54) report bullfrog invasions to be
prevalent in northwestern Chihuahua and northwestern Sonora, where the
northern Mexican gartersnake is thought to occur. In many areas, native
leopard frogs were completely displaced where bullfrogs were observed.
Rosen and Melendez (2006, p. 54) also demonstrated the relationship
between fish and amphibian communities in Sonora and western Chihuahua.
Native leopard frogs, a primary prey item for the northern Mexican
gartersnake, only occurred in the absence of nonnative fish and were
absent from waters containing nonnative species, which included several
major waters. In Sonora, Rorabaugh (2008, p. 25) also considers the
bullfrog to be a significant threat to the northern Mexican gartersnake
and its prey base.
Unmack and Fagan (2004, p. 233) compared historical museum
collections of nonnative fish species from the Gila River basin in
Arizona and the Yaqui River basin in Sonora, Mexico, to gain insight
into the trends in distribution, diversity, and abundance of nonnative
fishes in each basin over time. They found that nonnative species are
slowly but steadily increasing in all three parameters in the Yaqui
Basin (Unmack and Fagan 2004, p. 233). Unmack and Fagan (2004, p. 233)
predicted that, in the absence of aggressive management intervention,
significant extirpations or range reductions of native fish species are
expected to occur in the Yaqui Basin of Sonora, Mexico, which may have
current populations of northern Mexican gartersnake, as did much of the
Gila Basin before the introduction of nonnative species. Loss of native
fishes will impact prey availability for the northern Mexican
gartersnake and threaten its persistence in these areas.
Summary of Factor C. While disease is not currently considered a
direct threat to northern Mexican gartersnakes, Bd does have a
widespread effect on anuran prey availability for the species. In
addition, stress placed on northern Mexican gartersnakes as a result of
threats discussed under Factor A may affect the health condition of
individuals within populations affected by these threats, which may
increase the potential for disease within current populations in the
future.
Direct predation by nonnative bullfrogs, crayfish, and fishes on
northern Mexican garter snakes is a significant threat rangewide, as is
predation on gartersnake prey species (competition) by these same
groups of nonnative taxa. Nonnative fish, crayfish, and bullfrogs have
reduced native populations of prey species throughout the range.
D. The Inadequacy of Existing Regulatory Mechanisms
Currently, the northern Mexican gartersnake is considered ``State
Endangered'' in New Mexico. In the State of New Mexico, an ``Endangered
Species'' is defined as ``any species of fish or wildlife whose
prospects of survival or recruitment within the State are in jeopardy
due to any of the following factors: (1) The present or threatened
destruction, modification, or curtailment of its habitat; (2)
overutilization for scientific, commercial or sporting purposes; (3)
the effect of disease or predation; (4) other natural or man-made
factors affecting its prospects of survival or recruitment within the
state; or (5) any combination of the foregoing factors'' as per New
Mexico Statutory Authority (NMSA) 17-2-38.D. ``Take,'' defined as
``means to harass, hunt, capture or kill any wildlife or attempt to do
so'' by NMSA 17-2-38.L., is prohibited without a scientific collecting
permit issued by the New Mexico Department of Game and Fish as per NMSA
17-2-41.C and New Mexico Administrative Code (NMAC) 19.33.6. However,
while the New Mexico Department of Game and Fish can issue monetary
penalties for illegal take of northern Mexican gartersnakes, the same
provisions are not in place for actions that result in loss or
modification of habitat (NMSA 17-2-41.C and NMAC 19.33.6) (Painter
2005).
The northern Mexican gartersnake is considered a ``Candidate
Species'' in the Arizona Game and Fish Department draft document,
Wildlife of Special Concern (WSCA) (AGFD In Prep., p. 12). A
``Candidate Species'' is one ``whose threats are known or suspected but
for which substantial population declines from historical levels have
not been documented (though they appear to
[[Page 71815]]
have occurred)'' (AGFD In Prep., p. 12). The purpose of the WSCA list
is to provide guidance in habitat management implemented by land-
management agencies. Additionally, the northern Mexican gartersnake is
considered a ``Tier 1b Species of Greatest Conservation Need'' in the
Arizona Game and Fish Department draft document, Arizona's
Comprehensive Wildlife Conservation Strategy (CWCS) (AGFD 2006a, p. 32;
2006b). The purpose for the CWCS is to ``provide an essential
foundation for the future of wildlife conservation and a stimulus to
engage the States, federal agencies, and other conservation partners to
strategically think about their individual and coordinated roles in
prioritizing conservation efforts'' (AGFD 2006a, p. 2). A ``Tier 1b
Species of Greatest Conservation Need'' is one that requires immediate
conservation actions aimed at improving conditions through intervention
at the population or habitat level (AGFD 2006a, p. 32).
Prior to 2005, the Arizona Game and Fish Department allowed for
take of up to four northern Mexican gartersnakes per person per year as
specified in Commission Order Number 43. The Arizona Game and Fish
Department defines ``take'' as ``pursuing, shooting, hunting, fishing,
trapping, killing, capturing, snaring, or netting wildlife or the
placing or using any net or other device or trap in a manner that may
result in the capturing or killing of wildlife.'' The Arizona Game and
Fish Department subsequently amended Commission Order Number 43,
effective January 2005. Take of northern Mexican gartersnakes is no
longer permitted in Arizona without issuance of a scientific collecting
permit (Ariz. Admin. Code R12-4-401 et seq.). While the Arizona Game
and Fish Department can seek criminal or civil penalties for illegal
take of northern Mexican gartersnakes, the same provisions are not in
place for actions that result in destruction or modification of
northern Mexican gartersnake habitat.
In addition to making the necessary regulatory changes to promote
the conservation of the northern Mexican gartersnake, the Arizona Game
and Fish Department continues as a strong partner in research and
survey efforts that further our understanding of current populations
within Arizona. They continue to assist with future conservation
efforts and the establishment of long-term conservation partnerships.
Gartersnakes are active, diurnal (daytime) foragers and humans
encounter gartersnake species in riparian areas used for recreational
purposes or for other reasons. These encounters can result in the
capture, injury, or death of the gartersnake due to the lay person's
fear or dislike of snakes (Rosen and Schwalbe 1988, p. 43; Ernst and
Zug 1996, p. 75; Green 1997, pp. 285-286; Nowak and Santana-Bendix
2002, p. 39). It is very difficult for the Arizona Game and Fish
Department or the New Mexico Department of Fish and Game to monitor or
even be aware of such forms of take. We believe that unregulated take
occurs, particularly in areas frequently visited by the public with
current populations of northern Mexican gartersnakes, such as at Page
Springs and Bubbling Ponds hatcheries and along Tonto Creek near the
town of Gisela. We are reasonably certain that the level of illegal
field collecting by the hobbyist community is low because gartersnakes
are relatively undesirable in amateur herpetological collections.
Neither the New Mexico Department of Game and Fish, nor the Arizona
Game and Fish Department have specified or mandated recovery goals for
the northern Mexican gartersnake, nor has either State developed a
conservation agreement or plan for this species.
Throughout Mexico, the Mexican gartersnake is listed at the species
level of its taxonomy as ``Amenazadas,'' or Threatened, by the
Secretaria de Medio Ambiente y Recursos Naturales (SEMARNAT) (SEDESOL
2001). Threatened species are ``those species, or populations of the
same, likely to be in danger of disappearing in a short or medium
timeframe, if the factors that negatively impact their viability, cause
the deterioration or modification of their habitat or directly diminish
the size of their populations continue to operate'' (SEDESOL 2001 (NOM-
059-ECOL-2001), p. 4). This designation prohibits taking of the
species, unless specifically permitted, as well as prohibits any
activity that intentionally destroys or adversely modifies its habitat
(SEDESOL 2000 (LGVS) and 2001 (NOM-059-ECOL-2001)). Additionally, in
1988, the Mexican Government passed a regulation that is similar to the
National Environmental Policy Act of the United States (42 U.S.C. 4321
et seq.). This Mexican regulation requires an environmental assessment
of private or government actions that may affect wildlife or their
habitat (SEDESOL 1988 (LGEEPA)).
The Mexican Federal agency known as the Instituto Nacional de
Ecolog[iacute]a (INE) is responsible for the analysis of the status and
threats that pertain to species that are proposed for listing in the
Norma Oficial Mexicana NOM-059 (the Mexican equivalent to a threatened
and endangered species list), and if appropriate, the nomination of
species to the list. INE is generally considered the Mexican
counterpart to the United States' Fish and Wildlife Service. INE
developed the Method of Evaluation of the Risk of Extinction of the
Wild Species in Mexico (MER), which unifies the criteria of decisions
on the categories of risk and permits the use of specific information
fundamental to listing decisions. The MER is based on four independent,
quantitative criteria: (1) Size of the distribution of the taxon in
Mexico; (2) state (quality) of the habitat with respect to natural
development of the taxon; (3) intrinsic biological vulnerability of the
taxon; and (4) impacts of human activity on the taxon. INE began to use
the MER in 2006; therefore, all species previously listed in the NOM-
059 were based solely on expert review and opinion in many cases.
Specifically, until 2006, the listing process under INE consisted of a
panel of scientific experts who convened as necessary for the purpose
of defining and assessing the status and threats that affect Mexico's
native species that are considered to be at risk and applying those
factors to the definitions of the various listing categories. In 1994,
when the Mexican gartersnake was placed on the NOM-059 (SEDESOL 1994
(NOM-059-ECOL-1994), p. 46) as a threatened species, the decision was
made by a panel of scientific experts.
Although the Mexican gartersnake is considered a federally
threatened species in Mexico, no recovery plan or other conservation
planning occurs because of this status. Enforcement of the regulation
protecting the gartersnake is sporadic, based on available resources
and location. Based upon the information on the status of the species
and the historic and continuing threats to its habitat in Mexico, our
analysis concludes that protections afforded to the northern Mexican
gartersnake may not be adequate to preclude the continued decline of
this species throughout its range.
Ortega-Huerta and Kral (2007, p. 1) found that land legislation
within Mexico has changed considerably over recent years to integrate
free market policies into local agricultural production methods. This
may result in the loss of land management practices that protect the
natural environment. In 1992, the Mexican Government made a
constitutional amendment ending the Ejido's special legal status and
permitting the sale of collectively controlled lands (Ortega-Huerta and
Kral 2007, p. 2). An Ejido is an
[[Page 71816]]
amalgamation of various types of ownership of a particular piece of
land, e.g., state, cooperative, communal, and private. Ejidos are
generally managed in traditional means, which generally have less of an
impact to the environment compared to more modern free market uses,
resulting in higher levels of biodiversity (Ortega-Huerta and Kral
2007, p. 2; Randall 1996, pp. 218-220; Kiernan 2000, pp. 13-23). The
loss of regulation that prevented the division and sale of collectively
controlled lands in Mexico is likely to reduce the protection of intact
northern Mexican gartersnake habitat.
Existing water laws in Arizona, New Mexico, and Mexico are
inadequate to protect wildlife. The presence of water is a primary
habitat constituent for the northern Mexican gartersnake. Gelt (2008,
pp. 1-12) highlighted the fact that, because the existing water laws
are so old, they reflect a legislative interpretation of the resource
that is not consistent with what we know today; yet the laws have never
been updated or amended to account for this discrepancy. For example,
over 100 years ago when Arizona's water laws were written, the
important connection between groundwater and surface water was not
known (Gelt 2008, pp. 1-12). Gelt (2008, pp. 8-9) suggested that
preserving stream flows and riparian areas may be better accomplished
by curtailing surface water uses rather than ground water uses, and
that the prior appropriation doctrine (appropriation of water rights
based upon the water law concept of ``first in use, first in rights'')
may be outdated and impractical for arid areas like Arizona.
The majority of current populations of northern Mexican gartersnake
in the United States occur on lands managed by the U.S. Bureau of Land
Management and U.S. Forest Service. Although both agencies have
riparian protection goals, neither agency has specific management plans
for the northern Mexican gartersnake. The U.S. Bureau of Land
Management considers the northern Mexican gartersnake as a ``Special
Status Species,'' and agency biologists actively attempt to identify
gartersnakes observed incidentally during fieldwork for their records
(Young 2005). Otherwise, no specific protection or land-management
consideration is afforded to the species on Bureau of Land Management
lands.
The U.S. Forest Service does not include northern Mexican
gartersnake on their Management Indicator Species List, but it is
included on the Regional Forester's Sensitive Species List. This means
that northern Mexican gartersnakes are considered in land management
decisions. Individual U.S. Forest Service biologists who work within
the range of the northern Mexican gartersnake may opportunistically
gather data for their records on gartersnakes observed incidentally in
the field, although it is not required.
Activities that could adversely affect northern Mexican
gartersnakes and their habitat continue to occur throughout their
current distribution on National Forest lands. Clary and Webster (1989,
p. 1) stated that ``* * * most riparian grazing results suggest that
the specific grazing system used is not of dominant importance, but
good management is--with control of use in the riparian area a key
item.'' Due to ongoing constraints in funding, staff levels, and time
and regulatory compliance pertaining to monitoring and reporting duties
tied to land management, proactive measures continue to be limited.
These factors affect a land manager's ability to employ adaptive
management procedures when effects to sensitive species or their
habitat could be occurring at levels greater than anticipated in
regulatory compliance mechanisms, such as in section 7 consultation
under the Act for listed species that may co-occur with the northern
Mexican gartersnake in an area. In other words, and due to the existing
regulatory framework, some land managers may not have the flexibility
required to adopt adaptive management where necessary to adequately
account for adverse effects of projects on public lands.
Riparian communities are complex and recognized as unique in the
southwestern United States but are highly sensitive to many human-
caused land uses, as evidenced by the comparatively high number of
federally listed riparian or aquatic species. Four primary prey species
for the northern Mexican gartersnake, the Chiricahua leopard frog, Gila
topminnow, Gila chub, and roundtail chub, are federally listed or were
petitioned for listing. Other listed or proposed riparian species or
their proposed or designated critical habitat overlap the current or
historical distribution of the northern Mexican gartersnake. Despite
secondary protections that may be afforded to the northern Mexican
gartersnake from federally listed species or their critical habitat,
riparian and aquatic communities continue to be adversely impacted for
reasons previously discussed, contributing to the declining status of
the northern Mexican gartersnake throughout its range in the United
States.
Summary of Factor D. Existing regulations within the range of the
northern Mexican gartersnake address the direct take of individuals
without a permit, and unpermitted take by recreationists or collectors
is not thought to be at levels that impact the subspecies. Arizona and
New Mexico statutes do not provide protection of habitat and
ecosystems. Legislation in Mexico prohibits intentional destruction or
modification of the snake's habitat, but neither that or prohibitions
on take appear to be adequate to preclude the continued decline of the
subspecies. Currently, there are no regulatory mechanisms in place that
specifically target the conservation of northern Mexican gartersnake
habitat. Legislation in Mexico has removed regulation of ejidos that
promoted intact protection of important riparian and aquatic habitats.
Regulations protecting the quantity and quality of water in riparian
and aquatic communities are inadequate to protect water resources for
the northern Mexican gartersnake, particularly in the face of the
significant population growth expected within the historical range of
the snake discussed under Factor A.
E. Other Natural or Manmade Factors Affecting Its Continued Existence
Competition With Other Species Within the Same Genus. Marcy's
checkered gartersnake (Thamnophis marcianus marcianus) may impact the
future conservation of the northern Mexican gartersnake in southern
Arizona, although supporting data are limited. Marcy's checkered
gartersnake is a semi-terrestrial species that is able to co-exist to
some degree with riparian and aquatic nonnative predators. This is
largely due to its ability to forage in more terrestrial habitats,
specifically in the juvenile size classes (Rosen and Schwalbe 1988, p.
31; Rosen et al. 2001, pp. 9-10). In every age class, the northern
Mexican gartersnake forages in aquatic habitats where bullfrogs,
nonnative sportfish, and crayfish also occur, which increases not only
the encounter rate between the species but also the juvenile mortality
rate of the northern Mexican gartersnake. As northern Mexican
gartersnake numbers decline within a population, space becomes
available for occupation by checkered gartersnakes. Marcy's checkered
gartersnake subsequently affects the maximum number of northern Mexican
gartersnakes that an area can maintain based upon available resources
and could potentially accelerate the decline of or preclude reoccupancy
by the northern Mexican gartersnake (Rosen and Schwalbe 1988, p. 31).
Rosen et al. (2001, pp. 9-10) documented the occurrence of Marcy's
[[Page 71817]]
checkered gartersnakes out-competing and replacing northern Mexican
gartersnakes at the San Bernardino National Refuge and surrounding
habitats of the Black Draw. They suspected that the drought from the
late 1980s through the late 1990s played a role in the degree of
competition for aquatic resources, provided an advantage to the more
versatile Marcy's checkered gartersnake, and expedited the decline of
the northern Mexican gartersnake. The competition between these two
species, in combination with other factors described above that have
adversely affected the northern Mexican gartersnake prey base and the
suitability of occupied and formerly occupied habitat, may be
contributing to the decline of this species.
Current and Future Effects from Changes in Climatic Patterns and
Drought. Seagar et al. (2007, pp. 1181-1184) analyzed 19 different
computer models of differing variables to estimate the future
climatology of the southwestern United States and northern Mexico in
response to predictions of changing climatic patterns. All but 1 of the
19 models predicted a drying trend within the Southwest; one predicted
a trend toward a wetter climate (Seager et al. 2007, p. 1181). A total
of 49 projections were created using the 19 models and all but 3
predicted a shift to increasing aridity (dryness) in the Southwest as
early as 2021-2040 (Seager, et al. 2007, p. 1181). The northern Mexican
gartersnake and its prey base depend on permanent or nearly permanent
water for survival. A large percentage of habitat within the current
distribution of the northern Mexican gartersnake is predicted to be at
risk of becoming more arid (Seager et al. 2007, pp. 1183-1184), which
has severe implications to the integrity of aquatic and riparian
ecosystems and the water that supports them. Potential drought
associated with changing climatic patterns may not only adversely
affect habitat of the northern Mexican gartersnake, but also its prey.
Amphibians may be among the first vertebrates to exhibit broad-scale
changes in response to changes in global climatic patters due to their
sensitivity to changes in moisture and temperature (Reaser and
Blaustein 2005, p. 61). Changes in temperature and moisture, combined
with the ongoing threat to amphibians from the persistence of Bd may
cause prey species to experience increased physiological stress and
decreased immune system function, possibly leading to disease outbreaks
(Carey and Alexander 2003, pp. 111-121; Pounds et al. 2006, pp. 161-
167).
Changes to climatic patterns are predicted to have implications for
the effect of, and management for, nonnative species within the
distribution of the northern Mexican gartersnake. Based upon climate
change models, nonnative species biology, and ecological observations,
Rahel et al. (2008, p. 551) conclude that climate change could foster
the expansion of nonnative aquatic species into new areas, magnify the
effects of existing aquatic nonnative species where they currently
occur, increase nonnative predation rates, and heighten the virulence
of disease outbreaks in North America. Many of the nonnative species
have similar, basic ecological requirements as our native species, such
as the need for permanent or nearly permanent water. Therefore, it is
likely that effects from changes to climatic patterns (such as a trend
towards a more arid environment) that negatively affect nonnative
species such as bullfrogs and nonnative fish may also negatively affect
native prey species for the northern Mexican gartersnake.
Changes to climatic patterns may warm water temperatures, alter
stream flow events, and may increase demand for water storage and
conveyance systems (Rahel and Olden 2008, pp. 521-522). Warmer water
temperatures across temperate regions are predicted to expand the
distribution of existing aquatic nonnative species by providing 31
percent more suitable habitat for aquatic nonnative species, which are
often tropical in origin and adaptable to warmer water temperatures.
This conclusion is based upon studies that compared the thermal
tolerances of 57 fish species with predictions made from climate change
temperature models (Mohseni et al. 2003, p. 389). Eaton and Scheller
(1996, p. 1,111) reported that while several cold-water fish species in
North America are expected to have reductions in their distribution
from effects of climate change, several warmwater fish species are
expected to increase their distribution. In the southwestern United
States, this situation may occur where the quantity of water is
sufficient to sustain effects of potential prolonged drought conditions
but where water temperature may warm to a level found suitable to
harmful nonnative species that were previously physiologically
precluded from occupation of these areas. Species that are particularly
harmful to northern Mexican gartersnake populations such as the green
sunfish, channel catfish, largemouth bass, and bluegill are expected to
increase their distribution by 7.4 percent, 25.2 percent, 30.4 percent,
and 33.3 percent, respectively (Eaton and Scheller 1996, p. 1,111).
Rahel and Olden (2008, p. 526) expect that increases in water
temperatures in drier climates such as the southwestern United States
will result in periods of prolonged low flows and stream drying. These
effects from changing climatic conditions may have profound effects on
the amount, permanency, and quality of habitat for the northern Mexican
gartersnake and its prey base. Warmwater nonnative species such as red
shiner, common carp, mosquitofish, and largemouth bass are expected to
benefit from prolonged periods of low flow (Rahel and Olden 2008, p.
527).
Data specific to changing climatic patterns in Mexico, other than
the Seager et al. (2007) climate change modeling, are limited. However,
because the predictive climate models include northern Mexico, we
assume that the changes predicted for the southwestern United States
will likely be similar.
The effects of the water withdrawals discussed above may be
exacerbated by the current, long-term drought facing the arid
southwestern United States. Philips and Thomas (2005, pp. 1-4) provided
streamflow records that indicate that the drought Arizona experienced
between 1999 and 2004 was the worst drought since the early 1940s and
possibly earlier. The Arizona Drought Preparedness Plan Monitoring
Technical Committee (ADPPMTC) (2008) assessed Arizona's drought status
through June 2008 in watersheds where the northern Mexican gartersnake
occurs or historically occurred. They found that the Verde, Agua Fria,
San Pedro, Santa Cruz, and Whitewater Draw watersheds continue to
experience moderate drought (ADPPMTC 2008). Whereas the Salt, Upper
Gila, Lower Gila, and Lower Colorado watersheds were abnormally dry
(ADPPMTC 2008). Ongoing drought conditions have depleted recharge of
aquifers and decreased baseflows in the region. While drought periods
have been relatively numerous in the arid Southwest from the mid-1800s
to the present, the effects of human-caused impacts on riparian and
aquatic communities have compromised the ability of these communities
to function under the additional stress of prolonged drought
conditions. Holycross et al. (2006, pp. 52-53) recently documented the
effects of drought on northern Mexican gartersnake habitat in the
vicinity of Arcosante along the Agua Fria River and at Big Bug Creek.
The streams were completely dry and therefore unsuitable northern
Mexican gartersnake habitats.
[[Page 71818]]
Summary of Factor E. It is unlikely that competition with other
gartersnakes will be a significant cause of decline in northern Mexican
gartersnake populations in comparison to other threats we have
discussed. All but one model evaluating changing climatic patterns for
the southwestern United States and northern Mexico predict a drying
trend for the region (Seagar et al. 2007, pp. 1181-1184). We
acknowledge that drought and the loss of surface water in riparian and
aquatic communities are related to changing climatic conditions (Seagar
et al. 2007, pp. 1181-1184). The extent to which changing climate
patterns will affect the northern Mexican gartersnake is not known with
certainty at this time. However, threats to the northern Mexican
gartersnake indentified in Factors A and C will likely be exacerbated
by changes to climatic patterns in the southwestern United States due
to resulting increasing drought and reduction of surface waters if the
predicted patterns are realized. Data specific to changes in climatic
patterns in Mexico are limited, but because the models for the
southwestern United States included northern Mexico, we believe that
the effect from the changing climatic patterns will exacerbate threats
due to Factors A and C in that country as well.
Foreseeable Future
When determining whether a species is in danger of extinction
throughout all or a significant portion of its range, or is likely to
become in danger of extinction in the foreseeable future, we must
identify that foreseeable future for the species. The Act does not
specifically define the term ``foreseeable future.'' In discussing the
concept of foreseeable future for the northern Mexican gartersnake, we
considered (1) the biological and demographic characteristics of the
species (such as generation times, population genetics, trends in age-
class distribution within current populations, etc.); (2) our ability
to predict or extrapolate the effects of threats facing the species
into the future; and (3) the relative permanency or irreversibility of
these threats. Of the threats to the northern Mexican gartersnake and
its prey base that have been discussed above in our analysis of the
threats, we believe the threat of nonnative species presents the most
widespread, imminent, and serious threat to the long-term
sustainability of this subspecies. Therefore, we concentrate primarily
upon this threat to the northern Mexican gartersnake in our analysis of
the subspecies' viability into the foreseeable future. Because our
knowledge of the threats to and status of the northern Mexican
gartersnake in Mexico is not as robust as that for the United States,
our analysis focuses on the United States and presumes (1) similar
human-caused threats occur to the subspecies' habitat in areas in
proximity to human population centers in Mexico, and (2) a time-lagged
effect, with respect to nonnative species invasions, within more remote
habitat in Mexico as postulated in Unmack and Fagan (2004, pp. 233-
243).
Based on museum records found in Holycross et al. (2006, Appendix
F), we expect the northern Mexican gartersnake retained its entire
historic distribution within the United States through the 1920s and
likely into the 1930s. Activities such as the construction of dams and
water diversions that occurred throughout the early to mid-1900s for
agriculture and regional economic development likely eliminated surface
flow throughout stream reaches with occupied habitat, which led to
subsequent and widespread extirpations of northern Mexican gartersnake
populations in areas such as the lower Gila and Salt rivers in Arizona.
After the period of dam construction and the subsequent creation of
reservoirs, widespread nonnative fish stocking efforts ensued
throughout Arizona beginning during the mid 1900's. In the Verde River
system alone, Rinne et al. (1998, p. 3) estimated that over 5,300
independent stocking actions occurred that involved 12 different
species of nonnative fish species since the 1930s and 1940s. If we
extrapolate that effort over the same timeframe for other historically
occupied, larger-order systems known as recreational fisheries such as
the Salt, upper Gila, Colorado, Santa Cruz, Agua Fria, and San Pedro
rivers, Tonto and Oak creeks, and other tributaries with significant
flow throughout central and southern Arizona, in addition to the other
private stockings of stock tanks and other isolated habitat, the
magnitude of the nonnative species invasion over this timeframe becomes
clear. Subsequent to these efforts, but to a lesser extent, the spread
of bullfrogs and crayfish, both purposefully and incidentally,
commenced during the 1970s and 1980s (Tellman 2002, p. 43). We estimate
that near 100 percent of the habitat that historically supported
northern Mexican gartersnakes has been invaded over-time, either
purposefully or indirectly through dispersal, by nonnative species
whether they be nonnative fish, bullfrogs, or crayfish. The effects
from this influx of nonnative species throughout the American Southwest
resulted in significant declines in native fish and ranid frog
distribution and abundance, and the subsequent listing of 19 of
Arizona's 31 native fish species throughout the last 35 years (see
discussion under ``Declines in the Northern Mexican Gartersnake Native
Fish Prey Base'' within Listing Factor C). The decline of native fish
species that depend on native riparian and aquatic systems provides
evidence of overall impacts to the affected biotic communities. These
effects were discussed in detail in Factor A and Factor C above.
In response to the impacts to the northern Mexican gartersnake and
its native prey base discussed above and in our analysis of threats,
the distribution of northern Mexican gartersnake has been reduced to
approximately 10 percent of its historic range within the United States
over the last 80 years. However, because of the sensitivity of the
northern Mexican gartersnake to community-wide effects from nonnative
species, we believe the most significant period of declines and
subsequent extirpations of entire populations likely coincided with the
proliferation of nonnative species beginning in the 1940s and 1950s,
most notably with the widespread introduction and expansion of
sportfish such as largemouth bass, green sunfish, and channel and
flathead catfish. In addition, further declines and extirpations likely
resulted from systematic bullfrog introductions, beginning in the 1970s
and early 1980s, caused by the bullfrog's natural capacity to disperse
and its predation behavior on the northern Mexican gartersnake and
associated prey base. In several areas where northern Mexican
gartersnakes remain in the United States, we have observed skewed age-
class distributions within populations that favor large-bodied, older
individuals with significantly less newborns and juveniles (Holm and
Lowe 1995, pp. 33-34; Holycross et al. 2006, pp. 41-44; Wallace et al.
2008, pp. 243-244). These trends are particularly apparent in areas
where habitat remains structurally intact, but where nonnative species
maintain stable populations.
The observed effects of nonnative species on age-class distribution
and recruitment are an important influence on the maintenance of
current populations to be considered in our evaluation of the
foreseeable future for this species. We were not able to locate any
quantitative studies on longevity of the northern Mexican gartersnake
in the wild, or on gartersnakes in general. However, Bowler (1975)
recorded longevity of amphibians and reptiles in captivity that
included several species
[[Page 71819]]
within the genus Thamnophis. Lifespans of six different gartersnake
species ranged from 2 to 10 years (Bowler 1975). These data are old,
however, and innovations in the captive care of specimens in the
subsequent three decades have improved our knowledge of captive
husbandry for these species, allowing longer lifespans in captivity.
Simply knowing that individuals of a certain species are capable of
living a certain number of years under ideal captive conditions means
that longevity in the wild might be longer than suspected, although
usually shorter than in captivity. Ernst and Zug (1996, p. 39) provide
one record on wild longevity in the common gartersnake (Thamnophis
sirtalis) as nine years. It is reasonable to conclude that the northern
Mexican gartersnake, a similarly sized snake of the same genus, may
have similar longevity in the wild.
The average age of sexual maturity is 2.5 years for female northern
Mexican gartersnakes, and 2 years for males. Females may only breed
once every 2 years (Rosen and Schwalbe 1988, pp. 16-17). Considering
these timeframes, a female northern Mexican gartersnake might reproduce
up to three times during a maximum lifespan in the wild. We are aware
of no studies on the survivorship of northern Mexican gartersnakes in
the wild. However, Jayne and Bennett (1990, pp. 1209-1221) studied
survivorship within a population of common gartersnakes, a similar
species, and found that, in two groups of similarly aged snakes within
that population, survivorship during the first year following birth was
29 percent and 43 percent in this 2-year study, although we are unaware
of the presence, type, or extent of threats that may have influenced
survivorship. Only 16 percent of one group survived into their second
year, while 50 percent of the second group survived into their second
year (Jayne and Bennett 1990, pp. 1209-1221). Jayne and Bennett (1990,
pp. 1209-1221) calculated that 15 percent of individuals live to be
older than 2 years. Adult survival rates in common gartersnakes appears
to be quite variable, however. In Manitoba, adult year-to-year
survivorship was calculated at 34 percent and at 67 percent in the
Northwest Territories (Larsen and Gregory 1989, pp. 84-85; Larsen et
al. 1993, pp. 338-342). Based on demographic studies on the common
gartersnake and making a conservative estimate on survivorship and
fecundity rates without consideration of the presence or degree of
threats, it is reasonable to presume that, on average, two individual
northern Mexican gartersnakes from each litter may reach reproductive
age. Whether or not these individuals find a mate and successfully
reproduce depends upon the population density and the degree of threats
that may be acting on a given population.
In Table 4 of Holycross et al. (2006, p. 64), capture rates of
northern Mexican gartersnakes during surveys in 2004 and 2005 along the
Mogollon Rim of Arizona were compared to those from a previous study,
Rosen and Schwalbe (1988, Appendix I). In total, capture rates in nine
different stream reaches surveyed by both sets of investigators were
compared. Rosen and Schwalbe (1988, Appendix I) spent 128 person-search
hours to capture a total of 10 individuals at six of the nine (66
percent) stream reaches. Holycross et al. (2006, p. 64) spent 142
person-search hours [11 percent more than Rosen and Schwalbe (1988,
Appendix I)] and found six total individuals in only two stream reaches
of the nine (22 percent) that were comparably surveyed. These data
indicate that Holycross et al. (2006, p. 64) found northern Mexican
gartersnakes at 66 percent fewer locations than did Rosen and Schwalbe
(1988, Appendix I) which indicate potential population extirpations in
two-thirds of populations during that 17-year time period. The averaged
number of person-search hours per capture was 12.8 hours in 1988 (Rosen
and Schwalbe 1988, Appendix I), but approximately twice that (23.6
person-search hours) in 2004-2005 (Holycross et al. 2006, p. 64).
Today, there remain three areas in the United States where the
northern Mexican gartersnake is most reliably found, the Upper Santa
Cruz River in the San Rafael Valley of south-central Arizona, Tonto
Creek from the vicinity of Gisela downstream to Roosevelt Lake, and the
Page Springs/Bubbling Ponds hatchery complex along Oak Creek slightly
upstream of its confluence with the Verde River. These populations are
geographically disjunct, genetically isolated from one-another, and
lack significant, nearby source populations to serve as a natural
source of individuals for recolonization should any one of them become
extirpated. Therefore, these populations remain highly vulnerable to
the effects of the threats discussed in detail in Factors A-E above,
and to stochastic events not previously anticipated. If we extrapolate
the last 20 years of population trends documented in the previous
paragraph, we anticipate that in approximately 15-20 years, these
remaining, currently reliable populations may become extirpated should
current trends persist into the future. This is not to say that the
northern Mexican gartersnake, in its entirety, will be extirpated from
the United States during this time frame because it would remain
plausible that extremely low-density populations of a few individuals
may persist in other areas past this time frame.
Considering the above discussion on (1) reproduction biology,
observed trends in population demographics, and age-class survivorship;
(2) the time periods that correlated to the onset of the most
significant threats to the species and number of years it has taken for
a 90 percent reduction of the distribution of the subspecies in the
United States; (3) the relative isolation and disjunct nature of
current populations and their inability to serve as a basis for genetic
exchange; (4) comparative analysis between comprehensive survey results
spread over 17 years over a significant portion of the subspecies'
historical distribution in the United States and subsequent
extrapolations for remaining populations; and (5) the future potential
for threats most detrimental to the long-term viability of the
subspecies in the United States (such as the continued proliferation of
nonnative species), we anticipate that northern Mexican gartersnake may
be predominantly extirpated from the U.S. within 25 years. We base this
estimate largely upon our most current observations of population
trends and their response to threats posed by nonnative species, as
discussed above.
We do not expect that current policies on native fish restoration
and recovery will change. These policies now focus activities on
replacing fisheries which contain nonnative species with wholly native
fisheries in stream types that are generally not suitable for northern
Mexican gartersnakes, rather than mainstem rivers of lower gradient
which provide preferred habitat for the northern Mexican gartersnake.
We have also discussed in Factor C above the widespread influence of
crayfish and bullfrogs on riparian and aquatic communities and the
significant difficulty of removing them from areas once they have
become established. As discussed in Factor E, climate change and
subsequent drought will likely exacerbate the threats to the northern
Mexican gartersnake related to habitat and prey base. Thus, the
foreseeable future for the northern Mexican gartersnake in the U.S. is
25 years to 2033.
With respect to the species' foreseeable future throughout its
distribution in Mexico, threats to the northern Mexican gartersnake
from human-related activities are most likely
[[Page 71820]]
in areas adjacent to human population centers, and these threats affect
the subspecies to a similar degree as observed in the United States. We
conclude that changes to climatic patterns will affect northern Mexican
gartersnake habitat in similar ways in the more northern latitudes of
Mexico as has been anticipated for the southwestern United States.
Therefore, we estimate the foreseeable future in populated areas of
Mexico within the range of the subspecies to be 25 years.
Unmack and Fagan (2004, p. 233) hypothesized that a time-lagged
effect is occurring in portions of Mexico with respect to nonnative
species invasions, due primarily to the remoteness of some areas.
However, there is widespread consensus that it is inevitable that
nonnative species will continue to invade new habitats throughout
Mexico, leading to further declines and extirpations of the northern
Mexican gartersnake and its prey species in Mexico (Conant 1974, pp.
471, 487-489; Contreras Balderas and Lozano 1994, pp. 383-384; Miller
et al. 2005, pp. 60-61; Abarca 2006; Luja and Rodr[iacute]guez-Estrella
2008, pp. 17-22). Consequently, for the more remote areas of Mexico,
the foreseeable future may be beyond 2033, but we are not confident
estimating how far beyond.
Significant Portion of the Range Analysis
As required by the Act, we considered the five potential threat
factors to assess whether the northern Mexican gartersnake is
threatened or endangered throughout all or a significant portion of its
range. When considering the listing status of the species, the first
step in the analysis is to determine whether the species is in danger
of extinction throughout all of its range. If this is the case, then we
list the species in its entirety. For instance, if the threats to a
species are directly acting on only a portion of its range, but they
are at such a large scale that they place the entire species in danger
of extinction, we would list the entire species.
We next consider whether any significant portion of the northern
Mexican gartersnake range meets the definition of endangered or is
likely to become endangered in the foreseeable future (threatened). On
March 16, 2007, a formal opinion was issued by the Solicitor of the
Department of the Interior, ``The Meaning of `In Danger of Extinction
Throughout All or a Significant Portion of Its Range' '' (USDOI 2007,
pp. 1-36). A portion of a species' range is significant if it is part
of the current range of the species and is important to the
conservation of the species because it contributes meaningfully to the
representation, resiliency, or redundancy of the species. The
contribution must be at a level such that its loss would result in a
decrease in the ability of the species to persist.
The first step in determining whether a species is threatened or
endangered in a significant portion of its range is to identify any
portions of the range of the species that warrant further
consideration. The range of a species can theoretically be divided into
portions in an infinite number of ways. To identify portions that
warrant further consideration, we determine whether there is
substantial information indicating that (1) the portions may be
significant, and (2) the species may be in danger of extinction there
or likely to become so within the foreseeable future. In practice, a
key part of this analysis is whether the threats are geographically
concentrated in some way. If the threats to the species are essentially
uniform throughout its range, no portion is likely to warrant further
consideration. Moreover, if any concentration of threats applies only
to portions of the range that are unimportant to the conservation of
the species, such portions will not warrant further consideration.
If we identify any portions that warrant further consideration, we
then determine whether the species is threatened or endangered in any
significant portion. If we determine that a portion of the range is not
significant, we do not determine whether the species is threatened or
endangered there.
The terms ``resiliency,'' ``redundancy,'' and ``representation''
are intended to be indicators of the conservation value of portions of
the range. Resiliency of a species allows it to recover from periodic
disturbances. A species will likely be more resilient if large
populations exist in high-quality habitat that is distributed
throughout its range in a way that captures the environmental
variability available. A portion of the range of a species may make a
meaningful contribution to the resiliency of the species if the area is
relatively large and contains particularly high-quality habitat, or if
its location or characteristics make it less susceptible to certain
threats than other portions of the range. When evaluating whether or
how a portion of the range contributes to resiliency of the species, we
evaluate the historical value of the portion and how frequently the
portion is used by the species, if possible. The range portion may
contribute to resiliency for other reasons; for instance, it may
contain an important concentration of certain types of habitat that are
necessary for the species to carry out its life-history functions, such
as breeding, feeding, migration, dispersal, or wintering.
Redundancy of populations may be needed to provide a margin of
safety for the species to withstand catastrophic events. This concept
does not mean that any portion that provides redundancy is per se a
significant portion of the range of a species. The idea is to conserve
enough areas of the range so that random perturbations in the system
only act on a few populations. Therefore, we examine each area based on
whether that area provides an increment of redundancy that is important
to the conservation of the species.
Adequate representation ensures that the species' adaptive
capabilities are conserved. Specifically, we evaluate a range portion
to see how it contributes to the genetic diversity of the species. The
loss of genetically based diversity may substantially reduce the
ability of the species to respond and adapt to future environmental
changes. A peripheral population may contribute meaningfully to
representation if there is evidence that it provides genetic diversity
due to its location on the margin of the species' habitat requirements.
Based upon factors that contribute to our analysis of whether a
species or subspecies is ``In Danger of Extinction Throughout All or a
Significant Portion of Its Range,'' and in consideration of the status
of and threats to the northern Mexican gartersnake discussed
previously, we find that significant threats to the continued existence
of the northern Mexican gartersnake occur throughout all of its range
in the United States and Mexico. Therefore, it is not necessary to
conduct further analysis with respect to the significance of any
portion of its range at this time.
Finding
We have carefully examined the best scientific and commercial
information available regarding the past, present, and future threats
faced by the northern Mexican gartersnake. We reviewed the petition,
information available in our files, other published and unpublished
information submitted to us during the public comment periods following
our 90-day and previous 12-month petition findings and consulted with
recognized northern Mexican gartersnake experts and other Federal,
State, Tribal, and Mexican resource agencies. On the basis of the best
scientific and commercial information available, we find that listing
of the northern Mexican
[[Page 71821]]
gartersnake as threatened or endangered throughout its range in the
United States and Mexico, based on its rangewide status, is warranted,
due to the present or threatened destruction, modification or
curtailment of its habitat; predation; and the inadequacy of existing
regulatory mechanisms. 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 recognize there have been remarkable declines in the
distribution and abundance of the northern Mexican gartersnake within
its distribution in the United States, which are primarily attributed
to individual and community interactions with nonnative species that
occur in every single locality where northern Mexican gartersnakes have
been documented. We identified the ecological mechanisms for which
nonnative interactions occur to include: (1) Direct predation on
northern Mexican gartersnakes by nonnative species; and (2) the effects
of a diminished prey base via nonnative species preying upon and
competing with native prey species as documented in a large body of
scientific research, which is cited and analyzed in our discussion of
threats under each of the listing factors.
Throughout the range of the northern Mexican gartersnake,
literature documents the cause and effect relationship of modification
of the food chains within native riparian and aquatic communities. The
substantial decline of primary native prey species, such as leopard
frogs and native fish, has contributed significantly to the decline of
a primary predator, the northern Mexican gartersnake. In this respect,
the northern Mexican gartersnake is considered an indicator species, or
a species that can be used to gauge the condition of a particular
habitat, community, or ecosystem. The synergistic effect of nonnative
species both reducing the prey base of, and directly preying upon,
northern Mexican gartersnakes has placed significant pressure upon the
viability and sustainability of current northern Mexican gartersnake
populations and has led to significant fragmentation and risks to the
continued viability of current populations. The evolutionary biology of
the northern Mexican gartersnake, much like that of native fish and
leopard frogs, has left the species without adaptation to and
defenseless against the effect of nonnative species invasions.
The decline of the northern Mexican gartersnake has been
exacerbated by historical and ongoing threats to its habitat in the
United States. The threats identified and discussed above in detail
under Factor A include: (1) The modification and loss of ecologically
valuable riparian and aquatic communities; (2) urban and rural
development; (3) road construction, use, and maintenance; (4) human
population growth; (5) groundwater pumping, surface water diversions,
and flood; (6) improper livestock grazing; (7) catastrophic wildfire
and wildfire in non-fire adapted communities; and (8) undocumented
immigration and international border enforcement and management. In
addition, disease and parasitism, climate change, and drought may pose
threats to the northern Mexican gartersnake and its prey base.
As a result of our assessment, we find that certain land use
activities, such as road construction and use, improper livestock
grazing, undocumented immigration and associated international border
enforcement and management activities, and some types of development,
pose a more significant risk to highly fragmented, low-density
populations of northern Mexican gartersnakes, particularly in the
presence of nonnative species. We know of no current population of
northern Mexican gartersnakes in the United States that does not occur
in the presence of nonnative species.
In this finding, we have emphasized the importance of the
protection of the ecosystems upon which the northern Mexican
gartersnake depends, and documented the status of riparian and aquatic
communities in the southwestern United States and much of Mexico.
Evidence of the current precarious status of native riparian and
aquatic ecosystems in the southwestern United States is the proportion
of riparian or aquatic obligate species that are either federally
listed under the Act or candidates for listing. In Arizona, there is a
total of 73 species that meet these criteria. Of these 73 species, 38
(52 percent) are riparian or aquatic. Of the 45 vertebrate species that
are either federally listed or candidates for listing in Arizona, 30
(67 percent) have riparian or aquatic life histories, and 19 (42
percent) are potential northern Mexican gartersnake prey species in
larval, juvenile, or adult forms, based on overlapping historical
distributions. These data suggest that the riparian and aquatic
ecosystems in Arizona, upon which the northern Mexican gartersnake
depends, cannot currently support many of the species that rely upon
them.
In making this finding, we acknowledge that the Mexican Government
has found the Mexican gartersnake to be in danger of disappearance in
the short-or medium-term future in their country from the destruction
and modification of its habitat or from the effects of shrinking
population sizes, or both, and has, therefore, listed the species as
Threatened, under the listing authority of SEMARNAT (SEDESOL 2001). We
have provided an assessment of the status of the northern Mexican
gartersnake and its habitat in Mexico, but we also rely on the
assessment of the species made by the Mexican Government in listing the
entity as Threatened. The available literature supports the assessment
of the species made by the Mexican Government, which indicates that
nonnative species and habitat modification and loss are adversely
affecting the status of northern Mexican gartersnakes in Mexico.
Additionally, land uses, such as urbanization and development,
improper livestock grazing, water diversions and groundwater pumping,
and impoundments, have resulted in losses of vegetative cover,
deforestation, erosion, and pollution that have modified or destroyed
historical northern Mexican gartersnake habitat in Mexico.
Collectively, the impacts of traditional rural land management
practices and growth of the economic sector, infrastructure, and
population growth are expected to continue into the future.
We have reviewed the available information to determine if the
existing and foreseeable threats pose an emergency. We have determined
that an emergency listing is not warranted for this subspecies at this
time because, within the current distribution of the subspecies in
Mexico, there are at least some populations of the northern Mexican
gartersnake that exist in relatively natural conditions that are
unlikely to change in the short-term. However, if at any time we
determine that emergency listing of the northern Mexican gartersnake is
warranted, we will initiate an emergency listing.
The Service adopted guidelines on September 21, 1983 (48 FR 43098)
to establish a rational system for allocating available appropriations
to the highest priority species when adding species to the Lists of
Endangered or Threatened Wildlife and Plants or reclassifying
threatened species to endangered status. The system places greatest
importance on the immediacy and magnitude of
[[Page 71822]]
threats, but also factors in the level of taxonomic distinctiveness by
assigning priority in descending order to monotypic genera, 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 northern
Mexican gartersnake a Listing Priority Number of 3, based on high
magnitude and immediacy of threats. One or more of the threats
discussed above is occurring in each known population in the United
States and throughout historically occupied habitats in Mexico. These
threats are ongoing and, in some cases (e.g., nonnative species),
considered irreversible. While we conclude that listing the northern
Mexican gartersnake is warranted, an immediate proposal to list this
species is precluded by other higher priority listing, which we address
below.
Preclusion and Expeditious Progress
Preclusion is a function of the listing priority of a species in
relation to the resources that are available and 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 proposed
listing regulation or whether promulgation of such a proposal is
warranted but 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
determinations on prior ``warranted but precluded'' petition findings
as required under section 4(b)(3)(C)(i) of the Act; 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. For example, during the past
several years, the cost (excluding publication costs) for preparing a
12-month finding, without a proposed rule, has ranged from
approximately $11,000 for one species with a restricted range and
involving a relatively uncomplicated analysis to $305,000 for another
species that is wide-ranging and involving a complex analysis.
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 which 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).
Recognizing that designation of critical habitat for species
already listed would consume most of the overall Listing Program
appropriation, Congress also put a critical habitat subcap in place in
FY 2002 and has retained it each subsequent year 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 FY 2007, we
were able to use some of the critical habitat subcap funds to fund
proposed listing determinations for high-priority candidate species;
however, in FY 2008 we were unable to do this due to our workload for
designating critical habitat.
Thus, 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. 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 also recognized that the availability of resources was the
key element in deciding whether, when making a 12-month petition
finding, we would prepare and issue a listing proposal or instead make
a ``warranted but precluded'' finding for a given species. The
Conference Report accompanying Public Law 97-304, which established the
current statutory deadlines and the warranted-but-precluded finding,
states (in a discussion on 90-day petition findings that by its own
terms also covers 12-month findings) that the deadlines 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.''
In FY 2008, expeditious progress is that amount of work that could
be achieved with $8,206,940, which is the amount of money that Congress
appropriated for the Listing Program (that is, the portion of the
Listing Program funding not related to critical habitat designations
for species that are already listed). Our process is to 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. The
$8,206,940 was used 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. The allocations for each specific listing
action are identified in the Service's FY 2008 Allocation Table (part
of our administrative record).
For FY 2009, on September 23, 2008 Congress passed a Continuing
Resolution to operate the Federal government at the FY 2008 level of
funding through March 6, 2009 (Pub. L.
[[Page 71823]]
110-329). Although we are currently developing the allocations for
specific listing actions that we will fund during FY 2009, we
anticipate funding work to comply with court orders and court-approved
settlement agreements, work on statutorily required petition findings,
final listing determinations for those species that were proposed for
listing with funds from FY 2008, and continued work on proposed listing
determinations for high-priority species.
In FY 2007, we had more than 120 species with an LPN of 2, based on
our September 21, 1983, guidance for assigning an LPN for each
candidate species (48 FR 43098). Using this guidance, we assign each
candidate an LPN of 1 to 12, depending on the magnitude of threats,
imminence of threats, and taxonomic status; the lower the LPN, 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 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, comprised a list 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 listing rules
for these 40 candidates, we are applying the ranking criteria to the
next group of candidates with LPN of 2 and 3 to determine the next set
of highest priority candidate species.
To be more efficient in our listing process, as we work on proposed
rules for these 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, available staff
resources are also a factor in determining high-priority species
provided with funding. Finally, proposed rules for reclassification of
threatened species to endangered are lower priority, since as listed
species, they are already afforded the protection of the Act and
implementing regulations.
We assigned the northern Mexican gartersnake an LPN of 3, based on
our finding that the subspecies faces immediate and high magnitude
threats from the present or threatened destruction, modification or
curtailment of its habitat; predation; and the inadequacy of existing
regulatory mechanisms. One or more of the threats discussed above are
occurring in each known population in the United States and throughout
historically occupied habitats in Mexico. These threats are on-going
and, in some cases (e.g., nonnative species), considered irreversible.
Pursuant to the 1983 Guidelines, a ``species'' facing imminent high-
magnitude threats is assigned an LPN of 1, 2, or 3 depending on its
taxonomic status. Because the northern Mexican gartersnake is a
subspecies, we assigned it an LPN of 3 (the highest category available
for a subspecies). Therefore, work on a proposed listing determination
for the northern Mexican gartersnake was, and will continue to be in
the next year, precluded by work on higher priority candidate species
(species with LPN of 2); 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 FY
2008. This work includes all the actions listed in the tables below
under expeditious progress.
As explained above, a determination that listing is warranted but
precluded must also demonstrate that expeditious progress is being made
to add or remove qualified species to and from the Lists of Endangered
and Threatened Wildlife and Plants. (We note that we do not discuss
specific actions taken on progress towards removing species from the
Lists because that work is conducted using appropriations for our
Recovery program, a separately budgeted component of the Endangered
Species Program. As explained above in our description of the statutory
cap on Listing Program funds, the Recovery Program funds and actions
supported by them cannot be considered in determining expeditious
progress made in the Listing Program.) As with our ``precluded''
finding, expeditious progress in adding qualified species to the Lists
is a function of the resources available and the competing demands for
those funds. Our expeditious progress in FY 2008 in the Listing Program
included preparing and publishing the following determinations:
FY 2008 Completed Listing Actions
----------------------------------------------------------------------------------------------------------------
Publication date Title Actions FR pages
----------------------------------------------------------------------------------------------------------------
10/09/2007......................... 90-Day Finding on a Notice of 90-day 72 FR 57278-57283.
Petition to List the Black- Petition Finding,
Footed Albatross Substantial.
(Phoebastria nigripes) as
Threatened or Endangered.
10/09/2007......................... 90-Day Finding on a Notice of 90-day 72 FR 57273-57276.
Petition To List the Giant Petition Finding, Not
Palouse Earthworm as substantial.
Threatened or Endangered.
10/23/2007......................... 90-Day Finding on a Notice of 90-day 72 FR 59983-59989.
Petition To List the Petition Finding, Not
Mountain Whitefish substantial.
(Prosopium williamsoni) in
the Big Lost River, ID, as
Threatened or Endangered.
10/23/2007......................... 90-Day Finding on a Notice of 90-day 72 FR 59979-59983.
Petition To List the Petition Finding, Not
Summer-Run Kokanee substantial.
Population in Issaquah
Creek, WA, as Threatened
or Endangered.
11/08/2007......................... Response to Court on Response to Court..... 72 FR 63123-63140.
Significant Portion of the
Range, and Evaluation of
Distinct Population
Segments, for the Queen
Charlotte Goshawk.
[[Page 71824]]
12/13/2007......................... 12-Month Finding on a Notice of 12-month 72 FR 71039-71054.
Petition To List the Petition Finding,
Jollyville Plateau Warranted but
salamander (Eurycea Precluded.
tonkawae) as Endangered
With Critical Habitat.
1/08/2008.......................... 90-Day Finding on a Notice of 90-day 73 FR 1312-1313.
Petition To List the Pygmy Petition Finding,
Rabbit (Brachylagus Substantial.
idahoensis) as Threatened
or Endangered.
1/10/2008.......................... 90-Day Finding on Petition Notice of 90-day 73 FR 1855-1861.
To List the Amargosa River Petition Finding,
Population of the Mojave Substantial.
Fringe-Toed Lizard (Uma
scoparia) as Threatened or
Endangered With Critical
Habitat.
1/24/2008.......................... 12-Month Finding on a Notice of 12-month 73 FR 4379-4418.
Petition To List the Petition Finding, Not
Siskiyou Mountains Warranted.
Salamander (Plethodon
stormi) and Scott Bar
Salamander (Plethodon
asupak) as Threatened or
Endangered.
2/05/2008.......................... 12-Month Finding on a Notice of 12-month 73 FR 6660 6684.
Petition To List the Petition Finding,
Gunnison's Prairie Dog as Warranted.
Threatened or Endangered.
02/07/2008......................... 12-Month Finding on a Notice of Review...... 73 FR 7236 7237.
Petition To List the
Bonneville Cutthroat Trout
(Oncorhynchus clarki utah)
as Threatened or
Endangered.
02/19/2008......................... Listing Phyllostegia Proposed Listing, 73 FR 9078 9085.
hispida (No Common Name) Endangered.
as Endangered Throughout
Its Range.
02/26/2008......................... Initiation of Status Review Notice of Status 73 FR 10218 10219.
for the Greater Sage- Review.
Grouse (Centrocercus
urophasianus) as
Threatened or Endangered.
03/11/2008......................... 12-Month Finding on a Notice 12 month 73 FR 12929 12941.
Petition To List the North petition finding, Not
American Wolverine as warranted.
Endangered or Threatened.
03/20/2008......................... 90-Day Finding on a Notice of 90-day 73 FR 14950 14955.
Petition To List the U.S. Petition Finding,
Population of Coaster Substantial.
Brook Trout (Salvelinus
fontinalis) as Endangered.
04/29/2008......................... 90-Day Finding on a Notice of 90-day 73 FR 23170 23172.
Petition to List the Petition Finding,
Western Sage-Grouse Substantial.
(Centrocercus urophasianus
phaios) as Threatened or
Endangered.
04/29/2008......................... 90-Day Finding on Petitions Notice of 90-day 73 FR 23173 23175.
To List the Mono Basin Petition Finding,
Area Population of the Substantial.
Greater Sage-Grouse
(Centrocercus
urophasianus) as
Threatened or Endangered.
05/06/2008......................... Petition To List the San Notice of 90-day 73 FR 24611 24915.
Francisco Bay-Delta Petition Finding,
Population of the Longfin Substantial.
Smelt (Spirinchus
thaleichthys) as
Endangered.
05/06/2008......................... 90-Day Finding on a Notice of 90-day 73 FR 24915 24922.
Petition to List Kokanee Petition Finding,
(Oncorhynchus nerka) in Substantial.
Lake Sammamish,
Washington, as Threatened
or Endangered.
05/06/2008......................... 12-Month Finding on a Notice of Status 73 FR 24910 24911.
Petition to List the White- Review.
tailed Prairie Dog
(Cynomys leucurus) as
Threatened or Endangered.
05/15/2008......................... 90-Day Finding on a Notice of 90-day 73 FR 28080 28084.
Petition To List the Ashy Petition Finding,
Storm-Petrel (Oceanodroma Substantial.
homochroa) as Threatened
or Endangered.
05/15/2008......................... Determination of Threatened Final Listing, 73 FR 28211 28303.
Status for the Polar Bear Threatened.
(Ursus maritimus)
Throughout Its Range;
Final Rule.
05/15/2008......................... Special Rule for the Polar Interim Final Special 73 FR 28305 28318.
Bear; Interim Final Rule. Rule.
05/28/2008......................... Initiation of Status Review Notice of Status 73 FR 30596 30598.
for the Northern Mexican Review.
Gartersnake (Thamnophis
eques megalops).
06/18/2008......................... 90-Day Finding on a Notice of 90-day 73 FR 34686 34692.
Petition To List the Long- Petition Finding, Not
Tailed Duck (Clangula substantial.
hyemalis) as Endangered.
[[Page 71825]]
07/10/2008......................... 90-Day Finding on a Notice of 90-day 73 FR 39639 39643.
Petition To Reclassify the Petition Finding,
Delta Smelt (Hypomesus Substantial.
transpacificus) From
Threatened to Endangered.
07/29/2008......................... 90-Day Finding on a Notice of 90-day 73 FR 43905 43910.
Petition To List the Petition Finding,
Tucson Shovel-Nosed Snake Substantial.
(Chionactis occipitalis
klauberi) as Threatened or
Endangered with Critical
Habitat.
8/13/2008.......................... Proposed Endangered Status Proposed Critical 73 FR 47257 47324.
for Reticulated Flatwoods Habitat, Proposed
Salamander; Proposed Listing, Endangered.
Designation of Critical
Habitat for Frosted
Flatwoods Salamander and
Reticulated Flatwoods
Salamander.
9/9/2008........................... 12-month Finding on a Notice 12 month 73 FR 52235 52256.
Petition to List the petition finding, Not
Bonneville Cutthroat Trout warranted.
as Threatened or
Endangered.
10/15/2008......................... 90-Day Finding on a Notice of 90-day 73 FR 61007 61015.
Petition To List the Least Petition Finding,
Chub. Substantial.
10/21/2008......................... Listing 48 Species on Kauai Proposed Listing, 73 FR 62591 62742.
as Endangered and Endangered; Proposed
Designating Critical Critical Habitat.
Habitat.
10/24/2008......................... 90-Day Finding on a Notice of 90-day 73 FR 63421 63424.
Petition to List the Petition Finding, Not
Sacramento Valley Tiger substantial.
Beetle as Endangered.
10/28/2008......................... 90-Day Finding on a Notice of 90-day 73 FR 63919 63926.
Petition To List the Dusky Petition Finding,
Tree Vole (Arborimus Substantial.
longicaudus silvicola) as
Threatened or Endangered.
----------------------------------------------------------------------------------------------------------------
Our expeditious progress also included work on listing actions,
which were funded in FY 2008, but have not yet been completed. These
actions are listed below. We have completed all work funded in FY 2008
on all actions 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 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 as compared to
preparing separate proposed rules for each of them in the future.
Actions Funded in FY 2008 But Not Completed
------------------------------------------------------------------------
Species Action
------------------------------------------------------------------------
Actions Subject to Court Order/Settlement Agreement
------------------------------------------------------------------------
NONE.................................... NONE.
------------------------------------------------------------------------
Actions with Statutory Deadlines
------------------------------------------------------------------------
Phyllostegia hispida.................... Final listing.
Yellow-billed loon...................... 12-month petition finding.
Black-footed albatross.................. 12-month petition finding.
Mount Charleston blue butterfly......... 12-month petition finding.
Goose Creek milk-vetch.................. 12-month petition finding.
Mojave fringe-toed lizard............... 12-month petition finding.
White-tailed prairie dog................ 12-month petition finding.
Pygmy rabbit (rangewide)................ 12-month petition finding.
Black-tailed prairie dog................ 90-day petition finding.
Lynx (include New Mexico in listing).... 90-day petition finding.
Wyoming pocket gopher................... 90-day petition finding.
Llanero coqui........................... 90-day petition finding.
American pika........................... 90-day petition finding.
Sacramento Mts. checkerspot butterfly... 90-day petition finding.
206 species............................. 90-day petition finding.
475 Southwestern species................ 90-day petition finding.
------------------------------------------------------------------------
High Priority Listing Actions
------------------------------------------------------------------------
21 Oahu candidate species (16 plants, 5 Proposed listing.
damselflies) (18 with LPN =2, 3 with
LPN = 3, 1 with LPN =9).
[[Page 71826]]
3 southeast aquatic species (Georgia Proposed listing.
pigtoe, interrupted rocksnail, rough
hornsnail) \1\ (all with LPN = 2).
Casey's june beetle (LPN = 2)........... Proposed listing.
Sand dune lizard (LPN = 2).............. Proposed listing.
2 southwest springsnails (Pyrgulopsis Proposed listing.
bernadina (LPN = 2), Pyrgulopsis
trivialis (LPN = 2)).
3 southwest springsnails (Pyrgulopsis Proposed listing.
chupaderae (LPN = 2), Pyrgulopsis gilae
(LPN = 11), Pyrgulopsis thermalis (LPN
11)).
2 mussels (rayed bean (LPN = 2), Proposed listing.
snuffbox No LPN).
2 mussels (sheepnose (LPN = 2), Proposed listing.
spectaclecase (LPN = 4),).
Ozark hellbender \2\ (LPN = 3).......... Proposed listing.
Altamaha spinymussel (LPN = 2).......... Proposed listing.
4 southeast fish (rush darter (LPN = 2), Proposed listing.
chucky madtom (LPN = 2), Cumberland
darter (LPN = 5), laurel dace (LPN =
5)).
2 Colorado plants (Parchute beardtongue Proposed listing.
(Penstemon debilis) (LPN = 2), Debeque
phacelia (Phacelia submutica) (LPN =
8)).
Pagosa skyrocket (Ipomopsis polyantha) Proposed listing.
(LPN = 2).
------------------------------------------------------------------------
\1\ Funds for listing actions for 3 of these species were also provided
in FY 2007.
\2\ We funded a proposed rule for this subspecies with an LPN of 3 ahead
of other species with LPN of 2, because the threats to the species
were so imminent and of a high magnitude that we considered emergency
listing if we were unable to fund work on a proposed listing rule in
FY 2008.
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.
The northern Mexican gartersnake will be added to the list of
candidate species upon publication of this 12-month finding. We will
continue to monitor the status of this species as new information
becomes available. This 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 action for the northern Mexican
gartersnake 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 all references cited in this document is
available upon request from the Field Supervisor at the Arizona
Ecological Services Office (see ADDRESSES section).
Author
The primary author of this notice is the Arizona Ecological
Services Office (see FOR FURTHER INFORMATION CONTACT section).
Authority
The authority for this action is section 4 of the Endangered
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).
Dated: November 12, 2008.
Kenneth Stansell,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. E8-27524 Filed 11-24-08; 8:45 am]
BILLING CODE 4310-55-P