[Federal Register Volume 71, Number 186 (Tuesday, September 26, 2006)]
[Proposed Rules]
[Pages 56228-56256]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 06-7784]



[[Page 56227]]

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Part II





Department of the Interior





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Fish and Wildlife Service



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50 CFR Part 17



Endangered and Threatened Wildlife and Plants; 12-Month Finding on a 
Petition To List the Northern Mexican Gartersnake (Thamnophis eques 
megalops) as Threatened or Endangered With Critical Habitat; Proposed 
Rule

Federal Register / Vol. 71, No. 186 / Tuesday, September 26, 2006 / 
Proposed Rules

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 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

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 scenarios for consideration by the 
Service: (1) Listing the United States 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. After thorough analysis and review of all available 
scientific and commercial information, we find that listing of the 
subspecies, under any of the three scenarios, is not warranted. Of the 
three listing scenarios specified above, we found scenario two provided 
the most rigorous evaluation of the status of the northern Mexican 
gartersnake and herein provide detailed discussion of our conclusions 
in that context. We also provide additional discussion of our 
evaluation of scenarios (1) listing the United States population as a 
DPS and (3) listing Thamnophis eques megalops throughout its range in 
the United States and Mexico based on its status in the United States.

DATES: The finding announced in this document was made on September 26, 
2006.

ADDRESSES: The complete supporting file for this finding is available 
for inspection, by appointment, during normal business hours at the 
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 species or this 
finding to the above address.

FOR FURTHER INFORMATION CONTACT: Steve Spangle, Field Supervisor, 
Arizona Ecological Services Office (see ADDRESSES) 602-242-0210.

SUPPLEMENTARY INFORMATION:

Background

    Section 4(b)(3)(B) of the Act (16 U.S.C. 1531 et seq.), requires 
that, for any petition to revise the Lists of Threatened and Endangered 
Wildlife and Plants that contains substantial scientific and commercial 
information 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 that 
the immediate proposal of a regulation implementing the petitioned 
action is precluded by other pending proposals to determine whether any 
species is 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 a petition for which the requested action is found to be 
warranted but precluded be treated as though resubmitted on the date of 
such finding, i.e., requiring a subsequent finding to be made within 12 
months. Each subsequent 12-month finding will be published 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.
    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 positive, 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). We are required, under the court-
approved stipulated settlement agreement, to submit to the Federal 
Register our 12-month finding pursuant to the Act [16 U.S.C. 
1533(b)(3)(B)] on or before September 15, 2006. This notice constitutes 
our 12-month finding for the petition to list the northern Mexican 
gartersnake as threatened or endangered.

Previous Federal Actions

    The Mexican gartersnake (Thamnophis eques) (which included the 
subspecies) 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. In addition, on January 4, 2006, we 
published a 90-day finding on a petition to list the northern Mexican 
gartersnake (71 FR 315), as discussed above.

Biology

    Species Description. The northern Mexican gartersnake may occur 
with other native gartersnake species and can be difficult for people 
without herpetological expertise to identify. With a maximum known 
length of 44 inches (in) (112 centimeters (cm)), it ranges in 
background color from olive to olive-brown to olive-gray with three 
stripes that run the length of the body. The middle dorsal stripe is 
yellow and darkens toward the tail. The pale yellow to light-tan 
lateral stripes distinguish the Mexican gartersnake from other 
sympatric (co-occurring) gartersnake species because a portion of the 
lateral

[[Page 56229]]

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 and the olive-gray ventrolateral fields. A 
conspicuous, light-colored crescent extends behind the corners of the 
mouth. The two dark brown to black blotches that occur behind the head 
of several gartersnake species may be diffuse or absent in the Mexican 
gartersnake. The coloration of the venter is bluish-gray or greenish-
grey. The dorsolateral scalation is keeled, the anal plate is single, 
and there are eight or nine upper labial scales (Rosen and Schwalbe 
1988, p. 4; Rossman et al. 1996, pp. 171-172).
    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). 
There are approximately 30 species that have been described in the 
gartersnake genus Thamnophis (Rossman et al. 1996, p. xvii-xviii). De 
Queiroz et al. (2002, p. 323) identified two large overlapping clades 
(related taxonomic groups) of gartersnakes that they called the 
``Mexican'' and ``widespread'' clades which were supported by allozyme 
and mitochondrial DNA genetic analyses. Thamnophis eques is a member of 
the ``widespread'' clade and is most closely related taxonomically to, 
although genetically and phenotypically distinct from, the checkered 
gartersnake (Thamnophis marcianus) (De Queiroz and Lawson 1994, p. 
217).
    Rossman et al. (1996, p. 175) noted that the current specific name 
eques was not applied at the time of the original description of the 
holotype because the specimen was mistakenly identified as a black-
necked gartersnake (Thamnophis cyrtopsis). 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). T. eques displays considerable phenotypic variability 
(variation in its physical appearance) across its distribution, and all 
subspecific descriptions under T. eques have been based on 
morphometrics or morphological characters. The subspecies T. e. eques 
and T. e. megalops are distinguished by average differences in sub-
caudal scale counts, while T. e. virgatenuis is distinguished from T. 
e. megalops based on having a darker background color and a narrower 
vertebral stripe (Rossman et al. 1996, p. 175). Rossman et al. (1996, 
p. 175) also noted that the discontinuous distributions of high-
elevation and low-elevation T. e. virgatenuis and T. e. megalops, 
respectively, are ``zoogeographically peculiar and unique among 
gartersnakes.''
    Rossman et al. (1996, p. 172) describe the distribution of T. e. 
eques as occurring from southern Nayarit eastward along the Transverse 
Volcanic Axis to west-central Veracruz, and identified an additional 
disjunct population in central Oaxaca. T. e. virgatenuis is distributed 
in three isolated, high-elevation populations in southwestern Durango 
and in west-central and northwestern Chihuahua (Rossman et al. 1996, p. 
172).
    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). These seven new 
subspecies were described based on morphological differences in 
coloration and pattern; have high endemism (degree of restriction to a 
particular area) with 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). We are not aware of any challenges 
within the scientific literature of the validity of current taxonomy of 
any of the 10 subspecies of T. eques.
    The most widely distributed of the 10 subspecies under Thamnophis 
eques is the northern Mexican gartersnake (Thamnophis eques megalops), 
which is the only subspecies that occurs in the United States and the 
entity we address in this finding. In Mexico, T. e. megalops 
historically occurred throughout the Sierra Madre Occidental south to 
Guanajuato, and east across the Mexican Plateau to Hidalgo, which 
comprised approximately 85 percent of the total rangewide distribution 
of the species (Rossman et al. 1996, p. 173). Robert Kennicott first 
described the northern Mexican gartersnake in 1860, as Eutenia megalops 
from the type locality of Tucson, Arizona (Rosen and Schwalbe 1988, p. 
2). In 1951, Dr. Hobart Smith renamed the subspecies with its current 
scientific name (Rosen and Schwalbe 1988, p. 3). A summary of this 
species' lengthy taxonomic history can be found in Rosen and Schwalbe 
(1988, pp. 2-3). Several common names have been applied to the northern 
Mexican gartersnake in the United States over the years, such as the 
Arizona ribbon snake, the Emory's gartersnake, and the Arizona 
gartersnake (Rosen and Schwalbe 1988, p. 2).
    In summary, while the taxonomic history of Thamnophis eques is 
robust, we found no indication in the significant body of taxonomic 
literature we reviewed that its current taxonomy is in doubt or in any 
way invalid (Rosen and Schwalbe 1988, pp. 2-3; De Queiroz and Lawson 
1994, pp. 215-217; Liner 1994, p. 107; Rossman et al. 1996, pp. 171, 
175; Conant 2003, p. 6; Crother et al. 2000, p. 72; 2003, p. 202; De 
Queiroz et al. 2002, p. 327).
    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 considered 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). Vegetation characteristics vary based on the type of habitat. 
For example, in source-area wetlands, dense vegetation consists of knot 
grass (Paspalum distichum), spikerush (Eleocharis), bulrush (Scirpus), 
cattail (Typha), deergrass (Muhlenbergia), sacaton (Sporobolus), 
Fremont cottonwood (Populus fremontii), Goodding's willow (Salix 
gooddingii), and velvet mesquite (Prosopis velutina) (Rosen and 
Schwalbe 1988, pp. 14-16).
    In riparian woodlands consisting of cottonwood and willow or 
gallery forests of broadleaf and deciduous species along larger rivers, 
the northern Mexican gartersnake may be observed in mixed grasses along 
the bank or in the shallows (Rossman et al. 1996, p. 176; Rosen and 
Schwalbe 1988, p. 16). Within and adjacent to the Sierra Madre 
Occidental in Mexico, it occurs in montane woodland, Chihuahuan 
desertscrub, mesquite-grassland, and Cordillera Volc[aacute]nica 
montane woodland (McCranie and Wilson 1987, pp. 14-17).

[[Page 56230]]

    In small streamside riparian habitat, this snake is often 
associated with Arizona sycamore (Platanus wrightii), sugar leaf maple 
(Acer grandidentatum), velvet ash (Fraxinus velutina), Arizona cypress 
(Cupressus arizonica), Arizona walnut (Juglans major), Arizona alder 
(Alnus oblongifolia), alligator juniper (Juniperus deppeana), Rocky 
Mountain juniper (J. scopulorum), and a number of oak species (Quercus 
spp.) (McCranie and Wilson 1987, pp. 11-12; 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. 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). 
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 maniculatus), lizards of the genera Aspidoscelis and 
Sceloporus, larval tiger salamanders (Ambystoma tigrinum), and leeches 
(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 juvenile fish, larval and juvenile bullfrogs, and 
mosquitofish (Gambusia affinis) (Holycross et al. 2006, p. 23).
    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 in their northern distribution 
followed by the live birth of between 7 and 26 neonates (newly born 
individuals) (average is 13.6) in July and August (Rosen and Schwalbe 
1988, p. 16). Approximately half of the sexually mature females within 
a population reproduce in any one season (Rosen and Schwalbe 1988, p. 
17).

Distribution

    Historical Distribution. The United States comprises the northern 
portion of the northern Mexican gartersnake's distribution. Within the 
United States, the northern Mexican gartersnake historically occurred 
predominantly in Arizona with a limited distribution in New Mexico that 
consisted of scattered locations throughout the Gila and San Francisco 
headwater drainages in western Hidalgo and Grant counties (Price 1980, 
p. 39; Fitzgerald 1986, Table 2; Degenhardt et al. 1996, p. 317; 
Holycross et al. 2006, pp. 1-2). Fitzgerald (1986, Table 2) provided 
museum records for the following historical localities for northern 
Mexican gartersnakes in New Mexico: (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.
    Within Arizona, the historical distribution of the northern Mexican 
gartersnake ranged from 130 to 6,150 ft (40 to 1,875 m) in elevation 
and spread variably based on the relative permanency of water and the 
presence of suitable habitat. In Arizona, the northern Mexican 
gartersnake historically occurred within several perennial or 
intermittent drainages and disassociated wetlands that included: (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; (5) the Santa Cruz River 
headwaters/San Rafael Valley and adjacent montane canyons; (6) the Salt 
River; (7) the Rio San Bernardino from International Border to 
headwaters at Astin Spring (San Bernardino National Wildlife Refuge); 
(8) Agua Fria River; (9) the Verde River; (10) Tanque Verde Creek in 
Tucson; (11) Rillito Creek in Tucson; (12) Agua Caliente Spring in 
Tucson; (13) the downstream portion of the Black River from the Paddy 
Creek confluence; (14) the downstream portion of the White River from 
the confluence of the East and North forks; (15) Tonto Creek from the 
mouth of Houston Creek downstream to Roosevelt Lake; (16) Cienega Creek 
from the headwaters to the ``Narrows'' just downstream of Apache 
Canyon; (17) Pantano Wash (Cienega Creek) from Pantano downstream to 
Vail; (18) Potrero Canyon/Springs; (19) Audubon Research Ranch and 
vicinity near Elgin; (20) Upper Scotia Canyon in the Huachuca 
Mountains; (21) Arivaca Creek; (22) Arivaca Cienega; (23) Sonoita 
Creek; (24) Babocomari River; (25) Babocamari Cienega; (26) Barchas 
Ranch, Huachuca Mountain bajada; (27) Parker Canyon Lake and 
tributaries in the Canelo Hills; (28) Big Bonito Creek; (29) Lake 
O'Woods, Lakeside area; (30) Oak Creek from Midgley Bridge downstream 
to the confluence with the Verde River; and (31) Spring Creek above the 
confluence with Oak Creek (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).
    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); however, any 
populations of northern Mexican gartersnakes that may have historically 
occurred in Nevada pertained directly to the Colorado River and are 
likely 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, which comprises approximately 70 to 80 percent of its 
historical rangewide distribution (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. Holycross et al. (2006, p. 12) 
included the northern Mexican gartersnake as a target species at 33 
sites surveyed within drainages along the Mogollon Rim. A total of 874 
person-search hours and 63,495 trap-hours were devoted to that effort, 
which resulted in the capture of 23 snakes total in 3 (9 percent) of 
the sites visited. This equates to approximately 0.03 snakes observed 
per person-search hour and 0.0004 snakes captured per trap-hour over 
the entire effort. For comparison, a population of northern Mexican 
gartersnakes at Page Springs, Arizona,

[[Page 56231]]

that we consider stable yielded 0.22 snakes observed per person-search 
hour and 0.004 snakes captured per trap-hour (an order of magnitude 
higher) (Holycross et al. 2006, p. 23). Survey sites were selected 
based on the existence of historical records for the species or sites 
where the species may occur based on habitat suitability within the 
historical distribution of the species. Holycross et al. (2006, p. 12) 
calculated the capture rates for the northern Mexican gartersnake as 
12,761 trap-hours per snake and 49 person-search hours per snake. 
Northern Mexican gartersnakes were found at 2 of 11 (18 percent) 
historical sites and 1 of 22 (4 percent) sites where the species was 
previously unrecorded (Holycross et al. 2006, p. 12). When compared 
with extensive survey data in Rosen and Schwalbe (1988, Appendix I), 
these data demonstrate dramatic declines in both capture rates and the 
total number of populations of the species in areas where multiple 
surveys have been completed over time. However, these data may be 
affected by differences in survey efforts and drought.
    In 2000, Rosen et al. (2001, Appendix I) resurveyed many sites in 
southeastern Arizona that were historically known to support northern 
Mexican gartersnake populations during the early to mid-1980s, and also 
provided additional survey data collected from 1993-2001. Rosen et al. 
(2001, pp. 21-22) reported their results in terms of increasing, 
stabilized, or decreasing populations of northern Mexican gartersnakes.
    Three sites (San Bernardino National Wildlife Refuge, Finley Tank 
at the Audubon Research Ranch near Elgin, and Scotia Canyon in the 
Huachuca Mountains) were intensively surveyed and yielded mixed 
results. The northern Mexican gartersnake population on the San 
Bernardino National Wildlife Refuge experienced ``major, demonstrable 
declines'' to near or at extirpation over the span of a decade. That 
population is now considered extirpated (Radke 2006). The status of the 
population at Finley Tank is uncertain. Scotia Canyon was the last area 
intensively resurveyed by Rosen et al. (2001, pp. 15-16). In comparing 
this information with survey data from Holm and Lowe (1995, pp. 27-35), 
northern Mexican gartersnake populations in this area suggest a 
possible decline from the early 1980s, as evidenced by low capture 
rates in 1993 and even lower capture rates in 2000.
    The remaining 13 sites in southeastern Arizona resurveyed by Rosen 
et al. (2001, pp. 21-22) also yielded mixed results. Population trend 
information is difficult to ascertain given the variability of survey 
sample design and effort used by Rosen et al. (2001). However, the 
survey results suggested population increases at one site (lower 
Cienega Creek), possible stability at two sites (lower San Rafael 
Valley, Arivaca), and negative trends at many other sites [Empire-
Cienega Creek, Babocomari, Bog Hole, O'Donnell Creek, Turkey Creek 
(Canelo), Post Canyon, Lewis Springs (San Pedro River), San Pedro River 
near Highway 90, Barchas Ranch Pond (Huachuca Mountain bajada), Heron 
Spring, Sharp Spring, and Elgin-Sonoita windmill well site (San Rafael 
Valley)] (Rosen et al. 2001, pp. 21-22). While this survey effort could 
not confirm any specific extirpations of northern Mexican gartersnake 
populations on a local scale in southeastern Arizona, most sites 
yielded no snakes during resurvey (Rosen et al. 2001, Appendix I).
    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 in the 
United States, and it is now considered extirpated from New Mexico 
(Nickerson and Mays 1970, p. 503; Rosen and Schwalbe 1988, pp. 25-26, 
Appendix I; Holm and Lowe 1995, pp. 27-35; Sredl et al. 1995b, pp. 2, 
9-10; 2000, p. 9; Rosen et al. 2001, Appendix I; Painter 2005, 2006; 
Holycross et al. 2006, p. 66; Brennan and Holycross 2006, p. 123; Radke 
2006; Rosen 2006; Holycross 2006). Fitzgerald (1986, pp. 9-10) visited 
33 localities of potential habitat for northern Mexican gartersnakes in 
New Mexico in the Gila River drainage and was unable to confirm its 
existence at any of these sites. The New Mexico Department of Game and 
Fish State Herpetologist, Charles Painter, provided several causes that 
have synergistically contributed to the decline of northern Mexican 
gartersnakes in New Mexico, including bullfrog and nonnative fish 
introductions, modification and destruction of habitat, commercial 
exploitation, direct human-inflicted harm, and fragmentation of 
populations. The last known observation of the northern Mexican 
gartersnake in New Mexico occurred in 1994 on private land (Painter 
2000, p. 36; Painter 2005).
    Our analysis of the best available information indicates that the 
northern Mexican gartersnake has likely been extirpated from a large 
portion of its historical distribution in 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 at least minimal 
survey efforts, and natural recovery at the site is not expected due to 
the presence of known threats. The perennial or intermittent stream 
reaches and disassociated wetlands where the northern Mexican 
gartersnake has likely been extirpated 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). Information pertaining to the cause or 
causes of extirpation of these sites is summarized in Table 1 below.
    Conversely, our review of the best available information indicates 
the northern Mexican gartersnake is likely extant in a fraction of its 
historical range in Arizona. We define populations as ``likely extant'' 
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 extant 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) Upper Scotia Canyon in the Huachuca Mountains; and (8) the 
Audubon Research Ranch and vicinity near Elgin

[[Page 56232]]

(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).
    The current status of the northern Mexican gartersnake is unknown 
in several areas in Arizona where the species is known to have 
historically occurred. We base this determination on mostly 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 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; and (9) Arivaca Cienega (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, after consultation with species' experts and land 
managers, and based upon our analysis of the best available scientific 
and commercial data, we conclude that the northern Mexican gartersnake 
has been extirpated from 85 to 90 percent of its historical 
distribution in the United States.
    Status in Mexico. Throughout this finding, and due to the 
significantly limited amount of available literature that addresses the 
status of and threats to extant populations of the northern Mexican 
gartersnake in Mexico, we rely in part on (1) information that 
addresses the status of and threats to both riparian and aquatic 
biological communities within the historical distribution of the 
northern Mexican gartersnake in Mexico; and (2) information that 
addresses the status of and threats to native freshwater fish within 
the historical distribution of the northern Mexican gartersnake in 
Mexico, which we use as ecological surrogates due to their similar 
habitat requirements and their role as important prey species utilized 
by the northern Mexican gartersnake. Observations on the status of 
riparian and aquatic communities in Mexico are available but limited in 
comparison to our knowledge of these communities in the United States. 
The current distribution of the northern Mexican gartersnake in Mexico 
is also not well understood, although its status is believed to be in 
decline in many areas due to historical and continuing threats to its 
habitat and prey base, as discussed below. A large number of springs 
have dried up in several Mexican states within the distribution of the 
northern Mexican gartersnake, namely, Chihuahua, Durango, Coahila, and 
San Luis Potos[iacute] (Contreras Balderas and Lozano 1994, p. 381). 
Contreras Balderas and Lozano (1994, p. 381) also stated that several 
streams and rivers throughout Mexico and within the distribution of the 
northern Mexican gartersnake have dried up or become intermittent due 
to overuse of surface and groundwater supplies. We further acknowledge 
that northern Mexican gartersnakes were historically distributed in 
several regions within Mexico that have remained roadless and isolated 
and, according to the information we were able to obtain regarding the 
status of the northern Mexican gartersnake in Mexico, few ecological 
investigations have occurred in these areas due to their remote nature 
and the logistical difficulties that face research in such areas. 
However, Mexican biologists Ramirez Bautista and Arizmendi (2004, p. 3) 
were able to provide general information on the principal threats to 
northern Mexican gartersnake habitat in Mexico which included the 
dessication 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). Given the lack of specific data on the status of the northern 
Mexican gartersnake in Mexico, we cannot conclude with any degree of 
certainty its overall status in Mexico.

Northern Mexican Gartersnake Distinct Population Segment

    In the petition to list the northern Mexican gartersnake, the 
petitioners specified several listing options for our consideration, 
including listing northern Mexican gartersnake in the United States as 
a DPS. Under the Act, we must consider for listing any species, 
subspecies, or DPSs of vertebrate species/subspecies, if information is 
sufficient to indicate that such action may be warranted. To implement 
the measures prescribed by the Act and its Congressional guidance, we 
developed a joint policy with the National Oceanic and Atmospheric 
Administration (NOAA) Fisheries entitled Policy Regarding the 
Recognition of Distinct Vertebrate Population (DPS Policy) to clarify 
our interpretation of the phrase ``distinct population segment of any 
species of vertebrate fish or wildlife'' for the purposes of listing, 
delisting, and reclassifying species under the Act (61 FR 4721; 
February 7, 1996). Under our DPS policy, we consider three elements in 
a decision regarding the status of a possible DPS as endangered or 
threatened under the Act. The elements are: (1) The population 
segment's discreteness from the remainder of the taxon to which it 
belongs; (2) the population segment's significance to the taxon to 
which it belongs; and (3) the population segment's conservation status 
in relation to the Act's standards for listing (i.e., when treated as 
if it were a species, is the population segment endangered or 
threatened?). Our policy further recognizes it may be appropriate to 
assign different classifications (i.e., threatened or endangered) to 
different DPSs of the same vertebrate taxon (61 FR 4721; February 7, 
1996).

Discreteness

    The DPS policy's standard for discreteness requires an entity given 
DPS status under the Act to be adequately defined and described in some 
way that distinguishes it from other populations of the species. A 
population segment may be considered discrete if it satisfies either 
one of the following conditions: (1) Marked separation from other 
populations of the same taxon resulting from physical, physiological, 
ecological, or behavioral factors, including genetic discontinuity; or 
(2) populations delimited by international boundaries within which 
differences in control of exploitation, management of habitat, 
conservation status, or regulatory mechanisms exist that are 
significant in light of 4(a)(1)(D) of the Act.
    Marked Separation from Other Populations of the Same Taxon as a 
Consequence of Physical, Physiological, Ecological or Behavioral 
Factors. We do not have any information to indicate that a marked 
separation exists between the United States and Mexico that would 
distinguish populations of northern Mexican gartersnake in the United 
States from those in Mexico. There is no information to indicate that a 
marked separation exists as a result of physical, physiological, 
ecological, or behavioral factors.
    There has been no genetic analysis completed for the northern 
Mexican gartersnake. Thus, we have no information to indicate that 
genetic differences exist.

[[Page 56233]]

    Populations Delimited by International Boundaries Within Which 
Differences in Control of Exploitation, Management of Habitat, 
Conservation Status, or Regulatory Mechanisms Exist that are 
Significant. In terms of the conservation status of the northern 
Mexican gartersnake, despite the significantly limited amount of 
monitoring and/or survey data for the northern Mexican gartersnake in 
Mexico, we believe there is a higher probability that the subspecies is 
fairing better overall in Mexico in terms of having more total 
populations, because a larger percentage of the overall range of the 
subspecies (approximately 70 to 80 percent of it historical 
distribution) occurs in Mexico. However, we have no information to 
indicate that the populations on either side of the United States-
Mexico border have a more stable or better conservation status.
    We recognize that differences in management regulatory protection 
of northern Mexican gartersnake populations may exist between 
populations within Mexico and those within the United States. These 
differences primarily pertain to protections afforded to occupied 
habitat. In Mexico, any activity that intentionally destroys or 
adversely modifies occupied northern Mexican gartersnake habitat is 
prohibited [SEDESOL 2000 (LGVS) and 2001 (NOM-059-ECOL-2001)]. Neither 
the Arizona Game and Fish Department or the New Mexico Department of 
Game and Fish can offer protections to occupied habitat. Instead, these 
agencies regulate take in the form of lethal or live collection of 
individuals which is prohibited in both states. However, any 
conclusions that may be drawn with reference to differences in 
management across the United States-Mexico border are largely 
speculative due to the lack of information available as to the efficacy 
and protections of these regulations in practice. Because we determine 
in the following section that populations of the northern Mexican 
gartersnake in the United States are not significant to the subspecies 
as a whole, we need not address further the ``discreteness'' test of 
the DPS policy. For further information on regulatory considerations, 
please see our discussion under Factor D below.

Significance

    Under our DPS policy, a population segment must be significant to 
the taxon to which it belongs. The evaluation of ``significance'' may 
address, but is not limited to, (1) evidence of the persistence of the 
discrete population segment in an ecological setting that is unique for 
the taxon; (2) evidence that loss of the population segment would 
result in a significant gap in the range of the taxon; (3) evidence 
that the population segment represents the only surviving natural 
occurrence of a taxon that may be more abundant elsewhere as an 
introduced population outside its historic range; and (4) evidence that 
the discrete population segment differs markedly from other populations 
of the species in its genetic characteristics.
    Ecological Setting. Throughout its rangewide distribution, the 
northern Mexican gartersnake occurs at elevations from 130 to 8,497 ft 
(40 to 2,590 m) (Rossman et al. 1996, p. 172). The northern Mexican 
gartersnake is considered a riparian obligate (restricted to riparian 
areas when not engaged in dispersal behavior) and occurs chiefly in the 
following general habitat types in both the United States and Mexico: 
(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). Based on this information, we determine that 
populations of the northern Mexican gartersnake in Arizona do not 
occupy an ecological setting differing enough from populations that 
occur in Mexico to be considered unique for the subspecies.
    Gap in the Range. The Service can determine that a gap in a taxon's 
range caused by the potential loss of a population would be significant 
based on any relevant considerations. One factor which may support such 
a determination is whether the loss of a geographic area amounts to a 
substantial reduction of a taxon's range and this reduction is 
biologically important. The United States comprised the most northern 
portion of the northern Mexican gartersnake's range and constituted 
approximately 20-30 percent of its rangewide historical distribution. 
Because we do not currently know exactly what the status of the 
northern Mexican gartersnake is in Mexico at this time, we are unable 
to ascertain what percentage of extant populations occur in the United 
States as compared to Mexico. However, this is not sufficient evidence 
to support a determination that loss of the northern Mexican 
gartersnake in the United States represents a substantial reduction in 
the subspecies' range based on the geographic area which would be lost. 
Furthermore, no area that is uniquely biologically significant to the 
northern Mexican gartersnake is located within the United States as 
compared to Mexico.
    Another factor relevant to determining whether a gap is significant 
is the biological significance of the number of total individuals of 
the taxon in the population that may be lost. Although we have no data 
on the absolute numbers of northern Mexican gartersnakes in the United 
States or Mexico, the best available science suggests that there are 
far more individuals in Mexico than in the United States, based on the 
more extensive range in Mexico and the current low density and number 
of extant populations in the United States. Therefore, we have no 
information to indicate that the loss of between 8 and 17 populations 
of northern Mexican gartersnakes known in the United States is 
biologically significant to the taxon as a whole.
    In conclusion, we have determined that the gap in the range of the 
northern gartersnake that would be caused by the loss of the United 
States population would not be significant because: (1) Loss of the 
United States population would not constitute a substantial and 
biologically important reduction of the range of the subspecies; (2) 
the loss of the individuals in the United States would not be 
biologically significant to the subspecies; and (3) we have not 
identified any other reason why loss of the United States population 
would result in a significant gap in the range of the subspecies.
    Marked Differences in Genetic Characteristics. Within the 
distribution of every species there exists a peripheral population, an 
isolate or subpopulation of a species at the edge of the taxon's range. 
Long-term geographic isolation and loss of gene flow between 
populations is the foundation of genetic changes in populations 
resulting from natural selection or change. Evidence of changes in 
these populations may include genetic, behavioral, and/or morphological 
differences from populations in the rest of the species' range. We have 
no information to indicate that genetic differences exist between 
populations of the northern Mexican gartersnake at the northern portion 
of its range in the United States from those in Mexico. Therefore, 
based on the genetic information currently available, the northern 
Mexican gartersnake in the United States should not be considered 
biologically or ecologically significant based simply on

[[Page 56234]]

genetic characteristics. Biological and ecological significance under 
the DPS policy is always considered in light of Congressional guidance 
(see Senate Report 151, 96th Congress, 1st Session) that the authority 
to list DPS's be used ``sparingly'' while encouraging the conservation 
of genetic diversity.
    Whether the Population Represents the Only Surviving Natural 
Occurrence of the Taxon. As part of a determination of significance, 
our DPS policy suggests that we consider whether there is evidence that 
the population represents the only surviving natural occurrence of a 
taxon that may be more abundant elsewhere as an introduced population 
outside its historic range. The northern Mexican gartersnake in the 
United States is not the only surviving natural occurrence of the 
subspecies. Consequently, this factor is not applicable to our 
determination regarding significance.

Conclusion

    Following a review of the available information, we conclude that 
the northern Mexican gartersnake in the United States is not 
significant to the remainder of the subspecies. We made this 
determination based on the best available information, which does not 
demonstrate that (1) these populations persist in an ecological setting 
that is unique for the subspecies; (2) the loss of these populations 
would result in a significant gap in the range of the subspecies; and 
(3) these populations differ markedly from populations of northern 
Mexican gartersnake in Mexico in their genetic characteristics, or in 
other considerations that might demonstrate significance. Further, 
available information does not demonstrate that the life history and 
behavioral characteristics of the northern Mexican gartersnake in the 
United States is unique to the subspecies. Therefore, on the basis of 
the best scientific and commercial information available, we find that 
proposing to list a DPS for the northern Mexican gartersnake in the 
United States is not warranted; these populations do not meet the 
definition of a distinct population segment. We are not addressing the 
third prong of the DPS policy (i.e. the population segment's 
conservation status in relation to the Act's standards for listing) 
since we find that the United States portion of the range of the 
northern Mexican gartersnake does not qualify as a listable entity 
pursuant to our DPS policy, as discussed above.

Significant Portion of the Range

    In the petition to list the northern Mexican gartersnake, the 
petitioners also requested that we consider listing the species 
throughout its range based on its status in the United States. As 
required by the Act, we have considered in this finding whether the 
northern Mexican gartersnake is in danger of extinction ``in all or a 
significant portion of its range'' as defined in the terms ``threatened 
species'' and ``endangered species'' pursuant to section 3 of the Act. 
In order to determine if Arizona constitutes a significant portion of 
the range of the subspecies, we evaluate whether threats in this 
geographic area imperil the viability of the subspecies as a whole due 
to any biological importance of this portion of the subspecies range. 
Based upon the best scientific information available, we find that the 
extant populations in the United States are not considered a stronghold 
for the subspecies, they do not represent core or important breeding 
habitat, we are not aware of any unique genetic or behavioral 
characteristics, and we are not aware that threats in this portion of 
its range threaten the whole subspecies with extinction. Therefore, we 
determine that the extant populations of the northern Mexican 
gartersnake in Arizona do not constitute a significant portion of the 
range of the subspecies because there is no particular characteristic 
to any segment within this portion of its range that would render it 
biologically more significant to the taxon as a whole than other 
portions of its current range.
    We note that the court in Defenders of Wildlife v. Norton, 258 F.3d 
1136 (9th Cir. 2001), appeared to suggest that a species could be in 
danger of extinction in a significant portion of its range if there is 
a ``major geographical area'' in which the species is no longer viable 
but once was. Although we do not necessarily agree with the court's 
suggestion, we have determined that the historical range of the 
subspecies within the United States does not constitute a ``major 
geographical area'' in this context. The portion of the northern 
Mexican gartersnake's historical range in United States (20 to 30 
percent) constitutes a small percentage of the total range of the 
subspecies.
    The petitioners also requested that we consider listing the species 
throughout its range based on its rangewide status. Below we respond to 
the petitioners request through our analysis of the five listing 
factors for the United States and Mexico.

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) 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 United States
         [All locations in Arizona unless otherwise specified.]
------------------------------------------------------------------------
                                                    Regional historical/
      Population locality         Current status      current threats
------------------------------------------------------------------------
Gila River....................  Extirpated.......  Considered extirpated
                                                    by nonnatives,
                                                    improper grazing,
                                                    recreation,
                                                    development,
                                                    groundwater pumping,
                                                    diversions,
                                                    channelization,
                                                    dewatering, road
                                                    construction/use,
                                                    wildfire,
                                                    intentional harm,
                                                    dams, prey base
                                                    reductions.
Gila and San Francisco          Extirpated.......  Considered extirpated
 Headwaters in New Mexico.                          by nonnatives,
                                                    improper grazing,
                                                    recreation, prey
                                                    base reductions.
Lower Colorado River from       Extirpated.......  Considered extirpated
 Davis Dam to International                         by nonnatives, prey
 Border.                                            base reductions,
                                                    recreation,
                                                    development, road
                                                    construction/use,
                                                    borderland security/
                                                    undocumented
                                                    immigration,
                                                    intentional harm,
                                                    dams.

[[Page 56235]]

 
San Pedro River in United       Extirpated.......  Considered extirpated
 States.                                            by nonnatives, prey
                                                    base reductions,
                                                    improper grazing,
                                                    groundwater pumping,
                                                    road construction/
                                                    use, borderland
                                                    security/
                                                    undocumented
                                                    immigrants,
                                                    intentional harm.
Santa Cruz River downstream of  Extirpated.......  Considered extirpated
 the Nogales area of the                            by nonnatives, prey
 International Border.                              base reductions,
                                                    improper grazing,
                                                    development,
                                                    groundwater pumping,
                                                    diversions,
                                                    channelization, road
                                                    construction/use,
                                                    borderland security/
                                                    undocumented
                                                    immigrants,
                                                    intentional harm,
                                                    contaminants.
Salt River....................  Extirpated.......  Considered extirpated
                                                    by nonnatives, prey
                                                    base reductions,
                                                    improper grazing,
                                                    recreation,
                                                    development,
                                                    diversions,
                                                    wildfire,
                                                    channelization, road
                                                    construction/use,
                                                    intentional harm,
                                                    dams.
Rio San Bernardino from         Extirpated.......  Considered extirpated
 International Border to                            by nonnatives, prey
 headwaters at Astin Spring                         base reductions,
 (San Bernardino National                           borderland security/
 Wildlife Refuge).                                  undocumented
                                                    immigration,
                                                    intentional harm,
                                                    competition with
                                                    Marcy's checkered
                                                    gartersnake.
Agua Fria River...............  Extirpated.......  Considered extirpated
                                                    by nonnatives, prey
                                                    base reductions,
                                                    improper grazing,
                                                    development,
                                                    recreation, dams,
                                                    road construction/
                                                    use, wildfire,
                                                    intentional harm.
Verde River upstream of         Extirpated.......  Considered extirpated
 Clarkdale.                                         by nonnatives, prey
                                                    base reductions,
                                                    improper grazing,
                                                    recreation,
                                                    development,
                                                    groundwater pumping,
                                                    diversions,
                                                    channelization, road
                                                    construction/use,
                                                    intentional harm.
Verde River from the            Extirpated.......  Considered extirpated
 confluence with the Salt                           by nonnatives, prey
 upstream to Fossil Creek.                          base reductions,
                                                    improper grazing,
                                                    recreation,
                                                    groundwater pumping,
                                                    diversions,
                                                    channelization, road
                                                    construction/use,
                                                    wildfire,
                                                    development,intentio
                                                    nal harm, dams.
Potrero Canyon/Springs........  Extirpated.......  Considered extirpated
                                                    by nonnatives, prey
                                                    base reductions,
                                                    improper grazing.
Tanque Verde Creek in Tucson..  Extirpated.......  Considered extirpated
                                                    by nonnatives, prey
                                                    base reductions,
                                                    improper grazing,
                                                    recreation,
                                                    development,
                                                    groundwater pumping,
                                                    road construction/
                                                    use, intentional
                                                    harm.
Rillito Creek in Tucson.......  Extirpated.......  Considered extirpated
                                                    by nonnatives, prey
                                                    base reductions,
                                                    improper grazing,
                                                    recreation,
                                                    development,
                                                    groundwater pumping,
                                                    road construction/
                                                    use, intentional
                                                    harm.
Agua Caliente Spring in Tucson  Extirpated.......  Considered extirpated
                                                    by nonnatives, prey
                                                    base reductions,
                                                    improper grazing,
                                                    recreation,
                                                    development,
                                                    groundwater pumping,
                                                    road construction/
                                                    use, intentional
                                                    harm.
Babocamari Cienega............  Extirpated.......  Considered extirpated
                                                    by nonnatives, prey
                                                    base reductions,
                                                    improper grazing.
Barchas Ranch, Huachuca         Extirpated.......  Considered extirpated
 Mountain bajada.                                   by nonnatives, prey
                                                    base reductions,
                                                    improper grazing,
                                                    borderland security/
                                                    undocumented
                                                    immigration,
                                                    intentional harm.
Parker Canyon Lake and          Extirpated.......  Considered extirpated
 tributaries in the Canelo                          by nonnatives, prey
 Hills.                                             base reductions,
                                                    improper grazing,
                                                    recreation, road
                                                    construction/use,
                                                    borderland security/
                                                    undocumented
                                                    immigration,
                                                    intentional harm,
                                                    dams.
Oak Creek at Midgley Bridge...  Extirpated.......  Considered extirpated
                                                    by nonnatives, prey
                                                    base reductions,
                                                    improper grazing,
                                                    recreation,
                                                    development,
                                                    intentional harm.
Santa Cruz River/Lower San      Extant...........  Nonnatives, prey base
 Rafael Valley (headwaters                          reductions, improper
 downstream to International                        grazing, borderland
 Border).                                           security/
                                                    undocumented
                                                    immigration,
                                                    intentional harm.
Verde River from the            Extant...........  Nonnatives, prey base
 confluence with Fossil Creek                       reductions, improper
 upstream to Clarkdale.                             grazing, recreation,
                                                    development,
                                                    groundwater pumping,
                                                    diversions,
                                                    channelization, road
                                                    construction/use,
                                                    intentional harm,
                                                    dams.
Oak Creek at Page Springs.....  Extant...........  Nonnatives, prey base
                                                    reductions.
Tonto Creek from mouth of       Extant...........  Nonnatives, prey base
 Houston Creek downstream to                        reductions, improper
 Roosevelt Lake.                                    grazing, recreation,
                                                    development,
                                                    diversions,
                                                    channelization, road
                                                    construction/use,
                                                    wildfire,
                                                    intentional harm,
                                                    dams.
Cienega Creek from headwaters   Extant...........  Nonnatives, prey base
 downstream to the ``Narrows''                      reductions, improper
 just downstream of Apache                          grazing.
 Canyon.
Pantano Wash (Cienega Creek)    Extant...........  Nonnatives, prey base
 from Pantano downstream to                         reductions, improper
 Vail.                                              grazing, wildfire.
Upper Scotia Canyon in the      Extant...........  Nonnatives, prey base
 Huachuca Mountains.                                reductions,
                                                    wildfire.
Audubon Research Ranch and      Extant...........  Nonnatives, prey base
 vicinity near Elgin.                               reductions, improper
                                                    grazing.
Downstream portion of the       Unknown..........  Nonnatives, prey base
 Black River drainage from the                      reductions, improper
 Paddy Creek confluence.                            grazing, recreation,
                                                    intentional harm.

[[Page 56236]]

 
Downstream portion of the       Unknown..........  Nonnatives, prey base
 White River drainage from the                      reductions, improper
 confluence of the East/North.                      grazing, recreation,
                                                    road construction/
                                                    use, intentional
                                                    harm.
Big Bonito Creek..............  Unknown..........  Nonnatives, prey base
                                                    reductions, improper
                                                    grazing.
Lake O' Woods (Lakeside)......  Unknown..........  Nonnatives, prey base
                                                    reductions,
                                                    recreation,
                                                    development, road
                                                    construction/use,
                                                    intentional harm.
Spring Creek above confluence   Unknown..........  Nonnatives, prey base
 with Oak Creek.                                    reductions,
                                                    development.
Bog Hole Wildlife Area........  Unknown..........  Nonnatives, prey base
                                                    reductions.
Upper 13 Tank, Patagonia        Unknown..........  Nonnatives, prey base
 Mountains bajada.                                  reductions, improper
                                                    grazing.
Babocamari River..............  Unknown..........  Nonnatives, prey base
                                                    reductions, improper
                                                    grazing.
Arivaca Cienega...............  Unknown..........  Nonnatives, prey base
                                                    reductions, improper
                                                    grazing, borderland
                                                    security/
                                                    undocumented
                                                    immigration,
                                                    intentional harm.
------------------------------------------------------------------------
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 and/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, and/or survey data is unavailable or
  insufficient, or where threats could preclude occupancy. The
  information used to develop this table can be found in the sources
  listed below.
Sources: Hyatt undated, p. 71; Nickerson and Mays 1970, pp. 495, 503;
  Hulse 1973, p. 278; Vitt and Ohmart 1978, p. 44; Hendrickson and
  Minckley 1984, p. 131, 138-162; Meffe 1985, pp. 179-185; Rosen 1987,
  p. 5; Ohmart et al. 1988, pp. 143-147, 150; Rosen and Schwalbe 1988,
  Appendix I; 1995, p. 452; 1996, pp. 1-3; 1997, p. 1; 2002b, pp. 223-
  227; 2002c, pp. 31, 70; Bestgen and Propst 1989, pp. 409-410; Clarkson
  and Rorabaugh 1989, pp. 531-538; Marsh and Minckley 1990, p. 265;
  Medina 1990, pp. 351, 358-359; Sublette et al. 1990, pp. 112, 243,
  246, 304, 313, 318; Abarca and Weedman 1993, pp. 2, 6-12; Girmendonk
  and Young 1993, pp. 45-52; Sullivan and Richardson 1993, pp. 35-42;
  Stefferud and Stefferud 1994, p. 364; Bahre 1995, pp. 240-252; Hale et
  al. 1995, pp. 138-140; Holm and Lowe 1995, pp. 5, 27-35, 37-38, 45-46;
  Rosen et al. 1995, p. 254; 1996b, pp. 8-9; 2001, Appendix I; Sredl et
  al. 1995a, p. 7; 1995b, p. 9; 1995c, p. 7; 2000, p. 10; Degenhardt et
  al. 1996, p. 319; Fernandez and Rosen 1996, pp. 6-19, 52-56; Stromberg
  et al. 1996, pp. 113-114, 123-128; Yuhas 1996; Drost and Nowak 1997,
  p. 11; Weedman and Young 1997, pp. 1, Appendices B, C; Inman et al.
  1998, Appendix B; Rinne et al. 1998, pp. 75-80; Nowak and Spille 2001,
  pp. 11, 32-33; Esque and Schwalbe 2002, pp. 161-193; Nowak and Santana-
  Bendix 2002, p. 39; Stromberg and Chew 2002, pp. 198, 210-213; Tellman
  2002, p. 43; USFWS 2002a, pp. 40802-40804; 2002b, Appendix H; 2006,
  pp. 91-105; Voeltz 2002, pp. 40, 45-81; Krueper et al. 2003, pp. 607,
  613-614; Bonar et al. 2004, pp. 1-108; Forest Guardians 2004, p. 1;
  Unmack and Fagan 2004, p. 233; Fagan et al. 2005, pp. 34-41; Olden and
  Poff 2005, pp. 75, 82-87; Painter 2005; Philips and Thomas 2005; Webb
  and Leake 2005, pp. 302, 305-310, 318-320; ADWR 2006; American Rivers
  2006; Brennan and Holycross 2006, p. 123; Holycross et al. 2006, pp.
  15-61; McKinnon 2006a, 2006b, 2006c, 2006d, 2006e; Paradzick et al.
  2006, pp. 88-93, 104-110; Segee and Neeley 2006, Executive Summary,
  pp. 5-7; 10-12, 15-16, 21-23.

    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. The majority of this assessment is 
specific to those factors that have contributed to its status in the 
United States. The following 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 we 
were unable to find specific information documenting that populations 
of the northern Mexican gartersnake in Mexico are directly affected by 
these threats. In some instances, we do include discussion on more 
refined geographic areas of Mexico when supported by the literature. 
However, many of the threats that affect the northern Mexican 
gartersnake in the United States are also present in Mexico. Thus, the 
relationship between the threats to the habitat and species in Mexico 
may be similar to what we have documented in the United States.

A. The Present or Threatened Destruction, Modification, or Curtailment 
of Its Habitat or Range

    In the following discussion, we elaborate on the physical threats 
to northern Mexican gartersnake habitats (i.e., riparian and aquatic 
communities) that have occurred and continue to occur within the 
distribution of the species in the United States and Mexico. Various 
threats that have affected and continue to affect riparian and aquatic 
communities include dams, diversions, groundwater pumping, introduction 
of nonnative species (vertebrates, plants, and crayfish), woodcutting, 
mining, contaminants, urban and agricultural development, road 
construction, 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). These activities 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 synergistically 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

[[Page 56237]]

Mexican gartersnake and to its native prey base.
    Threats to Riparian and Aquatic Biological Communities in the 
United States. The modification and destruction of aquatic and riparian 
communities in the post-settlement arid southwestern United States is 
well documented and apparent in the field (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). 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) 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 at length 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 in the United States. 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 soils.'' Many of these 
unique communities of the southwestern United States, and Arizona in 
particular, have been lost in the past century to streambed 
modification, improper livestock grazing, cultural impacts, stream flow 
stabilization by upstream dams, channelization, and stream flow 
reduction from groundwater pumping and 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 along 
many southwestern streams, including the San Pedro River. Conservation 
of the remaining natural cienegas in Arizona will be contingent on 
their protection from severe flooding and from lowering of groundwater 
levels (Hendrickson and Minckley 1984, p. 169).
    Many sub-basins where cienegas have been severely modified or lost 
entirely overlap, wholly or partially, 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 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 in the United States. 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). 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 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 
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. Medina (1990, 
pp. 358-359) concluded that perennial streams had greater tree 
densities in all diameter size classes of Arizona alder and box elder 
(Acer negundo) 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 
thermoregulation. Regional development and subsequent land use changes, 
spurred by increasing populations, along lower Tonto Creek and within 
the Verde Valley where northern Mexican gartersnakes are extant 
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 adverse effects to northern Mexican gartersnake 
habitat in the vicinity of Rock Springs along the Agua Fria River and 
also throughout the Verde Valley along the Verde River.
    The effects of urban and rural development are expected to increase 
as 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. 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 (SSDAR 2000). Over the same time period, 
population growth rates in Arizona counties where the northern Mexican 
gartersnake historically occurred or may still be extant have varied by 
county but are no less remarkable: 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,

[[Page 56238]]

and 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).
    Development growth predictions have also 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 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 
area (http://www.census.gov). All of these communities are near or 
within the vicinity of historical or extant northern Mexican 
gartersnake populations.
    Road Construction, Use, and Maintenance in the United States. Roads 
cover approximately one 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 (reptiles and amphibians) 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) an 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 and/or inhibition of reproduction; (7) 
contributions of pollutants to riparian and aquatic communities; and 
(8) population sinks 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 
visually-based hunting behaviors; and (3) filling in interstitial 
spaces of the substrate which reduces reproduction and foraging success 
of fish interfering with respiration, and restricting reproduction and 
foraging of fish. 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. Sediment can lead to several effects in resident fish species 
used by northern Mexican gartersnakes as prey species, which can 
ultimately cause the northern Mexican gartersnake's increased direct 
mortality, reduced reproductive success, lower overall abundance, lower 
species diversity, and reductions in food base as documented by Wheeler 
et al. (2005, p. 145). The underwater foraging ability of northern 
Mexican gartersnakes can also be directly compromised by excessive 
turbidity caused by sedimentation of water bodies. Metal contaminants, 
including iron, zinc, lead, cadmium, nickel, copper, and chromium, are 
bioaccumulative) and 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). 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 and lead to adverse health affects.
    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 have similar effects. 
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 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 effects 
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. There are several reasons for this 
phenomenon. First, all snakes are thigmotherms (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). Additionally, many 
species of snakes are active when traffic densities are greatest, as is 
the case with gartersnakes, which are generally diurnal (active during 
daylight hours) (Rosen and Lowe 1994, p. 147). 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, which highlights the seasonal variability in surface activity 
of this snake, and many other species of reptiles. 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 in general in modern-day society (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

[[Page 56239]]

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, such as the North American pit vipers in the genera 
Agkistrodon, Sistrurus, and Crotalus, 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.
    Roads create easy access to areas previously infrequently visited 
or inaccessible to humans, increasing the frequency and significance of 
anthropogenic threats to riparian areas and fragmenting the landscape, 
which may genetically isolate herpetofaunal populations (Rosen and Lowe 
1994, pp. 146-148; Andrews and Gibbons 2005, p. 772).
    While snakes of all species may suffer direct mortality from 
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). 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 
that roads may affect a snake's movement behavior by a variety of means 
and that generalizing these resultant behaviors does not adequately 
address this variability.
    In addition to altering the movement patterns of some snakes, roads 
can 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 trail females 
may exacerbate the effects of low population density and fragmentation 
that affect several species of snakes, including the northern Mexican 
gartersnake. Furthermore, roads can facilitate an increase in the 
distance traveled by male snakes seeking receptive females, which 
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 tend to adversely affect aquatic breeding anuran (frog and/or 
toad) populations more so than other species due to their activity 
patterns, population structures, and preferred habitats (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 affected more significantly 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 in the United States. As discussed above, population 
growth trends are expected to continue into the future. Expanding 
population growth leads to higher recreational use of riparian areas. 
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 neonates. 
Increased human visitation of occupied habitat also increases the 
potential for human-gartersnake interactions, which frequently does not 
bode well for snakes, as it often leads to their capture, injury, or 
death of the snake due to the lay person's fear 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).
    Groundwater Pumping, Surface Water Diversions, and Drought in the 
United States. 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 desiccation of riparian and 
wetland vegetative communities can follow. 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 
occurs by producing 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). Changes to the duration and timing of 
upwelling can potentially lead to localized extinctions in biota 
(Boulton and Hancock 2006, p. 139).
    To varying degrees, 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

[[Page 56240]]

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 being 
currently dominated by woody species more tolerant of declining water 
tables due to their associated deeper rooting depths.
    The full effects of largescale 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 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 ``Ten 
Most Endangered Rivers List (of 2006)'' (American Rivers 2006). This 
potential reduction or loss of baseflow in the Verde River could 
seasonally dry up large reaches and/or adversely affect the riparian 
community and the suitability of the habitat for extant 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 remains extant, 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 Tonto Creek regularly eliminates 
surface flows during parts of the year (Abarca and Weedman 1993, p. 2). 
The upper Gila River is also threatened by 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).
    Further evidence of the threat of groundwater depletion can be 
found in the management activities of the Arizona Department of Water 
Resources (ADWR). 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. 
Geographically, all five AMAs overlap the historical distribution of 
the northern Mexican gartersnake in Arizona and provide further 
evidence of the role groundwater pumping has had and continues to have 
on historical and occupied northern Mexican gartersnake habitat. Such 
overdrafts are capable of adversely impacting surface water flow of 
streams that are hydrologically connected to the aquifer under stress 
and are often exacerbated by the ever-growing number of surface water 
diversions for various purposes.
    In order to accommodate the needs of rapidly growing rural and 
urban populations, surface water is commonly diverted to serve many 
industrial and municipal uses. These 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 diversions for agriculture (Paradzick et al. 
2006, pp. 104-110).
    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) 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. 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 according to 
recorded history from the mid-1800s to the present, the effects of 
anthropogenic threats 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 where the streams were 
completely dry and therefore unsuitable northern Mexican gartersnake 
habitats.
    Improper Livestock Grazing in the United States. 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). 
Livestock grazing, as a resource use on public and private lands, has 
more than doubled quantitatively in 50 years; the number of cattle 
being grazed in the western United States increased from 25.5 million 
head in 1940, to 54.4 million head in 1990 (Belsky et al. 1999, p. 3).
    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 elucidate 
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 causes 
for subsequent fragmentation of populations and widespread 
extirpations.
    In the recent past, riparian and aquatic communities have been 
negatively impacted by poor livestock management (e.g., overgrazing, 
uncontrolled access to riparian areas,

[[Page 56241]]

improper pasture rotation, no monitoring of use, etc.) within several 
watersheds that the northern Mexican gartersnake historically occupied, 
and in some cases, poor livestock management may constitute the 
greatest impact to riparian vegetation. The specific ways in which 
improper livestock grazing can adversely affect northern Mexican 
gartersnakes and contribute to their decline is discussed below. 
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). 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 extant 
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).
    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 gartersnake itself from: (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). Stock tanks 
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). 
Specific attributes of ecosystems, such as composition, function, and 
structure, have been documented as being altered by improper livestock 
management through a variety of means including: (1) Decreasing the 
density and biomass of individual species, reducing species richness, 
and changing biological community organization; (2) interfering with 
nutrient cycling and ecological succession; and (3) changing vegetation 
stratification, contributing to soil erosion, and decreasing 
availability of water to biotic communities (Fleischner 1994, p. 631).
    The management of stock tanks is an important consideration for 
northern Mexican gartersnakes. Stock tanks can be intermediary 
``stepping stones'' in the dispersal of nonnative species from larger 
source populations to new areas (Rosen et al. 2001, p. 24). 
Additionally, 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. Poor management 
may also favor nonnative predators of the northern Mexican gartersnake 
(Rosen and Schwalbe 1988, pp. 47, 32). 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.
    A key to proper livestock management appears to be increasing the 
distribution of cattle across the entire grazing space. 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 removed by cattle was from a riparian area which amounted to 
only two 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).
    The northern Mexican gartersnake uses riparian herbaceous 
vegetation for cover, thermoregulation, and foraging. Clary and Webster 
(1989, p. 1) noted that excessive grazing and trampling from poor 
livestock management can affect riparian and stream communities by 
reducing or eliminating this vegetation, causing channel aggradation or 
degradation, causing widening or incisement of stream channels, and 
changing streambank morphology, with the cumulative result of lowering 
corresponding water tables. In support of findings made by Fleischner 
(1994, pp. 631-632), these effects can largely be attributed to the 
tendency of livestock in the arid Southwest to spend a 
disproportionately longer time in riparian areas than in upland range 
pasture (5-30 times longer, comparatively), which leads to overgrazing 
of the riparian vegetation (Clary and Medin 1990, p. 1). However, even 
when livestock's access to riparian areas is restricted, poor livestock 
management in the uplands leads to soil compaction and decreased 
filtering capacity of vegetation. These effects increase the speed and 
amount of runoff from the uplands, which contributes heightened, 
unnatural amounts of sediment in aquatic habitat. This damages the 
suitability of that habitat and fills in pools, which affects their 
permanency and suitability for many prey species of the northern 
Mexican

[[Page 56242]]

gartersnake (Sartz and Tolsted 1974, p. 354; Weltz and Wood 1986, pp. 
367-368; Orodho et al. 1990, p. 9; Trimble and Mendel 1995, pp. 235-
236; Pearce et al. 1998, p. 302). The response of riparian herbaceous 
vegetation after the removal of cattle was documented as dramatic, with 
a four to six fold increase in density, as observed in the upper San 
Pedro River (Krueper et al. 2003, pp. 607, 613-614). Schulz and 
Leininger (1990, p. 295) also remarked that riparian ecosystems can 
improve quickly when livestock are removed.
    As stated previously, dense vegetative cover is an essential 
component to habitat suitable for the northern Mexican gartersnake for 
several reasons (Szaro et al. 1985, p. 364; Rosen and Schwalbe 1988, p. 
47). The removal or severe alteration of this habitat component 
significantly affects the foraging success and heightens the predation 
risk of the northern Mexican gartersnake. Small, isolated populations 
of northern Mexican gartersnakes that use stock tanks as refugia may be 
extirpated within 1 year of vegetation removal (Rosen and Schwalbe 
1988, p. 33). Northern Mexican gartersnake populations that occur in 
isolated wetlands or stock tanks are not likely to recolonize naturally 
(i.e. without reestablishment efforts) once extirpated due to the 
species' tendency to avoid long overland movements (Rosen and Schwalbe 
1988. p. 33).
    Szaro et al. (1985, p. 360) assessed the effects of improper 
livestock management on the same stream 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 
accumulates 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.
    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 hoof action of 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 photo 
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 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.
    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. However, we recognize that well-
managed grazing can occur with limited effects to this species when 
management emphasis is directed to moderated access restrictions for 
occupied habitat combined with the use of remote drinkers 
(containerized water sources supplied by water pumped from a nearby 
source) as well as other livestock management protocols that lessen the 
effect of vegetation disturbance and removal adjacent to occupied 
habitat by increasing the distribution of cattle across an allotment. 
Lastly, as previously stated, we also recognize the value of well-
managed stock tanks in the conservation of northern Mexican 
gartersnakes.
    Catastrophic Wildfires in the United States. 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-type ecosystems 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 hydrographs, and increased sedimentation of streams. These 
effects can harm fish communities, as observed in the 1990 Dude Fire, 
in which corresponding ash flows decimated some fish populations in 
Dude Creek and the East Verde River (Voeltz 2002, p. 77). These effects 
can significantly lessen the prey base for northern Mexican 
gartersnakes and could lead to direct mortality in the case of fires 
that are within occupied habitat.
    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). 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, brome grasses may exhibit dramatic population

[[Page 56243]]

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 
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 has significant effects on lower-
elevation species, as observed in 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 in the United States. Undocumented immigrants attempt to 
cross the International border from Mexico into the United States in 
areas historically or currently occupied by the northern Mexican 
gartersnake. This method of immigration 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 concentrated levels of attempted 
undocumented immigrant 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).
    Use of new roads and trails from immigration 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. These activities also serve as a source of 
additional sediment to streams that affect their suitability as habitat 
for prey species of the northern Mexican gartersnake and affect the 
suitability and availability of pool habitats by filling them in with 
sediment. Riparian areas along the upper San Pedro River have been 
impacted by out of control fires that undocumented immigrants likely 
started to keep warm and/or prepare food (Segee and Neeley 2006, p. 
23). There also remains the threat of pursuit, capture, and death of 
northern Mexican gartersnakes when they are encountered by undocumented 
immigrants 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 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. These activities 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).
    There remains the possibility that adverse effects to riparian 
communities may increase in the future as land access and 
infrastructure restrictions in sensitive wildlife areas may be relaxed 
according to proposed policy changes that aim to boost border 
enforcement activities in these currently roadless areas and as 
concentrated enforcement efforts in urban locations funnel more 
undocumented immigrant traffic to remote wilderness areas (Segee and 
Neeley 2006, pp. 15-16).
    Habitat Threats in Mexico. 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; Contreras Balderas and 
Lozano 1994, p. 384; va Landa et al. 1997, p. 316; Miller et al. 2005, 
pp. 60-61; Abarca 2006). We experienced difficulty finding specific 
information documenting that populations of northern Mexican 
gartersnakes in Mexico are directly affected by these threats which is 
problematic in a rangewide analysis given that approximately 70 to 80 
percent of the historic distribution of the northern Mexican 
gartersnake occurs in Mexico. We did, however, find enough information 
to provide some refined discussion of smaller geographic areas within 
Mexico, and acknowledge that many of the threats that affect the 
northern Mexican gartersnake in the United States also occur in Mexico 
and could affect the northern Mexican gartersnake in similar ways but 
at potentially varying intensities.
    Conant (2003, p. 4) noted anthropogenic threats to seven 
fragmented, endemic subspecies of Mexican gartersnake in the 
Transvolcanic Belt Region of southern Mexico, which extends from 
southern Jalisco eastward through the state of M[eacute]xico to central 
Veracruz which comprises a small proportion of the subspecies' range. 
Although Conant (2003) addresses threats to a small percentage of the 
historic distribution, many of these rural land uses are regionally 
ubiquitous and therefore these threats can be extrapolated to the 
surrounding vicinity of the distribution of these seven recently 
described subspecies of the Mexican gartersnake in Mexico. Some of 
these threats included water diversions, pollution (e.g., discharge of 
raw sewage), sedimentation of aquatic habitats, and eutrophication 
(increase of dissolved nutrients and decrease of dissolved oxygen) of 
lentic (still water) habitats. Conant (2003, p. 4) expressed great 
concern that while many of these threats were evident during his field 
work in the 1960s, 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

[[Page 56244]]

biota. 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 downstream of Hoover (Boulder) Dam, have simply 
been destroyed by pollution and river alteration.'' Near 
Torre[oacute]n, Coahuila, where the northern Mexican gartersnake was 
historically distributed, groundwater pumping has resulted in flow 
reversal, which has driedup many local springs, drawn arsenicladen 
water, further contaminated the area, and resulted in adverse human 
health effects in that area. Severe water pollution from untreated 
domestic waste is evident downstream of large Mexican cities, and 
inorganic pollution from nearby industrialized areas and agricultural 
irrigation return flow has dramatically affected aquatic communities 
(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) where the northern Mexican 
gartersnake was historically distributed: ``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 historic distribution 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 Rio Colorado, 
where the northern Mexican gartersnake was distributed, 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 endemic, prey 
species of the northern Mexican gartersnake in several regions of 
Mexico, as discussed further in Factor C below (Miller et al. 2005, p. 
60).
    Miller et al. (2005) does provide some locality specific 
information on the status and threats of freshwater fishes and riparian 
and aquatic communities in specific waterbodies throughout Mexico that 
historically overlapped, or are adjacent to, the historic distribution 
of the northern Mexican gartersnake: the R[iacute]o Grande (dam 
construction, p. 78); the Rio Bravo (extirpations, pp. 82, 112); 
headwaters of the Rio Lerma (extinction/rediscovery, nonnatives, 
pollution, dewatering, pp. 60, 105, 197); Lago de Chapala and its 
outlet to the Rio Grande de Santiago (major declines, p. 106); medium-
sized streams throughout the Sierra Madre Occidental (localized 
extirpations, logging, dewatering, pp. 109, 177, 247); the Rio Conchos 
(extirpations, p. 112); the rios Casas Grandes, Santa Maria, del 
Carmen, and Laguna Bustillos (diversions, groundwater pumping, 
channelization, flood control practices, pollution, and introduction of 
nonnative species, pp. 124, 197); the Rio Santa Cruz (extirpations, p. 
140); the Rio Yaqui (nonnatives, pp. 148, Plate 61); the Rio Colorado 
(nonnatives, p. 153); the rios Fuerte and Culiacan (logging, p. 177); 
canals, ponds, lakes in the endorheic (closed) Valle de Mexico 
(nonnatives, extirpations, pollution, pp. 197, 281); the Rio Verde 
Basin (dewatering, nonnatives, extirpations, Plate 88); the Rio Mayo 
(dewatering, nonnatives, p. 247); the Rio Papaloapan (pollution, p. 
252); lagos de Zacapu and Yuriria (habitat destruction, p. 282); and 
the Rio Panuco Basin (nonnatives, p. 295).
    Conant (1974, pp. 486-489) described significant threats to 
northern Mexican gartersnake habitat within its historical distribution 
in various locations in western Chihuahua, Mexico, and within the Rio 
Concho system where it is known to occur. These threats specifically 
included impoundments, 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. McCranie and Wilson (1987, p. 2) discuss threats to the pine-oak 
communities of higher elevation habitats in the Sierra Madre 
Occidental, 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, especially if the road is paved as 
has been the case with (Mexican) Highway 40 through southern Durango. 
We feel fortunate to have worked in an area of this country of rapid 
population growth that is all too fast disappearing.'' In Mexico, as 
compared to the United States, there is believed to be a delay in the 
magnitude and significance of adverse effects to riparian communities, 
but it is believed that threats to riparian and aquatic communities 
that have been observed in Arizona as described below are currently 
occurring with increasing significance in several regions across Mexico 
within the historic distribution of the northern Mexican gartersnake 
(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).
    Collectively, the impacts described above 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. Mexico's human 
population grew 700 percent from 1910 to 2000 (Miller et al. 2005, p. 
60). More recently, 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 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). To increase forage and stocking rates for livestock 
production in the arid lowlands of northern Mexico, African buffelgrass 
(Pennisetum ciliare) was widely introduced in Mexico and has spread on 
its own (Burquez-Montijo et al. 2002, p. 131). Buffelgrass invasions 
pose a serious threat to native arid ecosystems because buffelgrass 
prevents germination of native 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 (Burquez-Montijo et al. 
2002, pp. 135, 138). Erosion affects the suitability of habitat for 
northern Mexican gartersnakes and their prey species. Recent estimates 
indicate that 80 percent of Mexico is affected by soil

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erosion with the most serious erosion occurring in the states of 
Guanajuato (43 percent of the state's land area), Jalisco (25 percent 
of the state's land area), and Mexico (25 percent of the state's land 
area) (va Landa et al. 1997, p. 317), the states in which the northern 
Mexican gartersnake historically occurred.
    The threats to riparian and aquatic communities in Mexico (such as 
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, pollution, impoundments, and dams) vary in 
their significance both geographically and ecologically, based on 
geographical distribution of land management activities and urban 
centers, but are expected to continue into the future. Threats that 
affect the amount of water within an occupied area directly affect its 
suitability to northern Mexican gartersnakes. Threats that alter the 
vegetation of occupied habitat reduce the habitat's suitability as 
cover for protection from predators, as a foraging area, and as an 
effective thermoregulatory site. Nonnative species, explained further 
in our Factor C discussion, compete with the northern Mexican 
gartersnake for prey as well as prey on juvenile and sub-adult northern 
Mexican gartersnakes, which hampers the recruitment of young snakes 
into the population and lessens the viability of that population over 
time. However, because specific and direct survey information is 
significantly limited concerning the presence and potential effect of 
these threats to the subspecies in Mexico, this discussion is based on 
extrapolation of how we understand these threats to affect the 
subspecies in the United States. Furthermore, the subspecies was 
historically distributed in several regions within Mexico that have 
remained roadless and isolated, thus suggesting that the severity of 
threats may be less than that found within the range in United States 
where lands have greater past and current economic pressures such as 
grazing and development. As such we can not conclude that the 
subspecies is likely to become endangered throughout its range in 
Mexico. Although we acknowledge that these threats are affecting the 
subpecies in the United States, we have determined that the portion of 
the subspecies' range in the United States does not constitute a 
significant portion of the range of the subspecies or a DPS. Therefore, 
on the basis of the best available information, we determine that it is 
not likely that the northern Mexican gartersnake will become an 
endangered species within the foreseeable future based on threats under 
this factor.

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 field 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 photo vouchers for university museum 
collections. Additionally, universities such as Arizona State 
University and the University of Arizona recently began to accept photo 
voucher record, versus physical specimens, in their respective museum 
collections. We believe these measures further 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 from formal biological field 
investigations and field specimen collections. We were unable to obtain 
any 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. The outbreak of 
chytrid fungus (of the genus Batrachochytrium) 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). The chytrid fungus 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 the chytrid fungus a serious threat to 
amphibian diversity. In Arizona, chytrid infections have been reported 
in several northern Mexican gartersnake native prey species (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). Declines of 
native prey species of the northern Mexican gartersnake from chytrid 
infections have contributed to the decline of this species in the 
United States. However, we do not have specific information regarding 
potential impacts of chytrid infections on northern Mexican gartersnake 
native prey species in Mexico.
    We also note that in a pure culture (uncontaminated growth medium), 
the fungus Batrachochytrium can grow on boiled snakeskin (keratin), 
which indicates the potential for the fungus to live saprobically 
(obtaining nutrients from non-living organic matter, commonly dead and 
decaying plant or animal matter, by absorbing soluble organic 
compounds) on gartersnake skin in the wild if other components of the 
ecosystem limit the growth of competing bacteria and oomycetes (a 
taxonomic group of fungi that produce oospores such as the genera 
Pythium, Phytophthora, and Aphanomyces) (Longcore et al. 1999, p. 227). 
While the genus Batrachochytrium has been grown on snakeskin in the 
laboratory, no reports of the organism on reptilian hosts in the wild 
have been documented. We anticipate diligence in monitoring the status 
of incidence of this disease in this species in the wild for early 
detection purposes should this potential threat come to fruition in 
wild populations of northern Mexican gartersnakes.
Nonnative Species Interactions
    A host of native predators prey upon northern Mexican gartersnakes

[[Page 56246]]

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). However, nonnative species, such as the 
bullfrog, the northern (virile) (Orconectes virilis) and red swamp 
(Procambarus clarki) crayfish, and numerous species of exotic sport and 
bait fish species continue to be the most prominent threat to the 
northern Mexican gartersnake and to its prey base from direct 
predation, competition, and modification of habitat in the United 
States and potentially in Mexico (Conant 1974, pp. 471, 487-489; 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; 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; Weedman and Young 1997, pp. 1, Appendices B, C; Inman et 
al. 1998, p. 17; Rinne et al. 1998, pp. 4-6; Fagan et al. 2005, pp. 34, 
34-41; Olden and Poff 2005, pp. 82-87; Unmack and Fagan 2004, p. 233; 
Miller et al. 2005, pp. 60-61; Abarca 2006; Brennan and Holycross 2006, 
p. 123; Holycross et al. 2006, pp. 13-15; Rosen and Melendez 2006, p. 
54).
    Nonnative Species Interactions in the United States. Nonnative 
species represent serious threats to the northern Mexican gartersnake 
through competition for prey, direct predation, and alteration of 
habitat. Riparian and aquatic communities have been dramatically 
impacted by a shift in species' composition. Specifically, riparian and 
wetland communities have experienced a shift from being historically 
dominated by native fauna to being increasingly occupied by an 
expanding assemblage of nonnative plant and animal species that have 
been intentionally or accidentally introduced, or have colonized new 
areas from neighboring occupied localities. For example, nonnative 
shrub species in the genus Tamarix 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 demise 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).
    Declines in the Northern Mexican Gartersnake Anuran Prey Base in 
the United States. The decline of the northern Mexican gartersnake 
within its historical and extant distribution was subsequent to the 
declines in its prey base (native amphibian and fish populations) from 
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, pp. 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). The northern Mexican 
gartersnake is 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 a hypothesis involving two 
reasons for the decline in northern Mexican gartersnakes following the 
loss or decline in the native prey base: (1) The northern Mexican 
gartersnake 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 will result (Rosen et al. 2001, pp. 10, 13).
    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.
    Declines in the native leopard frog populations in Arizona have 
significantly contributed to declines in the northern Mexican 
gartersnake, as a primary native predator. Scotia Canyon in the 
Huachuca Mountains of southeastern Arizona is a location where 
corresponding declines between leopard frog and northern Mexican 
gartersnake populations has 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 in low numbers 
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 stronghold for the northern Mexican gartersnake, the San 
Bernardino National Wildlife Refuge has also been affected by 
correlative declines between leopard frog and northern Mexican 
gartersnake populations (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). Declines of leopard frog 
populations, often correlated with nonnative species introductions (but 
also with the spread of chytridiomycosis, symptomatic disease caused by 
the chytrid fungus, and habitat modification and destruction), has not 
just occurred throughout southeastern Arizona, but throughout much of 
the U.S. distribution of the northern Mexican gartersnake based on 
survey data (Nickerson and Mays 1970, p. 495; Vitt and Ohmart 1978, p. 
44; Ohmart et al. 1988, p. 150; Rosen and Schwalbe 1988,

[[Page 56247]]

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.''
    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 in southeastern Arizona. Specifically, the authors 
identified the expansion of bullfrogs into the Sonoita grasslands (the 
threshold to the Canelo Hills) and the introduction of crayfish into 
Lewis Springs as being of particular concern in terms of future 
recovery efforts for the northern Mexican gartersnake. It should also 
be noted that Rosen et al. (2001, Appendix I) documented the decline of 
several native fish species in several locations visited, further 
affecting the prey base of northern Mexican gartersnakes. 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 ectothermic aquatic and 
semi-aquatic vertebrate species detected were nonnative. The most 
commonly encountered nonnative species was the bullfrog (Rosen et al. 
1995, p. 254).
    Declines in the Northern Mexican Gartersnake Native Fish Prey Base 
in the United States. Native fish species such as the federally 
endangered Gila chub, petitioned roundtail chub, and federally 
endangered Gila topminnow are among the primary prey species for the 
northern Mexican gartersnake (Rosen and Schwalbe 1988, p. 18). Similar 
to bullfrogs, predatory nonnative fish species such as largemouth bass 
also prey upon juvenile northern Mexican gartersnakes. Additionally 
both nonnative sport and bait 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.
    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. These native fish species 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 at risk (85.7 
percent, Stein 2002, p. 21).
    Fragmentation of extant listed native fish populations is 
exacerbating the decline of these species and may preclude their 
recovery as well as continue to affect their role in the prey base of 
northern Mexican gartersnakes. Fagan et al. (2005, pp. 34-41) examined 
the correlation between fragmentation of extant distributions and the 
relative risk of extinction of any given species. They found the 
strongest correlation to risk of extinction due to fragmentation of 
fish populations occurred at the intermediate to large spatial scales, 
which geographically correspond to tributaries and river basins (Fagan 
et al. 2005, p. 38). At this range in spatial scale, the effects of dam 
building, water diversions, and introduced nonnatives appear to be 
significant factors exacerbating the fragmentation by acting as 
barriers to the exchange of genetic material among listed fish 
populations (Fagan et al. 2005, pp. 38-39).
    Olden and Poff (2005, p. 75) stated that environmental degradation 
and the proliferation of nonnative fish species threaten the endemic 
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 (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; Voeltz 2002, p. 88; Bonar et al. 2004, pp. 1-
108).

[[Page 56248]]

    Several authors have identified both the presence of nonnative fish 
species 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 influence in 
the lower reaches where the northern Mexican gartersnake is considered 
extant. At the Gisela sampling point, four of six sampling attempts 
resulted in no fish captured; of the 41 fish captured in the remaining 
two attempts, 90 percent were nonnative, including 28 fathead minnows, 
5 green sunfish, 3 red shiner, and 1 yellow bullhead. 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).
    A report provided by Bonar et al. (2004, pp. 1-108) is the most 
current and perhaps one of the most complete assessments of native and 
nonnative fish species interactions in the Verde River mainstem. 
Overall, Bonar et al. (2004, p. 57) found that nonnative fishes were 
approximately 2.6 times more dense per unit volume of river than native 
fishes, and their standing crop was approximately 2.8 times that of 
native fishes per unit volume of river. Bonar et al. (2004, p. 79) 
verified the findings of Voeltz (2002, pp. 71, 88), in stating that red 
shiner were the most commonly encountered nonnative fish species in the 
Verde River by almost four-fold; they found the species to be present 
throughout the Verde River year-around, but noted the highest numbers 
in the reach between Beasley Flat to Sheep Bridge above Horseshoe 
Reservoir in riffle habitats. River reaches above Horseshoe Reservoir 
have resident self-sustaining populations of bass, green sunfish, 
catfish, and carp, with a low, unstable native fish community, which 
results in fewer native fish predation observations in sampling results 
for this reach (Bonar et al. 2004, pp. 80, 87). Reaches below Bartlett 
Reservoir had both high native and nonnative fish abundance, which 
resulted in more frequent observations of nonnative predation on native 
fish according to Bonar et al. (2004, p. 87). Lastly, Bonar et al. 
(2004, p. 6) found that channel and flathead catfish, green sunfish, 
largemouth and smallmouth bass, and yellow bullhead had the highest 
rates of piscivory (fish predation) on native and nonnative fish 
species in all river reaches; of these species, largemouth bass were 
documented as the most significant predator on native fish.
    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, are predatory on juvenile gartersnakes, and 
reduce the abundance of or completely eliminate native fish 
populations. This is particularly important in the wake of a stochastic 
event such as flooding, extreme water temperatures, or excessive 
turbidity. Native fish are adapted to the dramatic fluctuations in 
water conditions and flow regimes and persist in the wake of stochastic 
events as 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 extant populations. If an area is solely 
comprised of nonnative fish, the northern Mexican gartersnake may be 
faced with nutritional stress or starvation. The most conclusive 
evidence for the northern Mexican gartersnake's intolerance for 
nonnative fish remains in 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.
    Bullfrog Diet and Distribution in the United States. 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 juvenile 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). By 1982, the Arizona Game 
and Fish Department had systematically introduced some 682,000 bullfrog 
tadpoles into streams throughout the State (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). 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 conspecifics (other species within the same 
genus) which can encompass 80 percent of their diet (Casper and 
Hendricks 2005, p. 543). Bullfrogs have demonstrated astonishing 
variability in their diet, which has been documented to include 
vegetation, earthworms, leeches, insects, centipedes, millipedes, 
spiders, scorpions, crayfish, snails, numerous species of larval and 
metamorphosed amphibians, fish, small alligators, turtles, lizards, 
numerous species of snakes [seven genera; including six different 
species of gartersnakes, two species of rattlesnakes, and Sonoran 
gophersnakes (Pituophis catenifer affinis)], small mammals (e.g., 
chipmunks, cotton rats, shrews, mice, and voles), numerous species of 
birds, bats, muskrats, and even juvenile mink (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).
    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 documented the presence of bullfrogs 
through their survey efforts Statewide in specific regional areas, 
drainages, and disassociated wetlands that include 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);

[[Page 56249]]

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); Audubon 
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, 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); San Francisco River drainage (Holycross et al. 2006, 
pp. 49-50, 61); 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 Buenos Aires National Wildlife Refuge. 
Removal of adult bullfrogs resulted in a substantial increase in 
younger age-class bullfrogs where removal efforts were the most 
intensive (Rosen and Schwalbe 1997, p. 6). 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 (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). Consequently, this strategy was viewed as 
being potentially ``self-defeating'' and ``counter-productive'' but 
required further investigation (Rosen and Schwalbe 1997, p. 6).
    Bullfrog Effects on the Native Anuran Prey Base for the Northern 
Mexican Gartersnake in the United States. Bullfrog introductions in the 
United States and Mexico have adversely affected the native leopard 
frog prey base for northern Mexican gartersnakes (Conant 1974, pp. 471, 
487-489; Hayes and Jennings 1986, pp. 491-492; Rosen and Schwalbe 1988, 
p. 28-30; 2002b, pp. 232-238; Rosen et al. 1995, pp. 257-258; 2001, pp. 
2, Appendix I). Different age classes of bullfrogs within a community 
can affect native ranid populations via different mechanisms. Juvenile 
bullfrogs may affect native ranids by competition, male bullfrogs may 
affect native ranids by predation, and female bullfrogs may affect 
native ranids by 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 microhabitat use, but also suggested that an 
individual ranid frog species' physical ability to escape influences 
the effect of bullfrogs on each native ranid community.
    Kupferberg (1994, p. 95) found that where bullfrogs were present in 
California, native anurans were rare or absent. Effects of larval 
bullfrogs on native ranid frogs have also been described in the 
literature. Survivorship of larval threatened California red-legged 
frogs (Rana aurora) was 700 percent greater in the absence of bullfrog 
larvae (Lawler et al. 1999). Bury and Whelan (1986, pp. 9-10) 
implicated bullfrog introductions in the decline of several native 
ranid frogs in several States within the western United States 
including Nevada, California, Montana, Colorado, Oregon, and 
Washington. Hayes and Jennings (1986, pp. 500-501) conclude that while 
bullfrog introductions have affected the status of native ranid frogs 
throughout the western United States, the synergistic effect of other 
factors, such as habitat alteration and destruction, introduced 
nonnative fishes, commercial exploitation, toxicants, pathogens and 
parasites, and acid rain, likely also played significant roles.
    Bullfrog Predation on Northern Mexican Gartersnakes in the United 
States. 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 neonate (newborn) and juvenile age size classes due 
to bullfrogs preying on young small snakes, which ultimately leads to 
low recruitment levels (reproduction and survival of young) (Rosen and 
Schwalbe 1988, p. 18; Holm and Lowe 1995, p. 34).
    The tails of gartersnakes are easily broken-off through predation 
attempts (tails of gartersnakes do not regenerate), which may assist in 
escaping an individual predation attempt but may also lead to infection 
or compromise an individual's physical ability to escape

[[Page 56250]]

future predation attempts or successfully forage. 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. We believe this could be explained by higher basking 
rates associated with gravid (pregnant) females that increased their 
visibility to predators and that predation on juvenile snakes generally 
results in complete consumption of the animal, which would limit 
observations of tail injury in the juvenile 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) from the once-extant population of 
northern Mexican gartersnakes on the San Bernardino National Wildlife 
Refuge where 78 percent of specimens had broken tails with a ``soft and 
club-like'' terminus, which suggests repeated injury from multiple 
predation attempts. While palpating (medically examining by touch) 
gravid female northern Mexican gartersnakes, Rosen and Schwalbe (1988, 
p. 28) noted bleeding from this region which suggested 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 
neonates, 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.
    Effects of Crayfish on Northern Mexican Gartersnakes in the United 
States. Crayfish represent another category of nonnative species threat 
as they 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). 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 trophic structures (food 
chains) in riparian and aquatic ecosystems through their effect on 
vegetative structure, stream substrate 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 herpetofauna including narrow-headed 
gartersnakes (Thamnophis rufipunctatus rufipunctatus), 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 for 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 lotic (free-flowing) and lentic (still water) habitats 
throughout Arizona, many of which overlapped the historical and extant 
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. 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 recently observed at 
35 (61 percent) of the 57 sites surveyed across the Mogollon Rim 
(Holycross et al. 2006, p. 14).
    Several other authors have specifically documented the presence of

[[Page 56251]]

crayfish in many areas and drainages throughout Arizona, which is 
testament to their ubiquitous distribution in Arizona and their strong 
colonizing abilities. These areas included 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 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); 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).
    Bullfrog and Crayfish Eradication in the United States. As 
previously noted, nonnative species such as bullfrogs and crayfish have 
proven difficult, if not impossible, to eradicate once established in 
certain environments. Bullfrogs, for example, are particularly damaging 
to, and persistent in, riparian communities. A population of adult 
bullfrogs can sustain itself even when the native vertebrate prey base 
has been severely reduced or extirpated because adult bullfrogs are 
cannibalistic and larval bullfrogs can be sustained by grazing on 
aquatic vegetation (Rosen and Schwalbe 1995, p. 452). Effective removal 
of semi-aquatic nonnative species is possible in simple, geographically 
isolated systems that can be manipulated (e.g., stock tanks); however, 
it can be expensive, and specially designed fencing is likely needed to 
prevent reinvasion until entire landscapes (e.g., an entire valley) 
have been cleared of nonnative species (Rosen and Schwalbe 2002a, p. 7; 
Hyatt undated). No single method is available to effectively remove 
bullfrogs or crayfish from lotic, or complex inter-connected systems 
(Rosen and Schwalbe 1996a, pp. 5-8; 2002a, p. 7; Hyatt Undated, pp. 63-
71). The inability of land managers to effectively address the invasion 
of nonnative species in such communities highlights the serious nature 
of nonnative species invasions. Hyatt (undated, p. 71) concluded that 
successful eradication of crayfish in Arizona is highly unlikely. While 
potential threats to physical habitat from human land use activities 
can usually be lessened or removed completely with adjustments to land 
management practices, the concern for the apparent irreversibility of 
nonnative species invasions becomes paramount which leaves us to 
conclude that nonnative species are the greatest threat to the northern 
Mexican gartersnake due to the long-term implications.
    Nonnative Fish distribution and Community Interactions in the 
United States. 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; 
Audubon 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 
while surveying for narrow-headed and Mexican gartersnakes 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.
    Rinne et al. (1998, p. 3) documented over a dozen species of 
nonnative fish that have been stocked within the historical 
distribution of the northern Mexican gartersnake in the Verde Basin 
with over 850 stocking events occurring

[[Page 56252]]

in Horseshoe and/or Bartlett reservoirs and almost 4,500 in streams 
(mostly tributaries to the Verde) over the past 60 years. Rinne et al. 
(1998, pp. 4-6) found that in all but the uppermost reach, nonnatives 
predominated the sampling results in the Verde River. Voeltz (2002, p. 
88) documented an ``alarming trend'' in the Verde River with the 
reduction of native fish abundance corresponding with an explosion in 
red shiner populations.
    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, 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. Observations made 
by Dr. Phil Rosen at Finley Tank on the Audubon Research Ranch near 
Elgin, Arizona, of northern Mexican gartersnake populations and 
individual growth trends prior to the arrival of the nonnative 
bullfrog, provides information on the effects of nonnative fish 
invasions and the likely nutritional ramifications of a fish-only diet 
in a species that normally has a varied diet largely supported by 
amphibian prey items (Rosen et al. 2001, p. 19). The more energy 
expended in foraging, coupled by the reduced number of small to medium-
sized 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 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 fish species also facilitate the invasion of other 
aquatic nonnative species such as bullfrogs. Adams et al. (2003, pp. 
343, 349) found that the invasion of nonnative fish species indirectly 
facilitates the invasion of bullfrogs. Survivorship of tadpoles is 
increased when nonnative fish prey upon predatory macroinvertebrates, 
which reduces the densities of predatory macroinvertebrates and relaxes 
their predation rate on bullfrog tadpoles. These findings support the 
``invasional meltdown'' hypothesis, which suggests that when positive 
interactions among nonnatives are prevalent, that community of 
nonnative species can increase the probability of further invasions 
(Simberloff and Von Holle 1999, p. 21; Adams et al. 2003, pp. 343, 348-
350). While mutually facilitative interactions among introduced species 
have not been thoroughly examined, it has been concluded that 
nonnatives can and do facilitate the expansion of other nonnative 
species (Simberloff and Van Holle 1999, p. 21).
    Nonnative Species in Mexico. The native fish prey base for northern 
Mexican gartersnakes has been dramatically affected by the introduction 
of nonnative species in several regions of Mexico (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 and may still be extant, 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 (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 (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 the outlook for this 
trend looks ``bleak'' for 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 documented localities, several of 
which were previously noted in the discussion under Factor A.
    Bullfrogs were purposefully introduced nationwide in a concerted 
effort to establish the species in all lakes and canal systems 
throughout Mexico as a potential food source for humans although frog 
legs ultimately never gained popularity in Mexican culinary culture 
(Conant 1974, pp. 487-489). Rosen and Melendez (2006, p. 54) report 
bullfrog invasions to be prevalent in northwestern Chihuahua and 
northeastern Sonora where the northern Mexican gartersnake is thought 
to occur. In many areas, native leopard frogs were completely displaced 
(extirpated) where bullfrogs were observed. Rosen and Melendez (2006, 
p. 54) also demonstrated the relationship between fish and amphibian 
communities in Sonora and western Chihuahua in that 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 
addition to bullfrog invasions, the first record in Mexico for the 
nonnative Rio Grande leopard frog was recently documented in 
northwestern Sonora, Mexico where the northern Mexican gartersnake is 
considered likely extirpated (Rorabaugh and Servoss 2006, p. 102).
    Unmack and Fagan (2004, p. 233) compared historical museum 
collections of nonnative fish species from the Gila River basin in 
Arizona and the geographically small Yaqui River basin

[[Page 56253]]

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 
distribution, diversity, and abundance 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 and/or range reductions of native fish species are 
expected to occur in the Yaqui Basin of Sonora, Mexico which may have 
extant populations of northern Mexican gartersnake, as did much of the 
Gila Basin before the introduction of nonnative species. The 
implications of these declines in native fish to northern Mexican 
gartersnakes indicate a potentially serious threat to the gartersnake's 
persistence in these areas.
    However, because specific and direct survey information is 
significantly limited concerning the presence and potential effect of 
nonnative species on the northern Mexican gartersnake in Mexico, this 
discussion is based on extrapolation of how we understand these threats 
to affect the subspecies in the United States. Furthermore, based on 
the information available concerning the threats in Mexico we can not 
conclude that the subspecies is likely to become endangered throughout 
its range in Mexico. Although we acknowledge that these threats are 
affecting the subpecies in the United States, we have determined that 
the portion of the subspecies' range in the United States does not 
constitute a significant portion of the range of the subspecies or a 
DPS. Therefore, on the basis of the best available information, we 
determine that it is not likely that the northern Mexican gartersnake 
will become an endangered species within the foreseeable future based 
on threats under this factor.

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, only 
recommendations are afforded with respect to actions that result in 
destruction or modification of habitat (NMSA 17-2-41.C and NMAC 
19.33.6) (Painter 2005).
    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 has subsequently amended Commission Order Number 43, 
which closed the season on northern Mexican gartersnakes, effective 
January 2005. Take of northern Mexican gartersnakes is no longer 
permitted in Arizona without issuance of a scientific collecting permit 
as per Arizona Administrative 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, only recommendations are 
afforded with respect to actions that result in destruction or 
modification of northern Mexican gartersnake habitat.
    As previously mentioned, humans encounter gartersnake species 
somewhat regularly in riparian areas used for recreational purposes or 
for other reasons. This is partially due to gartersnakes having an 
active foraging strategy as well as diurnal behavior. Many such 
encounters 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 would be very difficult for the 
Arizona Game and Fish Department or the New Mexico Department of Fish 
and Game to cite lay people (who are not reptile hobbyists or amateur 
herpetologists in specific pursuit of herpetofauna) for such forms of 
take. Consequently, while the pursuit and intentional collection of 
reptiles, including the northern Mexican gartersnake, is regulated by 
these agencies, unregulated capture, collection, or killing likely 
occurs regularly.
    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. However, 
there remains the possibility that small, isolated, and/or low-density 
populations could be negatively affected by the collection of 
reproductive females (Painter 2000, p. 39; Painter 2005; Holycross 
2006).
    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 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.
    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.
    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 presence of water is a primary habitat constituent for the 
northern Mexican gartersnake. Public concern over the inadequacy of 
Arizona surface water laws to ensure that flow is maintained perennial 
streams was discussed by Arizona Republic columnist Shaun McKinnon 
(2006b). McKinnon (2006b) 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

[[Page 56254]]

years ago when Arizona's water laws were written, the important 
connection between groundwater and surface water was not known 
(McKinnon 2006b). Furthermore, meaningful changes to these regulations 
that account for the relative scarcity of surface water are unlikely to 
come about because Arizona is so ``entrenched in tradition and in 
property ownership'' and because the threat of litigation over proposed 
changes precludes such efforts (McKinnon 2006b). McKinnon (2006b) 
specifically, mentions the Gila, Salt, Verde, Santa Cruz, and San Pedro 
rivers as having habitat attributes that have directly suffered from 
inadequate surface water regulations.
    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 may 
opportunistically gather data on the gartersnakes observed incidentally 
in the field for their records, although it is not required.
    Activities that could adversely affect northern Mexican 
gartersnakes and their habitat continue to occur throughout their 
extant distribution on U.S. Forest Service 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 accounted for in 
regulatory compliance mechanisms, such as in section 7 consultation 
under the Act for other listed species that may co-occur with the 
northern Mexican gartersnake in an area.
    The majority of extant 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.
    Riparian communities are complex and recognized as unique in the 
southwestern United States but are highly sensitive to many 
anthropogenic 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 and/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.
    Throughout Mexico, the Mexican gartersnake is federally 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 time frame, if the factors that impact negatively their 
viability, cause the deterioration or modification of their habitat or 
directly diminish directly 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 and/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, 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 
recently developed the Method of Evaluation of the Risk of Extinction 
of the Wild Species in Mexico (MER) which unifies the criteria of 
decision 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 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, 
the Mexican gartersnake was placed on the NOM-059 [SEDESOL 1994 (NOM-
059-ECOL-1994), p. 46] as a threatened species as determined by a panel 
of scientific experts. However, we are uncertain of the specific 
information that was used as the basis for the listing in Mexico and 
were unable to obtain any information that was used to validate the 
Federal listing of the Mexican gartersnake in Mexico.
    Our review of the existing governmental regulatory mechanisms that 
pertain to the management of the northern Mexican gartersnake or its 
habitat in the United States leads us to conclude that the protections 
afforded by existing regulations may be insufficient to adequately 
address the declining status of the subspecies in the United States. 
However, the Mexican gartersnake (inclusive of the northern Mexican 
gartersnake) is considered a Federally-threatened species in Mexico. 
Although we do not have sufficient information to analyze the efficacy 
of existing regulatory mechanisms in Mexico, the best available data 
does not support the conclusion that the species is likely to become in 
danger of extinction within the foreseeable future due to the threats 
posed by the other factors. Therefore, uncertainty with respect to the 
efficacy of existing regulatory mechanisms is not dispositive as to the 
listing status of the subspecies, and it is not a threatened species on 
the basis of the lack of existing regulatory mechanisms.

[[Page 56255]]

E. Other Natural or Manmade Factors Affecting Its Continued Existence 
in the United States

    Marcy's checkered gartersnake (Thamnophis marcianus marcianus) may 
have ecological implications in the decline and future conservation of 
the northern Mexican gartersnake in southern Arizona. 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. Marcy's checkered gartersnake 
is a potential benefactor of this scenario. As northern Mexican 
gartersnake numbers decline within a population, space becomes 
available for occupation by checkered gartersnakes. Marcy's checkered 
gartersnake subsequently maintains pressure on the carrying capacity 
(the maximum number of a given species that an area can maintain based 
upon available resources) for an area and could potentially accelerate 
the decline of the northern Mexican gartersnake (Rosen and Schwalbe 
1988, p. 31).
    Rosen et al. (2001, pp. 9-10) documented the occurrence of Marcy's 
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 ecological relationship 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.
    We were unable to obtain any information on other natural or 
manmade factors affecting the continued existence of the northern 
Mexican gartersnake in Mexico.
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 period following 
our 90-day petition finding and consulted with recognized northern 
Mexican gartersnake experts and other Federal, State, and Mexican 
resource agencies. Because specific and direct survey information is 
significantly limited concerning the presence and potential effect of 
the threats discussed in this finding to the subspecies in Mexico, much 
of our discussion is based on extrapolation of how we understand these 
threats to affect the subspecies in the United States. Furthermore, 
based on the information available concerning the threats in Mexico we 
can not conclude that the subspecies is likely to become endangered 
throughout its range in Mexico. Although we acknowledge that several 
threats are affecting the subpecies in the United States, we have 
determined that the portion of the subspecies' range in the United 
States does not constitute a significant portion of the range of the 
subspecies or a DPS. On the basis of the best scientific and commercial 
information available, we determine that it is not likely that the 
northern Mexican gartersnake is likely to become an endangered species 
within the foreseeable future and that listing of the northern Mexican 
gartersnake throughout its range in the United States and Mexico based 
on its rangewide status is not warranted.
    In making this finding, we respectfully acknowledge that the 
Mexican government has found Thamnophis eques to be in danger of 
disappearance in the short-or medium-term future in their country from 
the destruction and modification of its habitat and/or from the effects 
of shrinking population sizes and has therefore listed the species as 
Threatened, under the listing authority of SEMARNAT (SEDESOL 2001). 
However, as discussed at length in Factor D above, we also note that 
the level of information required to list a species in Mexico may not 
be as rigorous as that required to list a species in the United States 
under the Endangered Species Act. Our conclusion that listing is not 
warranted under the Act is based on: (1) The apparent differences in 
listing protocols; (2) the significantly limited amount of information 
available on the status of and threats to the northern Mexican 
gartersnake in Mexico in comparison to our knowledge of the same in the 
United States; and most importantly (3) the relatively large percentage 
(70 to 80 percent) of the subspecies' historic distribution in Mexico 
for which we have little to no information about with respect to status 
and threats.
    In making this Finding, we also recognize there have been 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 locality where northern Mexican 
gartersnakes have been documented in the United States. As discussed in 
Factor C above, the documented mechanisms for which nonnative 
interactions occur 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 (Meffe 1985, pp. 179-185; Rosen and Schwalbe 1988, pp. 28-
31; 1995, p. 452; 2002b, pp. 223-227; 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; Rosen et al. 1995, 
pp. 257-258; 1996, pp. 2, 11-12; 2001, pp. 2, 21-22; Degenhardt et al. 
1996, p. 319; Fernandez and Rosen 1996, pp. 21-33; Weedman and Young 
1997, pp. 1, Appendices B, C; Inman et al. 1998, p. 17; Rinne et al. 
1998, pp. 4-6; Fagan et al. 2005, pp. 38-39; Olden and Poff 2005, pp. 
82-87; Holycross et al.2006, pp. 12-15; Brennan and Holycross 2006, p. 
123). However, we again note that the portion of the historic 
distribution of the northern Mexican gartersnake in the United States 
represents approximately 20 to 30 percent of its rangewide 
distribution. Furthermore, we were unable to obtain substantial 
information regarding the status of the northern Mexican gartersnake in 
Mexico (representing approximately 70 to 80 percent of its rangewide 
distribution).
    Throughout the range of the northern Mexican gartersnake, but most 
accurately within its distribution in the United States, literature 
documents the cause and effect relationship of disturbances to the 
trophic structure (food chain) of 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

[[Page 56256]]

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 extant northern Mexican 
gartersnake populations and has led to significant fragmentation and 
risks to the continued viability of extant 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.
    We further recognize that in addition to the deleterious effects 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 in Factor A, ``The Present or Threatened Destruction, 
Modification, or Curtailment of its Habitat or Range,'' effectively 
summarize our knowledge of the current and future status of its 
riparian and aquatic habitat in the United States. Chiefly, these 
threats include: (1) The modification and loss of ecologically valuable 
cienegas (Hendrickson and Minckley 1984, p. 161; Stromberg et al. 1996, 
p. 113); (2) urban and rural development (Medina 1990, p. 351; 
Girmendock and Young 1997, pp. 45-47; Voeltz 2002, p. 88; Wheeler et 
al. 2005, pp. 153-154); (3) road construction, use, and maintenance 
(Rosen and Lowe 1994, pp. 143, 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, p. 19; Shine et al. 
2004, pp. 9, 17-19; Andrews and Gibbons 2005, p. 772; Wheeler et al. 
2005, pp. 145, 148-149; Roe et al. 2006, pp. 163-166); (4) human 
population growth (Girmendock and Young 1993, p. 47; American Rivers 
2006; Arizona Republic, March 16, 2006); (5) groundwater pumping, 
surface water diversions, and drought (Abarca and Weedman 1993, p. 2; 
Girmendock and Young 1993, pp. 45-52; Sullivan and Richardson 1993, pp. 
35-42; Stromberg et al. 1996, pp. 124-127; Boulton et al. 1998, pp. 60-
62; Rinne et al. 1998, pp. 7-11; Voeltz 2002, p. 88; Philips and Thomas 
2005; Webb and Leake 2005, pp. 307-308; American Rivers 2006; Boulton 
and Hancock 2006, p. 139); (6) improper livestock grazing (Sartz and 
Tolsted 1974, p. 354; Kauffman and Krueger 1984, pp. 433-434; Szaro et 
al. 1985, pp. 361-363; Weltz and Wood 1986, p. 367-368; Clary and 
Webster 1989, pp. 1-3; Clary and Medin 1990, pp. 1-6; Orodho et al. 
1990, p. 9; Fleischner 1994; pp. 631-632; Trimble and Mendel 1995, p. 
233; Waters 1995, pp. 22-24; Girmendock and Young 1997, p. 47; Pearce 
et al. 1998, p. 302; Belsky et al. 1999, p. 1; Voeltz 2002, p. 88; 
Krueper et al. 2003, pp. 607, 613-614); (7) catastrophic wildfire and 
wildfire in non-fire adapted communities (Rinne and Neary 1996, p. 135; 
Esque and Schwalbe 2002, pp. 165, 190); and (8) undocumented 
immigration and international border enforcement and management 
activities (Segee and Neeley 2006, pp. 5-7; USFWS 2006, pp. 91-105).
    In our discussion under Factors A through E above, we have provided 
a comprehensive, in-depth analysis of all known threats that have or 
continue to affect the status of the northern Mexican gartersnake in 
the United States, including those which have not yet been documented 
but where potential effects exist. As a result of our assessment, we 
note that certain land use activities such as road construction and 
use, direct mortality from livestock grazing, undocumented immigration 
and 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. 
As noted on several occasions above, in these types of situations where 
the viability of a known northern Mexican gartersnake population is 
clearly at risk, the loss of a single reproductive female due to these 
threats is of concern. However, these types of threats are less 
significant to the northern Mexican gartersnake when the status of 
these at-risk populations improves through the implementation of 
conservation activities. We also remain optimistic that our local, 
State, and Federal partners in wildlife conservation will be proactive 
in monitoring populations and implementing conservation measures to 
ensure that apparent declines of the northern Mexican gartersnake in 
the United States are reversed and that this species remains a member 
of our native riparian and aquatic communities. But we do not rely upon 
any future conservation actions in making this finding.
    Notwithstanding our extensive discussion of the past and ongoing 
threats affecting this species, and the evidence of range contraction 
within the United States, neither the existence of the threats nor past 
range contraction means that a species meets the definition of a 
threatened or endangered species under the Act. Based on our evaluation 
of the best available data, we conclude that the northern Mexican 
gartersnake is not likely to become an endangered species in all or a 
significant portion of its range in the foreseeable future.

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 document is the Arizona Ecological 
Services Office (see ADDRESSES section).

    Authority: The authority for this action is the Endangered 
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).

    Dated: September 14, 2006.
H. Dale Hall,
Director, Fish and Wildlife Service.
[FR Doc. 06-7784 Filed 9-25-06; 8:45 am]
BILLING CODE 4310-55-P