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, 56228-56256 [06-7784]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

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



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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
                                                    im