Endangered and Threatened Wildlife and Plants; 90-Day Finding on a Petition To List the Sonoran Population of Desert Tortoise (Gopherus agasizzii, 44335-44344 [E9-20835]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 74, Number 166 (Friday, August 28, 2009)]
[Proposed Rules]
[Pages 44335-44344]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E9-20835]


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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R2-ES-2009-0032]
[92210-1117-0000-B4]


Endangered and Threatened Wildlife and Plants; 90-Day Finding on 
a Petition To List the Sonoran Population of Desert Tortoise (Gopherus 
agasizzii) as a Distinct Population Segment (DPS) With Critical Habitat

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Notice of petition finding and initiation of status review.

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SUMMARY: We, the U.S. Fish and Wildlife Service, announce a 90-day 
finding on a petition to list the Sonoran desert tortoise (Gopherus 
agasizzii) as a distinct population segment (DPS) under the Endangered 
Species Act of 1973, as amended, and designate critical habitat. On the 
basis of our review of the petition and information readily available 
in our files, we have determined that there is substantial information 
indicating that the Sonoran

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desert tortoise may meet the criteria of discreteness and significance 
as defined by our policy on distinct vertebrate population segments. 
Further, we find that the petition presents substantial scientific or 
commercial information indicating that listing the Sonoran population 
of the desert tortoise may be warranted. Therefore, with the 
publication of this notice, we are initiating a status review of the 
Sonoran population of the desert tortoise to determine if listing the 
population is warranted. To ensure that the status review of the 
Sonoran population of the desert tortoise is comprehensive, we are 
soliciting scientific and commercial data and other information 
regarding this population. At the conclusion of this review, we will 
issue a 12-month finding to determine if the petitioned action is 
warranted. We will make a determination on critical habitat for the 
Sonoran population of the desert tortoise if we initiate a listing 
action.

DATES: We made the finding announced in this document on August 28, 
2009. To allow us adequate time to conduct this review, we request that 
we receive information on or before October 27, 2009.

ADDRESSES: You may submit information by one of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov. Follow the instructions for submitting comments.
     U.S. mail or hand-delivery: Public Comments Processing, 
Attn: [FWS-R2-ES-2009-0032]; Division of Policy and Directives 
Management; U.S. Fish and Wildlife Service; 4401 N. Fairfax Drive, 
Suite 222; Arlington, VA 22203.
    We will post all information received on https://www.regulations.gov. This generally means that we will post any 
personal information you provide us (see the Information Solicited 
section below for more details).

FOR FURTHER INFORMATION CONTACT: Steve Spangle, Field Supervisor, 
Arizona Ecological Services Office, 2321 West Royal Palm Drive, Suite 
103, Phoenix, AZ 85021; by telephone 602-242-0210; or by facsimile 602-
242-2513. Persons who use a telecommunications device for the deaf 
(TDD), may call the Federal Information Relay Service (FIRS) at 800-
877-8339.

SUPPLEMENTARY INFORMATION:

Information Solicited

    When we make a finding that a petition presents substantial 
information indicating that listing a species may be warranted, we are 
required to promptly commence a review of the status of the species. To 
ensure that the status review is complete and based on the best 
available scientific and commercial information, we are soliciting 
information on the status of the Sonoran population of the desert 
tortoise (Sonoran desert tortoise). We request information from the 
public, other concerned governmental agencies, Native American Tribes, 
the scientific community, industry, or any other interested parties 
concerning the status of the Sonoran desert tortoise. We are seeking 
information regarding:
    (1) The historical and current status and distribution of the 
Sonoran desert tortoise (particularly with respect to Mexico), its 
biology and ecology, and ongoing conservation measures for the species 
and its habitat;
    (2) Information relating the importance of the Sonoran desert 
tortoise population to the species as a whole;
    (3) Information relevant to the factors that are the basis for 
making a listing determination for a species under section 4(a) of the 
Endangered Species Act of 1973, as amended (Act) (16 U.S.C. 1531 et 
seq.), which are:
    (a) the present or threatened destruction, modification, or 
curtailment of the species' 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 and threats to the species or its habitat; and
    (4) Information about any ongoing conservation measures for, or 
threats to, the Sonoran desert tortoise and its habitat.
    If we determine that listing the Sonoran desert tortoise is 
warranted, it is our intent to propose critical habitat to the maximum 
extent prudent and determinable at the time we would propose to list 
the Sonoran desert tortoise. Therefore, with regard to areas within the 
geographical range currently occupied by the Sonoran desert tortoise, 
we also request data and information on what may constitute physical or 
biological features essential to the conservation of the Sonoran desert 
tortoise, where these features are currently found, and whether any of 
these features may require special management considerations or 
protection. In addition, we request data and information regarding 
whether there are areas outside the geographical area occupied by the 
Sonoran desert tortoise that are essential to its conservation. Please 
provide specific comments and information as to what, if any, critical 
habitat should be proposed for designation if the Sonoran desert 
tortoise is proposed for listing, and why such habitat meets the 
requirements of the Act.
    Please note that comments merely stating support for or opposition 
to the action under consideration without providing supporting 
information, although noted, will not be considered in making a 
determination, as section 4(b)(1)(A) of the Act directs that 
determinations as to whether any species is a threatened or endangered 
species must be made ``solely on the basis of the best scientific and 
commercial data available.'' Based on the status review, we will issue 
a 12-month finding on the petition, as provided in section 4(b)(3)(B) 
of the Act.
    You may submit your information concerning this finding by one of 
the methods listed in the ADDRESSES section.
    If you submit information via https://www.regulations.gov, your 
entire submission--including any personal identifying information--will 
be posted on the website. If your submission is made via a hardcopy 
that includes personal identifying information, you may request at the 
top of your document that we withhold this information from public 
review. However, we cannot guarantee that we will be able to do so. We 
will post all hardcopy submissions on https://www.regulations.gov.
    Information and materials we receive, as well as supporting 
documentation we used in preparing this finding, will be available for 
public inspection on https://www.regulations.gov, or by appointment, 
during normal business hours, at the U.S. Fish and Wildlife Service, 
Arizona Ecological Services Office (see FOR FURTHER INFORMATION 
CONTACT).

Background

    Section 4(b)(3)(A) of the Act requires that we make a finding on 
whether a petition to list, delist, or reclassify a species presents 
substantial scientific or commercial information to indicate that the 
petitioned action may be warranted. We are to base this finding on 
information contained in the petition, supporting information submitted 
with the petition, and information otherwise available in our files. To 
the maximum extent practicable, we are to make this finding within 90 
days of receipt of the petition and publish our notice of this finding 
promptly in the Federal Register.
    Our standard for substantial scientific or commercial information 
within the

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Code of Federal Regulations (CFR) with regard to a 90-day petition 
finding is ``that amount of information that would lead a reasonable 
person to believe that the measure proposed in the petition may be 
warranted'' (50 CFR 424.14(b)). If we find that substantial scientific 
or commercial information was presented, we are required to promptly 
commence a status review of the species.
    On October 15, 2008, we received a petition dated October 9, 2008, 
from WildEarth Gardians and Western Watersheds Project (petitioners) 
requesting that the Sonoran population of the desert tortoise be listed 
under the Act as a distinct population segment (DPS), as threatened or 
endangered rangewide (in the United States and Mexico), and critical 
habitat be designated. The petition clearly identified itself as such 
and included the requisite identification information for the 
petitioners, as required in 50 CFR 424.14(a). The petition contained 
detailed information on the natural history, biology, current status, 
and distribution of the Sonoran population of the desert tortoise. It 
also contained information on what the petitioners reported as 
potential threats to the Sonoran population of the desert tortoise, 
such as livestock grazing, urbanization and development, mining, 
international border patrol activities, illegal collection, inadequacy 
of existing regulations, altered fire regimes, off-highway vehicle use, 
drought, and climate change. In a November 26, 2008, letter to the 
petitioners, we responded that we had reviewed the information 
presented in the petition and determined that issuing an emergency 
regulation temporarily listing the species as per section 4(b)(7) of 
the Act was not warranted. We also stated that we intended to make our 
finding on whether the petition presented substantial information that 
the requested action may be warranted, to the maximum extent 
practicable within 90 days of receipt of the petition, according to the 
provisions of section 4(b)(3) of the Act.

Previous Federal Actions

    Throughout this finding, we use ``Mojave'' to describe desert 
tortoise populations north and west of the Colorado River, which is 
consistent with the previous and current spelling of the common name in 
Federal actions that have addressed this population. We use ``Mohave'' 
in the geographic context to remain consistent with its reference by 
the U.S. Board of Geographic Names (e.g., Mohave Desert, Mohave 
County). In addition, while we do not currently recognize the Sonoran 
population of the desert tortoise as a unique taxonomic entity, for 
ease of reference, we refer to the Sonoran population of the desert 
tortoise as the ``Sonoran desert tortoise'' in this document.
    On December 30, 1982, we published a notice of review which 
determined the desert tortoise throughout its range in the United 
States and Mexico to be a Category 2 Federal Candidate species (47 FR 
58454); this was reaffirmed on September 18, 1985 (50 FR 37958). 
Category 2 status was granted to species for which information in our 
possession indicated that a proposed listing as threatened or 
endangered was possibly appropriate, but for which sufficient data were 
not available to make a determination of listing status under the Act. 
On April 2, 1990, we issued a final rule designating the Mojave 
population of the desert tortoise (occurring north and west of the 
Colorado River) as a threatened species under the Act (55 FR 12178; see 
final rule for a summary of previous actions regarding the Mojave 
population of the desert tortoise). Currently, the Mojave population of 
the desert tortoise is recognized as a DPS under the Act. As part of 
that rulemaking, we designated any desert tortoise from the Sonoran 
population as threatened when observed outside of its known range, due 
to similarity of appearance under section 4(a) of the Act.
    On December 5, 1996, we published a rule that discontinued the 
practice of keeping a list of category 2 candidate species (61 FR 
64481). Since that time, the Sonoran desert tortoise has had no Federal 
Endangered Species Act status.

Species Information

    The desert tortoise is a member of the Testudinidae family 
(terrestrial tortoises) of turtles in the genus Gopherus (Rafinesque 
1832), or gopher tortoises. Scientific nomenclature assigned to the 
desert tortoise has undergone a series of changes since its initial 
description by Cooper (1863) as Xerobates agassizii. The desert 
tortoise was also once known as Scaptochelys agassizii (Crother et al. 
2008, p. 70). Further information is available on classification of the 
desert tortoise in Van Devender (2002b), Lamb and McLuckie (2002), and 
McCord (2002).
    The desert tortoise is recognized by its gray to orange-brown, 
high, domed upper shell. The shell measures 8 to 15 inches (20 to 38 
centimeters) in length (Service 2008, p. 4). Adult desert tortoises may 
weigh 8 to 15 pounds (3.6 to 6.8 kilograms) (Service 2008, p. 4). Hind 
limbs of the desert tortoise are stocky and elephantine in appearance 
while the forelimbs are paddle-shaped and used for digging (Brennan and 
Holycross 2006, p. 54). In the wild, desert tortoises have an average 
lifespan of 35 years (Germano 1994).
    The Sonoran desert tortoise is closely associated with rocky 
bajadas (lower slopes of mountains) and hillsides, and, to a lesser 
extent, flat areas (including incised washes between or adjacent to 
flat terrain) (Riedle et al. 2008). Sonoran desert tortoises generally 
occur at elevations ranging from 510 to 5,300 feet (155 to 1,615 
meters) (Arizona Game and Fish Department 2001, p. 4).
    In the United States, the Sonoran desert tortoise occurs within 
Mohave desertscrub, Sonoran desertscrub, and semi-desert grassland 
habitat (Germano et al. 1994; Van Devender 2002a; Brennan and Holycross 
2006, p. 54). In Mexico, the Sonoran desert tortoise occurs in Sonoran 
desertscrub and semi-desert grassland (Germano et al. 1994; Fritts and 
Jennings 1994; Bury et al. 2002; Van Devender 2002a; Edwards et al. 
2009, p. 8). The Sonoran desert tortoise may also occasionally occur in 
the lower elevations of Madrean oak woodland (Germano et al. 1994; 
Fritts and Jennings 1994; Bury et al. 2002; Van Devender 2002a).
    Primarily herbivores, Sonoran desert tortoises consume a variety of 
plant material in their diet (Van Devender et al. 2002).
    Sonoran desert tortoises are largely inactive from mid-October to 
late February or early March when they overwinter in constructed 
burrows or rocky cavities or crevices (Averill-Murray 2000b). Sonoran 
desert tortoises tend to use or construct burrows differently, 
depending on habitat. Riedle et al. (2008) found that the availability 
of adequate shelter sites strongly influenced Sonoran desert tortoise 
densities.
    Tortoise activity spikes in the spring, especially following 
average or above-average winter precipitation that enhances annual 
plant production (Averill-Murray 2000b). However, the peak activity for 
the Sonoran desert tortoises occurs at the onset of the monsoon (summer 
rainy season) in mid- to late-summer when annual and perennial plants 
reach peak abundance and availability, and water sources become more 
widely dispersed across the landscape (Averill-Murray 2000b). During 
the hot and dry late-spring/early-summer season, Sonoran desert 
tortoises are less active or may become entirely dormant until the 
onset of the monsoon (Averill-Murray 2000b).
    The monsoon also marks the height of social interaction and 
reproductive behaviors for the Sonoran desert tortoise. During this 
time, female

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Sonoran desert tortoises lay their eggs, with an average clutch size of 
5 (Averill-Murray and Klug 2000). Hatchling Sonoran desert tortoises 
will emerge from the nest site (burrow) in late summer or they may 
overwinter, emerging the following spring (Wilson et al. 1999; Averill-
Murray 2000b). Sonoran desert tortoises reach sexual maturity at 
approximately 10 to 12 years of age (Averill-Murray 2000b).
    Desert tortoises are distributed from California, Nevada, Utah, and 
Arizona in the United States, south through the Mexican states of 
Sonora and Sinaloa. The specific distribution of desert tortoise is 
likely determined by habitat and climatic characteristics (e.g., 
vegetation community (food), soil and substrate characteristics 
(shelter), precipitation pattern (water availability)) within the 
appropriate elevation range. The distribution of the Sonoran desert 
tortoise in the United States is considered to be east and south of the 
Colorado River, extending south and east from northwestern Mohave 
County in Arizona (Germano et al. 1994; Van Devender 2002a, Brennan and 
Holycross 2006, p. 54), covering roughly the western portion of the 
state. The distribution in the United States is likely bounded to the 
northeast and east by habitat changes imposed by the Mogollon Rim. In 
Mexico, the distribution of the Sonoran desert tortoise extends from 
the International Border of Sonora and Arizona, south to the vicinity 
of Guaymas, north of the Yaqui River, in southern Sonora (Germano et 
al. 1994; Fritts and Jennings 1994; Bury et al. 2002; Van Devender 
2002a; Edwards et al. 2009, pp. 7-8), covering approximately the 
western half of the state of Sonora from the Gulf of California coast 
east roughly to the transition to unsuitable woodland and conifer 
forest areas in the higher elevations of the Sierra Madre Occidental. 
The Mojave and Sinaloan populations of desert tortoises represent two 
additional populations of this species recognized in the literature 
(Lamb and McLuckie 2002). The Mojave population, listed as threatened 
in 1990, includes those populations that occur north and west of the 
Colorado River in southern California, southern Nevada, southwestern 
Utah, and extreme northwestern Arizona; and the Sinaloan population is 
considered to be generally distributed along and within the western 
face of the Sierra Madre Occidental of central Sonora south into the 
border region between Sonora and Sinaloa at the extreme southern end of 
the species' range (Lamb and McLuckie 2002). Genotypes (genetic makeup 
of an organism) differ significantly between populations (Lamb and 
McLuckie 2002).

Distinct Population Segment

    Under section 3(15) of the Act, we may consider for listing any 
species, subspecies, or, for vertebrates, any DPS of these taxa. In 
determining whether an entity constitutes a DPS, and is therefore 
listable under the Act, we follow the Policy Regarding the Recognition 
of Distinct Vertebrate Population Segments Under the Endangered Species 
Act (DPS Policy) (61 FR 4722; February 7, 1996). Under our DPS Policy, 
three elements are considered in a decision regarding the status of a 
possible DPS: (1) the discreteness of the population segment in 
relation to the remainder of the taxon; (2) the significance of the 
population segment 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., whether the population segment, when 
treated as if it were a species, is endangered or threatened) (61 FR 
4722, February 7, 1996). The first two elements are used to determine 
if the population segments constitutes a valid DPS. If it does, then 
the third element is used to consider whether such DPS warrants 
listing. In this section, we will consider the first two criteria 
(discreteness and significance) to determine if the Sonoran desert 
tortoise may be a valid DPS (i.e., a valid listable entity). 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).
    The petitioners requested we examine the Sonoran desert tortoise as 
a DPS. The information discussed below was presented by the 
petitioners, unless otherwise noted.
    The petitioned DPS includes those populations that occur east and 
south of the Colorado River, south to the biogeographical boundary of 
the Yaqui River in southern Sonora, Mexico. In making this delineation 
for the petitioned DPS, the petitioners considered biogeographic 
isolation, ecological divergence, morphological and physiological 
characteristics, and genetic polymorphisms (genetic material occurring 
in multiple forms or configurations).
    The petitioners discuss a population of desert tortoise with the 
``Mojave'' genotype (i.e., having similar genetic characteristics to 
the those of the Mojave DPS of desert tortoise) which occurs in the 
Black Mountains of Mohave County, Arizona (isolated from the threatened 
Mojave DPS that occurs north and west of the Colorado River), and are 
seeking the inclusion of that population within the petitioned DPS 
because it does not currently have protection under the Act. We will 
evaluate this anomalous situation further in our 12-month finding.

Discreteness

    Under the DPS Policy, a population segment of a vertebrate species 
may be considered discrete if it satisfies either one of the following 
two conditions: (1) it is markedly separated from other populations of 
the same taxon as a consequence of physical, physiological, ecological, 
or behavioral factors. Quantitative measures of genetic or 
morphological discontinuity may provide evidence of this separation; or 
(2) it is delimited by international governmental boundaries within 
which significant differences in control of exploitation, management of 
habitat, conservation status, or regulatory mechanisms exist (61 FR 
4722, February 7, 1996).
Information Provided in the Petition on Discreteness
    The petitioners claim that the Sonoran population is discrete from 
the Mojave and Sinaloan populations due to differences in habitat use, 
reproduction strategies, physical characteristics, and genotype. The 
petitioners claim that the Colorado (United States) and Yaqui (Sonora, 
Mexico) Rivers act as biogeographical barriers to movement of tortoises 
between the Mojave and Sonoran populations, and between the Sonoran and 
Sinaloan populations, respectively. In view of this biogeographical 
isolation, the petitioners claim that significant ecological divergence 
has occurred between the Mojave and Sonoran populations of desert 
tortoise, largely due to significant differences in geology, vegetation 
types, and precipitation cycles where the populations are distributed. 
Desert tortoises in the Mojave population are most dense in the 
intermountain valleys that have soil types favorable to the 
construction of large, deep burrows (Bury et al. 1994). However, 
Sonoran desert tortoises reach maximum densities in the rocky bajadas 
and hillsides of higher slope, with reduced densities in the 
intermountain valleys (Averill-Murray et al. 2002b). The petitioners 
state that differences in precipitation cycle have led to notable 
differences in seasonal activity patterns between desert tortoises that 
occur in the Sonoran and Mojave deserts. Information in our files 
confirms these assertions. Specifically, analyzing the genetic 
population structure among desert tortoise populations in Mexico,

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Edwards et al. (2009, pp. 7-8) suggest the Sinaloan population of 
desert tortoise uses Sinaloan thornscrub and tropical deciduous forest 
habitats (which are created by higher precipitation levels). However, 
some level of gradation of the Sonoran and Sinaloan genotypes may occur 
in the vegetative transition zone between Plains of Sonora subdivision 
of Sonoran desertscrub and Sinaloan thornscrub habitats of central 
Sonora (Edwards et al. 2009, p. 8).
    Differences in reproduction strategies between the Sonoran and 
Mojave populations of desert tortoises were also discussed in the 
petition. In the Mojave population of desert tortoises, females lay up 
to three clutches of eggs per year with larger clutch sizes, earlier in 
the year (April to mid-July) while those in the Sonoran population lay 
one clutch per year of smaller size, later in the year (June through 
August) (Wallis et al. 1999; Averill-Murray et al. 2002a). These 
differences led Averill-Murray (2002b) and Henen (1997) to hypothesize 
that Sonoran desert tortoises invest all reproductive effort into a 
single clutch which hatches at the peak of forage and water 
availability and abundance, whereas desert tortoises in the Mojave 
population (maturing at younger ages and at smaller body sizes), have 
higher clutch numbers to account for higher mortality. Comparative 
reproduction strategies of the Sinaloan population of the desert 
tortoise were not discussed in the petition.
    The petitioners claim morphological and physiological 
characteristics, in particular, shell characteristics, differ between 
the Sonoran and Mojave populations of desert tortoises. Germano (1993) 
found that desert tortoise shells in the Sonoran population are 
narrower than those in the Mojave population, were less domed, and 
possessed shorter gular shields (plates projecting forward from the 
lower shell). Desert tortoises in the Sonoran population also have a 
smaller plastron (lower shell) and a broader carapace (upper shell) 
(McLuckie et al. 1999). The petitioners did not provide information on 
the potential differences in morphological and physiological characters 
between the Sonoran and Sinaloan populations of desert tortoises.
    Lastly, the petitioners rely on genetic polymorphisms (that is, 
genetic material occurring in multiple forms) as a primary basis to 
consider the Mojave, Sonoran, and Sinaloan populations of desert 
tortoises as evolutionarily significant units. The Mojave population of 
desert tortoise exhibits three related genotypes but the Sonoran desert 
tortoise possesses a single genotype that is closely associated with 
Arizona upland and lower Colorado River subdivisions of Sonoran 
desertscrub habitat where the species is generally found (Lamb et al. 
1989; Lamb and McLuckie 2002). Lamb and McLuckie (2002) suggest that 
regional inundation of the inland area from Yuma, Arizona, north to the 
Nevada border during the Miocene Epoch correlates with a single 
maternal ancestor of the Mojave population of desert tortoises, which 
would have presented significant isolation long enough to allow such 
genetic divergence between these two populations.
Evaluation of Discreteness
    The population of desert tortoises in the Black Mountains of Mohave 
County, Arizona, which possess a uniquely Mojavean genotype, present an 
anomaly in the argument for genetic divergence as a result of regional 
inundation and subsequent isolation. McLuckie et al. (1999) suggest 
three possible hypotheses that may have led to the occurrence of the 
Mojave genotype east of the Colorado River: (1) active dispersal from 
north of the Miocene Epoch inundation; (2) river meander and subsequent 
geomorphological features assisted in allowing tortoises to cross the 
river over time; and (3) aboriginal human transport across the river 
for food stock, ritualistic or ceremonial use, or for medicinal uses 
which may have resulted in released animals or escapes.
    The genetic differentiation between the entire Mojave and Sonoran 
populations of the desert tortoise has led some researchers to 
hypothesize that the two populations may represent different species 
entirely (Berry et al. 2002; Murphy et al. 2007). The Sinaloan 
population of desert tortoise, has been documented to have a 4.2 
percent divergence in genotype from the Sonoran desert tortoise, and a 
5.1 percent divergence in genotype from the Mojave population of desert 
tortoise (Lamb and McLuckie 2002). Lamb and McLuckie (2002) stated, 
``Given their geographic distribution, genealogical depth, and 
concordant suite of characters, the Mohave, Sonoran, and Sinaloan 
tortoise assemblages clearly qualify as [evolutionarily significant 
units].''
    We have reviewed the information presented in the petition, and 
have evaluated the information in accordance with 50 CFR 424.14(b). On 
the basis of our review, we find that the petition provided substantial 
information indicating that the Sonoran population of the desert 
tortoise as it occurs east and south of the Colorado River, south to 
the Yaqui River, in Sonora, Mexico, may be discrete from the Mojave and 
Sinaloan desert tortoise populations. We base this conclusion on 
ecological (habitat use), physiological (reproductive capacity), 
morphological (shell dimensions), and behavioral (seasonal activity 
patterns) differences that are further supported by analysis of genetic 
polymorphisms that concluded significant divergence has occurred among 
the Mojave, Sonoran, and Sinaloan populations of the desert tortoise 
over time.

Significance

    Under our DPS Policy, in addition to our consideration that a 
population segment is discrete, we consider its biological and 
ecological significance to the taxon to which it belongs. This 
consideration may include, but is not limited to: (1) evidence of the 
persistence of the discrete population segment in an ecological setting 
that is unique or unusual 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 historical range; and 
(4) evidence that the discrete population segment differs markedly from 
other populations of the species in its genetic characteristics (61 FR 
4721; February 7, 1996).
Information Provided in the Petition on Significance
    The current range of the Sonoran desert tortoise, as described in 
the discussion above pertaining to discreteness, represents several 
hundred miles or kilometers of occupied habitat spanning across an 
International Border. The petition contends that this population 
segment is confined by two large perennial rivers; the Colorado River 
in its northern periphery, which separates the Mojave and Sonoran 
populations of desert tortoises, and the Yaqui River at its southern 
periphery, which separates the Sonoran and Sinaloan populations of the 
desert tortoise. These two rivers represent significant biogeographical 
barriers to genetic exchange between adjacent population segments and, 
therefore, preclude recolonization of this expanse of habitat from 
adjacent populations should the Sonoran desert tortoise become 
extirpated. As a result, the loss of the Sonoran desert tortoise would 
constitute a significant gap of several hundred miles or kilometers in 
the range between the Mojave and Sinaloan populations of desert 
tortoises.

[[Page 44340]]

Evaluation of Significance
    We have reviewed the information presented in the petition, and 
have evaluated the information in accordance with 50 CFR 424.14(b). On 
the basis of our review, we find that the petition provided substantial 
information indicating that the Sonoran desert tortoise may be 
significant to the continued existence of the taxon. We base this 
conclusion on the large geographic range of the species, which may be 
significant to the taxon as a whole, a gap of several hundred miles or 
kilometers that would result from the loss of the Sonoran population, 
which would effectively bisect the species' range, and the genetic 
divergence between the three populations. These factors indicate that 
the loss of the Sonoran population may result in a significant gap in 
the range of the taxon that could not be filled over time due to 
presence of biogeographical barriers to movement.

DPS Conclusion

    We have reviewed the information presented in the petition, and 
have evaluated the information in accordance with 50 CFR 424.14(b). In 
a 90-day finding, the question is whether a petition presents 
substantial information that the petitioned action may be warranted. 
Based on our review, we find that the petition, supported by 
information in our files, presents substantial scientific or commercial 
information to demonstrate that the Sonoran population of desert 
tortoise may be discrete from the Mojave and Sinaloan populations and 
that the Sonoran population may be significant to the taxon as a whole. 
As a result, we have determined that the Sonoran population of desert 
tortoise may be a DPS. Thus, the Sonoran population of desert tortoise 
may be a listable entity under the Act.

Five-Factor Evaluation

    We next evaluated the level of threat to the potential DPS based on 
the five listing factors established by the Act. We thus proceeded with 
an evaluation of information presented in the petition, as well as 
information in our files, to determine whether there is substantial 
scientific or commercial information indicating that listing this 
population may be warranted.
    Section 4 of the Act (16 U.S.C. 1533), and its implementing 
regulations at 50 CFR 424, set forth the procedures for adding species 
to the Federal List of Endangered and Threatened Wildlife and Plants. A 
species, subspecies, or distinct population segment of vertebrate taxa 
may be determined to be endangered or threatened due to one or more of 
the five factors described in section 4(a)(1) of the Act: (A) The 
present or threatened destruction, modification, or curtailment of 
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 90-day finding, we evaluated whether information 
regarding the Sonoran desert tortoise, as presented in the petition and 
other information available in our files, is substantial, thereby 
indicating that the petitioned action may be warranted. Our evaluation 
of this information is presented below. The information discussed below 
was presented by the petitioners, unless otherwise noted.

A. Present or Threatened Destruction, Modification, or Curtailment of 
the Species' Habitat or Range

Information Provided in the Petition
    The petition states that habitat occupied by the Sonoran desert 
tortoise is threatened by livestock grazing, urbanization and 
development, mining, and international border patrol activities.
    The petitioners claim that livestock grazing in occupied habitat 
adversely affects the Sonoran desert tortoise in a number of ways 
including competition for forage, vegetative trampling, alteration of 
plant community structure, introducing or enhancing the establishment 
of nonnative plant species, altering fire ecology, damaging burrows and 
cover sites, and altering tortoise behavior (Bostick 1990; Fleischner 
1994; Oldemyer 1994; Averill-Murray 2000b; Kazmaier et al. 2001; 
Boarman 2002; Esque et al. 2002). Over 60 percent of habitat occupied 
by the Sonoran desert tortoise occurs on federally managed land, the 
majority of that on lands managed by the U.S. Bureau of Land Management 
(BLM). The petitioners claim that on BLM land livestock grazing occurs 
on 78 percent (on 273 allotments) of potentially occupied habitats for 
the Sonoran desert tortoise. The petitioners also state that on U.S. 
Forest Service lands, livestock grazing occurs on 86 percent of 
potentially occupied habitat for the Sonoran desert tortoise. The 
percentage of Sonoran desert tortoise habitat used for livestock 
grazing on State, private, or tribal lands is not identified in the 
petition.
    The petitioners claim that the Sonoran desert tortoise and its 
habitat are harmed by urbanization and development in approximately 29 
percent of its occupied range in the United States. The petitioners 
state that urbanization and development threaten the Sonoran desert 
tortoise and its habitat. Tortoise habitat within developing areas may 
be permanently lost or degraded, while patterns of development may 
fragment habitat, restrict gene flow, and hamper recolonization of 
formerly occupied habitat.
    The human population in Arizona increased by 394 percent from 1960 
to 2000; Arizona is the second-fastest growing State in terms of human 
population (Social Science Data Analysis Network 2000, p. 1). In 
particular, certain counties with habitat occupied by the Sonoran 
desert tortoise have experienced explosive human population growth over 
this timeframe: Maricopa (463 percent); Yavapai (579 percent); and 
Mohave (2,004 percent) (Social Science Data Analysis Network 2000). The 
petition did not specifically discuss the threat of urbanization and 
development in occupied habitat for the Sonoran desert tortoise in 
Mexico; however, information in our files suggests urbanization and 
development might affect the Sonoran desert tortoise there as well. 
Information in our files indicates that Mexico's human population grew 
700 percent from 1910 to 2000 (Miller et al. 2005, p. 60). Demand from 
a growing human population has spurred the need for more agricultural 
development, according to information from our files (Contreras 
Balderas and Lozano 1994, p. 384; va Linda et al. 1997, p. 316).
    The petitioners provided evidence that mining activities may also 
be a threat to the Sonoran desert tortoise and its habitat. Mining 
activities occur on Federal and private lands but are stated to be the 
most pervasive on BLM lands, with 4,670 mining claims occurring in 
habitat occupied by the Sonoran desert tortoise. As of 2003, 1,096 of 
these claims remained active and 3,574 had been closed, according to 
the petitioners. The petitioners state that mining activities (both 
small- and large-scale) adversely affect the Sonoran desert tortoise 
through habitat fragmentation, loss, and degradation; introduction of 
contaminants and fugitive dust (dust that cannot be attributed to a 
single point of origin, such as a smokestack); off-road travel 
associated with mining activities or roads created for said activities; 
and entrapment of tortoises in mine spoil

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heaps (Averill-Murray 2000b; Woodman et al. 2001, 2004; Boarman 2002).
    Occupied habitat for the Sonoran desert tortoise occurs along the 
International Border in Yuma, Pima, and Santa Cruz counties in Arizona. 
The petitioners state that patrol activities on the international 
border present threats to the Sonoran desert tortoise and its habitat. 
Specifically, the petitioners state that border patrol activities 
threaten the Sonoran desert tortoise and its habitat through road 
mortality, and loss or degradation of occupied habitat. In particular, 
the petitioners claim that the recently constructed border fence 
fragments the habitat of Sonoran desert tortoise populations in Mexico 
and the United States, and also directly and indirectly threatens the 
Sonoran desert tortoise habitat from construction and maintenance 
activities associated with the border fence.
Evaluation of Information
    In consideration of the threats summarized above and discussed in 
the petition, we find that the petition provides substantial 
information that listing the Sonoran desert tortoise due to the present 
or threatened destruction, modification, or curtailment of its habitat 
or range may be warranted.

B. Overutilization for Commercial, Recreational, Scientific, or 
Educational Purposes

Information Provided in the Petition
    The petition claims that the Sonoran desert tortoise is threatened 
by poaching, illegal collection for use as pets, shooting, and 
vandalism (physical harassment or disturbance of the animals) 
throughout its range in the United States and Mexico. Illegal 
collection of desert tortoises for food, for commercial trade, and as 
pets has been documented (Fritts and Jennings 1994, Averill-Murray 
2000b; Bury et al. 2002). Information in our files suggests that the 
simple act of handling a Sonoran desert tortoise may cause an 
individual tortoise to void the contents of its bladder in defense. 
This loss of water may jeopardize its life (Averill-Murray 2002, p. 
434; Boarman 2002). Shooting and vandalism of Sonoran desert tortoises 
has been reported in Howland and Rorabaugh (2002) and Woodman et al. 
(2002).
Evaluation of Information
    In our evaluation of the petition, we find that the petitioners 
provided substantial information that listing the Sonoran desert 
tortoise due to overutilization for commercial, recreational, 
scientific, or educational purposes may be warranted.

C. Disease or Predation

Information Provided in the Petition
    The petitioners cite upper respiratory tract disease (URTD) as a 
threat to the Sonoran desert tortoise and reference the significant 
threat URTD is, and has been, for the Mojave population; a primary 
reason that population was listed as threatened in 1990. This disease 
is irreversible and fatal once acquired. Two species of Mycoplasma (a 
genus of small parasitic bacteria that lack cell walls and can survive 
without oxygen), Mycoplasma agassizii and M. testudineum, are known to 
cause URTD in desert tortoises and are easily transmitted between 
individual tortoises from casual contact (Brown et al. 1999; Wendland 
et al. 2007). Appendix 2 of the petition summarizes disease incidence 
reports within Sonoran desert tortoise populations. The petitioners 
state that Sonoran desert tortoises have tested positive for one or 
both of these antibodies at Saguaro National Park, and in the Ragged 
Top, Hualapai, Harcuvar, Little Shipp, and Sand Tank mountains among 
other locations. Dickinson et al. (2002) suspected that URTD may not be 
as serious a threat to the Sonoran population of desert tortoises as it 
has been for the Mojave population because tortoises in the Sonoran 
population do not occur in as high of densities as those in the Mojave 
and because Sonoran populations are more isolated from one another. In 
addition, the Sonoran population can take advantage of a bimodal 
precipitation cycle (two distinct rainy seasons). This offers 
additional opportunities for rehydration, lessening physiological 
stress, and, therefore, lessening susceptibility to the disease.
    In addition to URTD, cutaneous dyskeratosis (shell disease) has 
been observed in numerous Sonoran desert populations (Appendix 2 of the 
petition). The petitioners claim that, while no serious deleterious 
effects of the disease have been observed in affected tortoises, Homer 
et al. (2001) indicated higher mortality rates in some populations 
where the disease has been documented. Lastly, the petitioners state 
that additional pathogens have been noted in free-ranging Sonoran 
desert tortoises including Pasteurella sp., Streptococcus sp., 
Staphylococcus sp., herpesvirus, Pseudomonas sp., and Salmonella sp. 
and that these diseases may be correlated with physiological stress 
induced by habitat destruction and modification discussed above in 
Factor A (Pettan-Brewer et al. 1996; Dickinson et al. 2001).
    There are numerous natural predators of the Sonoran desert 
tortoise, including the jaguar (Panthera onca) and mountain lion (Felis 
concolor) (the only predators known to be able to break an adult 
tortoise's shell), coyote (Canis latrans), common raven (Corvus corax), 
kit fox (Vulpes macrotis), bobcat (Lynx rufus), gray fox (Urocyon 
cinereoargenteus), badger (Taxidea taxus), Gila monster (Heloderma 
suspectum), golden eagle (Aquila chrysaetos) and other raptors, greater 
roadrunner (Geococcyx californianus), coachwhip (Coluber flagellum), 
gophersnake (Pituophis melanoleucus), and kingsnake (Lampropeltis 
getula) (Averill-Murray et al. 2002b). The petitioners state that urban 
encroachment within the distribution of the Sonoran desert tortoise has 
created, or threatens to create, elevated levels of unnatural 
predation, mainly by ravens, coyotes, and feral domestic dogs. As 
explained below, petitioners claim these predators have benefitted, or 
been ``subsidized,'' by human activities within the wild-urban 
interface areas.
    Ravens can effectively prey on juvenile tortoises because their 
shells have not yet hardened (particularly the plastron) and the ravens 
are able to pierce the shells (Boarman 2002). Ravens, noted as a 
significant threat to desert tortoises in the Mojave population, have 
increased their numbers 14-fold within Arizona (Appendix 3 of the 
petition; Boarman and Kristen 2008). The petitioners suggest that 
increases in the number of ravens within the Sonoran desert may be 
linked to increased availability of food and water resources at 
landfills, rural and urban developments, along heavily traveled roads, 
and at agricultural areas in particular dairies. These land uses were 
also suspected by the petitioners to result in increased predation of 
Sonoran desert tortoises from coyotes and feral dogs; the latter being 
documented at 4 of 17 Sonoran desert tortoise study plots (Appendix 1 
of the petition).
Evaluation of Information
    In our evaluation of the petition, we find that the petitioners 
provide substantial information that listing the Sonoran desert 
tortoise due to the incidence of disease and high predation levels may 
be warranted.

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D. The Inadequacy of Existing Regulatory Mechanisms

Information Provided in the Petition
    In 1988, the Sonoran and Mojave populations of the desert tortoise 
were closed to collection in Arizona by the Arizona Game and Fish 
Department, except as authorized under their scientific collecting 
permit program. This status means that it is illegal to kill or capture 
desert tortoises from the wild (unless under a special permit). 
Possession for trade, sale, or other commercial purposes is prohibited 
(Howland and Rorabaugh 2002). Prior to 1988, the Arizona Game and Fish 
Department allowed the possession of one lawfully obtained tortoise per 
person, which likely contributed to their popularity as pets (Averill-
Murray 2000b). The Arizona Game and Fish Department has developed a 
draft Comprehensive Wildlife Conservation Strategy: 2005-2015, in which 
the Sonoran desert tortoise has been identified as a Species of 
Greatest Conservation Need for which immediate conservation is 
necessary (Tier 1b under the Vulnerable category) (Arizona Game and 
Fish Department 2006a, pp. 485-487; 2006b, p. 4). The Arizona Game and 
Fish Department has been a significant contributor in the conservation 
and management of the Sonoran desert tortoise, producing many documents 
for public education, administering an adoption program for individual 
Sonoran desert tortoises that cannot be returned to the wild, and 
conducting or funding monitoring and research on wild Sonoran desert 
tortoise populations (Arizona Game and Fish Department 1990, 1996, 
2000, and 2004; Arizona Interagency Desert Tortoise Team 1996, 1997, 
and 2000; Averill-Murray 2000).
    The Sonoran desert tortoise does not currently have special status 
under the Endangered Species Act. The desert tortoise is included in 
Appendix I of the Convention on International Trade in Endangered 
Species of Wild Fauna and Flora and a permit is required for the export 
of tortoises (Howland and Rorabaugh 2002).
    Several Federal agencies have management authority for Sonoran 
desert tortoise habitat, including the BLM, the National Park Service, 
the U.S. Forest Service, the U.S. Bureau of Reclamation, the U.S. 
Department of Defense, and the Service. Significant land use 
protections are afforded the Sonoran desert tortoise on National Park 
Service lands and U.S. Fish and Wildlife Service refuges, in particular 
where they occur adjacent to U.S. Department of Defense lands such as 
the Barry M. Goldwater Range and the Yuma Proving Grounds, because of 
the relatively large amounts of primarily undisturbed habitat within 
the boundary zone between these managed lands.
    The Sonoran desert tortoise is considered a ``sensitive species'' 
by the BLM. In 1988, the BLM adopted a rangewide management strategy 
for desert tortoise habitat (BLM 1988; Howland and Rorabaugh 2002). 
Subsequently, habitat for the Mojave and Sonoran populations of desert 
tortoise was categorized into one of three categories: Category one 
being the highest quality; Category three, the lowest. In 1991, the 
BLM, the Service, and state wildlife agencies (Arizona, Nevada, Utah, 
and California) developed a policy whereby persons who disturbed 
occupied habitat were required to pay monetary compensation (usually in 
the form of land acquisition). The monetary compensation was weighted 
using the BLM's habitat categorization criteria. Mitigation ratios 
ranged from 1:1 (acres protected: acres disturbed) for category three 
habitat, to 6:1 for category one habitat (Howland and Rorabaugh 2002). 
The petitioners also cite numerous reports, management strategies, and 
formal actions taken by the BLM with regard to management of the 
Sonoran desert tortoise, but conclude that, based on their review, 
these measures may be insufficient to adequately protect the Sonoran 
desert tortoise on BLM lands.
    The Sonoran desert tortoise occurs on both the Tonto and Coronado 
National Forests. The Sonoran desert tortoise is on the Regional 
Forester's Sensitive Species List, which means it is considered in 
land-management decisions. The petitioners claim that, despite this 
recognition, threats to the Sonoran desert tortoise continue to occur 
within these National Forests and that potential protections, such as 
those afforded under the National Environmental Policy Act (42 U.S.C. 
4321-4327), have failed to come to fruition, particularly with respect 
to livestock grazing (see Table 6, p. 55 of the petition).
    There are currently 10 Native American reservations within Arizona 
that contain known or potential Sonoran desert tortoise habitat: Fort 
Mojave Indian Tribe, Colorado River Indian Tribe, Hualapai Tribe, Fort 
McDowell Yavapai Nation, Salt River Pima-Maricopa Indian Community, 
Gila River Indian Community, Ak Chin, Tohono O'odham Nation, Pasqua 
Yaqui Tribe, and San Carlos Apache Tribe, although the status of 
populations on these reservations has not been established (Averill-
Murray 2000b). The petitioners state that historically no reservations 
conducted surveys or performed active management for the Sonoran desert 
tortoise or its habitat. However, the petitioners note that recently 
the Tohono O'odham Nation developed the Wildlife and Vegetation 
Management Program and now has oversight over the desert tortoise on 
their land. This program authorizes surveys for Sonoran desert tortoise 
and the establishment of monitoring plots, but does not provide funding 
to implement these activities (Averill-Murray 2000b). The petitioners 
also suggest that many Native American tribes have a historical 
relationship with desert tortoises that is of important cultural and 
spiritual significance, which may provide added protection of the 
species on their lands (Nabhan 2002).
    On State lands, the Arizona State Land Department manages occupied 
Sonoran desert tortoise habitat, according to the petition, with the 
goal of ``maximizing revenue to benefit education, health and penal 
institutions,'' and works cooperatively with the Arizona Game and Fish 
Department in management of Sonoran desert tortoises (Averill-Murray 
2000b). Specifically, the petitioners state that the Arizona Game and 
Fish Department ``recommends mitigation measures for tortoise impacts 
for which it is consulted ... (and) comments on State land projects 
related to urban planning, land sales and exchanges, rights of way, and 
commercial leases,'' but these recommendations are not binding 
(Averill-Murray 2000b).
    The petition also notes that Pima County has considered the Sonoran 
desert tortoise in its habitat conservation planning by acknowledging 
that populations are decreasing in Pima County. However, Pima County 
offers few specific protections for the species.
    In Mexico, the Secretaria de Deserrollo Social lists both the 
Sonoran and Sinaloan populations of the desert tortoise as threatened 
(Secretaria de Deserrollo 2008, p. 99). Populations of the Sonoran 
desert tortoise in Mexico are reportedly in decline. Factors believed 
to contribute to this decline are related to lack of resources for 
enforcement and include habitat destruction or modification, capture of 
tortoises for food or pets, and predation by feral dogs (particularly 
in areas adjacent to settlements or urban areas) (Fritts and Jennings 
1994; Bury et al. 2002).
    In the United States, as part of a multi-agency collaborative 
project, the Arizona Interagency Desert Tortoise

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Team was formed in 1985 to coordinate research and management of 
Sonoran desert tortoise populations in Arizona. Participating agencies 
in the Arizona Interagency Desert Tortoise Team include the Arizona 
Game and Fish Department, Arizona State Lands Department, the U.S. 
Forest Service, the BLM, the U.S. Bureau of Reclamation, the U.S. 
Bureau of Indian Affairs, the Service, the National Park Service, the 
U.S. Geological Survey, and several U.S. Department of Defense military 
reservations (Arizona Interagency Desert Tortoise Team 1996). Since its 
inception, the Arizona Interagency Desert Tortoise Team has 
collaborated in the development of numerous publically available 
documents addressing conservation of the Sonoran desert tortoise 
(Averill-Murray 2000a, 2000b; Arizona Game and Fish Department 2007a, 
2007b; Arizona Interagency Desert Tortoise Team 2008).
    The Arizona Interagency Desert Tortoise Team's Memorandum of 
Understanding, signed in 1995, established specific objectives for the 
team including: (1) ensuring the survival of the species; (2) 
preventing loss of the species; and (3) improving the quality of 
Sonoran desert tortoise habitat in Arizona, with the team to function 
as an advocate for the Sonoran desert tortoise (Arizona Interagency 
Desert Tortoise Team 1996). A management plan for the Sonoran desert 
tortoise completed in 1996 called for improved monitoring protocols, 
the implementation of threat-minimization activities, and the creation 
of Sonoran Desert Management Areas for conservation of the Sonoran 
desert tortoise (Arizona Interagency Desert Tortoise Team 1996). 
However, the petitioners claim that the 1996 plan: (1) lacked 
meaningful goals and objectives; (2) lacked political willpower without 
legal protection for the Sonoran desert tortoise; (3) failed to 
designate Sonoran Desert Management Areas; and (4) was poorly funded, 
which hampered implementation of threat minimization activities 
outlined in the plan. These shortcomings in the 1996 plan were 
collectively recognized by the Arizona Interagency Desert Tortoise Team 
members who in 2002 reconvened to initiate the development of a revised 
plan in the form of a State Conservation Agreement for the Sonoran 
desert tortoise. The State Conservation Agreement, when finalized, is 
expected to: (1) mandate more practical conservation recommendations; 
(2) garner a higher level of commitment and responsibility from its 
signatories; (3) set measurable goals and objectives; and (4) establish 
Key Habitat Areas on public lands where management strategies for the 
Sonoran desert tortoise will focus.
Evaluation of Information
    There are significant protections in place with respect to 
management for the Sonoran desert tortoise on lands managed by the 
Service, National Park Service, and to a lesser degree, lands managed 
by the U.S. Department of Defense. The Arizona Interagency Desert 
Tortoise Team has also provided technical expertise and guided habitat-
management decisions of participating agencies with marginal success. 
Despite these protections, we conclude that the petition and 
information in our files present substantial information that existing 
regulatory mechanisms may be inadequate to prevent declines of the 
Sonoran desert tortoise, particularly on lands managed as ``multiple-
use'' such as U.S. Forest Service, BLM, and the Arizona State Land 
Department, where threats continue to occur. An additional concern is 
the limited implementation of recommendations of the Arizona 
Interagency Desert Tortoise Team's 1996 management plan.
    In our evaluation of the petition, we find that the petitioners 
provided substantial information that listing the Sonoran desert 
tortoise due to the inadequacy of existing regulatory mechanisms may be 
warranted.

E. Other Natural or Manmade Factors Affecting the Species' Continued 
Existence

Information Provided in the Petition
    The petitioners state that off-highway vehicle (OHV) use, 
alteration of fire frequency in the Sonoran Desert resulting from 
nonnative plant invasion, mortality on roads, drought, and climate 
change are among additional threats to the Sonoran desert tortoise. The 
petitioners claim that OHV use has increased significantly on public 
lands within the distribution of the Sonoran desert tortoise, 
especially on U.S. Forest Service and BLM lands, and particularly in 
incised washes, which are important habitat for the Sonoran desert 
tortoise (Averill-Murray 2000b; Averill-Murray and Averill-Murray 2002; 
Riedle et al. 2008). We have information in our files that indicates 
the use of OHVs has grown considerably in Arizona. For example, as of 
2007, 385,000 OHVs were registered in Arizona (a 350-percent increase 
since 1998) and 1.7 million people (29 percent of Arizona's population) 
engaged in off-road activity from 2005-2007 (Sacco 2007). Over half of 
OHV users reported that merely driving off-road was their primary 
activity, versus using the OHV for the purpose of seeking a destination 
to hunt, fish, or hike (Sacco 2007). Specific threats cited by the 
petitioners to the Sonoran desert tortoise or its habitat from OHV use 
include crushing tortoises, collapsing occupied and unoccupied burrows, 
changes in plant abundance and species composition, reduced habitat 
connectivity, soil compaction, soil erosion, reduced water 
infiltration, higher soil temperatures, and increased fire-starts 
(Boarman 2002; Ouren et al. 2007, pp. 6-7, 11, 16). The petitioners 
further claims that OHV use causes destruction of cryptogamic soils, 
which are soils with crusts formed by an association of algae, mosses, 
and fungi, which stabilize desert soil, retain moisture, and protect 
germinating seeds (Boarman 2002, pp. 46-47; Ouren et al. 2007, pp. 7-
8).
    Nonnative plant species such as Mediterranean splitgrass (Schismus 
barbatus), red brome (Brombus rubens), and African buffelgrass 
(Pennisetum cilare) have significantly degraded Sonoran desert tortoise 
habitat by out-competing more nutritional, native plant species and 
altering the frequency and magnitude of wildfires in many areas within 
its distribution (Howland and Rorabaugh 2002). The petitioners state 
that in addition to injury and mortality of Sonoran desert tortoises, 
wildfire within occupied habitat is expected to result in the complete 
conversion of desertscrub to grasslands at higher elevations and to 
barren landscapes at lower elevations (Esque et al. 2002). Pennisetum 
cilare poses unique problems for the Sonoran desert tortoise in Sonora, 
Mexico, because Sonoran desertscrub is actively cleared in favor of 
planting P. cilare as forage for livestock; P. cilare disperses 
naturally from these sites into adjacent habitat where it self-
perpetuates, and is ``likely to dominate the entire area'' (Bury et al. 
2002).
    The petitioners cite several adverse effects to the Sonoran desert 
tortoise from roads. Among these threats were direct mortality, injury, 
facilitation of increased raven populations, increased roadside 
foraging by tortoises (as a result of increased plant growth from 
precipitation runoff), population fragmentation, and contamination of 
roadside habitat (Homer et al. 2001; Boarman 2002). Boarman and Kristin 
(2008, Appendix 3 of the petition) states that roads are one of the 
most prevalent threats in the study plots they reviewed.
    Lastly, the petitioners claim that drought and climate change pose 
additional threats to the Sonoran desert tortoise. Drought increases 
the

[[Page 44344]]

physiological stress of desert tortoises and reduces reproductive rates 
within populations because of reduced forage quality and abundance 
(Averill-Murray and Klug 2000). The petitioners also state that the 
effects of drought can act synergistically with other threats to the 
Sonoran desert tortoise such as disease and habitat destruction or 
modification. Increased magnitude and frequency of drought is expected 
to occur as a result of climate change. Weiss and Overpeck (2005) 
predict that the Sonoran Desert may be displaced in the south by 
hotter, drier habitats and may expand to the north and to higher 
elevations, displacing cooler, drier habitats. In our review of 
available files, we find that Seagar et al. (2007, pp. 1181-1184) 
analyzed 19 different computer models of differing variables to 
estimate the future climatology of the southwestern United States and 
northern Mexico in response to predictions of changing climatic 
patterns. All but one of the 19 models predicted a drying trend within 
the Southwest; one predicted a trend toward a wetter climate (Seagar et 
al. 2007, p. 1181). A total of 49 projections were created using the 19 
models and all but three predicted a shift to increasing aridity 
(dryness) in the Southwest as early as 2021-2040 (Seagar et al. 2007, 
p. 1181).
Evaluation of Information
    In consideration of the above, we find that the petition and 
information in our files provide substantial information to indicate 
that OHV use, altered fire regimes, roads, and effects from prolonged 
drought, exacerbated by climate change, may be threats to the Sonoran 
desert tortoise.

Finding

    On the basis of our determination under section 4 of the Act and 
our evaluation of the five factors, we have determined that the 
petition presents substantial information indicating that listing the 
Sonoran population of desert tortoise may be warranted.
    The petitioners presented substantial information indicating that 
the Sonoran population of desert tortoise may be discrete and 
significant and, therefore, may be a listable entity (DPS) under the 
Act. Further, the petitioners presented substantial information that 
the Sonoran population of desert tortoise may be threatened by Factors 
A through E throughout the entire range, with the exception of Factor C 
where the petitioners did not provide information on disease or 
predation in Mexico, nor did we have information in our files on 
disease or predation of the Sonoran desert tortoise in Mexico. Based on 
this review and evaluation, we find that the petition has presented 
substantial scientific or commercial information that listing the 
Sonoran population of desert tortoise throughout its range in the 
United States and Mexico as a DPS may be warranted due to current and 
future threats presented in our discussion of the five listing factors. 
As such, we are initiating a status review to determine whether listing 
the Sonoran desert tortoise under the Act is warranted. We will issue a 
12-month finding as to whether any of the petitioned actions are 
warranted. To ensure that the status review is comprehensive, we are 
soliciting scientific and commercial information regarding the Sonoran 
desert tortoise, particularly with respect to its status and threats in 
Mexico.
    The ``substantial information'' standard for a 90-day finding 
differs from the Act's ``best scientific and commercial data'' standard 
that applies to a status review to determine whether a petitioned 
action is warranted. A 90-day finding does not constitute a status 
review under the Act. In a 12-month finding, we will determine whether 
a petitioned action is warranted after we have completed a thorough 
status review of the species, which is conducted following a 
substantial 90-day finding. Because the Act's standards for 90-day and 
12-month findings are different, as described above, a substantial 90-
day finding does not mean that the 12-month finding will result in a 
warranted findi