Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List Sonoran Desert Tortoise as an Endangered or Threatened Species, 60321-60335 [2015-25286]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 80, Number 193 (Tuesday, October 6, 2015)]
[Proposed Rules]
[Pages 60321-60335]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2015-25286]



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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R2-ES-2015-0150; 4500030113]


Endangered and Threatened Wildlife and Plants; 12-Month Finding 
on a Petition To List Sonoran Desert Tortoise as an Endangered or 
Threatened Species

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 Sonoran desert tortoise 
(Gopherus morafkai) as an endangered or threatened species under the 
Endangered Species Act of 1973, as amended (Act). After review of the 
best available scientific and commercial data, we find that listing the 
Sonoran desert tortoise is not warranted at this time. However, we ask 
the public to submit to us any new information that becomes available 
concerning the threats to the Sonoran desert tortoise or its habitat at 
any time.

DATES: The finding announced in this document was made on October 6, 
2015.

ADDRESSES: This finding is available on the Internet at https://www.regulations.gov at Docket Number FWS-R2-ES-2015-0150. Supporting 
documentation we used in preparing this finding is available for public 
inspection, by appointment, during normal business hours at the U.S. 
Fish and Wildlife Service, Arizona Ecological Services Field Office, 
2321 W. Royal Palm Road, Suite 103, Phoenix, AZ 85021. Please submit 
any new information, materials, comments, or questions concerning this 
finding to the above address.

FOR FURTHER INFORMATION CONTACT: Steve Spangle, Field Supervisor, 
Arizona Ecological Services Field Office (see ADDRESSES); by telephone 
at 602-242-0210; or by facsimile at 602-242-2513. If you use a 
telecommunications device for the deaf (TDD), please call the Federal 
Information Relay Service (FIRS) at 800-877-8339.

SUPPLEMENTARY INFORMATION: 

Background

    Section 4(b)(3)(B) of the Act (16 U.S.C. 1531 et seq.), requires 
that, for any petition to revise the Federal Lists of Endangered and 
Threatened Wildlife and Plants that contains substantial scientific or 
commercial information that listing the species may be warranted, we 
make a finding within 12 months of the date of receipt of the petition. 
In this finding, we will determine that the petitioned action is: (1) 
Not warranted, (2) warranted, or (3) warranted, but the immediate 
proposal of a regulation implementing the petitioned action is 
precluded by other pending proposals to determine whether species are 
endangered or threatened, and expeditious progress is being made to add 
or remove qualified species from the Federal Lists of Endangered and 
Threatened Wildlife and Plants. Section 4(b)(3)(C) of the Act requires 
that we treat a petition for which the requested action is found to be 
warranted but precluded as though resubmitted on the date of such 
finding, that is, requiring a subsequent finding to be made within 12 
months. We must publish these 12-month findings in the Federal 
Register.

Previous Federal Actions

    On December 30, 1982, we published a notice of review, which 
determined the desert tortoise (Gopherus agassizii) throughout its 
range in the United States and Mexico to be a Category 2 Candidate 
species (47 FR 58454); this determination was reaffirmed on September 
18, 1985 (50 FR 37958). Category 2 Candidate 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). Currently, the Mojave 
population of the desert tortoise is recognized as a distinct 
population segment (DPS) under the Act. As part of the Mojave DPS 
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(e) 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). From 1996 to 2010 
(see below), the Sonoran populations of desert tortoise did not have 
any Federal status inside their known range (south and east of the 
Colorado River).
    On October 15, 2008, we received a petition dated October 9, 2008, 
from WildEarth Guardians 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. On August 28, 2009, we made our 90-day finding 
that the petition presented substantial scientific information 
indicating that listing the Sonoran DPS of the desert tortoise may be 
warranted. The finding and notice of our initiation of a status review 
was published in the Federal Register on August 28, 2009 (74 FR 44335). 
On December 14, 2010, we published our 12-month finding that listing 
the Sonoran DPS of the desert tortoise was warranted, but precluded by 
other higher priority actions, and the entity was added to our list of 
candidate species (75 FR 78094).
    Candidate status for the Sonoran DPS of desert tortoise was 
reaffirmed in the 2011 Candidate Notice of Review (76 FR 66370; October 
26, 2011). In 2012, new information was assessed that elevated the 
Sonoran populations of the desert tortoise to a full species (Gopherus 
morafkai). We noted this taxonomic change in the 2012 Candidate Notice 
of Review and revised its accepted nomenclature to ``Sonoran desert 
tortoise'' (77 FR 69994; November 21, 2012). We also reaffirmed its 
candidate status in the Candidate Notices of Review published in 2012 
(77 FR 69994; November 21, 2012), 2013 (77 FR 70104; November 22, 
2013), and 2014 (79 FR 72450; December 5, 2014).
    In 2011, the Service entered into two settlement agreements 
regarding species on the candidate list at that time (Endangered 
Species Act Section 4 Deadline Litigation, No. 10-377 (EGS), MDL Docket 
No. 2165 (D.D.C. May 10, 2011)). This finding fulfills our obligations 
regarding the Sonoran desert tortoise under those settlement 
agreements.

Species Information

    We collaborated with species experts from public and private 
sectors to complete the Species Status Assessment Report for the 
Sonoran Desert Tortoise (SSA Report; Service 2015, entire), which is 
available online at https://www.regulations.gov, Docket No. FWS-R2-ES-
2015-0150, and at https://www.fws.gov/southwest/es/Arizona. The SSA 
Report documents the results of the comprehensive biological status 
review for the Sonoran desert tortoise (tortoise) and provides an 
account of the species' overall viability through forecasting of the 
species' condition in the future (Service 2015, entire). In the SSA

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Report, we summarized the relevant biological data and a description of 
past, present, and likely future risk factors and conducted an analysis 
of the viability of the species. The SSA Report provides the scientific 
basis that informs our regulatory decision regarding whether this 
species should be listed as an endangered or threatened species under 
the Act. This decision involves the application of standards within the 
Act, its implementing regulations, and Service policies (see Finding 
below). The SSA Report contains the risk analysis on which this finding 
is based, and the following discussion is a summary of the results and 
conclusions from the SSA Report. We solicited peer review of the draft 
SSA Report from five qualified experts. Responses were received from 
four of the reviewers, and the SSA Report was modified as appropriate.
Species Description
    The Sonoran desert tortoise was first described by Cooper in 1863 
(pp. 118-123). Since that time, the Sonoran desert tortoise was 
recognized as a population of the desert tortoise (Gopherus agassizii) 
until advanced genetic analysis supported elevating the Sonoran 
population of the desert tortoise as a unique species, Morafka's desert 
tortoise (Gopherus morafkai) (Murphy et al. 2011, p. 53). As a result, 
the Sonoran desert tortoise is recognized as a distinct species (G. 
morafkai) but retains its common name of ``Sonoran desert tortoise'' as 
recommended in Crother et al. (2012, pp. 76-77) to avoid potential 
confusion of the abbreviation for Morafka's desert tortoise with that 
of the Mojave desert tortoise (G. agassizii).
    The Sonoran desert tortoise occupies portions of western, 
northwestern, and southern Arizona in the United States, and the 
northern two-thirds of the Mexican State of Sonora. In Arizona, adult 
Sonoran desert tortoises range in total carapace (top shell) length 
from 8 to 15 inches (in) (20 to 38 centimeters (cm)), with a relatively 
high domed shell (Arizona Game and Fish Department (AGFD) 2001, p. 1; 
Brennan and Holycross 2006, p. 54). The maximum recorded length for a 
Sonoran desert tortoise in Arizona is 19.4 in (49 cm) total carapace 
length (Jackson and Wilkinson-Trotter 1980, p. 430). The hind limbs are 
very stocky and elephantine; forelimbs are flattened for digging and 
covered with large conical scales (AGFD 2001, p. 1; Brennan and 
Holycross 2006, p. 54). Male Sonoran desert tortoises are 
differentiated from females by having elongated gular (throat) shields, 
chin glands visible on each side of the lower jaw (most evident during 
the breeding season), and a concave plastron (bottom shell) (AGFD 2001, 
p. 1).
    Sonoran desert tortoises are coldblooded species, which rely on 
their environment to regulate body temperature (thermoregulation). They 
feed on a variety of vegetation and spend the majority of their time in 
underground shelters, coming out mainly to drink, forage, and breed. 
Tortoises, especially young, small tortoises, are subject to predation 
by a variety of natural predators, including lizards, snakes, and 
mammals.
    In general and compared to many other animals, tortoises have 
relatively low fecundity (females lay about 5 eggs on average every 
other year), are slow-growing (they may take 15 years to reach sexual 
maturity), are long-lived (they may live more than 50 years in the 
wild), experience high survivorship in the wild, and have a relatively 
long generation time (25 years). The Sonoran desert tortoise's breeding 
season generally occurs from July through October.
Habitat and Range
    The tortoise occurs primarily in rocky, steep slopes and bajadas 
(broad slope extending from the base of a mountain range out into a 
basin) in various desertscrub habitat types. Tortoise home range size 
varies with precipitation levels, contracting during wet years and 
expanding during dry years in response to the availability of forage 
plants (Averill-Murray and Klug 2000, p. 67). Estimates for average 
home range sizes for males have varied from 0.04 to 0.10 square miles 
(sq mi) (10 to 26 hectares (ha)); females generally have smaller home 
ranges, with averages ranging from 0.01 to 0.09 sq mi (2.6 to 23 ha) 
(Barrett 1990, p. 203; Averill-Murray and Klug 2000, pp. 55-61; 
Averill-Murray et al. 2002a, pp. 150-151).
    We conducted a coarse geospatial analysis (see Overview of 
Analytical Tools) of potential habitat based on elevation, slope, and 
vegetation type across the species' range. We categorized the potential 
habitat as high, medium, or low suitability based on the presence of 
the habitat features that support tortoises (a combination of 
elevation, vegetation type, and slope). This rangewide geospatial 
analysis resulted in a prediction of approximately 38,000 sq mi (9.8 
million ha) of potential tortoise habitat (see Map 1--Current Sonoran 
Desert Tortoise Predicted Potential Habitat). Of this total, 64 percent 
occurs in the United States, and 36 percent occurs in Mexico.
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BILLING CODE 4333-15-C

Species Needs

    Individual tortoises need access to plants, shelters, and 
freestanding water. A variety of plants are used for forage, shelter 
for thermoregulation, and cover from predators. Access to shelter sites 
is also important for predator avoidance

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and thermoregulation. Freestanding water is needed for hydration. 
Finally, tortoises need enough available space to complete movements to 
support life-history functions of feeding and breeding. Tortoises have 
a specific combination of habitat needs (forage plants, cover, shelter 
sites, water), but those habitat needs can be found throughout a wide 
geographic area.
    For the Sonoran desert tortoise to maintain viability over the long 
term, it needs populations of adequate size and distribution to support 
resiliency, redundancy, and representation. While we do not know the 
size of a viable population of Sonoran desert tortoise, populations 
with larger numbers of individuals have improved chances of 
withstanding stochastic events (a measure of resiliency). The tortoise 
also needs to have resilient populations spread across its range, 
supported by suitable habitat quantity and quality, to provide for 
rangewide redundancy (species ability to withstand catastrophic events 
such as potential large-scale drought) and representation (species 
genetic and ecological diversity to maintain adaptive capacity).

Overview of Analytical Tools

    We used two analytical tools to synthesize and summarize our 
understanding of the best available information about the current and 
future conditions of the tortoise. These tools include a geospatial 
analysis of habitat and a population simulation model. Here we describe 
these tools conceptually to provide context for the discussions that 
follow. More explanation of these tools is available in the SSA Report 
(Service 2015, entire).
    One tool we used was a coarse geospatial analysis to determine the 
extent of potential habitat based on elevation, slope, and vegetation 
type across the species' range. Potential habitat was categorized by 
suitability (high, medium, and low) based on presence of habitat 
features that support tortoises. We then categorized the potential 
habitat into primary, secondary, or tertiary quality categories. The 
categorization of habitat quality is based on the current suitability 
of potential habitat (high, medium, and low) and the possible presence 
of risk factors that could have population-level effects (see Risk 
Factors discussion below). The habitat quality analysis was conducted 
under two alternative assumptions related to the effects of the risk 
factors (high or low threats) and two alternative assumptions regarding 
the effects of conservation measures (high or low management). We were 
able to use the results of this geospatial analysis to estimate the 
amount and condition of current and future potential habitat, as well 
as evaluate the scope of various stressors on the landscape. It is 
important to note that potential habitat is categorized as high, 
medium, and low suitability, and habitat quality (a combination of 
potential habitat and risk factors) is categorized as primary, 
secondary, and tertiary.
    Another tool we used was a population simulation model. The 
population model takes a given starting abundance of tortoises and 
calculates the future abundance over time by applying reproductive and 
survival rates (i.e., vital rates). These vital rates are the 
proportion of the total tortoises in a population that are surviving, 
being adding to the population through reproduction, or being removed 
from the population each year. By calculating the number of tortoises 
being added to the population through reproduction and taken away from 
the population through death each year, it allows us to project the 
change in the abundance of tortoises over time based on those vital 
rates.
    We used a combination of geospatial analysis and population 
simulation modeling to project the condition of tortoise populations. 
The geospatial analysis predicts the amount and condition of habitats 
available to tortoises currently and in the future, and the population 
simulation model projects the abundance of tortoises that can be 
supported by that habitat based on rates of survival, growth, and 
reproduction (i.e., vital rates). The population simulation model 
projects higher densities of tortoises in higher quality habitat. As a 
result, the population simulation model projects abundance based on 
both the amount and condition of habitats.
    The geospatial analysis and population simulation model combine to 
project the amount, condition, and distribution of potential habitat; 
and the abundance, growth rate, and quasi-extinction risk for tortoise 
populations. We are using the term quasi-extinction to encompass the 
idea that, before a species actually goes extinct, it will decline to a 
point where extinction will likely be inevitable as a result of genetic 
and ecological impacts, even though it has multiple surviving 
individuals. Because there is a great deal of uncertainty around where 
the precise quasi-extinction threshold is for each species, our 
population simulation model assesses a higher and lower threshold of 
quasi-extinction. Taking into account these and other uncertainties, 
results of the population simulation modeling are presented as a range 
in the following discussions.
    Finally, in the models, areas in the United States and Mexico were 
treated as two separate areas of analysis because there are meaningful 
differences in the quality and level of information available about 
status and risk factors between the two areas, and because there are 
actual differences in habitat quality due to differences in land 
management between the two countries.

Risk Factors

    We reviewed the potential risk factors (i.e., threats, stressors) 
that could be affecting the tortoise. Owing to the relatively wide 
geographic range of the species, individual tortoises may be impacted 
by a variety of factors. However, in this document we will discuss only 
those factors in detail that could meaningfully impact the status of 
the species. Concerns about the tortoise's status revolve around six 
primary risk factors: (1) Altered plant communities; (2) altered fire 
regimes; (3) habitat conversion of native vegetation to developed 
landscapes; (4) habitat fragmentation; (5) human-tortoise interactions; 
and (6) climate change and drought.
    We evaluated each of these factors in detail for their potential to 
have population- and species-level effects to the Sonoran desert 
tortoise. While many of them could be having effects on individual 
tortoises, most have not been shown or are not expected to have 
population-level effects on the species. Some factors may have 
population-level effects, but, because of the long lifespan, relatively 
high abundance, and wide range of the Sonoran desert tortoise, these 
effects would likely take many decades or longer to have measurable 
impacts on the species if they occur. In addition, many of these 
factors are ameliorated to some degree by ongoing conservation efforts 
or land management considerations; an estimated 73 percent of potential 
habitat in the United States has some conservation management, and 55 
percent of potential habitat in the United States was included in a 
recent interagency conservation agreement committing Federal land 
managers to continuing conservation efforts for the tortoise (see 
Conservation Measures and Land Management).
Altered Plant Communities
    Altered plant communities are a concern due to the presence of 
nonnative grasses in tortoise habitats. Nonnative grass species can 
compete with native grass species for space, water, and nutrients, 
thereby affecting

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native plant species density and species composition within invaded 
areas (Stevens and Fehmi 2008, pp. 383-384; Olsson et al. 2012a, 
entire; 2012b, pp. 10, 18-19; McDonald and McPherson 2011, pp. 1150, 
1152; Franklin and Molina-Freaner 2010, p. 1664). This process is 
primarily driven by the timing and amount of precipitation. Geospatial 
analysis of available data indicates that about 15 percent of the 
current predicted suitable habitat for tortoises in Arizona and 20 
percent in Mexico may have nonnative vegetation.
    Presence of nonnative grasses does not preclude use of an area by 
tortoises, but it may impact tortoises by reducing available plants for 
forage and cover. Reduced access to quality native plants may cause 
tortoises to expend additional time and energy foraging, thereby 
reducing fitness and exposing them to additional predation. However, 
tortoises can and do utilize nonnative grasses as forage, and no 
studies have confirmed that the nonnative species are significantly 
less nutritious to tortoises. Reduction in plant cover can negatively 
impact thermoregulation and increase exposure to predators. A reduction 
in cover plants used by tortoises can limit thermoregulatory 
opportunities and reduce periods of potential surface activity, making 
individuals more susceptible to dehydration, as well as increase 
predation risk when the individuals are active on the surface (Gray 
2012, entire).
    Theoretically, the effects of nonnative grasses on individual 
tortoises discussed above may manifest in population-level effects if 
reduced fitness and increased predation resulted in population-level 
declines. However, such population-level effects have not been 
identified through long-term monitoring, despite the fact that some 
species of nonnative grass have occurred within monitoring plots for 
decades, nor have population-level effects been documented. Further, 
population-level effects, if they are occurring, would only become 
discernible (with current research and monitoring methods) over an 
extremely long period of time (decades to centuries) due to the life 
history and longevity of the species. Adequate time periods are well 
outside of both the existing period of monitoring and our ability to 
reasonably predict such population-level effects in the future.
Altered Fire Regime
    The presence of nonnative plants has the potential to result in 
more severe, frequent fires in tortoise habitats than would have 
occurred naturally. In some conditions, wildfire can occur naturally in 
tortoise habitats, but fire has not historically been a significant 
influence in these habitats. In desertscrub communities that are free 
of nonnative grasses, wildfire has a long return interval and is rarely 
able to carry itself over a spatially significant area due to the 
extent of bare ground between vegetated patches. In areas invaded by 
nonnative grasses, the density of fine fuels increases while open space 
between vegetation decreases, causing changes in fire behavior and, 
ultimately, in the fire regime.
    Altered fire regimes resulting in more severe, frequent fires may 
impact tortoises directly through exposure to fire and indirectly via 
impacts to plants used as forage and cover. Direct effects to tortoises 
can include fatality or injury through incineration, elevated body 
temperature, poisoning from smoke inhalation, and asphyxiation. Fire 
burns plants used for food and cover, which indirectly impacts 
tortoises by increasing forage effort and prolonging exposure to 
predators, both of which reduce fitness of individuals. The magnitude 
of the impact of fire on tortoises largely depends on the severity of 
the fire (e.g., a less severe fire may leave patches of usable forage 
and microhabitat for shelter and thermoregulation).
    The scope of fire as a risk factor in Arizona is associated with 
presence of nonnatives in conjunction with ignition sources and fire 
suppression. Geospatial analysis suggests that fire may be a concern in 
23 percent of predicted suitable habitat in Arizona. However, despite 
the fact that many wildfire ignitions occur annually in desertscrub 
communities within the range of the Sonoran desert tortoise, aggressive 
wildfire suppression practices are widely implemented by agencies and 
municipalities across the landscape in desertscrub communities. As a 
result of these practices, a very limited amount of tortoise habitat 
has burned in comparison to the total area considered potential habitat 
for Sonoran desert tortoises across their range. We expect that 
aggressive wildfire suppression practices will continue in Arizona into 
the future in order to protect ecological values and human health and 
property and, therefore, do not expect this stressor to have an 
appreciable effect on Sonoran desert tortoises at the population-level 
in Arizona.
    Geospatial analysis suggests that fire may be a concern in 20 
percent of predicted suitable habitat in Mexico where fire occurs more 
regularly to manage buffelgrass (Pennisteum cilare) pastures. 
Buffelgrass is a nonnative species that is cultivated more widely in 
Mexico to support grazing. Fires set intentionally in Mexico to benefit 
buffelgrass pastures could potentially affect tortoise populations. 
However, while these buffelgrass pasture areas are within the absolute 
range of the tortoise, pastures are generally found in flat valley 
bottoms, and tortoises generally prefer rocky slopes, thus tortoises 
likely have reduced exposure to fire in cultivated pastures. 
Additionally, the best available information does not suggest that 
fires to benefit buffelgrass pastures in Mexico are affecting tortoises 
at a magnitude or frequency that would result in population-level 
effects. Therefore, we do not expect this stressor will have an 
appreciable effect on Sonoran desert tortoises in Mexico.
Habitat Conversion
    Conversion of natural habitat via urban and agricultural 
development can have a variety of direct and indirect impacts on 
tortoises depending on the intensity and size of the development. 
Habitat conversion can directly impact tortoises via fatalities during 
the construction or development process. If tortoises survive the 
initial construction, conversion may impact tortoises by making areas 
entirely unusable (i.e., nonhabitat) or by removing forage and cover 
sites thus making the habitat less productive for tortoises. Habitat 
areas converted to dense urban uses likely displace animals into 
surrounding areas, if adjacent suitable habitat exists. Tortoises that 
survive the initial development, but are not entirely displaced, likely 
have reduced access to plants used as forage and cover and, therefore, 
likely have reduced fitness and are subject to additional predation. 
Habitat conversion may also result in fragmentation that can impact 
short- and long-range movements (see Habitat Fragmentation discussion 
below). However, population-level effects to Sonoran desert tortoises 
from habitat conversion have not been documented in the literature.
    To assess the potential historical loss of habitat due to 
conversion to urban landscape, we calculated the amount of area 
currently designated as urban land within the range boundary of the 
Sonoran desert tortoise. About 1,279 sq mi (331,260 ha) of area is 
currently designated as urban in Arizona. If all of this urban area had 
previously been potential tortoise habitat, which is unlikely, this 
area would represent approximately 5 percent of all estimated 
historical habitat. In Mexico, about 53 sq mi (13,730 ha) of area is 
designated as urban. This represents less than 1 percent of all 
estimated historical habitat. Even considering additional

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areas potentially lost historically due to agricultural or other 
development (which we have not quantified due to data limitations), 
historical habitat loss appears to be relatively small.
    Looking into the future, urban development in Arizona is expected 
to occur primarily within a zone referred to as the Sun Corridor 
Megapolitan, driven primarily by its association with major 
transportation routes and other existing infrastructure. In a northward 
direction from the U.S.-Mexico border, this development zone occurs 
within the range of the Sonoran desert tortoise along Interstate (I)-
19, I-10, and I-17 (Gammage et al. 2008 entire; 2011 entire). 
Additional suburban development zones are expected to occur along I-40 
near Kingman and along State Route 93, which connects Wickenburg to 
Kingman, especially if the latter route is converted into an interstate 
(proposed I-11). The majority of projected development in Arizona is 
not anticipated to occur in potential tortoise habitat. However, we 
expect as much as 9 percent of potential tortoise habitat in Arizona 
could be developed within the next 50-100 years. In contrast, an 
estimated 73 percent of potential tortoise habitat in Arizona is not 
likely subject to development due to land ownership and management. 
These areas are lands managed for a purpose not compatible with 
widespread development including military lands, state and municipal 
parks, and areas owned by Bureau of Land Management, Bureau of 
Reclamation, National Park Service, Forest Service, and U.S. Fish and 
Wildlife Service. Small areas on these land ownership types may 
experience development, but significant urban development in these 
areas is unlikely.
    In Arizona, the number of acres dedicated to irrigated agriculture 
has been on the decline (U.S. Department of Agriculture 2009, p. 273). 
These areas are likely being converted into areas re-zoned for 
residential or commercial purposes or, rarely, left fallow for natural 
recovery. This observed declining trend of agricultural use will likely 
continue in Arizona, unless farming practices or technology change, or 
a novel crop significantly influences market forces and reverses this 
trend. Therefore, we do not anticipate appreciable future habitat 
conversions in Arizona due to agricultural development. Additionally, 
areas that may be converted to agricultural uses likely would not be 
preferred tortoise habitat because these uses generally occur in flat 
valley bottoms while tortoises prefer rocky slopes.
    Within the species' range in Sonora, Mexico, and according to 
recent reports, urban development is also expected to continue into the 
future, but at a slower pace and smaller scale than Arizona. Hermosillo 
is the largest population center in Sonora (approximately 778,000 per 
the 2014 census) and could expand north and east, which could 
potentially affect adjacent tortoise populations (Rosen et al. 2014a, 
pp. 22-23). Limited urban expansion could also be predicted for a small 
number of other communities within Sonora (Rosen et al. 2014a, pp. 22-
23). With respect to agriculture in Sonora, the majority occurs on 
large river deltas, which are not occupied by tortoises (Rosen et al. 
2014a, pp. 22-23). Therefore, neither urban nor agricultural 
development is considered to be significantly affecting tortoise 
populations over a large area in Sonora currently, or into the future.
Habitat Fragmentation
    Habitat fragmentation via infrastructure and other forms of linear 
development may impact tortoises by restricting movement within and 
between home ranges, direct fatality, and enabling human collection. 
The source of habitat fragmentation is any linear feature such as roads 
of varying capacities, railroad tracks, and canals. These forms of 
linear development are largely ubiquitous across the range of the 
tortoise; however, the severity of the impact of linear development 
depends on the permeability of the feature to tortoise movement.
    Tortoises move within and outside their home ranges for different 
purposes depending on sex, age class, and size class. Tortoises will 
move to find preferred plant forage species that may be in season 
(Oftedal 2007, entire); to a different shelter site with a different 
exposure, depth, or substrate (Averill-Murray and Klug 2000, p. 62); or 
to search for potential mates (Averill-Murray et al. 2002a, pp. 139-
144). Tortoises will also move to disperse outside of their home 
ranges, with distances ranging from a few hundred yards to several 
miles or more (Edwards et al. 2004, entire). When individuals are 
unable to successfully complete these movements within their home 
ranges or on the landscape, basic natural-history functions can be 
compromised to varying degrees. Individual tortoises may spend more 
time active and exposed if they are unable to access preferred sites 
for forage and shelter, which may result in reduced fitness.
    Fragmentation can also be a concern if it prevents movements 
between populations. This degree of fragmentation could impact species' 
representation through effects on genetic diversity, and it could 
impact species' redundancy if recolonization of an area extirpated by a 
stochastic event is precluded.
    Roads can also be a source of injury, mortality, and collection. 
Unlike some other species, tortoises do not appear to avoid roads and 
are thus susceptible to impacts there. However, the severity of these 
kinds of impacts is likely correlated with road width, road type (e.g., 
rugged, improved gravel, paved), speed limits, traffic volume, 
availability of washes or other means of crossing under roads, and 
quality of tortoise habitat being transected. See ``Human-Tortoise 
Interactions'' for further discussion of these kinds of impacts.
    More severe effects to tortoise individuals and populations as a 
result of fragmentation are possible where fragmenting features are 
less permeable to tortoises or where fragmenting features are more 
dense. For example, a multi-lane road is less permeable to tortoises 
than a single lane dirt road. Similarly, an area bisected by multiple 
roads and canals is likely to have a greater affect on tortoises 
because there are multiple obstacles to navigate while moving through 
an area. In these situations, impacts to tortoises could be more severe 
because there is higher potential for human interactions, and 
fragmentation of home ranges and populations may be more complete.
    While the effects of fragmentation, as discussed above, could 
theoretically manifest in population-level effects, there is no 
evidence of such population-level effects. Population-level effects due 
to fragmentation would only become discernible (with current research 
and monitoring methods) over an extremely long period of time (decades 
to centuries) due to the life history and longevity of the species. 
Adequate time periods are well outside of both the existing period of 
monitoring and our ability to reasonably predict such population-level 
effects in the future.
Human-Tortoise Interactions
    Inadvertent or purposeful human interactions with tortoises can 
result in injury or death of tortoises. Human interactions can also 
result in collection of tortoises, thereby removing them from the wild 
population. Sources of interaction include roads, wild-urban interface 
zones, and general recreation areas. Human interaction can lead to 
either inadvertent or intentional impacts to tortoises. Inadvertent 
interactions can have incidental effects on tortoises that are not 
otherwise the intent or purpose

[[Page 60327]]

of the activity itself. Examples of activities that could lead to human 
interactions with tortoises (when in occupied tortoise habitat) include 
the use of vehicles (Lowery et al. 2011, entire), target shooting, 
hunting, hiking, rock crawling, trail bike riding, rock climbing, and 
camping (Howland and Rorabaugh 2002, pp. 339-342; AGFD 2010, p. 9). In 
addition, dogs that escape captivity or are intentionally abandoned can 
form feral packs, which have been shown to impact individual Sonoran 
desert tortoises (Zylstra 2008, entire). Other forms of human 
interaction with tortoises are direct and intentional, such as 
collection of wild tortoises, release of captive tortoises into wild 
populations, or physically handling wild tortoises (Grandmaison and 
Frary 2012, entire).
    These types of human interactions with tortoises occur at highest 
frequency in the wild-urban interface zone and are thought to lessen 
with increasing distance from human population centers (Zylstra et al. 
2013, pp. 112-113). In fact, one study found that adult tortoise 
survivorship has been shown to improve with increasing distance from 
urbanized areas; specifically, the odds of a Sonoran desert tortoise 
surviving 1 year increases 13 percent for each 6.2-mile (mi) (10-
kilometer (km)) increase in distance from a city of at least 2,500 
people (Zylstra et al. 2013, pp. 112-113).
    To assess the potential geographic scope of human interactions, we 
calculated the acreage of predicted potential habitat areas within 6.2-
mi (10-km) rings of cities greater than 2,500 in population size. While 
the potential for human interactions exists beyond these areas, we 
assumed that the closer tortoises are to human population centers, the 
more likely that these interactions will occur. Overall, 29 percent of 
predicted potential tortoise habitat occurs within 12.4 mi (20 km) of 
urban areas in Arizona and 9 percent in Sonora.
    While the effects of human interactions, as discussed above, could 
theoretically manifest in population-level effects, there is no 
evidence of such population-level effects. Population-level effects due 
to human interactions would only become discernable (with current 
research and monitoring methods) over an extremely long period of time 
(decades to centuries) due to the life history and longevity of the 
species. Adequate time periods are well-outside of both the existing 
period of monitoring and our ability to reasonably predict such 
population-level effects in the future.
Climate Change and Drought
    There is unequivocal evidence that the earth's climate is warming 
based on observations of increases in average global air and ocean 
temperatures, widespread melting of glaciers and polar ice caps, and 
rising sea levels, with abundant evidence supporting predicted changes 
in temperature and precipitation in the southwestern deserts (IPCC 
2014, entire). Predicted temperature trends for the region encompassing 
the range of the Sonoran desert tortoise include warming trends during 
winter and spring, lowered frequency of freezing temperatures, longer 
freeze-free seasons, and higher minimum temperatures during the winters 
(Weiss and Overpeck 2005, p. 2075). In this same region, predictions of 
potential changes in precipitation due to climate change are less 
certain, but climate scientists largely agree that annual precipitation 
totals are likely to decrease as compared to historical averages 
(Seager et al. 2007, entire; Cook et al. 2015, p. 4). Climate models 
generally agree that winter and spring precipitation may be influenced 
by climate change, with predicted decreases in precipitation during 
these seasons. However, modeling results vary considerably with respect 
to how climate change could affect summer (monsoon) precipitation in 
Arizona and northern Mexico. While annual precipitation totals are 
predicted to decrease, summer precipitation totals may increase (IPCC 
2007, p. 20), with wide fluctuation in scope and severity of summer 
precipitation events.
    Climate change may impact Sonoran desert tortoises, primarily 
through impacts on drought severity and duration as a result of 
increased air temperature and reduced precipitation. Increased drought 
severity and duration may impact tortoise access to freestanding water 
for drinking and plants for forage and cover. Climate change is 
predicted to reduce precipitation in the southwest and, therefore, has 
potential to reduce availability of freestanding water. Reduced 
precipitation could also reduce abundance of plants available for 
forage and cover, thereby increasing energy expenditures while finding 
forage, impairing thermoregulation, and exposing tortoises to 
predators. All of this can result in reduced fitness and rates of 
reproduction and survival. Sonoran desert tortoises evolved in a desert 
ecosystem and have adaptations to withstand drought; however, long-term 
climate change may stress tortoises beyond those tolerances.
    One study has shown a measurable effect to tortoise populations due 
to drought. Zylstra et al. (2013, pp. 113-114) showed that, in tortoise 
populations that experience localized, prolonged drought conditions, 
annual adult survival can decrease by 10-20 percent, and abundance of 
adults can be reduced by as much as 50 percent or more in local 
instances. However, when drought conditions affecting these populations 
subsided, Sonoran desert tortoise numbers began to increase, reaching 
near pre-drought status, and the overall rate of change in population 
size was found to be greater than 1, indicating overall positive 
population growth in the populations monitored for a period of more 
than 20 years (Zylstra et al. 2013, pp. 112-114).
    We anticipate that climate change is likely to have population-
level impacts to Sonoran desert tortoises to some degree in the future. 
However, the severity, scope, and timing of those impacts are unknown 
because the intensity of the environmental changes is unknown and the 
response at the species level is unknown. In particular, output from 
climate change models exhibits noticeably increasing confidence 
intervals, and therefore increased uncertainty, beyond the 50- to 75-
year timeframe (Seager et al. 2007, p. 1182). Based on the best 
available information, we cannot predict the magnitude of environmental 
change or the severity of the species' response over time with a 
reasonable degree of certainty. However, due to the potential for 
climate change to affect tortoises, we carefully analyzed this risk 
factor to the best of our ability in our population model (see Future 
Condition and Viability below).
Cumulative Impacts
    It is possible that several risk factors may be impacting Sonoran 
desert tortoise populations cumulatively now and into the future. 
Theoretically, for every additional risk factor occurring in a 
population area, the likelihood of population-level impacts increases. 
However, no areas are currently known to be in decline due to 
individual or cumulative impacts, including impacts from potential 
stressors that were not discussed in detail in this document, and just 
as with assessment of the individual risk factors, the theoretical 
population-level effects due to cumulative impacts at current and 
predicted levels would only become discernible (with current research 
and monitoring methods) over an extremely long period of time (decades 
to centuries) due to the life history and longevity of the species. 
Adequate time

[[Page 60328]]

periods are well outside of both the existing period of monitoring and 
our ability to reasonably predict such population-level effects in the 
future.

Conservation Measures and Land Management

    There are a number of conservation actions that have been 
implemented to minimize stressors and maintain or improve the status of 
the Sonoran desert tortoise, including a candidate conservation 
agreement (AIDTT 2015, entire) with AGFD, Bureau of Land Management, 
Department of Defense, National Park Service, U.S. Fish and Wildlife 
Service, Bureau of Reclamation, Customs and Border Protection, U.S. 
Forest Service, Natural Resources Conservation Service, and Arizona 
Department of Transportation (collectively referred to as ``Parties''). 
Candidate conservation agreements are formal, voluntary agreements 
between the Service and one or more parties to address the conservation 
needs of one or more candidate species or species likely to become 
candidates in the near future. Participants voluntarily commit to 
implement specific actions designed to remove or reduce stressors to 
the covered species, so that listing may not be necessary. The 
agreement for the Sonoran desert tortoise, which formalizes many 
existing conservation measures and land management practices, was 
completed by the Parties in March 2015 and was signed by the final 
signatory, the Service, on June 19, 2015. The agreement applies to 
approximately 13,000 sq mi (3.4 million ha) of Sonoran desert tortoise 
habitat in Arizona. This area represents approximately 55 percent of 
the species' predicted potential habitat in Arizona and 34 percent of 
its predicted potential habitat rangewide.
    The agreement is designed to encourage, facilitate, and direct 
effective tortoise conservation actions across multiple agencies and 
entities having the potential to directly influence conservation of the 
species in Arizona. Parties to the agreement identified existing 
tortoise conservation measures and designed a comprehensive 
conservation framework for these measures that encourages coordinated 
actions and uniform reporting, integrates monitoring and research 
efforts with management, and supports ongoing conservation partnership 
formation. Management actions in the agreement include, but are not 
limited to, reducing the spread of nonnative grasses, reducing or 
mitigating dispersal barriers, reducing the risk and impact of desert 
wildfires, reducing the impact of off-highway vehicles, population 
monitoring, and reducing illegal collection of tortoises. A complete 
list of the stressor-specific conservation measures can be found in 
Appendix A of the CCA (AIDTT 2015).
    Additionally, as discussed above, an estimated 73 percent of 
potential tortoise habitat in Arizona is not likely subject to 
development due to land ownership and management. These areas are lands 
managed for a purpose not compatible with widespread development 
including military lands, state and municipal parks, and areas owned by 
Bureau of Land Management, Bureau of Reclamation, National Park 
Service, Forest Service, and U.S. Fish and Wildlife Service. Small 
areas on these land ownership types may experience development, but 
significant development on these lands is unlikely.

Current Condition

    Generally, the best available scientific information suggests that 
the Sonoran desert tortoise has not experienced any appreciable 
reduction in its overall range or abundance relative to presumed 
historical levels. Certainly some areas of former habitat have been 
lost due to conversion to urban and agricultural uses, but our 
geospatial analysis suggests that the magnitude of these loses is 
relatively minimal (see ``Habitat Conversion'' discussion above). This 
suggests that the species has potential to retain historical levels of 
resiliency, redundancy, and representation (and, therefore, viability) 
if the habitat condition now and into the future is in acceptable 
condition relative to risk factors.
    As discussed above, we conducted a coarse geospatial analysis of 
potential habitat based on elevation, slope, and vegetation type across 
the species' range. This rangewide geospatial analysis resulted in a 
prediction of approximately 38,000 sq mi (9.8 million ha) of potential 
tortoise habitat. We then evaluated the current condition (status) of 
the tortoise by categorizing habitat into primary, secondary, or 
tertiary quality categories. The categorization of habitat is based on 
the current suitability of potential habitat (high, medium, and low) 
and the possible presence of risk factors that could have population-
level effects. We used four geospatial layers to measure those risk 
factors: Land management, presence of nonnative vegetation, high fire 
risk potential, and proximity to urban areas. The habitat quality 
analysis was conducted under two alternative assumptions related to the 
effects of the risk factors (high or low threats) and two alternative 
assumptions regarding the effects of conservation measures (high or low 
management).
    For the U.S. analysis area, this geospatial analysis resulted in 8 
to 25 percent of potential tortoise habitat being categorized primary 
quality, 62 to 75 percent categorized as secondary quality, and 13 to 
17 percent categorized as tertiary quality (see Table 1--Modeled 
Current Habitat Quality-Arizona). In Mexico, this analysis resulted in 
0 to 2 percent of potential habitat being categorized as primary 
quality, 79 to 98 percent categorized as secondary quality, and 0.2 to 
21 percent categorized as tertiary quality (see Table 2--Modeled 
Current Habitat Quality-Mexico). The amount in each category is 
presented as a range due to the four alternative assumptions related to 
the effects of risk factors and effects of conservation measures.

                                                    Table 1--Modeled Current Habitat Quality-Arizona
                                               [Please note that some numbers do not add due to rounding]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                      High management and low threats assumptions         Low management and high threats assumptions
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                    Primary     Secondary     Tertiary      Total       Primary     Secondary     Tertiary      Total
--------------------------------------------------------------------------------------------------------------------------------------------------------
Area (sq mi)....................................        6,090       15,010        3,100       24,200        1,820       18,270        4,100       24,190
Area (ha).......................................    1,577,300    3,887,570      802,900    6,267,770      471,380    4,731,910    1,061,900    6,265,190
--------------------------------------------------------------------------------------------------------------------------------------------------------


[[Page 60329]]


                                                     Table 2--Modeled Current Habitat Quality-Mexico
                                               [Please note that some numbers do not add due to rounding]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                      High management and low threats assumptions         Low management and high threats assumptions
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                    Primary     Secondary     Tertiary      Total       Primary     Secondary     Tertiary      Total
--------------------------------------------------------------------------------------------------------------------------------------------------------
Area (sq mi)....................................          330       13,400           30       13,760            0       10.550        3,210       13,760
Area (ha).......................................       85,470    3,470,580        7,770    3,563,820            0    2,732,440      831,390    3,563,830
--------------------------------------------------------------------------------------------------------------------------------------------------------

    We then used the amount of habitat in each quality category 
combined with reported density estimates for tortoises to produce 
rangewide abundance estimates under varying assumptions of habitat 
conditions and density estimates. The current rangewide abundance 
estimates ranged from 470,000 to 970,000 total adult tortoises. The 
current estimate in the United States was 310,000 to 640,000 adult 
tortoises, and the estimate in Mexico was 160,000 to 330,000 adult 
tortoises.

Future Condition and Viability

    The tortoise continues to occupy a large portion of its historical 
range, with much of that range considered to be primary or secondary 
quality habitat. Looking to the future, the risk factors that could 
affect the tortoise include: (1) Altered plant communities; (2) altered 
fire regimes; (3) habitat conversion of native vegetation to developed 
landscapes; (4) habitat fragmentation; (5) human-tortoise interactions; 
and (6) climate change and drought. By its very nature, any status 
assessment is forward-looking in its evaluation of the risks faced by a 
species, and future projections will always be dominated by 
uncertainties, which increase as we project further and further into 
the future. This analysis of the tortoise is no exception. In spite of 
these uncertainties, we are required to make decisions about the 
species with the best information currently available. We have 
attempted to explain and highlight many of the key assumptions as part 
of the analytical process documented in the SSA Report (Service 2015). 
We recognize the limitations in available information, and we handled 
them through the application of scenario planning, geospatial modeling, 
and population simulation modeling.
    As discussed above, to project the future condition of the 
tortoise, we used a combination of geospatial analysis and population 
simulation modeling. Essentially, the geospatial analysis predicts the 
amount and condition of habitats available to tortoises in the future, 
and the population simulation model projects the abundance of tortoises 
that can be supported by that habitat based on rates of survival, 
growth, and death. The geospatial analysis and population simulation 
model combine to project the amount, condition, and distribution of 
suitable habitat; and the abundance, growth rate, and quasi-extinction 
risk for tortoise populations.
    The geospatial analysis includes direct consideration of projected 
habitat losses due to urban development (urban growth potential) and 
the potential for impacts to tortoises due to altered plant communities 
(invasive vegetation), altered fire regimes (fire risk), and human 
interactions (urban influence). Land management, as a surrogate for 
presence of fire suppression and other ongoing conservation activities, 
is also included in the geospatial analysis. Finally, the potential 
effect of climate change is included in the population simulation model 
by simulating an increasing extent of drought and variation in the 
magnitude of the effects of drought on tortoise survival.
    For future scenarios in Arizona where we considered a potential 
loss of overall habitat due to urban development, we calculated an 
annual rate of habitat loss in each habitat quality category. We 
calculated this annual rate by dividing the area identified by Gammage 
et al. (2008, entire; 2011, entire) as potential for urban growth by 60 
years. The Gammage et al. estimate was published in 2008 as a possible 
2040 projection. However, this estimate was made at the height of an 
economic expansion during the mid-2000's, which is no longer a 
realistic assumption to carry forward. We therefore accounted for the 
slowed rate of urban growth by using the Gammage et al. projection to 
represent a potential future 60 years from the present. We have no data 
to reliably predict the potential for urban growth beyond 60 years. 
While the population simulation model continues to include loss of 
habitat to urban development beyond the 60 year horizon, the geospatial 
analysis does not because after the 60 year horizon, there is no 
information suggesting where those developments may occur. As a result, 
maps and calculations of area in the future conditions use the 60-year 
future. In contrast, the results of the population simulation model can 
be presented at any point in time. We have presented those results most 
often at the 50- and 75-year future conditions because this is the 
timeframe considered to be the foreseeable future for this decision 
(see Threatened Species Throughout Range).
    We developed multiple future condition scenarios to capture the 
range of uncertainties regarding population-level effects to the 
tortoise. As we discussed above, with the exception of climate change 
and drought, none of the risk factors have been shown to result in 
population-level impacts to the tortoise. However, given that 
population-level effects may be occurring that current methodologies 
would not allow us to detect in the short term, we have included 
scenarios in the geospatial and population modeling that assume impacts 
from these factors may be greater than is currently understood. All of 
the scenarios we developed are considered to be within the realm of 
reasonable possibility. In other words, the worst- and best-case 
scenarios are not the absolutely worst and best scenarios that one 
could imagine, but are instead grounded in the realm of realistic 
uncertainty. Additionally, we have not identified a most likely future 
scenario. In many cases in this finding, we have only presented the 
results of the worst-case scenario, but that does not mean it is the 
most likely scenario.
    The growth rates and quasi-extinction probabilities projected by 
the model provide a characterization of resiliency. Because each area 
of analysis (Arizona and Mexico) is treated as a large population, the 
characterization of resiliency applies at the scale of the area of 
analysis rather than at the scale of traditional populations within 
those areas. The resulting population growth rates for all time periods 
for all scenarios ranged from 0.9915 to 0.9969, indicating slightly 
decreasing numbers of tortoises in the areas of analysis. All of the 
scenarios showed declining overall abundances into the future in each 
of the areas of analysis. However, because of the relatively large 
current estimated population sizes and the long lifespan of these 
tortoises, our population simulation model suggests no measurable risks 
of quasi-extinction in the next 50 years in either the U.S.

[[Page 60330]]

or Mexican areas of analysis under any scenarios, even though slow 
population declines are projected. At 75 years, the risks of quasi-
extinction increased, ranging from 0 in some scenarios to as high as 
0.033 probability of quasi-extinction (in other words, a 3.3 percent 
risk of quasi-extinction in 75 years) in the worst-case future scenario 
for the Mexican analysis area. All but 3 (of 18) scenarios resulted in 
less than 0.01 probability of quasi-extinction in 75 years. When we 
look further into the future at 100 years, our simulation model 
suggests the risks of quasi-extinction for some scenarios increased to 
near 0.05 probability of quasi-extinction (ranging from 0 to 0.089, 
with 8 of 18 scenarios exceeding 0.03 probability of quasi-extinction). 
At 200 years, several scenarios exceeded 0.2 probability of quasi-
extinction (ranging from 0.07 to 0.323, with 14 of 18 scenarios 
exceeding 0.1 probability of quasi-extinction).
    We characterized the redundancy (number and distribution of 
tortoise populations) and representation (ecological diversity) 
indirectly through projecting the likely quality and quantity of 
tortoise habitat distributed across the species range under different 
scenarios. Generally, the scenarios that showed the best and worst 
result for tortoises in the Arizona area of analysis were also the best 
and worst case for the Mexican area of analysis. Under the worst-case 
future scenarios, the distribution of habitats in the United States 
(considering a 60-year future condition) is projected to include about 
11,800 sq mi (3 million ha) of habitat categorized as primary or 
secondary quality. In Mexico, under the worst-case scenario, about 
10,550 sq mi (2.7 million ha) of secondary quality habitat is projected 
to be maintained (no habitat was projected in the primary quality 
category). Other scenarios project more favorable conditions in both 
the United States and Mexico. The habitat quality under the worst-case 
condition is projected to be distributed across the species' range, 
although in Arizona the habitat for this scenario is quite reduced 
compared to more favorable scenarios or current conditions (see Map 2--
Future Sonoran Desert Tortoise Predicted Potential Habitat). For this 
worst-case condition, the estimated abundance of tortoises expected to 
be supported by these habitats is 316,000 in 50 years and 278,000 in 75 
years, which is a reduction of 33 percent in 50 years and 41 percent in 
75 years, when compared to the current low end abundance estimates of 
470,000.
BILLING CODE 4333-15-P

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Finding

Standard for Review

    Section 4 of the Act, and its implementing regulations at 50 CFR 
part 424, set forth the procedures for adding species to the Federal 
Lists of Endangered and Threatened Wildlife and Plants. Under section 
4(b)(1)(a), the Secretary is to make endangered or threatened 
determinations required by subsection 4(a)(1) solely on the basis of 
the best scientific and commercial data available to her after 
conducting a review of the status of the species and after taking into 
account conservation efforts by States or foreign nations. The 
standards for determining whether a species is endangered or threatened 
are provided in section 3 of the Act. An endangered species is any 
species that is ``in danger of extinction throughout all or a 
significant portion of its range.'' A threatened species is any species 
that is ``likely to become an endangered species within the foreseeable 
future throughout all or a significant portion of its range.'' Per 
section 4(a)(1) of the Act, in reviewing the status of the species to 
determine if it meets the definition of endangered or of threatened, we 
determine whether any species is an endangered species or a threatened 
species because of any of the following five factors: (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; and (E) other natural or manmade 
factors affecting its continued existence.

Summary of Analysis

    The biological information we reviewed and analyzed as the basis 
for our findings is documented in the SSA Report (Service 2015, 
entire), a summary of which is provided in the Background section of 
this finding. The projections for the condition of future populations 
are based on our expectations of the potential risk factors (in other 
words, threats or stressors) that may have population-level effects 
currently or in the future. The six risk factors we evaluated in detail 
are: (1) Altered plant communities (Factor A from the Act); (2) altered 
fire regimes (Factor A); (3) habitat conversion of native vegetation to 
developed landscapes (Factor A); (4) habitat fragmentation (Factor A); 
(5) human-tortoise interactions (Factor E); and (6) climate change and 
drought (Factor A). We also reviewed the effects of environmental 
contaminants, grazing, and litter (Factor A); overutilization (Factor 
B); disease and predation (Factor C); regulatory mechanisms (Factor D); 
and undocumented human immigration (Factor E). However, we did not 
evaluate these latter factors individually in further detail because 
they are not known or suspected to have meaningful effects on the 
status of the tortoise.
    For the six risk factors that were evaluated in detail, we used 
geospatial analysis to assess the scope of those factors currently and 
into the future. The geospatial model predicts the amount and condition 
of habitat based on application of several scenarios with varying 
degrees of effects. We then used a population simulation model to 
forecast the abundance of the species within those habitats. The 
results of this analysis are presented in terms of the amount, 
distribution, and condition of potential habitats; and the abundance, 
growth rates, and probabilities of quasi-extinction of tortoise 
populations. These are the metrics we use to describe the resiliency, 
redundancy, and representation of the species now and in the future in 
order to determine if the species is likely in danger of extinction now 
or in the foreseeable future.

Application of Analysis to Determinations

    The fundamental question before the Service is whether the species 
warrants protection as endangered or threatened under the Act. To make 
this determination, we evaluated the projections of extinction risk, 
described in terms of the condition of current and future populations 
and their distribution (taking into account the risk factors and their 
effects on those populations). For any species, as population condition 
declines and distribution shrinks, the species' extinction risk 
increases and overall viability declines.
    As described in the determinations below, we first evaluated 
whether the Sonoran desert tortoise is in danger of extinction 
throughout its range now (an endangered species). We then evaluated 
whether the species is likely to become in danger of extinction 
throughout its range in the foreseeable future (a threatened species). 
We finally considered whether the Sonoran desert tortoise is an 
endangered or threatened species in a significant portion of its range 
(SPR).

Endangered Species Throughout Range

Standard
    Under the Act, an endangered species is any species that is ``in 
danger of extinction throughout all or a significant portion of its 
range.'' Because of the fact-specific nature of listing determinations, 
there is no single metric for determining if a species is currently in 
danger of extinction. We used the best available scientific and 
commercial data to evaluate the current viability (and thus risk of 
extinction) of the Sonoran desert tortoise to determine if it meets the 
definition of an endangered species.
Evaluation and Finding
    Our review found that the Sonoran desert tortoise continues to 
occupy a very large portion of its estimated historical range. We 
estimate approximately 5 percent of historical range may have been lost 
due to conversion to urban uses. The remaining portion of the range is 
made up of approximately 38,000 sq mi (9.8 million ha) of modeled 
potential habitat, and we estimate that approximately 470,000 to 
970,000 tortoises inhabit this area. This amount and distribution of 
habitat and tortoises supports sufficient resiliency to sustain the 
species into the near future. These levels of tortoises and suitable 
habitat are commensurate with historical levels, and there is no 
information available to suggest that the species will not persist at 
these levels. Furthermore, the habitat available and tortoise 
populations are spread widely over the known range of the species, 
suggesting that the species retains the redundancy and representation 
it had historically.
    Additionally, given the current wide distribution of tortoise 
habitat and land uses therein, there are no known risk factors that are 
likely to reduce the status of the species significantly in the near 
term. The stressors facing the species are relatively slow-moving and, 
if impacts are seen, will likely be measurable over many years (dozens 
to hundreds). In other words, there are no immediate, high-magnitude 
threats acting on the species such that it would be expected to undergo 
a meaningful decline over the near term.
    This current estimated abundance and distribution of tortoises 
across the species' range provides resiliency, redundancy, and 
representation to sustain the species into the near future. Because 
this estimate of the current condition and distribution of habitat and 
populations provides sufficient resiliency, redundancy, and 
representation for the species, we conclude that the current risk of 
extinction of the Sonoran desert tortoise is sufficiently low that it 
does not meet the definition of an endangered species under the Act.

[[Page 60333]]

Threatened Species Throughout Range

    Having found that the Sonoran desert tortoise is not an endangered 
species throughout its range, we next evaluated whether the species is 
a threatened species throughout its range.
Standard
    Under the Act, a threatened species is any species that is ``likely 
to become an endangered species within the foreseeable future 
throughout all or a significant portion of its range.'' The foreseeable 
future refers to the extent to which the Secretary can reasonably rely 
on predictions about the future in making determinations about the 
future conservation status of the species (U.S. Department of the 
Interior, Solicitor's Memorandum, M-37021, January 16, 2009). A key 
statutory difference between a threatened species and an endangered 
species is the timing of when a species may be in danger of extinction, 
either now (endangered species) or in the foreseeable future 
(threatened species).
Evaluation and Finding
    In considering the foreseeable future as it relates to the status 
of the Sonoran desert tortoise, we considered the risk factors acting 
on the species and looked to see if reliable predictions about the 
status of the species in response to those factors could be drawn. We 
considered whether we could reliably predict any future effects that 
might affect the status of the species, recognizing that our ability to 
make reliable predictions into the future is limited by the variable 
quantity and quality of available data about impacts to the tortoise 
and the response of the tortoise to those impacts. For the tortoise, 
the most significant risk factor looking into the future is climate 
change. While we have high certainty that environmental conditions will 
change as a result of climate change, we do not have reasonable 
certainty about the extent of those changes or the species' response to 
the changes. In particular, output from climate change models exhibits 
noticeably increasing confidence intervals, and therefore increased 
uncertainty, beyond the 50- to 75-year timeframe (see, for example, 
Seager et al. 2007, p. 1182). We have chosen to use a timeframe of 50 
to 75 years as the foreseeable future for this analysis because the 
available data does not allow us to reasonably rely on predictions 
about the future beyond that time period.
    The Sonoran desert tortoise is not likely to be in danger of 
extinction in the foreseeable future (50-75 years) and, therefore, does 
not meet the definition of a threatened species throughout its range. 
There are two parallel lines of rationale to explain why the Sonoran 
desert tortoise does not meet the definition of a threatened species, 
one more qualitative and one more quantitative.
    Most simply and qualitatively, the best available data does not 
show that any one or more risk factors are likely to result in 
meaningful population declines in the foreseeable future. Looking to 
the future, several risk factors may contribute to population- or 
species-level declines. These stressors sort into three general 
categories.
    The first category of stressors is those that are low in magnitude 
or scope, like effects from human interactions (e.g., collection, 
vehicle strikes) and habitat conversion. Human interactions can occur 
throughout the range of the species, but are usually relatively 
isolated events that generally would not make habitat unsuitable for 
other tortoises. Habitat conversion is likely limited largely to 
expansion of existing urban areas. As long as the scope of these 
stressors and tortoises' exposure to them remain narrow, as they are 
expected to for the foreseeable future, there is no information to 
suggest that population-level declines will result due to these 
stressors.
    The second category of stressors is those that have the potential 
for population-level impacts, but for which we have limited to no data 
to support that conclusion at this time. Risk factors that fit into 
this category include altered plant communities, altered fire regime, 
and habitat fragmentation. Because the species is so long lived, 
population declines due to these kinds of stressors, if they are 
occurring, are very difficult to detect with current techniques in 
short-term studies. As a very simplistic mathematical example, if we 
presume a species with a generation time of 5 years is displaying a 10 
percent population decline every generation, it would take about 35 
years for an overall population decline of 50 percent to manifest. For 
the Sonoran desert tortoise, which has a generation time of 
approximately 25 years, it would take nearly 175 years for that 50 
percent decline to manifest.
    The last category includes stressors that are likely to impact 
tortoise populations in the future; however, those impacts are not 
likely to manifest measurable species responses during the foreseeable 
future. In other words, those impacts, should they occur, are not 
likely to occur at a meaningful level until after the time period that 
we can rely on as reasonably foreseeable. These stressors include the 
effects of climate change and drought. The magnitude of those impacts 
and the response of the species cannot be reasonably predicted at this 
time. These kinds of environmental changes that are relatively slow 
moving on the geological time scale are expected to take many decades 
or longer to manifest in measurable declines of the tortoise at the 
species level.
    The Act does not require absolute proof of impacts and responses in 
order to consider an entity to be in danger of extinction. However, in 
order to draw a conclusion that a stressor (or cumulative stressors) 
will cause a species to be in danger of extinction, the best available 
information needs to show that an impact is likely to occur and that 
the species response would likely cause it to be in danger of 
extinction. Because we do not know what magnitude of impacts would 
likely cause a discernable response in tortoise populations, we cannot 
conclude that stressors are or will occur at a level that causes the 
species to be in danger of extinction.
    Therefore, from a purely qualitative perspective, the tortoise is 
not facing any stressors that are likely to cause meaningful population 
declines within the foreseeable future that would cause the species to 
become in danger of extinction in the foreseeable future.
    Taking a more quantitative approach, looking to the future, several 
risk factors could contribute to population- or species-level declines. 
Our geospatial and population simulation models consider the impacts of 
altered plant communities, altered fire regimes, habitat conversion, 
habitat fragmentation, human interaction, and climate change, including 
various scenarios to capture uncertainties around these risk factors 
and the model parameters. The results of these analyses project that 
even under worst-case future scenarios the distribution of habitats in 
the United States (considering a 60-year future condition) is projected 
to include about 11,800 sq mi (3 million ha) of habitat categorized as 
primary or secondary quality. In Mexico, even under the worst-case 
scenario, about 10,550 sq mi (2.7 million ha) of secondary quality 
habitat is projected to be maintained (no habitat was projected to be 
in the primary quality category). The abundance of tortoises predicted 
to be supported by these habitats is 316,000 to 698,000 in 50 years and 
278,000 to 632,000 in 75 years. Further, our analysis projected no 
measurable risks of quasi-extinction in the next 50 years in either the 
U.S. or Mexican areas of analysis under any scenarios. At 75 years, the 
risks of quasi-

[[Page 60334]]

extinction increased, ranging from 0 in some scenarios to as high as 
0.033 probability of quasi-extinction (in other words, a 3.3 percent 
risk of quasi-extinction in 75 years) for the Mexican analysis area and 
0.015 in the U.S. analysis area in the worst-case future scenario.
    The relatively high abundance projected in the future condition 
suggests that the species is likely to retain sufficient resiliency, 
and the wide distribution of modeled habitats suggests the species is 
likely to retain sufficient redundancy and representation. Therefore, 
the low predicted risk of quasi-extinction combined with the large 
numbers and wide distribution of habitat and tortoises in the 
foreseeable future suggest the species will have sufficient resiliency, 
redundancy, and representation such that it will not become in danger 
of extinction in the foreseeable future. Therefore, we find that the 
Sonoran desert tortoise does not meet the definition of a threatened 
species.

Endangered or Threatened in a Significant Portion of the Range

    Having found that the Sonoran desert tortoise is not endangered or 
threatened throughout all of its range, we next consider whether there 
are any significant portions of its range in which the Sonoran desert 
tortoise is in danger of extinction or likely to become so.
Standard
    Under the Act and our implementing regulations, a species may 
warrant listing if it is in danger of extinction or likely to become so 
throughout all or a significant portion of its range. The Act defines 
``endangered species'' as any species which is ``in danger of 
extinction throughout all or a significant portion of its range,'' and 
``threatened species'' as any species which is ``likely to become an 
endangered species within the foreseeable future throughout all or a 
significant portion of its range.'' The term ``species'' includes ``any 
subspecies of fish or wildlife or plants, and any distinct population 
segment (DPS) of any species of vertebrate fish or wildlife which 
interbreeds when mature.'' Last year, we published a final policy 
interpreting the phrase ``Significant Portion of its Range'' (SPR) (79 
FR 37578, July 1, 2014). The final policy states that (1) if a species 
is found to be endangered or threatened throughout a significant 
portion of its range, the entire species is listed as an endangered 
species or a threatened species, respectively, and the Act's 
protections apply to all individuals of the species wherever found; (2) 
a portion of the range of a species is ``significant'' if the species 
is not currently endangered or threatened throughout all of its range, 
but the portion's contribution to the viability of the species is so 
important that, without the members in that portion, the species would 
be in danger of extinction, or likely to become so in the foreseeable 
future, throughout all of its range; (3) the range of a species is 
considered to be the general geographical area within which that 
species can be found at the time FWS or NMFS makes any particular 
status determination; and (4) if a vertebrate species is endangered or 
threatened throughout an SPR, and the population in that significant 
portion is a valid DPS, we will list the DPS rather than the entire 
taxonomic species or subspecies.
    The SPR policy is applied to all status determinations, including 
analyses for the purposes of making listing, delisting, and 
reclassification determinations. The procedure for analyzing whether 
any portion is an SPR is similar, regardless of the type of status 
determination we are making. The first step in our analysis of the 
status of a species is to determine its status throughout all of its 
range. If we determine that the species is in danger of extinction, or 
likely to become so in the foreseeable future, throughout all of its 
range, we list the species as an endangered species (or threatened 
species) and no SPR analysis will be required. If the species is 
neither endangered nor threatened throughout all of its range, we 
determine whether the species is endangered or threatened throughout a 
significant portion of its range. If it is, we list the species as an 
endangered species or a threatened species, respectively; if it is not, 
we conclude that listing the species is not warranted.
    When we conduct an SPR analysis, we first identify any portions of 
the species' range that warrant further consideration. The range of a 
species can theoretically be divided into portions in an infinite 
number of ways. However, there is no purpose to analyzing portions of 
the range that are not reasonably likely to be significant and either 
endangered or threatened. To identify only those portions that warrant 
further consideration, we determine whether there is substantial 
information indicating that (1) the portions may be significant and (2) 
the species may be in danger of extinction in those portions or likely 
to become so within the foreseeable future. We emphasize that answering 
these questions in the affirmative is not a determination that the 
species is endangered or threatened throughout a significant portion of 
its range--rather, it is a step in determining whether a more detailed 
analysis of the issue is required. In practice, a key part of this 
analysis is whether the threats are geographically concentrated in some 
way. If the threats to the species are affecting it uniformly 
throughout its range, no portion is likely to warrant further 
consideration. Moreover, if any concentration of threats applies only 
to portions of the range that clearly do not meet the biologically 
based definition of ``significant'' (i.e., the loss of that portion 
clearly would not be expected to increase the vulnerability to 
extinction of the entire species), those portions will not warrant 
further consideration.
    If we identify any portions that may be both (1) significant and 
(2) in danger of extinction or likely to become so, we engage in a more 
detailed analysis to determine whether these standards are indeed met. 
As discussed above, to determine whether a portion of the range of a 
species is significant, we consider whether, under a hypothetical 
scenario, the portion's contribution to the viability of the species is 
so important that, without the members in that portion, the species 
would be in danger of extinction or likely to become so in the 
foreseeable future throughout all of its range. This analysis considers 
the contribution of that portion to the viability of the species based 
on the conservation biology principles of redundancy, resiliency, and 
representation. (These concepts can similarly be expressed in terms of 
abundance, spatial distribution, productivity, and diversity.) The 
identification of an SPR does not create a presumption, prejudgment, or 
other determination as to whether the species in that identified SPR is 
endangered or threatened. We must go through a separate analysis to 
determine whether the species is endangered or threatened in the SPR. 
To determine whether a species is endangered or threatened throughout 
an SPR, we will use the same standards and methodology that we use to 
determine if a species is endangered or threatened throughout its 
range.
    Depending on the biology of the species, its range, and the threats 
it faces, it may be more efficient to address the ``significant'' 
question first, or the status question first. Thus, if we determine 
that a portion of the range is not ``significant,'' we do not need to 
determine whether the species is endangered or threatened there; if we 
determine that the species is not endangered or threatened in a portion 
of

[[Page 60335]]

its range, we do not need to determine if that portion is 
``significant.''
Evaluation and Finding
    We evaluated the current range of the Sonoran desert tortoise to 
determine if there are any apparent geographic concentrations of 
potential threats to the species. Generally speaking, the risk factors 
affecting the tortoise occur throughout the range of the species; 
however, portions of the range that are within and near areas subject 
to urban development may be subject to impacts not found throughout the 
range of the species. If we assume that the entire area on unprotected 
land identified as having potential for urban development is developed 
and made entirely unusable to tortoises, that conversion would 
represent a loss of 9 percent of available habitat. At this scale, we 
have no information to suggest that the remaining 91 percent of 
available habitat would not continue to support sufficient resiliency 
and redundancy. Additionally, there is no information available that 
suggests there are unique genetic values in this area that would need 
to be maintained to support representation due to a lack of known 
genetic structuring for the tortoise. Based on this analysis, we 
conclude that the portion of the range of the tortoise outside the 
urban development area contains sufficient redundancy, resiliency, and 
representation that, even without the contribution of the urban 
development area, the tortoise would not be in danger of extinction. 
Therefore, we find that the Sonoran desert tortoise is not in danger of 
extinction in a significant portion of its range.

Conclusion

    Our review of the best available scientific and commercial 
information indicates that the Sonoran desert tortoise is not in danger 
of extinction (endangered) nor likely to become endangered within the 
foreseeable future (threatened), throughout all or a significant 
portion of its range. Therefore, we find that listing the Sonoran 
desert tortoise as an endangered or threatened species under the Act is 
not warranted at this time, and as such the Sonoran desert tortoise 
will be removed from the candidate list.
    We request that you submit any new information concerning the 
status of, or threats to, the Sonoran desert tortoise to our Arizona 
Ecological Services Field Office (see ADDRESSES) whenever it becomes 
available. New information will help us monitor the Sonoran desert 
tortoise and encourage its conservation. If an emergency situation 
develops for the Sonoran desert tortoise, we will act to provide 
immediate protection.

References Cited

    A complete list of references cited is available in the SSA Report 
(Service 2015), available online at https://www.regulations.gov, under 
Docket Number FWS-R2-ES-2015-0150.

Author(s)

    The primary author(s) of this notice are the staff members of the 
Arizona Ecological Services Field Office.

Authority

    The authority for this section is section 4 of the Endangered 
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).

    Dated: September 22, 2015.
Cynthia T. Martinez,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. 2015-25286 Filed 10-5-15; 8:45 am]
 BILLING CODE 4333-15P