[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]
[[Page 60321]]
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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 http://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 http://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
[[Page 60322]]
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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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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[[Page 60332]]
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 http://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]
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