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Federal Register / Vol. 86, No. 146 / Tuesday, August 3, 2021 / Rules and Regulations
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under the Act. It does, however, provide the scientific basis that informs our regulatory decisions, which involve the further application of standards within the Act and its implementing regulations and policies. The following is a summary of the key results and conclusions from the SSA report; the full SSA report can be found at Docket No. FWSR8ES20190006 on http
www.regulations.gov and on the Sacramento Fish and Wildlife Offices website at https www.fws.gov/
sacramento/.
To assess the Sierra Nevada DPSs viability, we used the three conservation biology principles of resiliency, redundancy, and representation Shaffer and Stein 2000, pp. 306310. Briefly, resiliency supports the ability of the species to withstand environmental and demographic stochasticity for example, wet or dry, warm or cold years, redundancy supports the ability of the species to withstand catastrophic events for example, droughts, large pollution events, and representation supports the ability of the species to adapt over time to long-term changes in the environment for example, climate changes. In general, the more resilient and redundant a species is and the more representation it has, the more likely it is to sustain populations over time, even under changing environmental conditions. Using these principles, we identified the species ecological requirements for survival and reproduction at the individual, population, and species levels, and described the beneficial and risk factors influencing the species viability.
The SSA process can be categorized into three sequential stages. During the first stage, we evaluated the individual species life-history needs. The next stage involved an assessment of the historical and current condition of the species demographics and habitat characteristics, including an explanation of how the species arrived at its current condition. The final stage of the SSA involved making predictions about the species responses to positive and negative environmental and anthropogenic influences. This process used the best available information to characterize viability as the ability of a species to sustain populations in the wild over time. We use this information to inform our regulatory decision.
Summary of Biological Status and Threats The summary below of our analyses represents an evaluation of the biological status of the DPS, based upon our assessment of the effects anticipated from each of the identified threats. We
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also consider the cumulative impact of all effects anticipated from the identified threats, and how that cumulative impact may affect the Sierra Nevada DPSs continued existence currently and in the future. We used the best available scientific and commercial information, and the expert opinions of the analysis team members. The threats identified as having the greatest potential to act upon the DPS include:
1 Deleterious impacts associated with small population size, such as inbreeding depression and increased effects of deleterious stochastic events Factor E; 2 over-hybridization with nonnative red fox Factor E; and possibly 3 competition with coyotes Factor E resulting from reduced snowpack levels. We also evaluated the existing regulatory mechanisms Factor D and implementation of conservation efforts.
The environmental characteristics that are most important for Sierra Nevada DPS population resiliency include cold subalpine habitat with low primary productivity, high snowpack, and rodent and leporid prey Service 2018, pp. 1420. Additional demographic characteristics contributing to the species redundancy and representation include 1 Either a single large or multiple populations, which would help insure that large portions of the DPS remain even after a catastrophic loss over a large area; 2 a populations situated to include habitat variations occurring from northern to southern portions of the range rather than clustering in one general area; and 3 representative genetic diversity to avoid genetic swamping and loss of the species adaptive native genes, which could result from continuing and overbroad levels of interbreeding with nonnative red fox subspecies.
The best available scientific and commercial information at this time indicates that the Sierra Nevada DPS
population size needs to be larger to help ensure its viability into the future.
The minimum population size necessary for the Sierra Nevada DPS to maintain viability is unknown, but that number has been estimated at about 150
individuals for the Santa Catalina Island fox Urocyon littoralis catalinae Kohlmann et al. 2005, p. 77, which has a small range compared to suitable habitat available for the Sierra Nevada DPS. Lacking better data, we use this number as an example of what the minimum viable population size for the Sierra Nevada DPS could be. The current estimated population size of 18
to 39 individuals is well below that number, meaning that the population is likely vulnerable to stochastic
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disturbance in addition to other threats discussed below.
When considering redundancy, there is currently only one small, isolated population of Sierra Nevada DPS known within the Sierra Nevada mountain range. In general, given the low number of foxes currently known within this DPS and the limited range they inhabit, the DPS appears to have a low ability to withstand catastrophic events should they occur. Additionally, there do not appear to be any other populations within the range of this DPS to serve as a source to recover from a catastrophic loss of individuals.
When considering the breadth of genetic and environmental diversity within and among populations representation, the Sierra Nevada DPS
historically occurred throughout the high elevations of the Sierra Nevada.
The current, small population has been experiencing genetic challenges, including inbreeding depression, as well as hybridization with non-Sierra Nevada red fox individuals, which can potentially lower survivorship or reproductive success by interfering with adaptive native genes or gene complexes Allendorf et al. 2001, p. 617; Frankham et al. 2002, pp. 386388. Having broad genetic and environmental diversity would help the DPS withstand environmental changes. However, at this time, the Sierra Nevada DPS does not have this broad diversity.
Summary of Existing Regulatory Measures and Voluntary Conservation Efforts Since 1998, the USFS have identified the Sierra Nevada DPS as a sensitive species where it occurs on National Forest lands. The current range of the DPS includes portions of the Stanislaus, El Dorado, Humboldt-Toiyabe, Inyo, and Sierra National Forests. Sensitive species receive special consideration during land use planning and activity implementation to ensure species viability and to preclude population declines USFS 2005, section 2670.22.
The USFS included Sierra Nevada red fox-specific protection measures in the Sierra Nevada Forest Plan Amendment SNFPA Standards and Guidelines given the extensive overlap of suitable and in some cases occupied habitat for the Sierra Nevada red fox with USFS
lands. These specific protection measures require the USFS to conduct and analyze potential impacts of activities within 8 km 5 mi of a verified Sierra Nevada red fox individual sighting USFS 2004, p. 54.
The protection measures also limit the time of year that certain activities may occur to avoid adverse impacts to Sierra
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