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Federal Register / Vol. 86, No. 171 / Wednesday, September 8, 2021 / Rules and Regulations principles of resiliency, redundancy, and representation the 3 Rs described in detail in the SSA report 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 historical range of the slenderclaw crayfish included two known populations, Short and Town Creeks, in watersheds leading into the Tennessee River in Alabama. Within the Short Creek population, a total of 90
slenderclaw crayfish, with 56 of those being juveniles, were collected during the period 19701974 Bouchard and Hobbs 1976, entire; Schuster 2017, unpublished data. Historically, only one crayfish was collected in the Town Creek population in the period 1970
1974 Bouchard and Hobbs 1976, entire;
Schuster 2017, unpublished data.
Surveys conducted from 2009 through 2017 have documented the slenderclaw crayfish within the same two populations, Short Creek three sites in Shoal Creek and Town Creek one site in Bengis Creek and one site in Town Creek Kilburn et al. 2014, pp. 116117;
Bearden et al. 2017, pp. 1718; Schuster 2017, unpublished data; Taylor 2017, unpublished data.
Of the five historical sites, the slenderclaw crayfish is no longer found and is presumed extirpated at three sites in the Short Creek population one site in Short Creek and two sites in Scarham Creek and one site in the Town Creek population one site in Bengis Creek despite repeated survey efforts Kilburn et al. 2014, pp. 116117; Bearden et al.
2017, pp. 1718; Schuster 2017, unpublished data; Taylor 2017, unpublished data. Across current survey efforts from 2009 through 2017, researchers collected 28 slenderclaw crayfish, including 2 juveniles, within the Short Creek population, and 2 adults and 2 juveniles from the Town Creek
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population. There are no actual historical or current population estimates for slenderclaw crayfish, and the abundance numbers total number collected reported are not population estimates.
At the population level, the overall current condition in terms of resiliency was determined to be low for both Short Creek and Town Creek populations. We estimate that the slenderclaw crayfish currently has some adaptive potential i.e., representation due to the habitat variability features occurring in the Short Creek and Town Creek populations. The Short Creek population occurs in streams with predominantly large boulders and fractured bedrock, broader stream widths, and greater depths, and the Town Creek population occurs in streams with larger amounts of gravel and cobble, narrower stream widths, and shallower depths Bearden 2017, pers. comm.. At present, the slenderclaw crayfish has two populations in low condition resiliency with habitat types that vary between populations. Therefore, given the variable habitat in which the slenderclaw crayfish occurs, the species may have some level of adaptive capacity. Given the low resiliency of both populations of the slenderclaw crayfish, current representation is reduced.
The slenderclaw crayfish exhibits limited redundancy given its narrow range and that four out of five sites within the species historical range are presumed extirpated. In addition, connectivity between the Short Creek and Town Creek populations is likely low, because both Short and Town Creek streams flow downstream into, and thus are separated by, Guntersville Lake. To date, no slenderclaw crayfish have been documented in impounded areas including Guntersville Lake.
Multiple sites in the same population could allow recolonization following a catastrophic event e.g., chemical spill that may affect a large proportion of a population; however, given the species limited redundancy and current low resiliency of both populations, it might be difficult to reestablish an entire population affected by a catastrophic event, as the connectivity between the two populations is low. Further, the currently occupied sites in the Short Creek population are in a single tributary, and one catastrophic event could impact this entire population.
Risk Factors for Slenderclaw Crayfish The Act directs us to determine whether any species is an endangered species or a threatened species because
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of any factors affecting its continued existence. Under section 4a1 of the Act, we may list a species based on A
The present or threatened destruction, modification, or curtailment of its habitat or range; B overutilization for commercial, recreational, scientific, or educational purposes; C disease or predation; D the inadequacy of existing regulatory mechanisms; or E
other natural or manmade factors affecting its continued existence.
We reviewed the potential risk factors i.e., threats or stressors that are affecting the slenderclaw crayfish now and are expected to affect it into the future. Because we have determined that the species is currently in danger of extinction throughout its range, in this final rule we will discuss in detail only those threats that we conclude are driving the current status and viability of the species. We have determined that competition from a nonnative species Factors A and E, habitat degradation resulting from poor water quality Factor A, and low abundance Factor E pose the largest risk to the current viability of the slenderclaw crayfish.
Other potential stressors to the specieshydrological variation and alteration Factors A and E, land use Factor A, and scientific collection Factor Bare discussed in the SSA
report and proposed rule. Currently existing regulatory mechanisms, such as regulations implemented under the Clean Water Act to protect water quality and instream habitat, address the habitat degradation threat to the slenderclaw crayfish. However, we also found that existing regulatory mechanisms do not address, nor do they contribute to, the threat of the nonnative virile crayfish, which is the primary threat to the slenderclaw crayfish. We find the species does not face significant threats from disease or predation Factor C. We also reviewed the conservation efforts being undertaken for the habitat in which the slenderclaw crayfish occurs.
Nonnative Species The virile crayfish Faxonius virilis, previously recognized as Orconectes virilis Crandall and De Grave 2017, p.
5, is a crayfish native to the Missouri, upper Mississippi, lower Ohio, and the Great Lakes drainages Service 2015, p.
1. The species has spread from its native range through dispersal as fishing bait, as pets, and through commercial human consumption Schwartz et al.
1963, p. 267; Service 2015, p. 4. Virile crayfish inhabit a variety of watersheds in the United States, including those with very few to no native crayfish species, and have been found in lake, wetland, and stream environments
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