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Federal Register / Vol. 86, No. 167 / Wednesday, September 1, 2021 / Proposed Rules address objectives related to the restoration of ecological resources e.g., section 1135 of the Water Resources Development Act of 1986, as amended, 33 U.S.C. 2201 et seq..
Protections associated with the CWA
and State wildlife laws will continue to provide some protection to the snail darter. The fear that the species notoriety would result in increased collection or other forms of take has not been realized since we reclassified the species to threatened, and collection is unlikely to have a major impact on species resilience in the foreseeable future. Additionally, even if range States were to cease protecting the snail darter, its wide range and current redundancy should minimize its risk of extinction for the foreseeable future.
In addition to the threats mentioned in the downlisting rule 49 FR 27510;
July 5, 1984 that are addressed above, we now consider other threats or stressors that reasonably could affect the snail darter in the foreseeable future.
One such potential threat is climate change. In the southeastern United States, clear trends in climate predictions are limited. However, annual temperatures are projected to increase, cold days will become less frequent, the freeze-free season will lengthen by up to a month, temperatures exceeding 95 degrees Fahrenheit F 35
degrees Celsius C will increase, heat waves will become longer, and the number of category 5 hurricanes will increase Ingram et al. 2013, p. 32.
Variability in weather is predicted to increase, resulting in more frequent and more extreme dry years and wet years over the next century, but a directional shift in overall precipitation is not anticipated in the Tennessee River Valley Mulholland et al. 1997, pp. 951
955; Ingram et al. 2013, pp. 15, 35.
There is some evidence that the increased variability may already be taking effect. 2018 and 2019 were the two wettest years on record for the Tennessee River Valley Simmons 2020, unpublished data. During the late summer and early fall of 2019, the second wettest year overall, parts of the Valley temporarily experienced abnormally dry or drought conditions USDA Drought Monitor for Tennessee River Valley, October 1, 2019.
Increased rainfall will result in increased runoff, higher river levels, and longer periods of spilling from the top of dams by TVA. During periods of spilling at dams, there is the chance for more oxygenation of tailwaters and temperature mixing that could benefit the snail darter. However, increased rainfall, especially extreme events, would increase runoff of sediment and
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pollutants into tributaries and eventually into the mainstem. These inputs could potentially degrade spawning and foraging habitat for the snail darter. Increased flows during the spawning season could also increase the distance that the pelagic larvae of snail darters drift before becoming benthic. If the larvae found suitable habitat, increased flow could expand the range of the species and contribute to genetic mixing; however, there is also the chance that larvae could be pushed into unsuitable habitat, which would result in reduced survival. Drought would most likely impact the shallower habitats inhabited by snail darters in tributaries. The area of shoal habitat available during periods of low flow could be reduced during a drought. The flows could be further reduced by water extraction for irrigation. These reductions of spawning habitat could result in lower spawning success. If discharge is reduced enough, the cleanswept gravel habitats that the snail darter relies on in the mainstem could begin to retain silt, reducing habitat quality.
There is evidence that the habitat and life history of the snail darter will protect it from predicted changes in climate over the next 30 years. In a 2017
climate change vulnerability assessment of 700 species, the Appalachian Landscape Conservation Cooperative LCC ranked the snail darter as presumed stable through 2050 under predicted climate conditions Appalachian LCC 2017, supplemental data. Being adapted to large river habitats, the snail darter is less susceptible to impacts from high-flow events. As much of its habitat in the mainstem is already impounded, the effects of high water are less meaningful, and TVA flood control efforts may offset some of the strong flow peaks associated with extreme rain events. The species preference for deeper water habitats and late winter spawning period protects it from drought. Deep water habitats are not impacted by droughts as drastically as shallow habitats. The RRIP in TVA
tailwaters ensures availability of suitable water for the mainstem populations throughout the year despite the occurrence of drought. Drought is also unlikely to impact spawning events on shoals in tributaries because late winter and early spring are typically the wettest times of the year within the Tennessee River Valley. The snail darter is likely also protected from the projected temperature increases by adaptation to larger streams and the
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thermal buffering of the large reservoirs on the mainstem.
If we examine current projections beyond our 30-year foreseeable future, under plausible future greenhouse gas concentrations termed representative concentration pathways RCP, warming temperatures and precipitation projections continue to suggest mixed effects to the species. Relative to 1981
2010, over 20502074, the 50th percentile median for the Tennessee Region, maximum air temperature warms by 4.4 F 2.4 C in RCP 4.5, whereas the region warms by 6.4 F 3.6
C in RCP 8.5 Alder and Hostetler 2013, entire. Changes in precipitation are not as apparent. Relative to 1981
2010, over 20502074, the 50th percentile median for the Tennessee Region, precipitation increases by only 0.2 in 5.1 mm per month in both RCP
4.5 and RCP 8.5 Alder and Hostetler 2013, entire. We are not extending the foreseeable future timeline beyond 2050
because the snail darters response to changing climatic conditions is less certain after 2050. We have greater certainty about the species response to changing climactic conditions between now and 2050 because we have both the projections and scientific sources that predict the species response, such as the LCC report. Further, the climate projections are more reliable between now and 2050 as compared to beyond 2050 because the models diverge after 2050. As a result, we do not consider the snail darter to be vulnerable to the effects of climate change in the foreseeable future.
The increases documented in the abundance and distribution of the snail darter since it was listed in 1975 have led to a better understanding of the current and future condition of the species resiliency, redundancy, and representation across the range. The observed variations in population size, density, or distribution of the snail darter are typical of metapopulation dynamics. Surveys have shown that individual populations may decline based on localized stressors e.g., severe sedimentation, toxic spills, streamflow alteration or their cumulative effects.
When threats occur together, one may exacerbate the effects of another, causing effects not accounted for when threats are analyzed individually.
However, the best available information does not demonstrate that cumulative effects are occurring at a level sufficient to negatively affect the species.
Determination of the Snail Darters Status Section 4 of the Act 16 U.S.C. 1533
and its implementing regulations 50

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