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Federal Register / Vol. 86, No. 167 / Wednesday, September 1, 2021 / Proposed Rules
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effects of the threatsin light of those actions and conditions that will ameliorate the threatson an individual, population, and species level. We evaluate each threat and its expected effects on the species, then analyze the cumulative effect of all of the threats on the species as a whole.
We also consider the cumulative effect of the threats in light of those actions and conditions that will have positive effects on the speciessuch as any existing regulatory mechanisms or conservation efforts. The Secretary determines whether the species meets the definition of an endangered species or a threatened species only after conducting this cumulative analysis and describing the expected effect on the species now and in the foreseeable future.
The Act does not define the term foreseeable future, which appears in the statutory definition of threatened species. Our implementing regulations at 50 CFR 424.11d set forth a framework for evaluating the foreseeable future on a case-by-case basis. The term foreseeable future extends only so far into the future as the Services can reasonably determine that both the future threats and the species responses to those threats are likely. In other words, the foreseeable future is the period of time in which we can make reliable predictions. Reliable does not mean certain; it means sufficient to provide a reasonable degree of confidence in the prediction. Thus, a prediction is reliable if it is reasonable to depend on it when making decisions.
It is not always possible or necessary to define foreseeable future as a particular number of years. Analysis of the foreseeable future uses the best scientific and commercial data available and should consider the timeframes applicable to the relevant threats and to the species likely responses to those threats in view of its life-history characteristics. Data that are typically relevant to assessing the species biological response include speciesspecific factors such as lifespan, reproductive rates or productivity, certain behaviors, and other demographic factors.
Analytical Framework To assess species viability, we use 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
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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 change. 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.
Summary of Biological Status Resiliency Analysis As explained above in Evaluating Populations, the existing data available do not allow us to estimate population sizes for snail darter. However, collections over multiple years and the presence of multiple age classes provide evidence of persistence in tributaries throughout the snail darters range. In the reservoirs, the capture of multiple individuals and evidence of multiple age classes typically represents a sustainable population. Where available, presence of snail darters in breeding condition is used as additional evidence of spawning, because snail darters move onto the spawning ground before spawning commences Starnes 1977, p. 64. We used IBI scores from fixed monitoring stations to address stream health where possible for tributary populations. These scores are generated from fish assemblage surveys throughout the Tennessee River Valley and rank streams from 12 to 60 poor to excellent based on metrics such as total number of species, proportions of intolerant and tolerant species, and the numbers of species in various ecological guilds TVA 2005, pp. 57. We use these measures to describe the resiliency of the snail darter populations and their contributions to the species recovery.
Tributary ResiliencyWe characterized snail darter population resiliency in 14 tributaries 11 extant populations, one extirpated, and two apparently not established with only one collection each and no evidence of reproduction using data related to three factors: Collections in multiple years since 2009, presence of multiple year classes in these samples, and TVA IBI
scores for the tributary populations see resiliency scores for these factors in Table 1, below. Detection of the species
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in multiple years provides evidence of persistence within a tributary.
Consistent collections also indicate population numbers that are high enough to be detected using nondepletion methods not every fish in a sample reach is caught, which is relevant for species like the snail darter that are difficult to capture with standard fish sampling equipment. The presence of multiple age classes is evidence of successful reproduction in the population. Given that snail darters only live 4 years and likely do not mature until their second year, it would only take a few years of failed reproduction for a population to be extirpated Etnier and Starnes 1993, p.
588. We reviewed the available data to determine population scores for each of the tributaries. The best available data are not sufficient to determine snail darter population size or trends due to the typically small numbers collected at any given site; however, we can address resiliency of the tributary populations by looking at persistence over time and evidence of reproduction. To do this, we used data from snail darter collections and observations from TVA and Conservation Fisheries, Inc., and data compiled by the Tennessee Aquarium Conservation Institute.
We used IBI scores to address stream community health where possible for tributary populations. Measuring the overall fish community is a way to investigate habitat quality, water quality, and ecosystem stability by proxy of the fish that live in the stream.
The IBI incorporates 12 metrics to measure fish community health based on the number of species or proportion of individuals in different guilds group of species with similar life history compared to what is expected in a reference condition stream. These metrics are adjusted based on stream size and physiographic region in order to be relevant to the differences in natural conditions across the Tennessee River Basin. Each metric is assigned a value matching a ranking of good 5, fair 3, or poor 1. The 12 metrics are then summed for each, yielding an overall rating of the stream community health. An IBI score of 12 to 22 equates to a very poor rating, 28 to 34 to a poor rating, 40 to 44 to a fair rating, 48 to 52
to a good rating, and 58 to 60 to an excellent rating. Scores between these ranges received intermediate ratings TVA 2005, entire. To determine potential IBI trends, we compared overall IBI scores for sites within the range of snail darters in each tributary from 2009 to 2019. Roughly half of the tributaries French Broad River, Little
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