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Federal Register / Vol. 86, No. 109 / Wednesday, June 9, 2021 / Rules and Regulations 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 process involved making predictions about the species responses to positive and negative environmental and anthropogenic influences.
Throughout all of these stages, we 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.

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Summary of Biological Status and Threats In this discussion, we review the biological condition of each species and its resources, and the threats that influence each species current and future condition, in order to assess the species overall viability and the risks to that viability.
Carolina Madtom To evaluate the current and future viability of the Carolina madtom, we considered a range of conditions to allow us to assess the species resiliency, representation, and redundancy. We assessed resiliency for the Carolina madtom using population factors Management Unit MU
occupancy over time, approximate abundance, and recruitment and habitat elements water quality, water quantity, habitat connectivity, and instream substrate. For the purposes of this assessment, populations were delineated using the same three river basins that Carolina madtoms have historically occupied, namely the Tar, Neuse, and Trent River basins.
Populations were further delineated using MUs, defined as one or more hydrologic unit code HUC 10
watersheds that species experts identified as the most appropriate unit for assessing population-level resiliency. To assess resiliency, we analyzed population factors as well as habitat elements that were determined in our analysis of the species needs to have the most influence on the species.
We then assessed the overall condition of each population. Overall population condition rankings were determined by combining the two population factors and four habitat elements. For a more detailed explanation of the condition
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categories, see the SSA report Service 2021a, pp. 1519.
Metrics that speak to a species adaptive potential, such as genetic and ecological variability, can be used to assess representation. Representation for the Carolina madtom can be described in terms of ecological variation seen in river basin variability Tar, Trent, and Neuse River basins and physiographic variability eastern Piedmont and Coastal Plain. We assessed Carolina madtom redundancy by first evaluating occupancy within each of the hydrologic units that constitute MUs, and then we evaluated occupancy at the MU, and ultimately the population level.
Current Condition of Carolina Madtom The historical range of the Carolina madtom included streams and rivers in the Tar-Pamlico, Neuse, and Trent basins, with documented historical distribution in 31 HUC10s in 11 MUs across the three populations see Table 1, below. The results of surveys conducted from 2011 to 2018 suggest that the currently occupied range of the Carolina madtom includes four MUs from two populations, corresponding to the Tar and Neuse River basins;
however, only one population Tar has multiple documented occurrences within the past 5 years. The species has been extirpated from the southern portion of its range, including a large portion of the Neuse River basin and the entire Trent River basin. The Carolina madtom currently occupies 9 of the 31
historically occupied HUC10s with currently defined as the observation of at least one specimen from 2011 to 2018, 7 of which are in the Tar River basin and 2 in the Neuse River basin. At the population level, the overall current condition = resiliency was estimated to be moderate for the Tar population, very low for the Neuse population, and likely extirpated for the Trent population.

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TABLE 1POPULATION AND MANAGEMENT UNIT MU NAMING FOR
CAROLINA MADTOMContinued Population/management unit Trent:
Trent.

We estimated that the Carolina madtom currently has low adaptive potential due to limited representation in two river basins and two physiographic regions. The species retains 33 percent of its known river basin variability, considering greatly reduced variability observed in the Neuse River population. In addition, compared to historical occupancy, the species currently retains very limited physiographic variability in the Coastal Plain 14 percent and moderate variability in the Piedmont 56 percent.
The range of the Carolina madtom has always been very narrow, limited to the Tar, Neuse, and Trent River drainages.
Within the identified representation areas, the species retains redundancy within the Tar River population three MUs currently extant; however, it has limited redundancy two MUs extant in the Neuse River population and no redundancy extirpated in the Trent River population. Overall, the species has lost 55 percent of its redundancy across its narrow, endemic range.

Neuse River Waterdog To evaluate the current and future viability of the Neuse River waterdog, we assessed a similar range of conditions as described above for Carolina madtom to allow us to consider the species resiliency, representation, and redundancy. As with the madtom, populations were delineated using the three river basins that Neuse River waterdogs have historically occupied i.e., Tar-Pamlico, Neuse, and Trent River basins. Tar-Pamlico refers to the lower portion of the Tar River basin, which includes the Pamlico River.
TABLE 1POPULATION AND MANAGEBecause the river basin level is at a very coarse scale, populations were further MENT UNIT MU NAMING FOR
delineated using MUs. MUs were CAROLINA MADTOM
defined as one or more HUC10
watersheds that species experts Population/management unit identified as most appropriate for assessing population-level resiliency.
Tar:
Resiliency is characterized, and overall Upper Tar.
population condition rankings and Middle Tar.
Lower Tar.
habitat condition rankings were Fishing Creek Subbasin.
determined, similarly as for the Sandy-Swift.
madtom.
Neuse:
Representation for the Neuse River Upper Neuse.
waterdog can be described in terms of Middle Neuse.
the size and range of the river systems Lower Neuse.
it inhabits medium streams to large Little River.
rivers in three river basins, and Contentnea Creek.

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