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Federal Register / Vol. 86, No. 131 / Tuesday, July 13, 2021 / Proposed Rules
information pertaining to the habitat requirements of the species and identify specific areas within the geographical area occupied by the species at the time of listing and any specific areas outside the geographical area occupied by the species at the time of listing to be considered for designation as critical habitat.
The current distribution of the pearl darter is reduced from its historical distribution, and we anticipate that recovery will require continued protection of the existing population and habitat, as well as establishing a population within its historical range, to ensure there are adequate numbers of pearl darters occurring in stable populations for the species continued conservation. Furthermore, rangewide recovery considerations, such as maintaining existing genetic diversity and striving for representation of all major portions of the species historical range, were considered in formulating this proposed critical habitat designation.
We are proposing to designate critical habitat in areas within the geographical area occupied by the species at the time of listing. We identified areas with current occurrence records that we deemed suitable habitat see delineation steps, below and that had one or more of the physical or biological features identified for the pearl darter which may require special management considerations or protection. We also are proposing to designate specific areas outside of the geographical area occupied by the species at the time of listing because we have determined that a designation limited to occupied areas would be inadequate to ensure the conservation of the species. For those unoccupied areas, we have determined that it is reasonably certain that the unoccupied areas will contribute to the conservation of the species and contain one or more of the physical or biological features that are essential to the conservation of the species. We have also determined that the unoccupied areas fall within the regulatory definition of habitat at 50 CFR 424.02.
Threats to pearl darters occurring in the Pascagoula River drainage are compounded by the species naturally low numbers and short life span, but the species conservation potential is primarily limited by its extirpation from the Pearl River drainage and, therefore, its lack of redundancy. The documented Pearl River drainage extirpation was rapid and system-wide, including all mainstem and tributary collection sites seemingly simultaneously. As such, we consider pearl darters occurring within the Pascagoula River and its tributaries
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as a single population. The loss of the species redundancy, with its extirpation from the Pearl River drainage, has also diminished its genetic and ecological representation, and, therefore, increased the species vulnerability to catastrophic events and population changes. A successful reintroduction into the Pearl River drainage would restore the species redundancy within the historical range.
In addition, the pearl darters representation would increase from current levels by allowing for local environmental adaptation and increasing genetic representation. Thus, reintroducing the species into the Pearl River drainage would contribute to the resilience and conservation of the pearl darter.
Factors implicated in the Pearl River extirpation include geomorphic instability i.e., channel erosion and degradation, sedimentation, and point source pollution from municipalities and industries e.g., Bart and Suttkus 1995, p. 14; Tipton et al. 2004, pp. 59
60. One or all of these factors may have been responsible for the diminishment or loss of some or all of the physical or biological features essential to the conservation of the pearl darter within the drainage e.g., channel stability, substrate, water quality, prey base. We now find that these factors have been reduced to a degree that the pearl darter may be successfully reintroduced into the Pearl River.
For example, active channel erosion and degradation that may have been precipitated by the 1956 construction of the Pearl River navigation system in the lower basin, and aggravated by the 1963
construction of the Ross Barnett Reservoir in the upper basin, have diminished, and instream mining is now prohibited by the States of Mississippi and Louisiana, resulting in more stable channel habitats within the basin. In addition, point-source pollution from untreated municipal and industrial discharge into the Pearl River has been significantly reduced by enactment and enforcement of the Clean Water Act of 1972 33 U.S.C. 1251 et seq.. The improvement of the physical or biological features within the Pearl River drainage is also demonstrated by recent observed increases in other benthic fish species e.g., crystal darter Crystallaria asprella and frecklebelly madtom Noturus munitus, which experienced declines concurrent with the extirpation of the pearl darter Piller et al. 2004, pp. 10071011; Tipton et al.
2004, pp. 5760; Wagner et al. 2018, p.
13. These improvements leave us reasonably certain that all of the physical or biological features essential
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to the conservation of the pearl darter are now present within the Pearl River drainage. Because the Pearl River drainage habitat contains the physical or biological features for the pearl darter and supports other benthic fish species with similar life processes, we conclude that the drainage contains the resources and conditions necessary to support the life processes for the pearl darter.
For this proposed rule, we completed the following steps to delineate critical habitat:
1 We compiled all available current and historical occurrence data records for the pearl darter in both the Pascagoula and Pearl River drainages;
2 We used confirmed presence from 19942019 as the foundation for identifying areas currently occupied in the Pascagoula River drainage;
3 We evaluated habitat suitability of stream segments that contain the identified physical or biological features and that are currently occupied by the species, and we retained all occupied stream segments;
4 We evaluated unoccupied segments of the Pearl River drainage for suitability of spawning and recruitment, darter reintroduction, and monitoring and management of a reintroduced population; and 5 We evaluated unoccupied segments of the Pearl River drainage for connectivity with reaches historically occupied and identified areas containing the physical or biological features essential to the conservation of the species that may require special management considerations or protection.
Sources of data for this proposed critical habitat designation include the proposed and final listing rules 81 FR
64857, September 21, 2016; 82 FR
43885, September 20, 2017, fish collection databases provided by the MDWFP, survey reports and observations, and peer-reviewed publications.
Areas Occupied at the Time of Listing We used reports and collection data to map species site collections and occurrences between 1994 and 2019 to determine areas occupied at the time of listing. Based on the best available scientific data, we determined that all currently known occupied habitat for the pearl darter was also occupied by the species at the time of listing, and that these areas contain the physical or biological features essential to the conservation of the species and which may require special management considerations or protection.
As stated above, we delineated units based on documented occurrences and
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