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Federal Register / Vol. 86, No. 131 / Tuesday, July 13, 2021 / Proposed Rules
expected to initiate any such threat. In our final listing determination for the pearl darter, we determined that the present or threatened destruction, modification, or curtailment of habitat or range is a threat to this species and that those threats in some way can be addressed by section 7a2
consultation measures. The species occurs wholly in the jurisdiction of the United States, and we are able to identify areas that meet the definition of critical habitat. Therefore, because none of the circumstances set forth in our regulations at 50 CFR 424.12a1 has been met and because there are no other circumstances the Secretary has identified for which this designation of critical habitat would be not prudent, we have determined that the designation of critical habitat is prudent for the pearl darter.

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Critical Habitat Determinability Having determined that designation is prudent, under section 4a3 of the Act we must find whether critical habitat for the pearl darter is determinable. Our regulations at 50 CFR 424.12a2 state that critical habitat is not determinable when one or both of the following situations exist:
i Data sufficient to perform required analyses are lacking, or ii The biological needs of the species are not sufficiently well known to identify any area that meets the definition of critical habitat.
When we published the proposed listing rule 81 FR 64857; September 21, 2016 and then the final listing rule 82
FR 43885; September 20, 2017 for the pearl darter, a careful assessment of the economic impacts of an associated critical habitat designation was incomplete, leading us to find that critical habitat was not determinable.
We continued to review the available information related to the draft economic analysis, as well as newly acquired biological information necessary to perform this assessment.
This and other information represent the best scientific data available, and we now find the data are sufficient for us to analyze the impacts of critical habitat designation. Accordingly, we conclude that the designation of critical habitat is determinable for the pearl darter.
Physical or Biological Features Essential to the Conservation of the Species In accordance with section 35Ai of the Act and regulations at 50 CFR
424.12b, in determining which areas we will designate as critical habitat within the geographical area occupied by the species at the time of listing, we
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consider the physical or biological features that are essential to the conservation of the species and which may require special management considerations or protection. The regulations at 50 CFR 424.02 define physical or biological features essential to the conservation of the species as the features that occur in specific areas and that are essential to support the lifehistory needs of the species, including, but not limited to, water characteristics, soil type, geological features, sites, prey, vegetation, symbiotic species, or other features. A feature may be a single habitat characteristic or a more complex combination of habitat characteristics.
Features may include habitat characteristics that support ephemeral or dynamic habitat conditions. Features may also be expressed in terms relating to principles of conservation biology, such as patch size, distribution distances, and connectivity. For example, physical features essential to the conservation of the species might include gravel of a particular size required for spawning, alkaline soil for seed germination, protective cover for migration, or susceptibility to flooding or fire that maintains necessary earlysuccessional habitat characteristics.
Biological features might include prey species, forage grasses, specific kinds or ages of trees for roosting or nesting, symbiotic fungi, or a particular level of nonnative species consistent with conservation needs of the listed species.
The features may also be combinations of habitat characteristics and may encompass the relationship between characteristics or the necessary amount of a characteristic essential to support the life history of the species.
In considering whether features are essential to the conservation of the species, the Service may consider an appropriate quality, quantity, and spatial and temporal arrangement of habitat characteristics in the context of the life-history needs, condition, and status of the species. These characteristics include, but are not limited to, space for individual and population growth and for normal behavior; food, water, air, light, minerals, or other nutritional or physiological requirements; cover or shelter; sites for breeding, reproduction, or rearing or development of offspring;
and habitats that are protected from disturbance.
Habitats Representative of the Historical, Geographical, and Ecological Distributions of the Species The pearl darter is historically known from rivers and streams within the Pearl River and Pascagoula River drainages in
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Mississippi and Louisiana, and the species was described from the lower Strong River within the Pearl River drainage of Mississippi Suttkus et al.
1994, pp. 1520. The darter has been extirpated from the Pearl River drainage for several decades, apparently due to system-wide channel and water quality degradation occurring in the late 1960s to early 1970s Wagner et al. 2017, entire. With this extirpation, at least half of the historical, geographical, and ecological habitats of the pearl darter are no longer occupied. Channel integrity and water quality within the Pearl River drainage has since improved due to the enactment of State and Federal laws and regulations addressing water pollution and in-channel sand and gravel mining.
In the lower Strong River, channel integrity is controlled and protected by natural bedrock outcrops, and water quality has improved, as indicated by the resurgence of other benthic fish species that historically co-occurred with the pearl darter Piller et al. 2004, pp. 10071011; Tipton et al. 2004, pp.
5760; Wagner et al. 2018, entire.
Within the Pascagoula River drainage, the pearl darter occurs within the Pascagoula, Chickasawhay, Leaf, Chunky, and Bouie Rivers and the Okatoma and Black Creeks Wagner et al. 2017, pp. 310, 12; Clark et al. 2018, pp. 100103; Schaefer et al. 2020, pp.
2627, 4344.
The lower Strong River within the Pearl River drainage and the rivers and streams identified above within the Pascagoula River drainage are representative of the historical, geographical, and ecological distribution of the species.
Space for Individual and Population Growth and for Normal Behavior The pearl darter is found in freeflowing, low-gradient streams and rivers with pools and scour holes associated with channel bends and runs Slack et al. 2002, p. 10; Bart et al. 2001, p. 13.
Presence of the darter is associated with coarse sand and gravel substrates and woody debris, which also supplies habitats for its prey. Other bottom substrates associated with the species include sand, silt, loose clay, and gravel, with organic matter in the form of coarse and fine particulates and snag material Slack et al. 2005, pp. 9, 11.
Pearl darter occurrence within these habitats may be seasonal, with spawning occurring in upstream reaches, and growth and recruitment in downstream reaches Bart et al. 2001, pp. 13, 15. Therefore, a continuum of perennial, uninterrupted, and interconnected natural small stream-toriver channel habitat is required for the
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