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Federal Register / Vol. 86, No. 131 / Tuesday, July 13, 2021 / Proposed Rules downstream drift of larvae or movement of juveniles, and the upstream migration of spawning adults.

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Food, Water, Air, Light, Minerals, or Other Nutritional or Physiological Requirements The pearl darter requires unimpeded and interconnected stretches of perennial and flowing streams and rivers with adequate water quality.
Water temperatures at pearl darter collection sites has ranged from 8 to 30
degrees Celsius C 46.4 to 86.0
degrees Fahrenheit F Suttkus et al.
1994, pp. 1719; Bart et al. 2001, p. 13, Slack et al. 2002, p. 10, with dissolved oxygen of 5.8 to 9.3 milligrams per liter mg/1 Suttkus et al. 1994, pp. 1719;
Bart et al. 2001, pp. 7, 1314; Slack et al. 2002, p. 10. The species is apparently sensitive to warmer water temperatures and may seasonally require tributaries with canopy shading and/or cool spring flows as seasonal refugia from warmer, unshaded river channels Bart et al. 2001, p. 14.
The natural diet of the pearl darter is poorly known; however, other species within the genus feed on chironomids midges, small crustaceans, mayflies, and caddisflies Kuehne and Barbour 1983, p. 49. Food availability is likely affected by adequate flow, channel stability, and water quality. Pearl darters have been maintained in captivity for at least 2 years on a diet of bloodworms Campbell 2019, p. 1.

during March through May Suttkus et al. 1994, pp. 1920, and young of year were collected in June Suttkus et al.
1994, p. 19. Based on collection occurrence patterns, some researchers have postulated that adult pearl darters migrate upstream during the fall and winter to spawn in suitable upstream gravel reaches, with elevated river discharge during the spring dispersing the larvae and juveniles into downstream reaches Bart et al. 2001, p.
14; Ross et al. 2000, p. 11. Other studies have hypothesized that the species disperses locally from shallow spawning habitats into nearby deeper habitats where their presence is more difficult to detect Slack et al. 2002, p.
18. The pattern of the disappearance of the pearl darter from all stream orders in the Pearl River drainage over a relatively short period of time suggests that some degree of seasonal interchange between tributary and river channel subpopulations may have been a factor in the species extirpation from that drainage. Therefore, until more is known relative to seasonal dispersal, connectivity between instream habitats should be considered essential for successful breeding and rearing of the pearl darter.

Summary of Essential Physical or Biological Features We derive the specific physical or biological features essential to the conservation of the pearl darter from studies of this species habitat, ecology, Sites for Breeding, Reproduction, or and life history. Additional information Rearing or Development of Offspring can be found in the September 21, 2016, Pearl darters have been collected at proposed listing rule 81 FR 64857 and sites with cool to warm water the September 20, 2017, final listing temperatures 8 to 30 C 46.4 to rule 82 FR 43885. We have determined 86.0 F, high dissolved oxygen 5.8 to that the following physical or biological 9.3 mg/l, slightly acidic to basic pH
features are essential to the conservation values 6.3 to 7.6, and apparently low of the pearl darter:
levels of pollution Suttkus et al. 1994, 1 Unobstructed and stable stream pp. 1719; Bart et al. 2001, pp. 7, 13
and river channels with:
14; Slack et al. 2002, p. 10. Spawning a Connected sequences of channel in the Strong River was associated with runs and bends associated with pools bedrock and broken rubble Suttkus et and scour holes; and al. 1994, p. 19, and three probable b Bottom substrates consisting of spawning sites in the Pascagoula River fine and coarse sand, gravel, bedrock, system were characterized by extensive silt, clay, organic matter, or woody outcrops of limestone or sandstone Bart debris.
2 A natural flow regime necessary to and Pillar 1997, p. 8. Pearl darters in maintain instream habitats and their spawning condition in the Pascagoula connectivity.
River drainage have also been collected 3 Water quality conditions, over firm gravel in relatively shallow, including cool to warm water flowing water from April to early May Bart et al. 2001, p. 13. Ideal conditions temperatures 8 to 30 C 46.4 to 86.0 F, high dissolved oxygen 5.8 to for spawning have been described as 9.3 mg/l, slightly acidic to basic pH 6.3
channel reaches with good canopy to 7.6, and low levels of pollutants and shading, an extensive buffer of mature forest, and good water quality Bart et al. nutrients meeting the current State of Mississippi criteria, as necessary to 2001, p. 15.
maintain natural physiological Spawning in the Pearl and Strong processes for normal behavior, growth, Rivers Mississippi was documented
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and viability of all life stages of the species.
4 Presence of a prey base of small aquatic macroinvertebrates, including midges, crustaceans, mayflies, caddisflies, and zooplankton.
Special Management Considerations or Protection When designating critical habitat, we assess whether the specific areas within the geographical area occupied by the species at the time of listing contain features that are essential to the conservation of the species and which may require special management considerations or protection. The pearl darter is threatened by water quality degradation from point and nonpoint source pollution, discharges from municipalities, and geomorphological changes to its channel habitats 82 FR
43885, September 20, 2017, pp. 43888
43893. The features essential to the conservation of this species may require special management considerations or protection to reduce the following threats: 1 Actions that alter the minimum or existing flow regime, including impoundment, channelization, or water diversion; 2
actions that significantly alter water chemistry or temperature by the release of chemicals, biological pollutants, or heated effluents into the surface water or connected groundwater at a point or non-point source; and 3 actions that significantly alter channel morphology or geometry, including channelization, impoundment, road and bridge construction, or instream mining.
Examples of special management actions that would minimize or ameliorate these threats include: a Restoration and protection of riparian corridors; b implementation of best management practices to minimize erosion such as State and industry practices for road construction, forest management, or mining activities; c stream bank restoration projects; d private landowner programs to promote watershed and soil conservation such as the U.S. Department of Agricultures Farm Bill and the Services Private Lands programs; e implementation of best management practices for storm water; and f upgrades to industrial and municipal treatment facilities to improve water quality in effluents.
Criteria Used To Identify Critical Habitat As required by section 4b2 of the Act, we use the best scientific data available to designate critical habitat. In accordance with the Act and our implementing regulations at 50 CFR
424.12b, we review available
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