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Federal Register / Vol. 86, No. 124 / Thursday, July 1, 2021 / Rules and Regulations
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ammonia toxicity. Increased stream temperatures and decreased dissolved oxygen concentrations are important secondary effects associated with flow reduction and cessation Haag and Warren 2008, pp. 11741176. Sensitive mussel species like the Suwannee moccasinshell may suffer lethal and nonlethal effects to low dissolved oxygen levels and elevated stream temperatures Gagnon et al. 2004, p.
672; Golladay et al. 2004, p. 501; Haag and Warren 2008, pp. 11741176;
Spooner and Vaughn 2008, p. 313, and are particularly susceptible to these conditions during early life stages Sparks and Strayer 1998, pp. 132133;
Pandolfo et al. 2010, p. 965;
Archambault et al. 2013, p. 247. Water temperatures of not more than 91 F
32 C, and DO concentrations of not less than 5.0 milligrams per liter mg/L
represent important thresholds for freshwater mussels Sparks and Strayer 1998, pp. 132133; Gagnon et al. 2004, p. 672; Pandolfo et al. 2010, p. 965;
Khan et al. 2019, p. 6. The specific physical and chemical tolerance ranges needed by the Suwannee moccasinshell for normal behavior, growth, and viability of all life stages have not been investigated. In the absence of speciesspecific data, we are using the current numeric standards for water quality criteria adopted by the States under the Clean Water Act CWA. We find these criteria represent sustainable levels for aquatic life that would provide for the conservation of the species.
Sites for Breeding, Reproduction, or Rearing or Development of Offspring Sites for breeding, reproduction, and development are tied to areas in stable rivers and creeks where flow velocities are sufficient to maintain habitats, and bottom substrates are composed of sand or a mixture of sand and gravel see Space for Individual and Population Growth and for Normal Behavior above.
Juvenile mussels depend upon areas where substrates remain stable during high flow events. The presence of large embedded logs may contribute to substrate stability and act as flow refuges. The larvae of most freshwater mussels are parasitic, requiring a period of encystment on a fish host in order to transform into juvenile mussels. Thus, the presence of appropriate host fishes to complete its reproductive life cycle is essential to the Suwannee moccasinshell. In laboratory host trials, Suwannee moccasinshell larvae transformed primarily on the blackbanded darter Percina nigrofasciata and to a lesser extent on the brown darter Etheostoma edwini Johnson et al. 2016, p. 171. The
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blackbanded darter is one of the most abundant darter species in coastal plain streams, and the distribution of both fish species overlap with the historical distribution of the Suwannee moccasinshell Kuehne and Barbour 1983, pp. 2930; Robins et al. 2018, pp.
317, 336.
Habitats Protected From Disturbance The Suwannee moccasinshells habitat has been impacted by pollution and reduced flows throughout its range, and by channel instability and excessive sedimentation in portions of its range see Factor A, The Present or Threatened Destruction, Modification, or Curtailment of Its Habitat or Range of the proposed listing rule.
An environment free from toxic levels of pollutants is essential to the Suwannee moccasinshell, especially to its early life stages. There is no specific information on the sensitivity of the species to common municipal, agricultural, and industrial pollutants.
However, as a group, freshwater mussels are more sensitive to pollution than many other aquatic organisms and are one of the first species to respond to water quality impacts Haag 2012, p.
355. A detailed discussion of pollution issues in the basin and potential effects to the Suwannee moccasinshell is provided in the proposed listing rule 80
FR 60335 under Factor A.
The Suwannee moccasinshell depends upon a natural flow regime to maintain its benthic habitats. Altered flow regimes including higher peak flows, lower base flows, and changes to seasonal flow pulses within the basin are attributable to altered stormwater runoff patterns, lowering of the groundwater table, recent periods of drought, and climate change. Developed areas and some agricultural lands shed water extremely quickly during storm events. Urban areas significantly affect water quantity because of the high percentage of impervious cover and increases in water consumption.
Rainfall on impervious surfaces is immediately transported to stream channels, causing increases in flow volume and velocity. These effects are discussed further in the next section and in the final listing rule under Factor A, Stream Channel Instability.
Because less infiltration occurs in developed areas, less groundwater recharge occurs and stream base flows may be reduced. The distinctive geology of the Suwannee River basin relies heavily on spring discharge to buffer the tannic waters of the mainstem, and groundwater recharge is limited in the region due to confinement of the aquifer. Over 250 springs located in this
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system have been threatened by increased demand for water resources within the basin and adjacent basins.
The combined effects of groundwater pumping and prolonged droughts have resulted in lower groundwater tables and reduced flow and dewatering of basin streams and springs for extended periods Grubbs and Crandall 2007, p.
78; Torak et al. 2010, pp. 4647. The springs provide refugia for aquatic organisms during periods of drought when groundwater has the most influence on water quality and quantity.
Recent surveys found the species only in portions of the basin with significant contributions from spring discharge and failed to locate the species in areas without this influence Holcomb et al.
2018, pp. 99100. The strong connection between spring discharge and Suwannee moccasinshell occupancy indicates that groundwater discharge via springs is important to maintaining flows and water quality needed by the species, especially during drought Holcomb et al. 2018, p. 95.
Reductions in stream flow may also alter hydraulically mediated sediment sorting throughout the river, which may displace or otherwise alter Suwannee moccasinshell habitat. Climate scenarios for the years 2050 and 2080 predict changes to seasonal and annual hydrology of the Suwannee River basin due to a wetter and warmer climate in the region Neupane et al. 2018, pp.
22322238. Within the basin, surface runoff is projected to increase as a result of increased precipitation, and summer stream flow is projected to decrease substantially up to 25% by 2080 due to the effects of higher air temperature Neupane et al. 2018, p. 2240.
Because freshwater mussels are relatively long-lived and have limited mobility, habitat stability is a requirement shared by nearly all freshwater mussels Haag 2012, p. 106.
Optimal substrate conditions for the Suwannee moccasinshell include consolidated sand or sand and gravel mixtures, without excessive accumulations of sediment or detritus, and that remain stable during high flows. These substrates are dependent on geomorphically stable stream channels and intact riparian areas Allan et al. 1997, p. 149; Rosgen 1996, pp. 811. Stable stream channels consistently transport their sediment load, such that the stream bed neither degrades nor aggrades, and have lower suspended sediment loads Rosgen 1996, pp. 13, which mussels require in order to efficiently feed, respire, and reproduce. Stable stream channels are formed and maintained by natural flow regimes, channel features dimension,
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