Proposal to list eight mussel species as threatened or endangered

In October 2011, the US Fish and Wildlife Service published a proposed rule to list eight species of freshwater mussels as endangered or threatened and to designate 1,495 miles of stream and river channels as critical habitat (76 FR 61482– 61529). The eight species include the Alabama pearlshell (Margaritifera marrianae), round ebonyshell (Fusconaia rotulata), southern sandshell (Hamiota australis), southern kidneyshell (Ptychobranchus jonesi), and Choctaw bean (Villosa choctawensis), which are proposed for listing as endangered, as well as the tapered pigtoe (Fusconaia burkei), narrow pigtoe (Fusconaia escambia), and fuzzy pigtoe (Pleurobema strodeanum), which are proposed for listing as threatened. The mussels are endemic to portions of the Escambia River, Yellow River, and Choctawhatchee River basins of Alabama and Florida, and to localized portions of the Mobile River Basin in Alabama.

In the proposed rule, the Service suggests that these species have declined in abundance and disappeared from portions of their natural ranges “primarily due to habitat deterioration and poor water quality as a result of excessive sedimentation and environmental contaminants”.

In its comments on the proposed rule, NCASI noted that there are significant gaps in knowledge about the life history, population trends, and ecological relationships of these eight mussel species. These gaps and the complexity of issues interacting with water quality in these river systems indicate a need for a thoughtful science-based assessment of the relative importance of factors potentially affecting viability of the eight mussel species. Such an assessment is generally lacking in the proposed rule.

In particular, the proposed rule relies too heavily on general descriptions of factors that “could” affect these eight mussels and does not provide adequate justification for proposed water quality metrics. The Service should be aware that climate change models do not provide information appropriate for use in listing decisions and that silvicultural activities generally have only a small, short-lived impact on water quality, especially when compared with other land uses such as agriculture or urban development.

With regard to point source discharges, suspended solids from biological wastewater treatment plants are often comprised largely of organic matter and such solids would not be expected to contribute to sedimentation or to
adversely affect habitat for mussels. Sediment issues in the southeastern US are complicated by a legacy of poor agricultural practices during the 1800s and early 1900s, which raises questions about sources of sediment problems and the relative magnitudes of different sediment sources today.


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