Rare and Endangered Mussel Fauna Suffer Due to Lack of Knowledge

The Tennessee River at Muscle Shoals was historically home to more species of freshwater mussel than any other location in the world.  A cumulative total of 79 species of mussels was known from this reach of river, but the fauna suffered greatly with construction of Wilson, Wheeler and Pickwick dams.  However, tailwaters downstream of these dams continue to hold some of the best remaining examples of a mussel fauna typical of large rivers.  Four to six federally endangered species are currently found in the tailwaters of Wilson Dam, and several others were recently designated species of high conservation concern in the State.  This area includes the last known population of the white wartyback species of mussel.  Pickwick Reservoir is the most productive area for commercial mussels in Alabama, with the harvest being exported primarily for use in the cultured pearl industry.

During the summer of 2004, a massive die-off of mussels occurred in a reach of Wilson Dam tailwater and upper Pickwick Reservoir, from the lower end of the back channel of Seven Mile Island downstream past Colbert Steam Plant.  The estimated number of dead mussels in the kill zone approached 54 million individuals, representing the most common 11 species.

The American Fisheries Society (AFS) recently developed replacement values for various species of freshwater mussels.  The values represent the total cost required to produce a given species in captivity for restocking an affected stream.  Similar values have been used to assess damages for fish kills for several years.  Based on AFS values, damages assessed in the recent mussel kill on Pickwick Reservoir totaled $40.5 million.

The cause of the mussel kill remains a mystery.  There have been periodic mussel kills in the Tennessee River believed to be attributable to events such as drought. Most of these kills were on a larger scale than the current one. The latest kill on Pickwick Reservoir is confined to a relatively small area; therefore it appears to be related to a specific event affecting only that area.  However, determination of factors causing the kill is hampered by a poor understanding of many aspects of freshwater mussel biology.  For example, very little is known about diseases of these animals, types of bacteria which are routinely associated with them, and what triggers adverse reactions.  The effects of many pollutants on various stages of the freshwater mussel life cycle are also poorly known.  Several agencies, including Alabama’s Division of Wildlife and Freshwater Fisheries, Alabama’s Department of Environmental Management, U.S. Fish and Wildlife Service, Tennessee Valley Authority, U.S. Environmental Protection Agency and the U.S. Geological Survey, have been involved in the investigation and/or discussion of the recent mussel kill.  The search for the cause of the kill continues, but basic biological research may be needed before an answer can be found.

For more information on commercial mussels in Alabama and mussel biology, including pictures, click here.

The Alabama Department of Conservation and Natural Resources promotes wise stewardship, management and enjoyment of Alabama’s natural resources through five divisions: Marine Police, Marine Resources, State Parks, State Lands, and Wildlife and Freshwater Fisheries.