The return of the clams.
A small group of biologists makes its way down the steep, rain-slicked river bank, taking care not to expose their bare legs to the prolific patches of briars and stinging nettle growing there. Finding a path to a remote river shoal, they carry snorkeling gear and small coolers. The coolers contain vials filled with thousands of lab-cultured, weeks-old aquatic snails and mussels waiting to be released.
The young mollusks will soon find a new home in and on the river bottom, where it is hoped they will grow, reproduce, and become self-sustaining members of the aquatic community. This is only one event in ambitious recovery programs to restore populations of critically imperiled species through adult and cultured juvenile translocations into stream reaches scattered about the Cumberlandian Region and the Mobile River Basin of the southeastern United States.
The Cumberlandian Region is an area encompassing the Cumberland and Tennessee River systems within the Mississippi River basin. The Mobile Basin drains portions of the central southern states into the Gulf of Mexico. Together, they encompass portions of seven states and support the highest level of freshwater molluscan biodiversity in the world.
Known widely during the nineteenth century for their large river shoals and unique fauna, these basins served as primary centers of speciation and endemism for mollusks, fishes, crayfishes, and other aquatic organisms. These basins also have the dubious distinction of having lost the highest number of species to extinction in North America. Virtually all of these extinctions were aquatic species, primarily mussels and snails. Impoundment and channelization eliminated river species from many areas, and modified and fragmented creek and river habitats, leaving their fauna more vulnerable to sedimentation and chemical pollution. Many of the surviving mollusk species are highly imperiled and largely restricted to suitable habitat in relatively few isolated streams. Today, however, federal, state, and other conservation biologists are working diligently to prevent other mussels and snails from being added to that infamous list of bygone species.
Recovery plans for nearly all southeastern mollusks include tasks for propagating juveniles and restoring wild populations through population augmentation and reintroduction activities. Until fairly recently, very little was known about these animals, including their natural history, habitat requirements, and interactions with other aquatics. Since the 1980s, however, biologists have been working to fill these gaps, and information from these efforts has been used in developing the technology needed to culture imperiled mollusks under artificial conditions. The complex and usually poorly known life history of freshwater mollusks--particularly mussels, which have specialized larvae (glochidia) that are parasites of host fish--was only one stumbling block on the path to achieving this critical recovery goal. Diets to meet the nutritional needs of juvenile mollusks are also poorly known and difficult to develop. Vast experimental networks of tubing, wiring, pumps, and tanks at mussel culture facilities have been refined over time to improve propagation success. Currently, several facilities are conducting propagation related research on snails and mussels of the Cumberlandian Region and Mobile Basin.
The complexity of restoring often highly endemic species of mollusks required the development of augmentation and reintroduction strategies for each basin. The Mobile Basin strategy includes 24 federally listed mussels and snails, along with 10 other endemic species of concern. The Cumberlandian Region strategy focuses only on the most imperiled mussels, which includes 29 federally listed species, 5 listing candidates, and 21 species of concern. Both basin strategies call for coordination with partners to 1) prioritize species based on level of imperilment, 2) identify stream segments with habitat suitable to mussel augmentation or reintroduction, 3) rank stream segments according to their relative importance for each species' recovery, 4) develop individual site augmentation and reintroduction plans for specific restoration activities, and 5) outline the propagation, restoration, and monitoring activities needed for each species' recovery.
The task of developing these strategies and making augmentation and reintroduction programs a reality has required coordination and cooperation among numerous partners: Fish and Wildlife Service field offices in the northeast and southeast, other federal agencies (U.S. Forest Service, U.S. Geological Survey, and National Park Service), state agencies (Alabama Division of Wildlife and Freshwater Fisheries, Georgia Department of Natural Resources, Kentucky Department of Fish and Wildlife Resources, Mississippi Museum of Natural Science, North Carolina Wildlife Resources Commission, Tennessee Wildlife Resources Agency, and Virginia Department of Game and Inland Fisheries), universities (Tennessee Technological University and Virginia Polytechnic Institute and State University), and non-governmental organizations (Tennessee Aquarium Research Institute, The Nature Conservancy, and World Wildlife Fund).
These agencies and organizations share the tasks of 1) surveying streams to locate and assess targeted mollusk populations, 2) collecting broodstock for culture activities, 3) identifying stream segments for potential population restoration activities, 4) conducting life history research, 5) developing propagation technologies, and 6) funding the various aspects of the propagation and larger recovery program.
This hard work is beginning to pay off. For example, researchers have determined the fish hosts for dozens of imperiled mussels. Life history studies have led to the development of propagation technologies for a number of species, and hundreds of thousands of juvenile mussels and snails are being produced and released for population augmentations or reintroductions in several states. Restoration activities are beginning to spread to other watersheds and species as well. New facilities are being planned or are soon coming on line to share the increasing workload. Reversing the decline of our unique molluscan fauna has begun.
Robert S. Butler and Paul Hartfield are listing and recovery biologists working with aquatic organisms in the Fish and Wildlife Service's Asheville, North Carolina (828/258-3939, ext. 235), and Jackson, Mississippi (601/321-1125), field offices.
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|Author:||Butler, Robert S.; Hartfield, Paul|
|Publication:||Endangered Species Bulletin|
|Date:||Mar 1, 2006|
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