Fat Pocketbook

Potamilus capax

Description

The fat pocketbook pearlymussel, Potamilus capax, has a smooth, shiny yellow to brown shell that lacks rays or other distinctive markings. The nearly spherical shell averages 4 in (10 cm) in length. The strong S-curve of its hinge differentiates fat pocketbook from similar bivalves. The beautifully iridescent inner shell surface (nacre) is bluish white. This species has also been classified as Proptera capax.

Behavior

See the Upland Combshell (Epioblasma metastriata ) entry.

Habitat

The fat pocketbook has been found in the sand, mud, or gravel bottoms of flowing streams and rivers in stretches less than 8 ft (2.5 m) deep.

Distribution

This species has been documented in the Wabash River in Indiana and the Ohio River in Illinois. It was reported from the upper and lower Illinois River in Illinois, and from discrete populations in the mainstream of the Mississippi River between Wabasha, Minnesota, and Grafton, Illinois. The fat pocketbook appears to have been eliminated from most of its historic range by dam construction, artificial channeling, dredging, siltation, and agricultural chemical contamination.

The fat pocketbook was subsequently discovered in a Mississippi River tributary in Arkansas. Although geographically widespread, the fat pocketbook never occurred in large concentrations.

Surveys of the St. Francis River, conducted in 1979 and 1980, discovered a population of the fat pocketbook near the town of Madison, Arkansas (in St. Francis County). The stretch above Madison, which consists of a series of shoals and islands, is the only section of the St. Francis River that has not been dredged. A 1986 survey confirmed that the fat pocketbook was the most common mussel in the St. Francis River, numbering more than 11,000 post-juveniles.

In 1975 several specimens were found in the Wabash River near New Harmony, Indiana (in Posey County). In 1976 one live and three dead specimens were found in the White River (a tributary of the Wabash) near Bowman, Indiana (in Pike County). It is uncertain whether the fat pocketbook survives in this watershed as a viable, reproducing population.

Threats

Major rivers within the fat pocketbook's historic range have been dammed, artificially channeled, and repeatedly dredged for flood control and navigation. Sediment loosened by dredging and topsoil runoff from poor agricultural practices smother mussel beds. Agricultural pesticides, herbicides, and fertilizers are carried into streams in rain runoff, generally degrading water quality.

Conservation and Recovery

Seasonal flooding is an acknowledged problem along the St. Francis River, and there is heavy public pressure for continued dredging. The U. S. Fish and Wildlife Service recovery plan for this species recommends that dredging be prohibited in the stretch of river above Madison, and biologists hope to establish at least two other populations in suitable habitat within the St. Francis watershed. The U. S. Army Corps of Engineers has recommended that transplant attempts be made on the White River in Indiana, at two sites on the upper Mississippi River, or in the Hatchie River in Tennessee. Although the Hatchie River is not part of the historic range of this mussel, it supports similar species and is currently protected under the Wild and Scenic Rivers Act. Transplantation outside the fat pocket-book's historic range would require special dispensation under the Endangered Species Act, but it is considered a possible recovery strategy.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1 Federal Drive
BHW Federal Building
Fort Snelling, Minnesota 55111
Telephone: (612) 713-5360
http://midwest.fws.gov/

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

References

Bates, J. M., and S. D. Dennis. 1983. "Mussel (Naiad) Survey—St. Francis, White, and Cache Rivers, Arkansas and Missouri." Report no. DACW66-78-C-0147. U. S. Army Corps of Engineers, Memphis.

Clark, A. H. 1984. "Draft Report Mussel (Naiad) Study; St. Francis and White Rivers; Cross, St. Francis, and Monroe Counties, Arkansas." Report no. 84M 1666R. U. S. Army Corps of Engineers, Memphis.

U. S. Fish and Wildlife Service. 1985. "Fat Pocketbook Pearly Mussel Recovery Plan." U. S. Fish and Wildlife Service, Atlanta.