Northern Riffleshell

Epioblasma torulosa rangiana

Description

The northern riffleshell can have a shell length up to about 3 in (7.5 cm). The shells of adult females are obovate in outline and appear swollen and rounded along the postventral area of the shell. Males have an ovate shell with a wide shallow sulcus. The shell's exterior surface (pereostricum) is brownish to yellowish-green with fine green rays. The inside of the shell (nacre) is usually white, but is occasionally pink.

Behavior

Although the food habits and reproductive biology of the northern riffleshell are unknown, they are probably similar to those of other freshwater mussels. Freshwater mussels feed on organic particles, algae, and minute plants and animals that they siphon out of the water. During feeding and respiration, females also take in the sperm that has been released into the water by males. Fertilized eggs remain in the gills until the larvae develop. When the larvae are released into the water, they attach and form cysts on the gills or fins of a fish host. The species of fish host used by this mussel is unknown. After the larvae's metamorphoses are complete, they drop to the streambed as juvenile mussels.

Habitat

This freshwater mussel occurs in a wide variety of streams, large and small, preferring runs with bottoms composed of firmly packed sand and fine to coarse gravel.

Distribution

Historically, the riffleshell occurred in the states of Illinois, Indiana, Kentucky, Michigan, Ohio, Pennsylvania, and West Virginia, and the species range also extended into western Ontario, Canada. It existed in the Ohio River basin in the Ohio, Allegheny, Scioto, Kanawha, Little Kanawha, Licking, Kentucky, Wabash, White, Vermillion, Mississinewa, Tippecanoe, Green, and Salt Rivers. It was found in the Maumee River basin and tributaries of western Lake Erie. The riffleshell also inhabited rivers in southern Michigan and western Ontario, such as the St. Clair, Black, Au Sable, and Sydenham Rivers.

In the late 1990s, this species survived in the Green River in Edmondson and Hart Counties, Kentucky; French Creek in Crowford, Venango, and Mercer Counties, Pennsylvania; Allegheny River in Warren and Forest Counties, Pennsylvania; LeBoeuf Creek in Erie County, Pennsylvania; Detroit River in Wayne County, Michigan; and Big Darby Creek in Pickaway County, Ohio. This distribution represented a range reduction of greater than 95%. Reproduction was documented in the late 1990s from only French Creek and the Detroit River.

The U. S. Fish and Wildlife Service considers this species to be endangered in Indiana, Kentucky, Michigan, Ohio, Pennsylvania, West Virginia.

Threats

The reduction in the riffleshell's range can be attributed to many factors. The primary factors, however, are impoundments, channelization, loss of riparian habitat, and the impacts of silt from poor land uses. Water pollution from municipalities, chemical discharges, coal mines, and reservoir releases have also impacted the species. The invasion of the exotic zebra mussel (Dreissena polymorpha ) poses another potential threat to this species. Zebra mussels in the Great Lakes have been found attached in large numbers to the shells of live and freshly dead native mussels, and zebra mussels have been implicated in the loss of entire mussel beds. The zebra mussel has recently been reported from the Ohio River system, including the Green River in Kentucky, but the extent of zebra mussel impacts on the basin's freshwater mussels are unknown.

Conservation and Recovery

To save the northern riffleshell, all existing state and federal legislation and regulations must be enforced. Management is needed to restore some of the species' habitat through repair of riparian habitat and control of nonpoint source pollution. Research is needed to identify the species' habitat requirements and fish host and to develop propagation and reintroduction techniques. The number of individuals needed to maintain a viable population should be determined. Also, more surveys are needed to better assess the condition of the existing populations and search for potential rein-troduction sites.

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/

U. S. Fish and Wildlife Service
Asheville Ecological Services Field Office
160 Zillicoa St.
Asheville, North Carolina 28801-1082
Telephone: (828) 258-3939
Fax: (828) 258-5330

U. S. Fish and Wildlife Service
West Virginia Ecological Services Field Office
P.O. Box 1278
Elkins, West Virginia 26241-1278
Telephone: (304) 636-6586
Fax: (304) 636-7824
http://www.fws.gov/r5fws/wv/wvfo.htm

References

Stansbery, D. H., K. Borror, and K. E. Newman.1982. "Biological Abstracts of Selected Species of Unionid Mollusks Recovered from Ohio." Unpublished. Prepared for the Ohio Heritage Foundation, Ohio Department of Natural Resources.

U. S. Fish and Wildlife Service. 22 January 1993. "Determination of Endangered Species Status for the Northern Riffleshell Mussel (Epioblasma turulosa rangiana ) and the Clubshell Mussel (Pleurobema clava )." Federal Register 58 (13): 5638-5642.