Tan Riffleshell

Epioblasma florentina walkeri

Description

The tan riffleshell, Epioblasma florentina walkeri, is a medium-sized freshwater mussel (2.8 in; 7 cm) characterized by a dull brownish green or yellowish green shell surface with numerous, evenly distributed, faint green rays. The subinflated valves are of unequal length and are marked with uneven growth rings. The inner shell surface is bluish white. The thin, posterior swelling of the female has one or more constrictions which give the shell a lobed appearance.

Behavior

See the Upland Combshell (Epioblasma metastriata ) entry.

Habitat

This mussel inhabits shallow riffles and shoals of mid-sized tributaries and the mainstream of larger rivers. It buries itself in a sand or gravel bottom.

Distribution

This mussel was first collected in the East Fork Stones River in Rutherford County, Tennessee, but appears to have disappeared from this locality. It was found in the headwaters of the Cumberland River downstream to Neeley's Ford in Cumberland County, Kentucky. In the 1970s it was found in the lower Red River (a Cumberland River tributary) in Montgomery County, Tennessee, and in the Duck and Buffalo Rivers.

In the upper Tennessee River drainage, this mussel was documented from the Middle Fork Holston River (Smyth County, Virginia), the South Fork Holston River (Washington County, Virginia, and Sullivan County, Tennessee), and the main stem of the Holston River (Grainger and Knox counties, Tennessee). It was also noted from the Flint River and Limestone Creek in northern Alabama.

The tan riffleshell has not been relocated in the Duck or Red Rivers, and probably survives only in the Middle Fork Holston River in Virginia. It has been collected from near Chilhowie (Smyth County) and further downstream at Craig Bridge (Washington County).

A new population was discovered in the upper Clinch River and a tributary, Indian Creek, in southwestern Virginia. Both are part of the greater Tennessee River system.

Threats

The drastic decline in range of the tan riffleshell is probably in response to the extensive alteration of the Cumberland and Tennessee River basins by the construction of more than 50 dams and reservoirs. The South Fork Holston River was impounded by the Ruthton Dam to create the South Holston Lake, inundating miles of former mussel habitat along the river. The cold tailwaters of the reservoir have proven inimical to endemic mussels and many species of fishes that serve as hosts for mussel larvae.

The general effects of impoundments on mussel habitat have been widely documented. In addition, water quality in most watersheds within the tan riffleshell's has deteriorated significantly. Distribution has also deteriorated because of heavy siltation caused by logging, strip-mining, dredging, and poor agricultural practices.

Conservation and Recovery

The Tennessee Valley Authority is currently developing a comprehensive water management plan for the region that would establish minimum, year-round flows in all rivers in the Tennessee and Cumberland basins by carefully timing water discharges from its many dams. The recovery of the tan riffleshell will depend on the success of this and other regional efforts to improve water quality and rehabilitate freshwater mussel habitat.

The newest population, located in the upper Clinch River drainage, included evidence of reproduction, which indicates the species' fish hosts are present. The U. S. Fish and Wildlife Service (FWS) is providing funds to determine which fish species host this mussel during its parasitic larval stage. If successful, this research could lead to additional efforts to culture the tan riffleshell and return young individuals to suitable habitat.

The FWS has also initiated actions to inform residents along the upper Clinch River of the importance and uniqueness of this species, and to enlist their support for its recovery. Early efforts to work with local citizens, county officials, and other individuals and agencies have been well-received.

Contact

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

Tennessee Valley Authority. 1978. "Water Quality Progress in the Holston River Basin." Report No. TVA/EP-78/08. Tennessee Valley Authority, Knoxville.

U. S. Fish and Wildlife Service. 1984. "Tan Riffleshell Mussel Recovery Plan." U. S. Fish and Wildlife Service, Atlanta.

Virginia State Water Control Board. 1982. "Water Quality Inventory: Report to EPA and Congress." Bulletin No. 546. Virginia State Water Control Board, Richmond, Virginia.