White Wartyback Pearlymussel

Plethobasus cicatricosus

Description

The shell of the white wartyback pearlymussel, Plethobasus cicatricosus, is somewhat egg-shaped, thick, solid, and inflated. The greenish yellow or yellow-brown shell surface is marked by uneven, concentric growth lines and a row of knobs (tubercles) in the middle portion of the shell. The iridescent inner shell surface is white. Individuals can live as long as 50 years. The white wartyback has sometimes been confused with a closely related species, Plethobasus cyphyus.

Behavior

See the Upland Combshell (Epioblasma metastriata ) entry.

Habitat

The white wartyback pearlymussel buries itself in sand and gravel substrates in shallow stretches of large rivers with slow to moderate currents.

Distribution

This pearlymussel was first collected in 1829 from the Wabash River in Indiana, and is thought to have enjoyed a widespread distribution in the Ohioan or Interior Basin. It was documented from the Kanawha River (West Virginia), the Ohio River (Ohio and Indiana), the Cumberland and Holston Rivers (Tennessee), and the Tennessee River below Wilson Dam (Alabama).

Since the mid-1960s, only two Tennessee River specimens have been discovered, both near Savannah, Tennessee, below the Pickwick Dam. The species may be extinct or near extinction in the Tennessee River. No live specimens have been taken from the Cumberland River since 1885. In spite of extensive surveys, there is no recent evidence of this species in the Ohio, Wabash, or Kanawha Rivers.

Threats

The white wartyback pearlymussel was historically found only in large rivers and was never very common. Possibly the single greatest factor in this mussel's decline has been the alteration of the Tennessee and Cumberland river basins by the construction of major dams for flood control, hydro-electric power production, and navigation. Dam reservoirs have inundated large stretches of river that once supported mussel populations, while sections of former habitat below the dams have been rendered uninhabitable by erratic water levels, altered water temperatures, and seasonal oxygen deficits.

In addition to numerous locks and dams, the historic conditions of the Wabash and Ohio Rivers have been significantly altered by deforestation and poor agricultural practices that have increased water turbidity and siltation. Water quality has been further degraded by chemical runoff, industrial effluents, and sewage.

Conservation and Recovery

Unless a viable reproducing population is found, little in the way of recovery can be considered. The white wartyback pearlymussel may benefit from more general efforts aimed at improving the environmental quality of the Interior Basin's major rivers. The Tennessee Valley Authority is currently working on a comprehensive water management plan, which would guarantee constant minimum flows in all rivers in the Tennessee and Cumberland basins by timing water discharges from its dams. Such an effort might mollify many of the negative effects of dams and reservoirs on remaining stretches of mussel habitat.

Although unfortunate from the standpoint of local residents, economic slowdown (the closing of steel mills and other major industrial polluters in the region of the Ohio River's headwaters) has resulted in almost immediate water quality improvement in the upper river. Recently, freshwater mussels have been rediscovered in stretches of the river where they have been absent for more than 70 years.

Contact

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

References

Bogan, A., and P. Parmalee. 1983. "Tennessee's Rare Mollusks." In Tennessee's Rare Wildlife, Final Report. Tennessee Heritage Program of the Department of Conservation and the University of Tennessee, Knoxville.

Isom, B. G. 1969. "The Mussel Resources of the Tennessee River." Malacologia 7(2-3):397-425.

Jenkinson, J.J. 1981."The Tennessee Valley Authority Cumberlandian Mollusk Conservation Program." Bulletin of the American Malacological Union 1980:662-63.

U.S. Fish and Wildlife Service. 1984. "Recovery Plan for the White Wartyback Pearly Mussel (Plethobasus cicatricosus )." U.S. Fish and Wildlife Service, Atlanta.