Orangefoot Pimpleback

Plethobasus cooperianus

Description

The orangefoot pimpleback, Plethobasus cooperi-anus, is nearly circular, attains a mature shell length of up to 3.7 in (9.5 cm), and a thickness of 1.8 in (4.6 cm). Valves are solid and moderately swollen. The shell surface is yellowish brown to chestnut brown and is marked by dark, concentric, irregular growth lines. The posterior two-thirds of the shell is covered with numerous raised knobs (turbercles). Greenish rays are found only in younger specimens. The inner shell surface (nacre) varies in color from white to pink.

Behavior

The orangefoot pimpleback is probably a "tachytictic bivalve," or short-term breeder—one that breeds in spring and releases glochidia (larvae) by late summer. Individuals can live as long as 50 years. For more on the reproduction and diet of freshwater mussels, see the Upland Combshell (Epioblasma metastriata ) entry.

Habitat

The orangefoot pimpleback is found in medium to large rivers in depths of 12-29 ft (3.6-8.8 m). It buries itself into sand and gravel with only the margin of the shell and feeding siphons exposed to the water.

Distribution

The orangefoot pimpleback is an Interior Basin species with distribution in the drainages of the Ohio, Cumberland, and Tennessee Rivers. This species was locally abundant in the Ohio River between St. Marys, West Virginia, and Marietta, Ohio, and around the confluence of the Wabash River in Indiana. In the lower Ohio River, it was found between the Cumberland and Tennessee Rivers and the Mississippi River in Illinois. It was locally abundant in the Wabash River in Indiana and common to rare in the mainstream of the Cumberland River in Tennessee. It has been documented in the Rough River of Kentucky; the Duck, French Broad, Holston, and Clinch Rivers of Tennessee; and the Kanawha River of West Virginia. The orangefoot pimpleback has been extirpated from the Kanawha, upper Ohio, and Wabash Rivers, and its range elsewhere has been greatly reduced. In the Tennessee River, orangefoot pimplebacks have been found below the Fort Loudoun Dam (Loudon County, Tennessee), Guntersville Dam (Marshall County, Alabama), and several clustered sites below Pickwick Dam (Hardin County, Tennessee).

The mussel survives in the Cumberland River only below Cordell Hull Dam (Smith County, Tennessee). Other populations survive in the lower Ohio River between Metropolis and Mound City (Massac and Pulaski counties, Illinois). The U. S. Fish and Wildlife Service lists the species as endangered in Alabama, Illinois, Indiana, Kentucky, Pennsylvania, and Tennessee.

Threats

Because it occurred in small numbers in localized beds, the orangefoot pimpleback has always been somewhat rare. 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 dams for flood control, hydroelectric power production, navigation, and recreation. Dam reservoirs have inundated stretches of river that once supported mussel populations, while sections of former habitat below the dams have been rendered uninhabitable by erratic water levels. In addition to numerous locks and dams, the historic conditions of the Wabash and Ohio Rivers have been altered by deforestation and poor agricultural practices, which increased water turbidity and siltation. Water quality has been further degraded by chemical runoff, industrial effluents, and sewage.

Conservation and Recovery

The recovery of this species will depend upon the success of larger efforts to reclaim river habitat throughout the Interior Basin. The Tennessee Valley Authority is working on water management to guarantee constant minimum flows in all rivers in the Tennessee and Cumberland basins by timing water discharges from its dams. Such an effort may mollify many of the negative effects of dams and reservoirs on remaining stretches of mussel habitat. In recent years, the water quality of the upper Ohio River has improved. If this improvement continues the orangefoot pimpleback may be reintroduced to its historic range above Marietta, Ohio.

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
Regional Office, Division of Endangered Species
300 Westgate Center Dr.
Hadley, Massachusetts 01035-9589
Telephone: (413) 253-8200
Fax: (413) 253-8308
http://northeast.fws.gov/

References

Clark, C. F. 1976. "The Freshwater Naiads of the Lower End of the Wabash River, Mt. Carmal, Illinois, to the South." Sterkiana 61: 1-14.

U. S. Fish and Wildlife Service. 1984. "Recovery Plan for the Orange-Footed Pearly Mussel." U. S. Fish and Wildlife Service, Asheville, N. C.