Heavy Pigtoe

Pleurobema taitianum

Description

The heavy pigtoe, Pleurobema taitianum, is a bivalve mollusk about 2 in (5 cm) long, 1.8 in (4.5 cm) high, and 1.2 in (3 cm) wide. The obliquely triangular shell is brown to brownish-black. The shell beaks are narrowly pointed forward with shallow cavities. The nacre (inner shell surface) is pinkish-white. The heavy pigtoe is also known as Judge Tait's mussel. In the late twentieth century, the identity of species within the genus Pleurobema was the focus of debate among malacologists. The U. S. Fish and Wildlife Service (FWS) adopted the majority view but acknowledged that further research could warrant reclassification of the heavy pigtoe and other mussels of the genus.

Behavior

See the Upland Combshell (Epioblasma metastriata ) entry.

Habitat

This mussel prefers clear, fast-flowing water in shallow reaches where the bottom is composed of relatively firm rubble, gravel, or sand. The current must be strong enough to scour the bottom of silt. Free-flowing, shallow riffles and shoals are increasingly rare due to extensive modification of the river channels.

Distribution

The heavy pigtoe mussel has been found in the Tombigbee River from the mouth of Tibbee Creek near Columbus, Mississippi, downstream to Demopolis, Alabama. Other populations were found far downstream in the Alabama River at Claiborne and Selma, in the lower Cahaba River, and possibly the Coosa River. In the early 1980s, several shells were found at one site on the Buttahatchie River, a Mississippi tributary of the Tombigbee River. This species has also been reported from the East Fork Tombigbee and Sipsey Rivers in Alabama.

Only four portions of suitable habitat remain for the heavy pigtoe mussel: the Gainesville Bendway of the Tombigbee River (Sumter County, Alabama); the Sipsey River (Pickens and Greene Counties, Alabama); and the East Fork Tombigbee and Buttahatchie rivers (Mississippi). A 1987 survey of the Gainesville Bendway documented extensive siltation caused by decreased water flows. No specimens of heavy pigtoe were found during this survey. This mussel was last collected from the East Fork Tombigbee River in 1972, but much of the habitat along the Tombigbee River has since been altered by the construction of the Tennessee-Tombigbee Waterway, a navigable canal built to connect the Tennessee and Tombigbee Rivers.

Threats

Habitat for the heavy pigtoe mussel on segments of the Buttahatchie and Sipsey Rivers is considered marginal, and remaining mussels must cope with siltation, reduced water flows, degraded water quality, and reduced populations of the fish hosts needed for larval development. These habitat alterations were induced by large-scale flood control and navigation projects.

Several ongoing and proposed water control projects threaten to eliminate this mussel's habitat altogether—a 59-mi (95-km) channel improvement project in the Buttahatchie, a 53-mi (85-km) clearing and snagging project in the East Fork Tombigbee, and a 84-mi (135-km) channel improvement project in the Sipsey River. These projects are directed by the U. S. Army Corps of Engineers or by the Soil Conservation Service of the U. S. Department of Agriculture.

Conservation and Recovery

The endangered status of the heavy pigtoe mussel provides the FWS with some control over these and other proposed projects that would damage or destroy remaining habitat. Under provisions of the Endangered Species Act, federal agencies are required to consult with the FWS to ensure that any actions they authorize or fund do not jeopardize federally protected wildlife. In the past, similar consultations have resulted in the redesign of projects to preserve significant portions of habitat.

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

Fuller, S. L. H. 1974. "Clams and Mussels (Mollusca:Bivalvia)." In Pollution Ecology of Freshwater Invertebrates, edited by C. Hart Jr. and S. Fuller. Academic Press, New York.

Stansbery, D. H. 1983. "Status of Pleurobema taitianum. " Unpublished report. U. S. Fish and Wildlife Service, Atlanta.