Fine-rayed Pigtoe Pearlymussel

Fusconaia cuneolus

Description

The fine-rayed pigtoe pearlymussel, Fusconaia cuneolus, is of medium size, up to 2.5 in (6.4 cm) in length. This Cumberlandian species is distinguished by the many fine green rays that radiate over the yellowish green to light brown background of its ovoid shell. The hinged end of the shell is rounded, while the front margin is straight. The shell surface has a smooth, satiny appearance and is indistinctly patterned with growth lines. The inner shell surface is white.

Behavior

This species is a short-term breeder, reproducing in the spring (tachytictic). For more about the reproduction and diet of freshwater mussels, see the Upland Combshell (Epioblasma metastriata ) entry.

Habitat

The fine-rayed pigtoe occupies shallow riffles and shoals of freshwater streams and rivers. It buries itself in the stream bottom in gravel or compacted sand but is rarely found in pools. It displays a higher tolerance for muddy bottoms than most other freshwater mussels.

Distribution

Endemic to the southern Appalachian Mountains, the fine-rayed pigtoe pearly mussel was first described in 1840 from the Holston River, where it occurred in the river's North Fork in Washington County, Virginia, downstream to Grainger County, Tennessee. It was subsequently documented in Big Moccasin Creek in Scott County, Virginia; the Powell River from Lee County, Virginia, downstream to Union County, Tennessee; Clinch Creek, Emory River, and Popular Creek from Clinchport, Virginia, downstream to Roane County, Tennessee; and in the Clinch River from Tazewell County, Virginia, downstream to the Norris Reservoir in Claiborne County, Tennessee.

In the early twentieth century it was discovered in the Tennessee River and its smaller tributaries at and below Knoxville. It is believed that the mussel has been extirpated from former locations in the Little and Sequatchie Rivers.

Although this species was thought to have disappeared from its original collection site in the Holston River, four freshly dead specimens were collected along the river in 1982 at Cloud Ford, Tennessee. Industrial and chemical pollution from upstream at Saltville, Virginia, has severely degraded the water quality there. Live specimens have yet to be found but may indeed exist. Recent surveys in other upper Tennessee River tributaries, such as the Nolichucky, French Broad, Flint, and Buffalo Rivers, failed to locate specimens.

From 1975 to 1981, surveys of the Powell River located populations at Buchanan Ford and Mc-Dowell Shoal in Tennessee, and at Fletcher Ford in Virginia. Water quality in this river has also deteriorated significantly due to strip mining, coal-washing runoff, and discharge of municipal wastes.

In the late twentieth century, this mussel was found at nearly 30 sites in the Clinch River and its smaller tributaries between Cedar Bluff, Virginia, and Kelly Branch, Tennessee. Since 1970, the fine-rayed pigtoe has been collected from the Elk and Paint Rock Rivers, which are tributaries of the Tennessee River above Muscle Shols, Alabama. The mussel's former range and habitat suggests that additional populations may be located on other tributary streams of the Tennessee River in Tennessee and Alabama.

Threats

Construction of dams and multi-purpose reservoirs across the former range of the fine-rayed pigtoe have altered the free-flowing character of these rivers. Such impoundments produce siltation, fluctuating water temperatures, changes in water acidity, and lowered oxygen content. Impoundments also fragment the range of the species into isolated populations, which are then unable to interbreed.

Increased stream turbidity, caused by soil erosion and industrial runoff, reduces light penetration, which affects the growth of aquatic vegetation and decreases the population of fish hosts. Suspended solids can be fatal to mussels. Dead and dying mussels are often found with silt clogging their gills. Mussels are very susceptible to agricultural and industrial pollutants, particularly heavy metals, which become concentrated in their tissues.

Conservation and Recovery

The fairly widespread distribution of the fine-rayed pigtoe affords it some protection against early extinction, if federal, state, and local agencies act quickly to reduce habitat degradation. The U. S. Fish and Wildlife Service recovery plan for this species recommends further systematic surveys to locate new populations and a program to reestablish populations in areas of suitable habitat. Additionally, better enforcement of state and federal environmental regulations is needed to prevent further degradation of water quality. Creation of mussel sanctuaries in the Virginia headwaters, similar to those on the Clinch and Powell Rivers in Tennessee, would be highly beneficial.

Contacts

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

Bogan, A. E., and P. W. Parmalee. 1983. Tennessee's Rare Wildlife: The Mollusks. Tennessee Wildlife Resources Agency, Tennessee Department of Conservation, and Tennessee Natural Heritage Program, University of Tennessee Press, Knoxville.

Carter, L. J. 1977. "Chemical Plants Leave Unexpected Legacy in Two Virginia Rivers." Science 198: 1015-1020.

Dennis, S. D. 1981. "Mussel Fauna of the Powell River, Tennessee and Virginia." Sterkiana 71: 1-7.

French, John R. P., III. November, 1990. "The Exotic Zebra Mussel: A New Threat to Endangered Freshwater Mussels." Endangered Species Technical Bulletin 15 (11).

Imlay, M. J. 1982. "Use of Shells of Freshwater Mussels in Monitoring Heavy Metals and Environmental Stresses: A Review." Malacology Review 15: 1-14.

U. S. Fish and Wildlife Service. 1984. "Fine-Rayed Pigtoe Pearly Mussel Recovery Plan." U. S. Fish and Wildlife Service, Atlanta.