Cumberland Bean Pearlymussel in North Carolina

Villosa trabalis (Conrad 1834)

FAMILY: Unionidae

STATUS:  Endangered, Federal Register, June 14, 1976

DESCRIPTION:

The Cumberland bean is a small to medium sized freshwater mussel with relatively thick, elongated, oval shells. The shells of the females are somewhat more rounded and slightly larger (maximum about 55 millimeters or 2.2 inches long). The periostracum (outer shell surface) is smooth (no ridges or bumps) and somewhat shinny; it is olive green, yellowish brown, or blackish with fine wavy dark green or blackish rays. However, these rays are often difficult to see unless the shell surface is cleaned. The nacre (inside shell surface) is bluish white or white with a bluish iridescence towards posterior end of the shell. The description is adapted from [Parmalee and Bogan 1998 and U.S. Fish and Wildlife Service (USFWS) 1984]. Ortmann (1915) described the species' internal anatomy.

HISTORIC AND CURRENT RANGE:

The Cumberland bean was historically known from ten river systems in the Cumberland and Tennessee river basins in Alabama, Georgia, Kentucky, Tennessee, and Virginia (USFWS 1984). Currently, the species survives in only a few streams in the upper Cumberland River system, Kentucky and Tennessee and in the upper Tennessee River system, Tennessee. A relatively strong population still exists in a short reach of the Hiwassee River downstream of the North Carolina/Tennessee State line in Polk County, Tennessee (Parmalee and Bogan 1998). Although no specimens have been collected in North Carolina, the habitat appears suitable, and we believe the species likely also occurs in small numbers in the North Carolina portion of the Hiwassee River below Appalachia Dam, Cherokee County (J. Fridell, USFWS, pers. Comm. 2000).

Habitat:

The Cumberland bean inhabits small rivers and streams in fast riffles with gravel or sand and gravel substrate.

REPRODUCTION:

Males release sperm into the water column, which are taken in by females through their siphons during feeding and respiration. The eggs are fertilized and retained in specialized portion of the gills (marsupium) until the larvae (glochidia) fully develop. After the glochidia are released into the water, they attach and encyst on the gills and/or fins of a host fish. When metamorphosis (change to a young mussel) is complete, they drop to the streambed as juvenile mussels. Spawning likely occur in late summer through early fall; the glochidia are likely released in late spring and early summer (Schultz 1996). Two fish have been identified as host--fantail darter (Etheostoma flabellare) and striped darter (Etheostoma virgatum) (Layzer and Madison 1995).

REASONS FOR CURRENT STATUS:

The Cumberland bean, like most mussels in the Ohio River basin, has been directly impacted by impoundments, siltation, channelization, and water pollution. Reservoir construction is the most obvious cause of the loss of mussel diversity in the basin's larger rivers. Most of the main stem of both the Tennessee and Cumberland River and many of their tributaries are impounded. For example: over 2,300 river miles or about 20 percent of the Tennessee River and its tributaries with drainage areas of 25 square miles or greater are impounded (Tennessee Valley Authority 1971). In addition to the loss of riverine habitat within impoundments, most impoundments also seriously alter downstream aquatic habitat; and mussel populations upstream of reservoirs may be adversely affected by changes in the fish fauna essential to a mussel's reproductive cycle.

Coal mining related siltation and associated toxic runoff have adversely impacted many stream reaches. Numerous streams have experienced mussel and fish kills from toxic chemical spills, and poor land use practices have fouled many waters with silt. Runoff from urban areas has degraded water and substrate quality. Because of the extent of habitat destruction, the overall aquatic faunal diversity in many of the basins' rivers has declined significantly (USFWS 1984).

MANAGEMENT AND PROTECTION:

A recovery plan for the species was approved August 22, 1984 (USFWS 1984). The delisting (removing the species from the protection of the Endangered Species Act) objectives in the recovery plan call for: (1) restoring the viability of its populations in Buck Creek, the Rockcastle River, and the Little South Fork River in Kentucky (at the time the recovery plan was written, we did not know that a population still existed in the Hiwassee River); (2) reestablishing or discovering viable populations in two additional rivers; and (3) ensuring that there are no foreseeable threats to the continued existence of any of the populations. No downlisting (reclassification to a threatened species) criteria are given in the recovery plan.

Currently, we are developing artificial propagation and reintroduction technology for this and other federally listed mussels. We are considering reintroducing the Cumberland bean into historic habitats in two reaches in the Tennessee River basin. We are also working with various partners to improve habitat quality for existing populations.

AUTHOR:

Richard G. Biggins (see address below)

REFERENCES:

Layzer, J.B., and L.M. Madison. 1995. Microhabitat used by freshwater mussels and recommendations for determining their instream flow needs. Regulated Rivers:Research & Management 10:329-345.

Ortmann, A.E. 1915. Studies of naiades. Nautilus 29:63-143.

Ortmann, A.E. 1915. Studies of naiades. Nautilus 29:63-143.

Parmalee, P.W., and A.E. Bogan. 1998. The Freshwater mussels of Tennessee. The University of Tennessee Press, Knoxville, Tennessee. 328 pp.

Schulz, C. 1996. Time-of-year restrictions for rare mussels in Virginia. Unpublished document prepared by U.S. Fish and Wildlife Service, Virginia Field Office, White Marsh, Virginia. 4 pp.

Tennessee Valley Authority. 1971. Stream length in the Tennessee River Basin. Tennessee Valley Authority, Knoxville, Tennessee. 25 pp.

U.S. Fish and Wildlife Service. 1984. Cumberland bean Pearlymussel recovery plan. Atlanta, GA. 58 pp.

For more information contact: Mr. Richard G. Biggins U.S. Fish and Wildlife Service 160 Zillicoa Street Asheville, North Carolina 28801 Telephone: (828)258-3939 ext. 228

Map: Not known from NC, but likely in Hiwassee below Appalachia Dam, Cherokee County

Species Distribution from known occurrences. Species may occur in similar habitats in other counties.Green counties indicate observed within 20 years. Yellow counties indicate an obscure data reference to the species in the county. Red counties indicate observed more than 20 years ago.

For additional information regarding this Web page, contact John Fridell, in Asheville, NC, at john_fridell@fws.gov

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