Quadrula cylindrica strigillata
|Listed||January 10, 1997|
|Description||A freshwater, bivalve mollusk.|
|Habitat||Medium-to large-sized rivers with clean, flowing water.|
|Food||Filter-feeds on phytoplankton, tiny zooplankton, and organic detritus.|
|Reproduction||Female siphons male spawn and fertilizes eggs in her gills; the larvae are parasitic on fish, and later metamorphose into the sedentary adult stage.|
|Threats||Habitat destruction by impoundment, and pollution by siltation, nutrients, and other chemicals originating with coal mining, agriculture, and other sources.|
The rough rabbitsfoot mussel (Quadrula cylindrica strigillata ), described in 1898, has an elongated, heavy, rough textured, and yellow-to-greenish-colored shell. The shell's surface is covered with green rays, blotches, and chevron patterns. The inside of the shell is silvery to white with an iridescence in the posterior area of the shell. This mussel is considered threatened by the State of Virginia, and it is deemed a species of special concern in Tennessee.
This tachytictic species has been observed spawning from May (when water temperature reached 68 to 71.6°F (20 to 22°C) through June. Fertilization success was high (95%) through late June, but by July only unfertilized ova were found. Unlike most amblemines, 65% of 82 gravid females examined utilized only the outer demibranchs as marsupia. Gravidity rates of from 30-60%, peaking in late May, then gradually declining have been documented. Females release lanceolate-shaped whitish to reddish brown conglutinates (0.4 in [10 mm] long) that contain 375-505 semicircular-shaped glochidia. Fecundity has been estimated at 115,000 embryos per female. Estimated age of the females studied was 10-22 years. Three cyprinid host fish species have been identified—the whitetail shiner, spot fin shiner (C. spiloptera), and bigeye chub (Hybopsis amblops). Infestation rates ranged from as few as five to 10 glochidia on individual fishes. Transformation took from 13-23 days, at 68.9-71.4°F (20.5 to 22°C).
This species inhabits medium-sized to large rivers m moderate to swift current but often exists in areas close to, but not in, the swiftest current. It is reported to live in silt, sand, gavel, or cobble in eddies at the edge of midstream currents and may be associated with macrophyte beds.
Historically, this mussel was restricted to the upper Tennessee River basin in the Clinch, Powell, and Holston river systems. Only three populations of limited distributions and scant numbers still persist in these three systems. These occurrences are in the Powell River, Lee County, Virginia and the Tennessee counties of Claiborne and Hancock counties; in the Clinch River, Scott County, Virginia and Hancock County, Tennessee; the Clinch River tributary Copper Creek, Scott County, Virginia; and North Fork Holston River, Washington County, Virginia.
The rough rabbitsfoot populations in the lower Clinch, Powell, and Holston river systems were extirpated by reservoirs. The decline of the species throughout the rest of its range was likely due to the adverse impacts of coal mining, poor land-use practices, and pollution, primarily from nonpoint sources. The population centers that remain are so limited that they are vulnerable to extirpation from random episodes such as toxic chemical spills.
Conservation and Recovery
The rough rabbitsfoot only survives in localized portions of the Powell River, Clinch River, Copper Creek (a Clinch River tributary), and North Fork Holston River. It is crucial that its few critical habitats are protected against the development of new dams or impoundments, from acid drainage associated with coal mining, from sedimentation and nutrient inputs associated with agricultural land-use, and from spills of petroleum or other toxic chemicals. The surviving populations of the rough rabbitsfoot should be monitored, and research undertaken into its biology and ecological needs, including work on its propagation and reintroduction techniques.
U.S. Fish and Wildlife Service
Asheville Ecological Services
160 Zillicoa Street
Asheville, North Carolina, 28801-1082
Telephone: (828) 258-3939
Fax: (828) 258-5330
U.S. Fish and Wildlife Service. 10 January 1997. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Cumberland Elktoe, Oyster Mussel, Cumberlandian Combshell, Purple Bean, and Rough Rabbitsfoot." Federal Register 62 (7): 1647-1658.