|Listed||March 17, 1993|
|Family||Unionidae (Freshwater Mussel)|
|Description||Small to medium mussel with an oval, moderately inflated dark reddish-brown shell with closely spaced, dark growth lines.|
|Habitat||Gravel riffles in streams.|
|Reproduction||Female stores sperm in gills; glochidia are released into the stream after hatching.|
|Threats||Impoundments, gravel and mining, water pollution.|
The dark pigtoe, Pleurobema furvum, is a small to medium-sized mussel, growing to lengths of 2.4 in (6 cm). The shell is oval and moderately inflated. Beaks are located in the anterior portion of the shell. The posterior ridge is abruptly rounded and terminates in a broadly rounded, subcentral, posterior point. The periostracum is dark reddish-brown with numerous and closely spaced, dark growth lines. The hinge plate is wide and the teeth are heavy and large, especially in older specimens. The nacre (inner shell surface) approaches white in the umbos, and is highly iridescent on the posterior margin.
See the Upland Combshell (Epioblasma metastriata ) entry.
The dark pigtoe inhabits high-quality lotic habitats with stable gravel and sandy-gravel substrates. Little else is known about the habitat requirements of this species.
The habitat of the glochidia is initially in the gills of the female, then in the water column, and finally attached to a suitable host fish. Habitat associations or requirements for the juvenile stage are unknown.
The historic distribution of this species was probably limited to the Black Warrior River system, Alabama, above the fall line.
Specimens were found in tributaries of the Black Warrior (Sipsey Fork, North River) in 1986, 1991, and 1992.
Habitat modification, sedimentation, and water quality degradation represent the major threats to this species. These freshwater mussels do not tolerate impoundments. More than 1,000 mi (1,609 km) of large and small river habitat in the Mobile River drainage has been impounded for navigation, flood control, water supply, and/or hydroelectric production purposes. During the construction and dredging of impoundments, some riverine mussels are killed. Additionally, impoundments lead to the accumulation of sediments that can suffocate mussels, a reduction in food and oxygen due to the reduction in water flow, and the local extirpation of host fish. Other forms of habitat modification such as channelization, channel clearing and desnagging, and gravel mining result in streambed scour and erosion, increased turbidity, reduction of ground-water levels, sedimentation, and changes in the aquatic community structure. Sedimentation may cause direct mortality by deposition and suffocation and eliminate or reduce recruitment of juvenile mussels. Suspended sediments can also interfere with feeding. Activities that historically caused sedimentation of streams and rivers in the drainages where this mussel occurs include channel modification, agriculture, forestry, mining, and industrial and residential development.
Other types of water quality degradation from both point and nonpoint sources affect this species. Stream discharge from these sources may result in decreased dissolved oxygen concentration, increased acidity and conductivity, and other changes in water chemistry that may affect the mussels and/or their fish hosts. Point sources of water quality degradation include municipal and industrial effluents, and coalbed methane-produced water discharge. Nonpoint sources include runoff from cultivated fields, pastures, private wastewater effluents, agricultural feedlots and poultry houses, active and abandoned coal mine sites, and highway and road drainages.
Conservation and Recovery
Actions needed for the recovery of freshwater mussels include: (1) Conduct population and habitat surveys to determine the status and range of the species. (2) Determine specific threats to the species and minimize or eliminate these threats. (3) Identify essential habitat areas in need of protection. Make use of land agreements, mussel sanctuaries, scenic river status, and land acquisition. (4) Introduce individuals back into the historic range, as it is unlikely that the species will recover unless new populations are established. Methods to accomplish this might include introduction of adult/juvenile mussels, glochidia-infected host fish, and artificially cultured individuals. (5) Control the incidental or illegal take of mussels by commercial and noncommercial collecting.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
U. S. Fish and Wildlife Service
Daphne Ecological Services Field Office
P.O. Box 1190
Daphne, Alabama 36526-1190
Telephone: (334) 441-5181
Fax: (334) 441-6222
Thorp, J. H., and A. P. Covich. 1991. Ecology and Classification of North American Freshwater Invertebrates. Academic Press, San Diego.
U. S. Fish and Wildlife Service. 17 March 1993. "De-termination of Endangered or Threatened Status for Eight Freshwater Mussels and Threatened Status for Three Freshwater Mussels in the Mobile River Drainage." Federal Register 58 (50): 14330-14340.