Southern Pigtoe

Pleurobema georgianum

Description

The southern pigtoe, Pleurobema georgianum, is a small to medium-sized mussel that is generally less than 2.4 in (6 cm) in length. The shell is elliptical to ovate and somewhat compressed. The posterior slope is smoothly rounded. The pseudocardinal teeth are small but well-developed, and the nacre (inner shell surface) is white. The periostracum is yellow to yellow-brown. Growth lines are numerous and may be dark brown. Small specimens may have green spots at the growth lines along the posterior ridge and near the umbo.

Behavior

See the Upland Combshell (Epioblasma metastriata ) entry.

Habitat

The southern pigtoe inhabits high-quality lotic habitats with stable gravel and sandy-gravel substrates. Little else is known about the habitat requirements of this species.

Distribution

The southern pigtoe's historic range apparently was restricted to the Coosa River system. Museum specimens of this species were collected from Coosa River, Shoal Creek, and the Chatooga and Conasauga Rivers.

Live specimens were collected from this river system in 1974, 1987, and 1990. One fresh dead specimen was collected from the Conasauga River in 1991. A 1991 survey did not find any live specimens in the Coosa River drainage.

Threats

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 groundwater 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.

About 230 mi (370 km) of the Coosa River have been impounded for hydropower by a series of six dams. Water quality degradation caused by textile and carpet mill wastes led to the loss of several known mussel communities in several streams of this river system.

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.

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
Daphne Ecological Services Field Office
P.O. Box 1190
Daphne, Alabama 36526-1190
Telephone: (334) 441-5181
Fax: (334) 441-6222

U. S. Fish and Wildlife Service
Cookeville Ecological Services Field Office
446 Neal St.
Cookeville, Tennessee 38501-4027
Telephone: (931) 528-6481
Fax: (931) 528-7075

Reference

U. S. Fish and Wildlife Service. 17 March 1993. "Endangered Status for Eight Freshwater Mussels and Threatened Status for Three Freshwater Mussels in the Mobile River Drainage." Federal Register 58 (50): 14330-14340.