Littlewing pearlymussel (Pegias fabula)
Federal Status: Endangered, Listed November 14, 1988
Description: The littlewing pearlymussel is small, rarely exceeding 1.5 inches (38 mm) in length and 0.5 inches in width. The shell’s outer surface (periostracum) is usually eroded, giving the shell a chalky appearance. When the periostracum is present, the shell is light green or dark yellowish with dark rays. The shells exhibit sexual dimorphism; females have an inflated posterior ridge and a more truncated posterior end. Much of the species’ life history is unknown. However, it is thought to be a winter breeder and reproduce like other freshwater mussels. Males release sperm into the water, which are taken in by females through their siphons during feeding and respiration. The fertilized eggs are retained in the gills until the larvae (glochidia) are fully developed. The glochidia are released into the water and must then attach and encyst on a fish host’s gill or fin. Here they transform into juvenile mussels and then drop off onto the stream bed. Greenside darters (Etheostoma blennioides) and emerald darters (E. baileyi) have been identified as host fish. The mussels specific food habits are unknown. However, adults are filter feeders and likely ingest food items similar to those consumed by other freshwater mussels (i.e., organic detritus, diatoms, phytoplankton, zooplankton, bacteria).
Habitat: It inhabits cool, clear, and relatively high gradient streams (of small to medium size) where it is sometimes found lying on a rocky stream bed in shallow water. However, it is more often hidden under large rocks.
Distribution: This once wide ranging species once inhabited numerous smaller tributaries of the upper Cumberland and Tennessee River basins in Alabama, North Carolina (Little Tennessee River, Swain County and Valley River, Cherokee County), Kentucky, Tennessee and Virginia. Currently, three populations may still survive in the Cumberland River system and three in the Tennessee River system, including a very small population in the Little Tennessee River, North Carolina.
Threats: Poor water quality and habitat conditions have led to the decline and loss of populations of the littlewing pearly mussel and threaten the remaining populations. Impoundments (dams), channelization projects, and in-stream dredging operations directly eliminate habitat. These activities also alter the quality and stability of remaining stream reaches by affecting water flow, temperature, and chemistry.
Agriculture (both crop and livestock) and forestry operations, roads, residential areas, golf courses, and other construction activities that do not adequately control soil erosion and water run-off contribute excessive amounts of silt, pesticides, fertilizers, heavy metals, and other pollutants that suffocate and poison freshwater mussels. The alteration of floodplains or the removal of forested stream buffers can be especially detrimental. Flood plains and forested stream buffers help maintain water quality and stream stability by absorbing, filtering, and slowly releasing rainwater. This also helps recharge groundwater levels and maintain flows during dry months.
Acid mine drainage and other water quality impacts associated with gas, oil, and mineral extraction also contribute to imperilment.
N.C. Natural Heritage Program. 2001. Guide to Federally Listed Endangered and Threatened Species of North Carolina: Littlewing pearlymussel. NC Department of Environment and Natural Resources, Raleigh, NC. Page 63.
U.S. Fish and Wildlife Service. 1989. Littlewing pearlymussel Recovery Plan. Atlanta, GA. 29 pp.
Bob Butler, Fish and Wildlife Biologist, 828-258-3939 ext. 235
Species profile revised on October 4, 2011.