Waccamaw Silverside

Menidia extensa

Description

Waccamaw silverside (Menidia extensa ), also known as the skipjack or glass minnow, is a small, slender, almost transparent fish with a silvery stripe along each side. It has large eyes, and its jaw is angled sharply upward. Adults reach about 2.5 in (6.4 cm) in length.

Behavior

Waccamaw silverside is a lake dweller. It forms schools near the lake surface over shallow, dark-bottomed shoals. The species reaches sexual maturity at one year of age and spawns from April through July; the spawning peak is reached when water temperature is 68-72°F (20-22.2°C). Neither sex exhibits any physical characteristics of spawning conditions; most silversides die shortly after spawning, but a few may survive a second winter. Females may develop eggs as early as November and will ultimately produce about 150 eggs.

The adults feed on plankton, primarily crustaceans, at the surface in open water. Feeding occurs day and night, and no seasonal behavior has been noted. If waters are rough, the silverside remains close to shore. Silversides are an important food source for larger fishes in Lake Waccamaw.

Habitat

This silverside's habitat, Lake Waccamaw, is rich in its diversity of aquatic fauna and flora. The Waccamaw basin supports more unique nonmarine mollusks than any other locale in North Carolina. About 50 fish species, including many popular game fish, are found in the lake and its drainages. Many endemic species are of special interest to biologists.

The lake has a surface area of 9,000 acres (3,642 hectares) and an average depth of only 7.5 ft (2.3 m). Although fed by acidic swamp streams, it has a virtually neutral pH. This neutral condition of the water, unusual among North Carolina's coastal plain lakes, is believed to be caused by the buffering effect of the calcareous Waccamaw Limestone formation, which underlies the lake and is exposed on the north shore. Lake Waccamaw is a registered North Carolina Natural Heritage Area and has been proposed as a National Natural Landmark.

Distribution

Waccamaw silverside is endemic to North Carolina's Waccamaw basin. Lake Waccamaw's 85-sq mi (220-sq km) watershed is predominantly rural, dominated by small farms and forested tracts owned by large timber companies.

This species inhabits Lake Waccamaw (Columbus County) and its feeder stream, Big Creek, upstream to the County Road 1947 crossing. It is found downstream only during periods of high water, when individuals are washed over Lake Waccamaw Dam into the river (where they do not appear to survive). The state of North Carolina administers the lake and Lake Waccamaw State Park, a relatively undeveloped 273-acre (110.5-hectare) tract. With the exception of the state park, the remainder of the lake shoreline is privately owned.

Threats

Studies of Lake Waccamaw and its fish and mussel fauna, conducted between 1979 and 1981 and funded through the North Carolina Wildlife Resources Commission, indicated that increasing amounts of organic matter and agricultural chemicals are being washed into the lake. Silt from upstream logging activities has also increased. This slow but steady deterioration in water quality could threaten much of Lake Waccamaw's fauna and, particularly, the silverside, which uses the clean, sandy bottom of the lake for spawning.

Because the lake is so shallow, changes in the level of the water table would change the chemical balance and cause the fish's extinction. Non-native aquatic weeds are a potential threat to the stability of the water, as is pesticide use anywhere within the watershed.

Because the population virtually turns over each year, the silverside is vulnerable to catastrophic events that could prevent it from reproducing in a season and thereby wipe out the species. Although the silverside is a major food source for the larger fish in the lake, it has adapted to heavy predation, and this does not seem to be a major threat.

Conservation and Recovery

In 1987 the U. S. Fish and Wildlife Service (FWS) initiated a program of water-quality monitoring to compile baseline data for the lake so that serious problems could be discovered at an early stage. All federally funded activities that might affect the fish's habitat currently require a consultation with the FWS to limit harm to the silverside.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
Telephone: (404) 679-4000
http://southeast.fws.gov/

References

Cooper, J. E., ed. 1977. Endangered and Threatened Plants and Animals of North Carolina. North Carolina Museum of Natural History, Raleigh.

Davis, J. R., and D. E. Louder. 1969. "Life History of Menidia extensa. " Transactions of the American Fisheries Society 98 (3):466-472.

Lindquist, D. G. 1981. "Endemic Fishes of Lake Waccamaw." Kin'Lin 2 (5):38-41.

U.S. Fish and Wildlife Service. 1987. "Endangered and Threatened Wildlife and Plants; Determination of Threatened Status and Critical Habitat for the Waccamaw Silverside." Federal Register 52 (67):11277-11286.