Waccamaw silverside (Menidia extensa)
Federal Status: Threatened, Listed April 8, 1987
Description: The Waccamaw silverside, also known as skipjack or glass minnow, is a small (growing to about 2.5 inches), slim, almost transparent fish with a silver lateral stripe along each side. Its body is laterally compressed, the eyes are large, and the jaw is sharply angled upward. There are two widely separated dorsal fins; the first has thin spines. It may often be seen jumping out of the water.
The Waccamaw silverside spawns in open water near the shoreline from March through July, peaking when water temperatures are between 68-72˚F. Fully developed larvae form small isolated schools by early May. No parental care of the young has been noted. The silversides reach sexual maturity by the following spring, spawn, and then shortly thereafter most of the adults die off. A few may survive a second winter.
This species is a surface-feeder and travels in schools. Food sources include zooplankton, particularly cladocerans (i.e., microcrustaceans). Silversides forage in areas of shallow, high quality clear, open water over clean, dark sand substrate with no vegetation.
Habitat: Lake Waccamaw is a natural lake with an approximate surface area of 8,934 acres and an average depth of 7.5 feet. Although it is fed by acidic swamp streams, the lake has a virtually neutral composition. This neutral condition, 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. The Waccamaw silverside inhabits open water throughout the lake, where schools are commonly found near the surface over shallow, dark-bottomed areas.
Distribution: Known only from Lake Waccamaw and the upper Waccamaw River in Columbus County, North Carolina, the silverside is found in the upper Waccamaw River only during periods of high water and is not a permanent resident. Lake Waccamaw (not to be confused with the town of Lake Waccamaw) is the property of the State of North Carolina and is administered by the North Carolina Department of Environment and Natural Resources' Division of Parks and Recreation. The species' population is estimated to be in the millions.
Threats: Runoff and siltation from nearby logging practices, land use changes such as stream channelization and bridge/road construction, and watershed development are the top threats to the Waccamaw silverside. Water quality issues (including increased temperature and nutrient enrichment) from pesticide/herbicide use and wastewater discharges are also prevalent threats. Because the Waccamaw Silverside has an annual life cycle, it is susceptible to rapid extinction given reproductive failure for even a single year. Additionally, the recent invasion of the lake by the Brook Silverside (Labidesthes sicculus), is of concern.
N.C. Natural Heritage Program. 2001. Guide to Federally Listed Endangered and Threatened Species of North Carolina: Waccamaw silverside. NC Department of Environment and Natural Resources, Raleigh, NC. Page 51.
U.S. Fish and Wildlife Service. 1993. Recovery Plan for Waccamaw silverside (Menidia extensa). Atlanta, GA. 24pp.
U.S. Fish and Wildlife Service. 2010. Waccamaw silverside (Menidia extensa) 5-Year Review: Summary and Evaluation. Raleigh, NC.
Sarah McRae, Fish and Wildlife Biologist, 919-856-4520 ext. 16