American shad are the largest members of the family Clupeidae (which includes herrings, alewives, menhaden and sardines) in the United States. Clupeids are generally deep-bodied, silvery fishes that have relatively large, easily-shed scales and often associate in large schools. They have rough scales, or scutes, along the ventral edge of the body, forming a "saw-belly," a single dorsal fin midway along the body, and a deeply forked caudal fin. In addition, Clupeids have no lateral line and lack spines on all their fins. American shad are a metallic green color dorsally with silvery sides and have a dark shoulder spot behind the gill cover, sometimes followed by a series of smaller spots.
Habitat and Biology
American shad are distributed from the Gulf of St. Lawrence to Florida and are most abundant between Connecticut and North Carolina. They are anadromous; that is, they migrate upriver from brackish water to spawn. Upstream migration coincides with favorable water temperatures and typically begins in the spring. In South Carolina, adult migration to freshwater begins in January, peaks in February and March, and ends in April. Similar to salmon, American shad return to the same tributary system where they were hatched.
Spawning usually occurs in tidal and nontidal freshwater areas over shallow flats, sometimes hundreds of miles inland, where currents are strong enough to keep the eggs suspended in the water. Usually, American shad travel far enough upstream that the drifting eggs hatch before reaching saltwater. Males are 3-4 years old and females are 4-5 years old at sexual maturity. They spawn only once or twice (rare in South Carolina) during their life. During spawning, females are followed by 1-3 males who fertilize the eggs as they are released into the water. Each female may release between 100,000 and 700,000 eggs over the spawning season. The eggs sink slowly and drift along the bottom of the river, hatching within 4-6 days. Larval and juvenile shad move downriver towards the ocean but remain in the rivers and estuaries until the following spring, when they move into the ocean and join the adult population. They remain there in large schools during fall and early winter. However, not all adults survive the spawning event. In northern latitudes, where water temperature changes gradually and shad do not migrate far upstream, large numbers of adults find their way back to the ocean and survive to spawn the following year. In the southern part of their range, however, water warms up rapidly in the spring and shad tend to move well upriver to find suitable spawning sites. Consequently, less than 10% of spawning adults survive the migration back out to sea. Juveniles spend an average of four years along the Atlantic coast before they undertake their first spawning migration. This species lives to be 5 to 7 years old.
American shad are primarily planktivores. Juvenile shad feed on small invertebrates, insects, fish eggs, and algae. Adults use their gill rakers (comb-like structures on the gill arches) to filter small planktonic animals from the water for food during the riverine and oceanic phases of their life cycle. Adults do not feed during the upstream migration to their spawning areas.
American shad are important commercial and game fish. Fisheries for American shad have existed along the Atlantic coast since the nineteenth century, but have been declining since then due to overfishing and degradation of spawning habitat. In South Carolina, the shad fishery is the single most important finfish fishery. Since 1987, there has been a continuous decline in numbers of shad landed; however, landings in 1996 were considerably higher than in previous years. Female shad, referred to as roe shad, are prized for their egg mass (roe), which is considered a delicacy. Male shad, called bucks, are popular for their meat. In South Carolina, a recreational fishery for American shad exists exclusively in fresh water where fish are taken with dip nets or with artificial lures during their spawning migration.
The once huge populations of shad started to decline in the mid nineteenth century due to dam construction, pollution, and overfishing. However, stocks have shown some recovery in recent years. In the Edisto, Ashepoo and Combahee Rivers, however, shad populations are not as healthy as they were in years past. This species is currently not threatened or endangered.
MacKenzie, C., L.S. Weiss-Glanz, and J.R. Moring 1985. Species profiles: Life histories and environmental requirements of coastal fishes and invertebrates (Mid-Atlantic): American shad. Biological Report 82(11.37). U.S. Department of Interior, Fish and Wildlife Service, Division of Biological Services, Washington, DC.
Moore, C. 1996. Review of the 1995 finfish season. South Carolina Department of Natural Resources, Charleston, SC.
Murdy, E.O., R.S. Birdsong, and J.A. Musick. 1997. Fishes of the Chesapeake Bay. Smithsonian Institution Press, Washington, DC.
Walburg, C.H. and P.R. Nichols. 1967. Biology and management of the American shad and status of the fisheries, Atlantic coast of the United States, 1960. Special Scientific Report - Fisheries No. 550. U.S. Department of Interior, Fish and Wildlife Service, Washington, DC.