American Shad Alosa sapidissima
Hickory Shad Alosa mediocris
Blueback Herring Alosa aestivalis
Contributor (2005): John W. McCord
Reviewers (2012): Allan Hazel, Bill Post, Brock Renkas, Corbett Norwood, Jarrett Gibbons, & Elizabeth Miller
Taxonomy and Basic Description
The American shad, Alosa sapidissima (Wilson 1811), belongs to the herring family, Clupeidae. It is the largest Atlantic Coast member of the family, with females in South Carolina reaching about 66 cm (26 inches) total length (TL). Sexually mature female American shad, often called roe shad because of the large, highly prized ovaries, rarely attain more than 3 kg (7 pounds). Mature male shad, or bucks, are generally smaller than females, rarely exceeding 2 kg (4.5 pounds). American shad, like other alosines and most members of the Clupeidae, are laterally compressed, with relatively large scales. Scales on the midline of the underside form sharp scutes that produce a saw-toothed ridge. Coloration is dark bluish, greenish or bronze on the back, silvery on the sides and white below, and varies depending on color and turbidity of water. The mouth is near the midline of the snout, and a series of several dark spots usually extends backward to below the dorsal fin from near the operculum and pectoral fin. The fins are dark and without spines and the tail is deeply forked.
Most shad spawning in South Carolina are between three and six years old, with males averaging about a year less than females. Shad migrate several hundred miles or kilometers inland in large river basins and arrive in South Carolina from mid-January through mid-May. Peak spawning activity is water temperature dependent, but generally occurs during March and April. Shad are sequential or batch spawners, with groups of eggs released as the fish move upriver. Eggs are semi-buoyant and drift in the water column when flows and depth are appropriate. Eggs usually hatch within a few days into tiny larvae that soon transform into juveniles. Juveniles closely resemble adults, but are generally more silvery, typically reaching only 10 to 12 cm (4 to 5 inches) TL before they move toward the ocean to complete growth and maturation, usually after about one year of development in the rivers, sounds and bays. However, some juveniles remain within the Santee-Cooper Lakes at least until the summer of their second year, presumably because of difficulties in using out-migration options, some of which are not functional when outflows are limited due to low lake levels (D. Cooke, SCDNR, pers. comm., 2005).
Juvenile American shad feed primarily on small invertebrates, including insect larvae and zooplankton. Adult shad prefer larger zooplankton and rarely feed while in freshwater as they are thought to die after their initial spawning run. Both outmigrating juveniles and adults that survive spawning generally move into the Atlantic and migrate into coastal areas of Maine and southern Canada, where they mingle with shad from all Atlantic populations and prey primarily on abundant zooplankton. By fall, the vast conglomerate population migrates south and overwinters off the Mid-Atlantic States. Sexually mature fish then disperse up or down the coast to their respective rivers as late winter and spring water temperatures moderate and become ideal for spawning (Neves and Depres 1979; McCord et al. 1987).
he hickory shad, Alosa mediocris (Mitchill 1814), also belongs to the herring family, Clupeidae. It is smaller than the American shad, with females in South Carolina reaching about 55 cm (22 inches) TL. Sexually mature female hickory shad, often called roe jacks, also carry highly prized ovaries, but rarely attain more than 2 kg (4.5 pounds). Adult male hickory shad are usually smaller than females, rarely exceeding 1 kg (2.2 pounds). Hickory shad are shaped much like American shad and also have large scales. General coloration is greenish or bronze on the back, silvery on the sides and white below. A small, indistinct spot can usually be seen beneath each lateral scale. The mouth is nearer the top of the snout than in American shad. Several dark spots usually extend backward to below the dorsal fin from near the operculum and pectoral fins. The fins are dark and spineless and the tail is deeply forked. Juvenile hickory shad resemble adults, but are less distinctively marked. Juveniles usually emigrate from inland habitats by early winter at approximately 15 cm (6 inches) TL. Larval and smaller juvenile fishes are primary dietary items for juvenile hickory shad.
Adult hickory shad migrate and spawn earlier than American shad and blueback herring; hickory shad move inland from December through mid-April. Peak spawning for hickory shad in South Carolina is during February and early March. Hickory shad typically spawn along channel edges of tidally influenced freshwater river reaches, usually within 80 km (50 miles) of the ocean. Otherwise, the general life cycle is similar to the American shad. However, most hickory shad are believed to survive after spawning, presumably because they feed primarily on small fishes that are generally available in inland habitats. Hickory shad apparently concentrate farther south, principally from Delaware Bay to New England coastal inlets, where they feed primarily on small fishes (ASMFC 1999).
The blueback herring, Alosa aestivalis (Mitchill 1814), is the smallest alosine in the Southeast. Adult female blueback herring in South Carolina reach about 31 cm (12 inches) TL and weigh 0.3 kg (0.7 pounds); while the slightly smaller mature males approach 28 cm
11 inches) TL and weighs 0.27 kg (0.6 pounds). Adult blueback herring are shaped and marked much like American shad. Juveniles, which usually emigrate to the ocean by mid-winter, resemble tiny adults and are about 10 cm (4 inches) TL.
Timing of inland migration, spawning and development of blueback herring closely follows patterns for American shad. However, blueback herring typically spawn in freshwater marshlands or small tributaries. Small zooplankton constitute much of the juvenile diet. Post-spawning survival rates are not well known for blueback herring, but probably exceed those for American shad. Migratory routes and timing of blueback herring are similar to those for American shad. During the spawning migration, herring move inland at distances intermediate to characteristics described for hickory and American shad. The distance that herring move upriver may be partly dependent upon the availability of habitats with suitable substrates for egg adhesion nearer the coast (Loesch and Lund 1977)
During all life stages, alosines contribute greatly to the dynamics of food chains in freshwater, estuarine or marine habitats (Facey et al. 1986; MacKenzie et al. 1985; Weiss-Glanz et al. 1986). While at sea, alosines are prey for many species including sharks, tunas, mackerel and marine mammals, including porpoises and dolphin (ASMFC 1999; Weiss-Glanz et al. 1986). In fresh and brackish waters, both adult and juvenile alosines are consumed by American eel and striped bass (Facey et al. 1896; Mansueti and Kolb 1953; Savoy and Crecco 1995; Walburg and Nichols 1967). Juvenile herring are high quality prey for largemouth bass (Micropterus salmoides); accelerated growth of young bass occurs when herring consumption is high (Yako et al. 2000). Tissues taken from predatory fish in tidal freshwaters following the residency of migrating alosines had between 35 and 84 percent of their carbon-biomass derived from marine sources (Garman and Macko 1998; MacAvoy et al. 2000). East Coast alosines, particularly populations in the southeast where post-spawning mortality is highest, likely provide nutrients and carbon into riverine systems, similar to nutrient dynamics provided by salmon in the Pacific Northwest (Freeman et al. 2003). For example, the James River, Virginia may have received annual biomass input from alosines of 155 kg/ha (138 pounds/acre) before dams blocked migrations above the fall line (Garman 1992).
More than 40 species of birds and mammals congregate to feed on migrating anadromous fish in southeastern Alaska (Willson and Halupka 1995; Willson et al. 1998). Similar relationships likely occur between East Coast alosines and birds and mammals. Fish-eating birds like osprey (Pandion haliaetus) and bald eagle (Haliaeetus leucocephalus), prey upon alosines (pers. obs.) and may have evolved their late winter and spring nesting strategies in response to the availability of food resources supplied by pre and post-spawning alosines. In addition, nutrients released from carcasses of post-spawning alosines can substantially subsidize aquatic food webs by stimulating productivity of bacteria and aquatic vegetation (Kline et al. 1993; Richey et al. 1975), thereby stimulating the assimilation of marine-derived nutrients into aquatic invertebrates and fish (Bilby et al. 1996).
American shad, hickory shad and blueback herring are experiencing coastwide reductions in all stocks compared to historical populations (ASMFC 1985; ASMFC 1999). Current spawning runs of east coast North American shad populations have been reduced to 10 percent of historical sizes and have been extirpated from over 4,000 km (2,500 miles) of riverine habitat (Limburg et al. 2003). Several alosine stocks (riverine populations) are of unknown status because no directed studies have been conducted. Hickory shad population status is very poorly known for South Carolina and historical data are virtually absent. The species is apparently not plentiful anywhere within South Carolina. Populations of blueback herring in the Waccamaw-Pee Dee and Santee-Cooper are presumably secure, though undoubtedly reduced from historical levels predating dams. Blueback herring populations for other drainages are perceived to be of poorer status, and perhaps absent. Because of these declines in current stocks, the Atlantic States Marine Fisheries Commission made the additions of Amendments 2 and 3 to the Shad and River Herring Fishery Management Plan. These amendments state, among other things, requires that participating states must submit and have approved river specific sustainability plans for American shad and blueback herring. These plans must demonstrate, by using targets, how fisheries are sustainable. If sustainability targets are not met or states cannot demonstrate a given river is sustainable, then fisheries on that river must be closed. South Carolina submitted both sustainability plans (shad and herring) in 2010 and 2011 respectively. Both plans have been accepted by the ASMFC shad and herring board. Sustainability targets, using 75% of the mean in most cases, were set for all rivers where fisheries occur and those systems where no fishing occur or no data were available have been or will be closed. In addition, On August 5 2011, the Natural Resources Defense Council submitted a petition to NOAA requesting that the agency consider river herring (alewife and blueback herring) for listing under the Endangered Species Act. In response, NOAA is required to make a determination of whether alewife and blueback herring should be listed as endangered or threatened, or not at all.
POPULATION DISTRIBUTION AND SIZE
American shad occurs along the Atlantic coast from Bay of Fundy, Canada to St. Johns River, Florida. The historical range of hickory shad is very similar, from Bay of Fundy, Canada to Tacoma River, Florida, but current distribution is uncertain with known occurrence as far north as Connecticut (ASMFC 1999). Blueback herring are distributed from Nova Scotia to northern Florida, though they are most abundant from the Chesapeake Bay and south (Scott and Scott 1988). In South Carolina, all three species are presumed to occur as unique populations by coastal river system with a minimum of eight populations (presumably for all three species): Waccamaw-Pee Dee, Santee-Cooper, Ashley, Edisto, Ashepoo, Combahee, Coosawhatchie and Savannah drainage basins. Relatively unique populations likely occur in the major tributaries within the Waccamaw – Pee Dee basin, including Waccamaw, Little Pee Dee, Great Pee Dee, Lynches, Black and Sampit Rivers.
Historical population estimates are nonexistent, but historical distribution records (USFWS 2001) and anecdotal information on abundance strongly indicates that all populations of alosines in South Carolina are reduced compared to historical levels (early 20th century and earlier). American shad and, to a lesser extent, blueback herring historically ascended large river basins of the state (Waccamaw-Pee Dee, Santee and Savannah) well inland of the fall line and into North Carolina and Georgia (USFWS 2001).
Trends in American shad stocks have been primarily monitored by observations in commercial gill-net fishery catch rates since 1979. Based on these trends, American shad populations in Waccamaw-Pee Dee Basin and Savannah River have remained relatively stable and healthy over the past 25 years, though almost certainly below levels of a century past (McCord 2003). Fortunately, the lowermost dams on both Savannah and Waccamaw–Pee Dee Basins are approximately 320-river km (200 mi) from the ocean. However, historical alosine spawning migrations in these basins extended beyond the point of these dams (USFWS 2001). Anecdotal information indicates that both blueback herring and hickory shad occur in the Savannah in small populations. Dam-locked populations of blueback herring now occur in several reservoirs, including Lakes Jocassee and Hartwell. Hickory shad may have also become dam-locked in Savannah Basin reservoirs, but spawning has not been recorded (D. Cooke, SCDNR, pers. comm. 2005).
Among the ACE Basin rivers, Edisto River’s shad populations apparently declined dramatically through the early 1990s, with overfishing indicated as a primary cause (McCord and Ulrich 1991). Directed management through restrictive commercial fishery regulations enacted in 1993 and a decline in the number commercial fishers has apparently promoted an increased population as indicated by improved catch rates for gill-net fishers (McCord 2003). However, this stock is considered to be in guarded condition until additional monitoring can better indicate stock status (McCord 2003). The Combahee River shad population was categorized as substantially declined in the late 1990s, presumably from an extended period of overfishing (McCord and Ulrich 1994; McCord 2003). Restrictive commercial fishery guidelines were established in 2000 and should allow for growth of this stock. The status of the American shad population in Ashepoo River, the smallest of the ACE Basin rivers, is unknown. Relatively few records exist for either hickory shad or blueback herring in the ACE Basin. Both species are presumed to occur in very small populations.
Both Ashley and Coosawhatchie Rivers are small, coastal plain drainages that historically supported limited commercial American shad fisheries. The current status of these populations is also unknown. Commercial fishing activity has been restricted substantially for the Ashley and banned for the Coosawhatchie since fishery laws were revised in 2000 in accordance with Act #245 of the 2000 South Carolina General Assembly. The status of alosine stocks in these small rivers, including whether any hickory shad and blueback herring are present, is unknown.
The Santee-Copper American shad population has grown substantially since 1985 and is among the largest on the Atlantic coast, with the population likely approaching one million adults annually (McCord 2003). The blueback herring population was estimated to average over six million in the five years following the rediversion of flows (Cooke and Leach 2003) and may be larger now following almost 20 years of increased flows and fish passage. Both American shad and blueback herring populations in the Santee-Cooper Basin have responded well to existing fish passage protocols and increased flows.
Hickory shad population status is poorly understood; however, based on anecdotal observations, the Santee-Cooper population is among the largest in the state, despite very low passage numbers recorded at St. Stephen Dam (Cooke and Leach 2001). All three alosines are thought to occur as secure stocks in the Waccamaw-Pee Dee Basin.