Primary Factors Affecting Sturgeon Populations in the Southeastern United States: Fishing Mortality and Degradation of Essential Habitats

Atlantic and shortnose sturgeons are highly valued for their eggs (caviar) and flesh, but stocks of both species are depleted. The shortnose sturgeon is listed as an endangered species, and a long-term (multidecade) moratorium on fishing for Atlantic sturgeon is specified in the recently updated fishery management plan of the Atlantic States Marine Fisheries Commission. Thus, identification, protection, and enhancement of essential habitats are priority issues for management agencies. As anadromous (Atlantic) and nearly anadromous (shortnose) species, these sturgeons use a wide variety of habitats; variations occur latitudinally, seasonally, and among different life stages. Spawning habitats have been identified in two southeastern rivers for shortnose sturgeon, but to date no spawning sites have been verified for Atlantic sturgeon. Some life stages of both species (including young juveniles) concentrate in or are restricted to small portions of estuaries during summer. Deterioration of water quality (especially dissolved oxygen) appears to be degrading the nursery function of these summer refugia, creating a recruitment bottleneck. Protection of essential habitats, especially nursery/summer habitats, from humancaused dissolved-oxygen reductions and other impacts is critical. By-catch, primarily in riverine/estuarine gillnet and estuarine/marine trawl fisheries, appears to be the second major source of mortality for southern sturgeons. Reserves, or no-fishing zones, could protect populations by reducing or eliminating by-catch mortality. This protection would be especially valuable in high salinity foraging areas (used primarily during cool months) and during spawning migrations. Proposed management strategies aimed at conservation and restoration of sturgeon populations therefore focus on two areas: protection of essential habitats and establishment of reserves to provide protection from fishing gears that generate substantial sturgeon by-catch. Specific management recommendations were developed on a system-by-system basis. Two anadromous or semianadromous sturgeon (Acipenseridae) species occur on the Atlantic coast of North America, shortnose (Acipenser brevirostrum) and Atlantic (A. oxyrinchus oxyrinchus) sturgeons (Vladykov and Greeley, 1963). Previously ranging southward to northern Florida, all known populations of these species in the South have been depleted or extirpated. The shortnose sturgeon was listed as an endangered species in the United States in 1967. North Carolina’s fishery for Atlantic sturgeon was closed in 1991, South Carolina’s in 1985, Georgia’s in 1996, and Florida’s (east coast) in 1983. A multidecade moratorium on the Atlantic sturgeon fisheries in all states was imposed in 1998 by the Atlantic States Marine Fisheries Commission (ASMFC, 1998). Biologists have studied shortnose and Atlantic sturgeons in the Southeast for over two decades. In general these research efforts were initially focused on documenting the commercial fishery (e.g., Leland, 1968) but then expanded into the areas of artificial propagation (e.g., Smith et al., 1980), habitat associations (Hall et al., 1991), physiology (Jenkins et al., 1993), and sources of mortality (Collins et al., 1996). However, information in certain areas, including habitat utilization patterns, has been difficult to obtain because of 918 BULLETIN OF MARINE SCIENCE, VOL. 66, NO. 3, 2000 the relative scarcity of these fishes in most systems. It now appears that the ecology of southern sturgeons differs from that documented for northern populations. Further, although the directed fisheries have been closed for up to 25 yrs, at least some populations in the South continue to decline. Fishing mortality is believed to be an important factor in at least some localities (Collins et al., 1996), and recent evidence suggests that degradation of essential habitat is another major factor in the declines (Rogers and Weber, 1995a). Here, we synthesize the habitat-use information collected in river systems and nearshore waters in Georgia, South Carolina, and North Carolina; integrate existing by-catch information; and provide management recommendations on a system-by-system basis.