Shortnose sturgeon Acipenser brevirostrum (family Acipenseridae) are considered the most endangered of the North American sturgeons (Birstein 1993). Like many other sturgeon species, shortnose sturgeon are well-adapted to the broad range of environmental variables that are found along the latitudinal distribution of their range. Historically, shortnose sturgeon occupied all major Atlantic coast rivers of North America (Vladykov and Greeley 1963; NMFS 1998), from the Saint John River, Brunswick, Canada, to the Saint Johns River, Florida (Vladykov and Greeley 1963; Kynard 1997). However, a review by Kynard (1997) suggests that the historical range of shortnose sturgeon has been greatly diminished, and as few as 16 rivers are currently thought to host populations of this once abundant species (Kynard 1997). Nineteen river populations of shortnose sturgeon have been recommended as distinct population segments (DPS; NMFS 1998). Of these, at least nine are significantly discrete from their neighboring populations (Wirgin et al. 2010). Shortnose sturgeon populations are notably small or entirely absent in rivers located between the Delaware River, New Jersey, and the Cape Fear River, North Carolina (Kynard 1997). The largest populations occur in the northern rivers, particularly the Hudson River, New York (>38,000 adults; Bain et al. 1995), the Saint John River, Canada (~18,000 adults; Dadswell 1979), and the Delaware River, New Jersey (~13,000 adults; O’Herron et al. 1993). The southern extent of their range is currently the Altamaha River, Georgia (~2,000 adults; Peterson and Bednarski 2013).
The timing and extent of shortnose sturgeon spawning migrations are not well understood, particularly in southern rivers, yet this information has been identified as a key information gap in the federal recovery plan for the species (NMFS 1998). Studies employing mark-recapture and biotelemetry have been effective in characterizing the movements and habitat use of other diadromous sturgeon species (e.g., Foster and Clugston 1997; Fox et al. 2000), yet relatively few studies have examined the spawning migrations of shortnose sturgeon. Synthesis of the available literature suggests adults typically spend most of the year near the freshwater–saltwater interface of their natal rivers, moving upstream to spawn in the winter and spring when water temperatures reach 8–12 °C (Hall et al. 1991; Rogers and Weber 1995). Successful spawning has been documented at 12–18 °C (Dadswell et al. 1984; Kynard 1997). At the northern end of their range, adults have been documented overwintering near spawning sites (Bain 1997) as part of a two-step spawning migration (Bemis and Kynard 1997); however, in southern rivers, shortnose sturgeon typically exhibit a one-step migration (Hall et al. 1991; Rogers and Weber 1995). Although Rogers and Weber (1995) suggested that both fall and spring migrations occur in the southern populations, fall migrations have been documented only in populations north of Cape Hatteras. Environmental cues for spawning are not well understood; however, most research suggests that moderately high flows are favorable for spawning (Dadswell 1979; Taubert 1980; Buckley 1982, Buckley and Kynard 1985; Kynard 1997; Peterson and Bednarski 2013).
