Habitat Utilization and Biological Characteristics of Adult Atlantic Sturgeon in Two South Carolina Rivers

Abstract

Thirty‐nine adult Atlantic sturgeon Acipenser oxyrinchus oxyrinchus (136–234 cm total length) were caught in gill nets fished at historical sturgeon‐fishing locations in the Combahee and Edisto rivers (South Carolina) during spring and fall 1998. All fish were tagged (with passive integrated transponders and darts), and radio and acoustic transmitters were surgically implanted in 29 fish. When possible, gonad biopsies were taken for sex and maturity‐stage determination. Locations of telemetered fish were determined several times per week from airplanes (radio) and boats (radio and acoustic). Nominal ages, based on microscopic examination of pectoral spine cross‐sections, ranged from 7 to 20 years. Of the 28 fish for which sex was definitively ascertained, 21 (aged 7–15) were male and 7 (aged 15–20) were female. All fish moved out of the rivers during the period extending from October to November. Twelve fish returned the following spring (most in March), and many took up residence at the same sites utilized the previous year. Fall and spring spawnings were documented based on histological examination of gonad biopsies and directed upriver movements of fish during both seasons. Habitats used during summer were diverse and included the lower and upper estuaries, tidal freshwater, river, and perhaps even the ocean, as some fish left the system entirely. One male was captured in two successive springs and was in spawning condition (running ripe) both years.

Estimating Sturgeon Abundance in the Carolinas Using Side‐Scan Sonar

“…Generally it is thought that juvenile Atlantic Sturgeon stay in riverine areas year-round, while adults move into rivers during spring for spawning but move out into marine environments during other times (Smith 1985;Bain 1997). Our study and others (Moser and Ross 1995;Collins et al 2000) have observed adult and subadult Atlantic Sturgeon in riverine areas during summer. In an ongoing study in the Roanoke RiverAlbemarle Sound system, most sonic-tagged adult Atlantic Sturgeon were present during the summer months (two of three in 2011, five of five in 2012, and three of six in 2013), not in offshore marine waters (authors' unpublished data).…”

“…This zone, the freshwater-saltwater interface, probably contained most of a river's available Atlantic Sturgeon encompassing 1 m, although side-scan detections of sturgeon sometimes occurred to the upper extent of survey reaches (Flowers and Hightower 2013, Supplement A). We did not observe sturgeon in our surveyed portion of the Santee River, resulting in a 0 population estimate, but sturgeon have been observed there in the past (Collins et al 2000). A different survey design would be required to produce estimates that would apply to each entire river.…”

“…Sturgeon have been observed in these rivers and sampled in various studies (Moser and Ross 1995;Collins and Smith 1997;Collins et al 2000;Armstrong and Hightower 2002;Oakley and Hightower 2007;authors' unpublished data), but no assessments have been undertaken. A recent range-wide study estimates that there may be 6,615-29,784 ocean-going Atlantic Sturgeon in the Carolina DPS (Kocik et al 2013).…”

“…Side-scan surveys.-Surveys were conducted in coastal rivers near the freshwater-saltwater interface where sturgeon have been observed (Moser and Ross 1995;Collins et al 2000;Peterson et al 2008). Repeated side-scan sonar surveys were performed over 3 d at each of the six rivers.…”

“…This anadromous species, spends large amounts of time feeding and migrating in marine environments, using freshwater rivers for spawning and a summer dormant period (ASSRT 2007). During summer, Atlantic Sturgeon may aggregate in lower portions of rivers, often in deep holes near the freshwater-saltwater interface, although locations vary with river characteristics and flow conditions (Moser and Ross 1995;Collins et al 2000).…”