Estimating Sturgeon Abundance in the Carolinas Using Side-Scan Sonar and Bayesian Models

Populations of endangered Atlantic sturgeon (Acipenser oxyrhincus) and shortnose sturgeon (Acipenser brevirostrum) in North and South Carolina have been significantly reduced from historic levels by a combination of intense fishing and habitat loss.  The conservation status of these species creates a need for estimates of current abundance. Hydroacoustics, such as side-scan sonar, have advantages over traditional techniques, such as the ability to sample large areas efficiently and potentially survey fish without physically handling them – important for species of conservation concern.  Our objective was to use data from side-scan sonar surveys to create estimates of abundance for sturgeons.  We surveyed lower reaches of six rivers in North and South Carolina, near the saltwater/freshwater interface, using a combination of side-scan sonar, telemetry, and video cameras (to sample jumping sturgeon) during summer 2011. We used both occupancy and N-mixture models with data acquired from side-scan sonar surveys to estimate abundance of sturgeon in each river. Estimated total abundance of sturgeon >1 m in length for all six rivers combined was greater than 600 individuals. The Pee Dee/Waccamaw and Santee Rivers in South Carolina had highest and lowest estimated abundances, respectively.