Using side-scan sonar to estimate the abundance of dual-spawning Atlantic Sturgeon in the Great Pee Dee River, South Carolina

ABSTRACT Objective Abundance estimates of spawning adult Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus are needed to assess current population status and to inform recovery efforts, especially for rivers with dual-spawning populations, where genetically distinct spring and fall spawning runs may differ in vulnerability. Our objective was to estimate the abundance of dual-spawning adult Atlantic Sturgeon engaged in spring and fall spawning runs in the Great Pee Dee River, South Carolina, by using side-scan sonar. Methods In 2021, we conducted side-scan sonar surveys weekly for a total of 11 weeks during the spring run (March 2–May 14) and 12 weeks during the fall run (August 10–November 7) in a 70-km freshwater reach of the Great Pee Dee River. We used N-mixture models to estimate abundance and detection probability of adult Atlantic Sturgeon while accounting for effects of environmental covariates, including water temperature, discharge, and channel sinuosity. Results Estimated maximum weekly abundance of spawning adult Atlantic Sturgeon in the study area was 587 (95% CI = 328–1,085) and 875 (95% CI = 511–1,607) individuals during the spring and fall spawning runs, respectively. Our methods identified differences in the seasonal and spatial abundance of Atlantic Sturgeon among spring and fall spawning runs as well as differences in the environmental factors affecting the abundance and detection of Atlantic Sturgeon between runs. Conclusions This study contributes to the growing knowledge of Atlantic Sturgeon spawning run abundance across the species’ range and suggests that the Great Pee Dee River contains a relatively large dual-spawning population of Atlantic Sturgeon. Differences in the environmental factors affecting abundance and detection between spring and fall runs are reflective of differences in migratory behavior among runs, emphasizing a need to consider the unique characteristics of dual-spawning populations in recovery plans.