Seasonal Occurrence, Relative Abundance, and Migratory Movements of Juvenile Sandbar Sharks, Carcharhinus plumbeus, in Winyah Bay, South Carolina

Winyah Bay, located on the coast of South Carolina, is the fourth largest U.S. estuary by discharge rate (Voulgaris et al. 2002), and provides an annually used habitat for juvenile C. plumbeus (Abel et al. 2006, Gary 2009). From May to September 2016 and 2017, we set a total of 303 bottom longlines in middle and lower Winyah Bay to assess sex ratios, size distributions, and catch per unit effort (CPUE), as well as the potential influence of abiotic parameters on CPUE. A subset of eleven juvenile C. plumbeus was tagged with VEMCO (V16-4H) acoustic transmitters to analyze seasonal occurrence, residency and detection distribution in Winyah Bay as well as to opportunistically document their migratory movements. Catches in the Bay were dominated by larger juvenile C. plumbeus measuring 81 – 95 cm PCL (n = 71) and approximately 4 – 6 yrs old (Sminkey & Musick 1995). Mean size did not vary by month or year (p > 0.05), indicating no ontogenetic shift of C. plumbeus utilizing the Bay. Juveniles were caught every month surveyed and CPUE did not significantly differ by month or year (p > 0.05). Tidal stage (p < 0.05) represented the only abiotic factor which significantly influenced CPUE. Juveniles were detected in Winyah Bay from April to November for up to 186 days (72.0 ± 19.7 days; mean ± SE). Detection frequency significantly differed by area, with the majority of detections in lower Winyah Bay and adjacent nearshore waters, less than 2% in middle bay, and none in upper bay (p < 0.001). Additionally, significantly more detections (57%) were recorded during the day compared to night (p < 0.001), and during low tide (62%) than high (p < 0.001). After emigrating from Winyah Bay from September to November, six juveniles were tracked moving southward as far as Cape Canaveral, FL. Three of these returned to Winyah Bay in April 2017. Consistency in southerly emigration routes in both years differed from overwintering data collected for juvenile C. plumbeus captured in the Chesapeake and Delaware Bays ...