Seasonal occurrence, relative abundance, and migratory movements of juvenile sandbar sharks, Carcharhinus plumbeus, in Winyah Bay, South Carolina

Abstract

In the past decade along the U.S. East coast, the overfished western North Atlantic stock of Carcharhinus plumbeus has been recovering; however, research investigating C. plumbeus habitats and seasonal habitat shifts is lacking. Accordingly, we studied the seasonal residency, catch abundance, and distribution of juvenile C. plumbeus in Winyah Bay, SC, as well as their migration patterns along the western North Atlantic. We set 303 bottom longlines from May through September in 2016 and 2017 and deployed 11 Vemco (V16-4H) acoustic transmitters in juvenile C. plumbeus. Catch abundance did not differ by month or year (p = 0.45) and was not significantly influenced by any tested water parameter (p = 0.58). C. plumbeus catches were dominated by individuals measuring 81–100 cm precaudal length, and mean size only significantly differed by year (p = 0.02) with slightly larger sharks (86.8 cm PCL) caught in 2017 than 2016 (81.4 cm PCL). Tidal stage and Bay region were positively correlated with catches (p = 0.02). From August 2016 through January 2019, juveniles were detected in Winyah Bay from April to November for 1–302 non-consecutive days (μ ± SE = 108.1 ± 32.6 days), with six juveniles exhibiting interannual return. Detection frequency and presence differed by Bay region, with most detections nearshore and in Lower Bay, fewest in Middle Bay, and none in Upper Bay. This study had two primary findings: monitored sharks utilized a previously unknown southern overwintering migration route, and Winyah Bay serves as a secondary nursery for C. plumbeus.