Survey of the Shark Fauna in Two South Carolina Estuaries and the Impact of Salinity Structure
Daniel C. Abel, Robert F. Young, Jason A. Garwood, Mario J. Travaline, and Bree K. Yednock
Abstract.—Winyah Bay is a 65-km2 estuary in northeast South Carolina, and North Inlet is a 32- km2, high-salinity estuary connected to both Winyah Bay and the Atlantic Ocean. The objectives of this study were to survey the shark fauna of these systems, determine the potential of these estuaries as shark nurseries, and assess the impact of salinity structure on shark diversity and abundance in these two estuaries. From May to November in 2002 (a drier than average year) and 2003 (a wetter than average year), 227 bottom longlines (16/0 and 12/0 hooks) were set in Winyah Bay. In 2002 and 2003, a total of 119 trammel net sets were also conducted from June to October in North Inlet. A total of 196 sharks (38 adults, 158 juveniles) representing 10 species were captured in Winyah Bay in 2002, whereas 73 sharks (17 adults and 56 juveniles) representing four species were caught in 2003. Catch per unit effort (CPUE) for all sharks caught in Winyah Bay was not significantly different between 2002 and 2003. Blacktip shark Carcharhinus limbatus and finetooth shark C. isodon CPUE declined significantly on 16/0 hook longlines set in Winyah Bay from 2002 to 2003. For 12/0 hook longlines set in Winyah Bay, CPUE for three species (sandbar shark C. plumbeus, Atlantic sharpnose shark Rhizoprionodon terraenovae, and finetooth shark) out of five declined significantly from 2002 to 2003. Within Winyah Bay, CPUE for sharks on both longline configurations was not significantly different between lower and middle bay sites for 2002 but was for 2003. In both years, CPUE correlated positively with bottom salinity in Winyah Bay. In North Inlet, in 2002, 30 sharks (20 adults, 10 juveniles) comprising five species were caught, whereas 57 sharks (26 adults and 31 juveniles) representing three species were caught in 2003. The CPUE in 2002 was significantly less than in 2003 in North Inlet for Atlantic sharpnose sharks, bonnetheads Sphyrna tiburo, and all sharks combined. This study documented the presence of adults and juveniles (including neonates and young of the year) for 10 species of sharks in Winyah Bay and 5 in North Inlet and thus identified these areas as shark habitat and potential primary and secondary nurseries for some shark species. We also observed salinity-related differences in the distribution of sharks in both estuaries, including differences in abundance and age-class, as a result of normal salinity regime and precipitation-induced salinity changes.