Shark Population Structure and Partitioning in Winyah Bay, SC

We conducted a longline survey from 2002 - 2006 in Winyah Bay SC, a 65 km2 partially-mixed coastal plain estuary, to 1) identify sharks inhabiting the system, 2) describe shark population structure, 3) examine their distribution, 4) investigate environmental parameters that may influence their distribution, 5) explore partitioning within this system, 6) determine the potential of this system as a shark nursery area, and 7) compare the shark composition of this system to that of nearby coastal waters . We caught 484 sharks comprising 12 species, these include Carcharhinus plumbeus (241), Rhizoprionodon terraenovae (117), Carcharhinus limbatus (50), Carcharhinus isodon (44), Squalus acanthias (11), Negaprion brevirostris (6), Sphyrna lewini (5), Sphyrna tiburo (4), Carcharhinus leucas (4), Ginglymostoma cirratum (1), Carcharhinus brevipinna (1), and Mustelis canis (1). Total size distribution of all sharks ranged between 24 cm to 272 cm. Mean monthly catch per unit effort (CPUE) (sharks/100 hooks, ± SEM) was as low as 1.38 ± 0.59 in lower bay and 0 in middle bay in April. CPUE peaked at 7.5 ± 2.0 in lower bay and 6.2 ± 1.4 in middle bay in August. Greatest abundance and diversity of shark catch occurred in June, July, and August (102 sharks/9 species, 84/8, and 129/8), respectively. Recursive partitioning showed that depth, month, and salinity were important factors correlated with partitioning. Regression analysis showed a significant relationship between mean CPUE and temperature, depth, salinity, Secchi depth, and day length. Shark species preferences and tolerances to salinity and temperature range at time of capture were apparent. C. plumbeus and R. terraenovae were the first warm water sharks caught in the season, tolerating the largest temperature range. C. plumbeus occurred throughout the largest salinity range. C. limbatus occurred in the narrowest salinity range. Sharks captured in Winyah Bay were found to partition in part by their sex. Juvenile C. plumbeus partition themselves from other sharks in Winyah Bay, including adult C. plumbeus C. limbatus and C. isodon. They also partition themselves from others by salinity, depth, and month. When both adult and juvenile C. plumbeus are present in the bay at the same time, they further partition by salinity. Of the 333 sharks tagged during this survey, six were recaptured that were either tagged by us or others. Tag and recapture data for one C. plumbeus indicates a growth rate of 5.7 cm/year FL and 9.3 cm/year TL. Winyah Bay estuary provided seasonal habitat to 12 shark species and may be a nursery area for C. plumbeus, an overfished species. Re- establishing shark populations through habitat preservation followed by sustainable fishing practices after recovery are important for conservation