Shark Nursery Grounds in Sapelo Island National Estuarine Research Reserve, Georgia
Christopher W. D. Gurshin
Abstract.—Data are lacking for shark nursery grounds along Georgia’s coast that would be useful in development of species-specific fishery management plans. The purpose of this survey was to describe the use of Sapelo Island National Estuarine Research Reserve, Georgia as nursery grounds for sharks. Relative abundance, length–frequency distribution, spatial and temporal occurrence, and feeding habits were determined for Atlantic sharpnose sharks Rhizoprionodon terraenovae (N = 305), blacktip sharks Carcharhinus limbatus (N = 65), finetooth sharks C. isodon (N = 38), and bonnetheads Sphyrna tiburo (N = 16) from 35 trammel net collections during June–August 1997. Catch per unit effort (CPUE) of Atlantic sharpnose sharks (26.4 sharks/h) was significantly higher than CPUE of blacktip sharks (5.6 sharks/h), finetooth sharks (3.3 sharks/h), and bonnetheads (1.4 sharks/h) for the entire study. Atlantic sharpnose sharks were significantly more abundant in early July (81.8 sharks/h) than in other periods in the summer season. In general, the trend of relative abundance (CPUE) for each species was higher in July than other months. All species occurred throughout most of the sampling area except in upper Duplin River for blacktip and finetooth sharks and middle Duplin River for finetooth sharks. Mean CPUE of Atlantic sharpnose sharks was significantly higher than CPUE of all other species in Doboy Sound and CPUE of finetooth sharks and bonnetheads in lower Duplin River. Blacktip sharks (7.6 sharks/h) were significantly more abundant than bonnetheads (0.3 sharks/h) in Doboy Sound. Water temperature and salinity during capture were 25–32°C and 22–31 parts per thousand (ppt) for Atlantic sharpnose sharks, 22–31°C and 22– 26 ppt for blacktip sharks, 25–30°C and 22–26 ppt for finetooth sharks, and 23–30°C and 23–26 ppt for bonnetheads. Atlantic sharpnose, blacktip, and finetooth sharks were mostly represented by young-of-the-year (YOY) individuals. A qualitative analysis of stomach contents suggested that teleosts formed the majority of the diet for blacktip and finetooth sharks, a variety of prey items, including teleosts, penaeids, stomatopods, cephalopods, and brachyurans for Atlantic sharpnose sharks, and exclusively crustaceans, particularly blue crabs Callinectes sapidus, for bonnetheads. The length–frequency distribution and occurrence of YOY- and juvenile-sized individuals feeding on a variety of prey common to the estuary indicates the use of this estuarine system as primary and secondary nursery grounds for Atlantic sharpnose, blacktip, and finetooth sharks and as a secondary nursery ground for bonnetheads during the summer of 1997.