FEEDING BEHAVIOR AND BIOLOGY OF YOUNG SANDBAR SHARKS, CARCHARHINUS PLUMBEUS (PISCES, CARCHARHINIDAE), IN CHINCOTEAGUE BAY, VIRGINIA* Robert J. Medved^ and Joseph A. Marshall^ ABSTRACT During the summers of 1977, 1978, and 1979 the feeding behavior and biology of young sandbar sharks were investigated in Chincoteague Bay, Virginia, using catch data obtained from rod and reel fishing. Mean catch per unit effort for the study was 1.02 sharks per hour, but yearly differences in catch per unit effort were found. Sandbar sharks were not caught before the first week in June despite substantial fishing effort prior to this time, both in 1977 and 1978. Catch per unit effort was higher at night than during the day but was not related to tidal current stage or speed. Captures were made at surface, mid, and bottom fishing depths. During the day, catch per unit effort was highest at the bottom fishing depth but did not differ among the three depths during the night. The blue crab, Callinectes sapidus, was found in 41.3'7e of the stomachs examined; 20% of the stomachs were empty, and the remainder contained various crustaceans and fishes. The proportion of empty or nearly empty stomachs was greater for night captures than for day captures. Yearly differences in sex ratio existed and the total length distribution of sharks measured suggested the presence of relatively distinct size classes. The natural history of the sandbar shark, Car-charhinus plumbeus, has received considerable attention and is relatively well known. Tag re-turns (Casey 1976) and analysis of commercial shark fishery records (Springer 1960) have pro-vided valuable information on the distribution and long-term movements of this species. These studies show the sandbar shark to be an abun-dant, migratory shark distributed in the western North Atlantic from Cape Cod, Mass., to West Palm Beach, Fla., during the summer and from the Carolinas into the Gulf of Mexico in the winter. From spring until late fall, young sand-bar sharks spend much of their time along the mid-Atlantic coast in nursery areas consisting of shallow bays and sounds. In late fall the young move farther offshore and south to wintering grounds between North Carolina and Florida. According to Casey (1976), the young may repeat this cycle for up to 5 yr and then begin to occupy areas farther offshore and undertake longer north-south migrations. Other studies have made contributions concerning growth (Wass 1973), ^Contribution No. 1, Wallops Island Marine Science Center. ^Department of Biology, West Virginia University, Morgan-town, W. Va.; present address: Graduate School of Oceanography, University of Rhode Island, Kingston, RI 02881. ^Department of Biology, West Virginia University, Morgan-town, WV 26506. reproduction (Taniuchi 1971), and general ecol-ogy (Bigelow and Schroeder 1948; Clark and von Schmidt 1965; Bass et al. 1973; Lawler 1977). One area in which information is lacking, not only for this species but for sharks in general, concerns feeding behavior. Although work has been conducted on the prey items of sharks (Bigelow and Schroeder 1948) and the role of various sensory modalities in locating prey (Hob-son 1963; Kleerekoper 1969; Myrberg et al. 1976; Hodgson and Mathewson 1978; Kalmijn 1978), these areas have received little attention and are little understood. Other areas of feeding behavior such as food requirements and feeding activity have received even less attention. The specific objective of this study was to determine patterns of feeding activity of young sandbar sharks in relation to the time of day, tidal cycle, and vertical positions within the water column. Because information on sandbar sharks in nursery areas is scarce, data concern-ing the food items, abundance, sex ratio, and age-class composition of this species in Chincoteague Bay are also presented. METHODS This study was conducted from early May through late August during 1977 and 1978 and on Manuscript accepted April 1981. FISHERY BULLETIN: VOL, 79, NO. 3, 1981. 441
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