FISHERY BULLETIN: VOL. 83, NO. 3 



In most investigations the food consumption of 

 fishes has been studied by methods that involve 

 laboratory techniques to estimate various 

 parameters relating to growth, metabolism, diges- 

 tion, and excretion (reviews by: Davis and Warren 

 1971; Mann 1978). These methods, however, are of 

 limited value for fishes such as sharks that are dif- 

 ficult to maintain in captivity. An alternate method 

 for determining food intake that can be applied to 

 fishes in the wild has been successfully used in 

 several studies (Bajkov 1935; Swenson and Smith 

 1973; Eggers 1977; Thorpe 1977; Elliott and 

 Persson 1978; Jobling 1981; Stillwell and Kohler 

 1982; Durbin et al. 1983). This approach requires in- 

 formation concerning the quantity of food found in 

 the stomachs of fishes sampled at regular intervals 

 over 24-h periods and the rate at which food is evacu- 

 ated from the stomach. The objective of the present 

 study was to obtain the quantitative stomach content 

 data needed to use this approach to estimate the 

 daily food ration of the sandbar shark, Carcharhinus 

 plumbeiis. The sandbar shark was selected for this 

 study because it is one of the few sharks for which 

 gastric evacuation data are available (Medved in 

 press). It is also an abundant, widely distributed 

 shark (Springer 1960; Casey 1976) known to feed on 

 commercially valuable species (Medved and Marshall 

 1981). In addition, it is a member of a large family of 

 sharks (Carcharhinidae) and data collected for this 

 species will provide the basis for making preliminary 

 estimates of food consumption for the other 

 members of the family. 



METHODS 



During the summer of 1983, young sandbar sharks 

 were collected from Chincoteague Bay, VA, for 

 stomach content analysis. The study area is located 

 within the summer distribution of this species and 

 supports a relatively large number of young sandbar 

 sharks from early June through September. The bay 

 is about 40 km long and 8 km wide at its widest 

 point, and the average water depth is 2 m. A tidal 

 inlet connects the bay with the Atlantic Ocean, and 

 the tidal range varies from 0.75 to 1.50 m. The area 

 is also characterized by strong tidal currents, vast 

 salt marshes, and brackish to seawater salinities. 



A 4.9 m outboard motor boat was used as a fishing 

 platform, and sharks were caught using monofila- 

 ment gill nets and rod and reel fishing gear. The gill 

 nets were 91m long, 1.8 m deep, and had a stretched 

 mesh size of 10.8 cm. They were anchored at both 

 ends and were buoyed so the foot rope touched the 

 bottom. Net retrieval was made every 1 to 2 h. The 



fishing rods were equipped with Penn^ reels of 3/0 

 size, and the terminal tackle consisted of two wire 

 leaders, each with a 4/0 fishing hook baited with 

 squid. The hooks were set 1 m off the bottom. Both 

 types of gear were used during all hours of the day. 

 Upon capture each shark was brought into the boat 

 where it was sexed, measured, and weighed. The 

 sharks were then cut open and the stomach contents 

 were removed and stored on ice in plastic bags. 



In the laboratory each food item was identified to 

 species and a length measurement was made when 

 possible. Each item in the stomach was also assigned 

 a stage-of-digestion value ranging from 1 to 6 with a 

 higher number indicating a greater extent of diges- 

 tion. The stage-of-digestion scale was based on a 

 gastric evacuation study (Medved in press) in which 

 sandbar sharks were fed preweighed meals of either 

 blue crab, Callinectes sapidus, or Atlantic menhaden, 

 Brevoortia tyrannus, and were maintained in an 

 enclosure constructed in the natural environment. 

 The range of water temperatures in the enclosure 

 (22.0°-30.0°C) was close to that recorded during the 

 present study (20.0°-27.3°C). The sharks were 

 sacrificed at various time intervals after feeding, and 

 the food remains were weighed and described. The 

 food item descriptions were used to arbitrarily esta- 

 blish six stages of digestion that were each one-sixth 

 of the total evacuation time. Each stage of digestion 

 was about 12 h long for crustacean prey and 15 h 

 long for fish prey. After identification of food items 

 and assignment of digestion values, the stomach con- 

 tents of each shark were separated into fish and crus- 

 tacean components that were weighed to 0.01 g 

 after draining off excess water. Each sample was 

 then dried at 80 °C to constant weight (about 72 h) 

 and again weighed to 0.01 g. 



RESULTS 



During the study 414 sharks were captured for 

 stomach content analysis. The numbers of sharks 

 caught by each fishing method and during various 

 time periods of the day are summarized in Table 1 . 

 The number of male and female sharks collected was 

 nearly equal (210 and 204 respectively), and they 

 ranged in size from 40.0 to 80.0 cm fork length (FL) 

 (x = 56.1, SD = 6.8). Body weights were obtained 

 from 369 (89.1%) of these sharks, and ranged from 

 720.0 to 5,690.0 g (x = 1,885.5, SD = 738.8). The 

 body weight of the sharks not weighed was esti- 

 mated from a regression equation derived from the 



^Reference to trade names does not imply endorsement by the Na- 

 tional Marine Fisheries Service, NOAA. 



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