FISHERY BULLETIN: VOL. 83. NO. 3 



of the first and last eaten food items within each 

 stomach was calculated to assess the amount of time 

 that passed during consumption of multiple item 

 meals. In 19 stomachs a food item in the sixth stage 

 of digestion and one in the first stage of digestion 

 were found. In these cases a time equivalent of 5 

 stage-of-digestion units had passed between con- 

 sumption of the two food items, and since a stomach 

 containing an item in stage 6 of digestion would be 

 relatively empty, the two food items were considered 

 to represent two different meals. Excluding the 

 above 19 stomachs from analysis, the mean differ- 

 ence between the stage-of-digestion values of the 

 first and last eaten food items was calculated for 

 stomachs containing from 2 to 5 items (Table 3). The 

 overall mean difference was 0.60 stage-of-digestion 

 units indicating that multiple food items in the 

 stomachs were in similar stages of digestion. 



The quantity of food in each stomach examined 

 was measured on a wet weight and drj' weight basis. 

 Excluding empty stomachs from analysis, the total 



Table 3.— Number of stomachs for wfilchi tfie stage-of- 

 digestion value of the first eaten food item minus the stage- 

 of-digestion value of the last eaten food item was equal to 

 the given difference. The data are broken down into groups 

 based on the number of food Items present in the stomachs. 

 Stomachs that contained an item at stage 1 of digestion and 

 an item at stage 6 of digestion are not included (see text). 



No. of stomachs with 



indicated difference between 



stage-of-digestion values of 



first and last food items eaten 



dry weight of food (TDW) was found to be linearly 

 related to the total wet weight of food (TWW) in the 

 stomachs (TDW = -0.24 + (0.22) TWW; n = 318, 

 R~ = 0.96). Since the two measurements were highly 

 correlated (r = 0.98) and wet weight measurements 

 have frequently been used in similar food studies on 

 other species, it seemed valid to express the food 

 quantity results in this paper on a wet weight basis. 

 Table 4 summarizes the descriptive statistics of the 

 quantity of food in 414 stomachs examined. The 

 mean total weight of food found in the stomachs of 

 sharks caught by gill nets was significantly higher 

 than that found for sharks caught by rod and reel 

 (18.91 and 13.09 g respectively; 2-test, P = 0.003). 

 Similar results were obtained when food quantity 

 was measured as a percentage of shark body weight 

 (0.96 vs. 0.76%; z-test, P = 0.043). This result, in 

 conjunction with the other differences between the 

 two capture methods mentioned above, suggested 

 that sharks caught by rod and reel may not have 

 been representative of the entire population (see sec- 

 tion on Discussion). Because the primary value of the 

 stomach content data in this study will be in the esti- 

 mation of food consumed by the population, the 

 following results concerning the amount of food in 

 the stomachs were based on sharks caught by gill 

 nets since they were probably more representative 

 of the entire population of young sandbar sharks in 

 the study area. For sharks caught by gill nets, crus- 

 taceans accounted for nearly twice as much of the 

 mean total wet weight of food in the stomachs than 

 did fish. The mean wet weight of crustaceans in the 

 236 stomachs (12.37 g) was significantly higher than 

 the mean of 6.53 g found for fish (z-test, P < 0.001). 

 Similar results were obtained when food quantity 

 was expressed as a percentage of shark body weight 

 (0.65 vs. 0.31%; z-test, P < 0.001). The mean 

 weights of the two food components in the stomachs 



Table 4 —Summary statistics of the amount of food In the stomachs of a sample of 414 

 sandbar sharks. Sharks were captured with gill nets and rod and reel gear. The z-test 

 statistic was used to test the equality of the indicated pairs of mean values. 



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