FISHERY BULLETIN: VOL. 83, NO. 3 



stage of digestion (12 or 15 h depending on prey 

 type) these sharl<s apparently had gone at least 48 h 

 without consuming additional food. Another 17.9% 

 of the sharks captured had empty stomachs. None of 

 these were found to have an everted stomach, in- 

 dicating that regurgitation of food was not respon- 

 sible for the high percentage of empty stomachs. 

 Additionally, 98 sandbar sharks fed preweighed 

 meals and released in an enclosure in the natural en- 

 vironment were not observed to regurgitate food 

 when recaptured at a later time (Medved in press). 

 Thus it appears that the sharks with empty stomachs 

 had not consumed food for a period of time greater 

 than the time required to evacuate the last meal (at 

 least 72 h). Given the long duration of gastric evacua- 

 tion, a shark feeding nearly continuously would have 

 many food items at various stages of digestion in the 

 stomach. Multiple food items were found in some 

 stomachs, but 90.6% of the stomachs contained less 

 than three food items. Multiple food items in a 

 stomach were also generally in similar stages of 

 digestion (Table 3). The sharks with a single food 

 item in their stomach consumed that meal in a very 

 short period of time. The mean difference between 

 the stage-of-digestion values of the first and last prey 

 item consumed by sharks with multiple items in their 

 stomach was 0.60 units (Table 3). Considering that 

 digestion was divided into six stages, the feeding 

 duration of sharks that consumed a meal of multiple 

 food items was also very short relative to the time re- 

 quired for complete gastric evacuation. Observations 

 made during a study of gastric evacuation in the 

 sandbar shark also suggested that feeding ceased 

 after the consumption of a meal (Medved in press). In 

 that study the stomachs of 98 sharks were lavaged to 

 remove all food and a preweighed meal was then fed 

 to each animal. The sharks were released in a large 

 enclosure in the natural environment that contained 

 an abundance of prey and were recaptured at various 

 times after feeding. Of the 54 sharks sacrificed 

 within 40 h of feeding, only 4 had consumed addi- 

 tional food. In contrast, of 11 sharks that had their 

 stomachs lavaged but were not fed a meal before 

 release all but 2 were found to have food in their 

 stomachs when sacrificed 24 h later. The results 

 discussed above indicate that the feeding activity of 

 sandbar sharks in the study area was intermittent 

 rather than continuous. Similar models have been 

 proposed in several other feeding behavior studies on 

 fishes. Diana (1979) proposed an intermittent feed- 

 ing model for the northern pike, Esox lucius, and 

 suggested that such a model was appropriate for 

 many top carnivores. Longval et al. (1982) have 

 shown that after captive lemon sharks, Negaprion 



brevirostris, have fed to satiation, it takes a few days 

 for the appetite to become reestablished. Carey et al. 

 (1982) suggested that the great white shark, Car- 

 charodon carcharias, may maintain itself for more 

 than a month on a single large meal. Holden (1966) 

 and Jones and Geen (1977) indicated that the spiny 

 dogfish, Squalus acanthias, consumes a meal and 

 then ceases to feed until digestion is complete. 

 Observations made by Sano (1959) suggest that this 

 may be typical of other shark species as well. 



The differences observed between the stomach 

 contents of sharks caught by the two capture 

 methods are consistent with the model of feeding 

 postulated above. The majority of sharks caught by 

 rod and reel had stomachs that were empty or that 

 contained food items in the first or last stage of 

 digestion (Fig. 1). The sharks with empty stomachs 

 had apparently not consumed food for a long period 

 of time. Those with a food item in the last stage of 

 digestion had relatively empty stomachs and had also 

 gone a considerable time without feeding. Finally, 

 the sharks with a food item in the first stage of diges- 

 tion had eaten within several hours of being caught. 

 Assuming that these sharks were actively feeding 

 since they were inclined to consume the squid used 

 as bait, it appears that the sharks in a "feeding mode" 

 were those with relatively empty stomachs that had 

 not fed for some time and those that had just eaten 

 but were inclined to consume additional food. The 

 stomachs of sharks caught by gill nets were empty or 

 contained a single food item or multiple food items in 

 similar stages of digestion suggesting, as indicated 

 above, that feeding was intermittent. However, the 

 stage-of-digestion values of the food items in the 

 stomachs were spread more evenly over the diges- 

 tion scale than for sharks caught by rod and reel, in- 

 dicating that these sharks were in various stages of 

 the feeding cycle (Fig. 1). The higher percentage of 

 empty stomachs and lower mean stomach content 

 weight found for sharks caught by rod and reel than 

 for those caught by gill nets also suggested that 

 sharks caught by red and reel were those in a "feed- 

 ing mode" and that sharks caught by gill nets were 

 probably more representative of the entire popula- 

 tion. 



For sharks caught by gill nets the mean quantity of 

 food in the stomach was 0.96% of BW and the max- 

 imum quantity was 5.28% of BW (Table 4). Con- 

 sidering that the mean stomach content was based 

 on sharks containing food in various stages of diges- 

 tion, it f)robably is a significant underestimation of 

 the average meal size of sharks in the area. In con- 

 trast, the maximum quantity of food found in a 

 stomach is undoubtedly an overestimate and the 



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