FISHERY BULLETIN: VOL. 81, NO. 3 



This illustrates the need for additional information 

 on the digestion rates of a variety of different prey 

 items, particularly fish prey. If different prey types 

 are digested at different rates, then the static picture 

 of the food web as provided by stomach content 

 analysis may not truly indicate the relative rates of 

 flow of the different elements through the food 

 web. 



Food Habits and Stomach Content 

 Weight 



The food habits and stomach content weight of 

 silver hake and Atlantic cod in the present study are 

 in general agreement with the results of other studies 

 (Rae 1967, 1968 a, b; Tyler 1971; Vinogradov 1972; 

 Daan 1973; Langton and Bowman 1980). 



Rae (1967, 1968a, b) provided a detailed descrip- 

 tion of the food habits of Atlantic cod in the North 

 Sea, the Faroes, and Iceland, and Vinogradov (1972) 

 described the food habits of silver hake in the North 

 Atlantic. These studies are not directly comparable 

 with the present study because they presented the 

 diet by the frequency of occurrence of prey, not by 

 weight. However, Rae reported that in general, fish 

 prey were seldom eaten by cod <21 cm, but became 

 increasingly important in the diet as the cod grew 

 larger. Cod >50 cm fed mostly on fish. Vinogradov 

 also found that hake became increasingly piscivorous 

 with increasing size, and that hake > 40 cm fed almost 

 entirely on fish. These results are consistent with the 

 present study. 



Langton and Bowman (1980) have described the 

 food habits of silver hake and Atlantic cod (> 20 cm in 

 length) that were caught during 1969-72 in the same 

 area as the present study. Silver hake averaged 27.5 

 cm in length, their mean stomach content weight was 

 2.5 g, and the proportion of fish in the diet was 70.9'/< 

 by weight. Atlantic cod averaged 54.7 cm in length, 

 their mean stomach content weight was 27.9 g, and 

 fish prey constituted 64.0'/ of the diet by weight. 

 These are very close to our present results with hake 

 >20 cm [mean length = 31.2 cm, mean weight of 

 stomach contents = 2.9 g (0.79'/v B W), proportion of 

 fish in the diet = 81.7% by weight], and cod >30 cm 

 [mean length = 60.9 cm, mean weight of stomach 

 contents = 29.6 g (0.68 f A BW), and mean proportion 

 of fish in the diet = 62.3 f A by weight]. These results 

 imply that no large-scale changes in the mean weight 

 of stomach contents in the two species occurred in 

 the study area between 1969 and 1976. Possible 

 changes in factors such as prey species or prey size, 

 however, are not evaluated in this report. 



The weight of the stomach contents of 15-40 cm 



Atlantic cod from Passamaquoddy Bay, New 

 Brunswick, was reported by Tyler (1970: figure 7). 

 During spring, the stomach content weights were 

 very similar to those of 15-40 cm cod reported here. 

 However, during late summer-fall, cod in Tyler's 

 study generally had more food in their stomachs 

 (usually > 1% BW; range 0.4-2.7% BW) than fish in 

 this study. 



Daan (1973) investigated the food habits of Atlantic 

 cod from the northern and southern portions of the 

 North Sea. In general, the weights of the stomach 

 contents of cod (divided into 10 cm size classes) in his 

 study were considerably higher than in the present 

 study (compare Daan's table XI with our Table 4). 

 Daan's samples were collected principally during the 

 daytime, but he considered that diel feeding 

 periodicity was not significant in his study area. In ad- 

 dition, Daan's cod were more piscivorous than the 

 cod collected during the present study (compare his 

 figure 2 with our Table 4). He found that fish prey 

 became increasingly important in the diet with in- 

 creasing size of cod. These results are in agreement 

 with the present study. 



The percentage of empty stomachs observed dur- 

 ing our study is in agreement with those reported by 

 Tyler (1971), Daan (1973), and Langton and Bow- 

 man (1980). 



Diel Changes in Stomach Contents 



Edwards and Bowman (1979) and Bowman and 

 Bowman (1980) concluded that silver hake >20 cm 

 were principally nocturnal feeders. Results of the 

 present study also indicate that hake >20 cm feed 

 more intensively at night. However, the lack of 

 significant diel changes in the stomach content 

 weight of hake <20 cm indicates that these small fish 

 may feed continuously throughout the day. 



The lack of evident feeding periodicity in Atlantic 

 cod was consistent with an extensive study by Rae 

 (1967) and with observations by Daan (1973). Sat- 

 tersdal (1967) reviewed several studies on feeding 

 periodicity in gadoids, and also concluded that with 

 cod, feeding may take place at any time during the 

 night or day. 



Daily Ration 



Daan (1973) estimated the daily ration of Atlantic 

 cod from the North Sea, where the mean temperature 

 (5°-9°C) was similar to that experienced by Atlantic 

 cod in the present study. Although these fish, on the 

 average, contained more food in their stomachs, the 

 estimates of the daily food intake were relatively 



448 



