FISHERY BULLETIN; VOL. 83, NO. 4 



RESULTS 

 Cod Diet 



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Of 455 Pacific cod stomachs examined, 435 con- 

 tained food. Data obtained from cod stomachs col- 

 lected in August 1980, May 1981, and September 

 1981 are presented in Ikble 2. Combining these data, 

 the most frequently occurring prey items were pink 

 shrimp (63%), euphausids (41%), walleye pollock 

 (27%), and capelin, Mallottis villosus, (26%). Crusta- 

 ceans, mostly shrimp, crab, and euphausids, were 

 present in 93% of the stomachs containing food and 

 comprised 45% of the volume Ifeleosts, mostly wall- 

 eye pollock and capelin, were present in 60% of the 

 stomachs containing food and comprised 54% of the 

 volume Gastropods, bivalves, sipunculids, and asci- 

 dians together comprised 1% of the volume 



Crustaceans made up the greatest part of the diet 

 in the May sample and teleosts comprised the 

 greatest part of the diet in the August and 

 September samples (Ikble 2). Shrimp, mostly pink 

 shrimp, made up 67% of the volume in May com- 

 pared with 28%, combining August and September 

 data. Crabs, mainly snow crab, comprised 10% of the 

 volume in May compared with 3% in August- 

 September. Teleosts, primarily walleye pollock and 

 capelin, made up 4% of the volume in May and 65% 

 in August-September. 



Data on the 10 most frequently occurring food 

 items was categorized by 10 cm length (FL) groups 

 of Pacific cod in a size range of 30 through 69 cm 

 (Tkble 3). Hurtubia's (1973) trophic diversity method 

 was used to assure that enough stomach samples had 

 been analyzed to give representative values for each 

 length group. Pink shrimp occurred most frequent- 

 ly in all but one length group (30-39 cm) and was 

 the dominant food item by volume in all length 

 groups. Pink shrimp and snow crab increased both 

 in frequency of occurrence and volume with in- 

 creasing cod size Conversely, euphausids were the 

 most frequently encountered food item in the 30-39 

 cm length group, but their frequency of occurrence 

 and volume decreased with increasing cod size No 

 trends were evident for the occurrence of teleosts. 

 Although data from the three surveys were combined 

 for Tkble 3, the above trends were evident in each 

 of the surveys. 



The size ranges and mean sizes of pink shrimp and 

 humpy shrimp consumed by Pacific cod were similar 

 in general to those found in the trawl (Tkble 4). Size 

 range and mean size of walleye pollock consumed by 

 cod were considerably smaller than those fish cap- 

 tured by the trawl. 



604 



