MURPHY ET AL.: SIZE AND DIET OF JUVENILE PACIFIC SALMON 



Table 1 . — Stomach contents of juvenile salmon in Porcupine Creek estuary, 26 May-7 July 1981 . %A/ is percent by 

 number, %W is percent by wet weight, %F0 is percent frequency of occurrence of fish with prey item /, and %IRI is 

 percent of total sum of IRI for all prey taxa. IRI = (%/V + %W)%fO. Taxa are omitted if %IRI is s3 for all salmon 

 species. 



1 Mostly adult Diptera. 



of insects was negatively correlated. As a conse- 

 quence of the selection of larger prey as the 

 salmon grew, total prey weight increased with 

 salmon FL, whereas total prey number did not 

 (Table 5). Although pink and chum salmon ate 

 prey of similar size, they foraged differently (Fig. 

 4). Pink salmon consumed about 95% pelagic 

 prey; chum salmon, only 74%. Individual taxa 

 changed, but the importance of pelagic prey did 

 not change significantly between sampling peri- 

 ods, estuary basins, or salmon FL classes. 



Diet of coho salmon, on the other hand, varied 

 widely depending on salmon FL, date, and loca- 

 tion (Fig. 4). Pelagic prey increased from 1% of 

 total prey for coho salmon <80 mm FL to 80% for 

 those >100 mm FL. Coho salmon ate fewer 

 pelagic prey in May, when most coho were in the 

 inner basin and feeding mainly on insects, than 

 in July when most were in the outer basin and 

 feeding mainly on fish (Table 1). Analysis of vari- 

 ance, however, showed that differences between 

 basins and sampling periods were not significant 



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