FISHERY BULLETIN: VOL. 84 NO. 1 



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Figure 4— Percentage frequency of occurrence and percentage stomach volume 

 of prey types for pink salmon. 



less Parathemisto, were eaten per individual 

 predator. The difference in predator response to 

 euphausids and Parathemisto may be examined in 

 relation to the size of the prey. The unit volumes of 

 an individual euphausiid were about four times 

 larger than those of an individual Parathemisto 

 (Table 2). In each salmon species examined, as the 

 predators increased in size, they switched from the 

 smaller Parathemisto to the larger euphausiids and 

 also crab larvae, consuming greater numbers of the 

 larger prey and decreasing numbers of the smaller 

 prey. Chinook and coho salmon also consumed 

 significantly larger Parathemisto than did sockeye 

 and pink salmon (F = 4.9; df = 3,98; P < 0.01). For 

 the invertebrate prey, an increase in predator size 



resulted in greater numbers of larger prey being 

 consumed. 



As predator size increased, there was an increase 

 in the size of the prey consumed (Table 2). Larger 

 predators consumed larger sand lance and herring. 

 Chinook and coho salmon consumed larger sand 

 lance (F = 3.7; df = 3,613; P < 0.05) and mixed fish 

 species (F = 2.9; df = 2,128; P < 0.05) than did sock- 

 eye and pink salmon. In coho and chinook salmon, 

 there was also a tendency for larger salmon to switch 

 prey types from the smaller sand lance to the larger 

 herring and rockfish. Increasing predator size pro- 

 duced shifts in both the type, number, and size of 

 the prey consumed. 



Changes in size of prey and predators were in- 



82 



