FISHERY BULLETIN: VOL. 84, NO. 1 



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Figure 6.— Percentage frequency of occurrence and percentage stomach volume 

 of prey types for chinook salmon. 



predator size increased, but not significantly (Table 

 3) (r = -0.24, n = 4, P > 0.05). For chinook and coho 

 salmon, mean size of the invertebrate prey increased 

 as predator size increased (r = 0.42, n = 4, P > 0.05). 

 However, the increase in prey size was considerably 

 less than the increase in predator size (Table 3). 



The results of the previous analyses are sum- 

 marized as follows. As predator size increased, in- 

 dividual predators selected larger fish prey of one 

 species, but not a greater number of the prey. There 

 was also a shifting from smaller prey species (sand 

 lance) to larger ones (herring, rockfish). As predator 

 size increased, there was a tendency to shift from 

 smaller invertebrate prey (Parathemisto) to larger 

 types (euphausiids, crab larvae). Greater numbers 



of the larger prey were consumed by an individual 

 predator, while numbers of smaller prey consumed 

 declined. Although larger invertebrate prey types 

 were preferred as predator size increased, larger in- 

 dividuals of each prey class were not necessarily 

 selected by larger predators. 



Species Comparisons 



The dietary components of the four species of 

 salmon investigated are different, and there is more 

 than one possible reason for the apparent partition- 

 ing of diet among the salmon species. Perhaps 

 because the salmon occupied different depth zones, 

 the differences in diet are attributable simply to dif- 



84 



