BEACHAM: FOOD OF PACIFIC SALMON OFF BRITISH COLUMBIA 



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Figure 3.— Percentage frequency of occurrence and percentage stomach volume 

 of prey types listed in Table 1 for sockeye salmon. 



that of sockeye and pink salmon (x 2 = 36.0, P < 

 0.01). 



Predator and Prey Size 



The effect of predator size on the abundance and 

 size of prey was examined for each of the four salmon 

 species investigated. Numbers of individuals con- 

 sumed for each prey type were tallied for each 

 salmon examined. For the fish prey species, only 

 sand lance was consumed at a high enough frequency 

 to enable one to investigate numbers of sand lance 

 consumed versus predator size For the four salmon 

 species, there was no consistent trend for sand lance 

 in this regard (Table 1). For both chinook and coho 



salmon— the two primary sand lance predators— the 

 number of sand lance eaten was greater in the mid- 

 dle size group than in either the small or large size 

 classes. Large chinook and coho salmon switched 

 from sand lance to larger fish species, such as her- 

 ring (Figs. 5, 6). There were, however, clear trends 

 for some of the invertebrate prey types. The average 

 number of euphausiids eaten per individual predator 

 increased with increasing fish size (Table 1). How- 

 ever, the average number of Parathemisto eaten 

 decreased with increasing predator size The other 

 prey types occurred at a low frequency (Figs. 3-6), 

 and thus it was not possible to determine reliable 

 trends. 

 As predator size increased, more euphausiids, but 



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