624 



Fishery Bulletin 88(4), 1990 



of this may be due to the months and areas sampled 

 in different years. Euphausiids were the main food item 

 by weight during 1981 and 1982. Although euphausiids 

 were important during the later years, their contribu- 

 tion to the diet was less compared with chaetognaths, 

 larval fishes, and calanoid copepods. 



Sockeye salmon 



General food habits The diet of juvenile sockeye 

 salmon was similar to that of chum salmon. Juvenile 

 euphausiids, calanoid copepods, chaetognaths, and fish 

 larvae were consumed by the small number of fish ex- 

 amined (Appendix Table 2). Although a large number 

 of prey taxa were identified, only a few were impor- 

 tant. Among these were the euphausiid T. ^pinifcra 



CD 



JUN MAYJUNJULAUQ MAYJUNSEP MAYJUNSEP JUN 



1980 1981 1982 1983 

 CRUISE 



JUN 



1985 



I 



I 

 1- 

 O 



cr 



CO 



n 



JUN MAYJUNJULAUQ MAYJUNSEP MAYJUNSEP JUNJULSEP 



1980 1981 1982 1983 1984 



CRUISE 



JUN 

 1985 



Figure 5 



Shannon-Weaver niche breadth (H ) valui'S fur juvenile coho and 

 chinook salmon for each cruise period. 



and larval osmerid fishes. Chaetognaths were found in 

 substantial numbers but were well digested and not 

 identifiable to species. The relatively small sample size 

 of sockeye salmon stomachs precluded a detailed 

 analysis of diet variability. 



All salmon species 



IMiche breadth Niclie bi-eadths, maximum possible 

 niche breadths, and evenness values are given for each 

 salmon species in Table 5. Chinook salmon had the 

 highest overall diversity of prey taxa (H' = 5.06), which 

 was consistent with the high numbers of prey taxa 

 found per stomach, and a high evenness ratio. Coho 

 and chum salmon also consumed a diverse array of prey 

 taxa, although coho stomachs frequently contained 

 small numbers of prey items and showed low evenness 

 overall. Chum salmon had a high diversity (H' = 4.35), 

 despite a substantial amount of unidentified and 

 digested prey, and had the highest evenness (0.77) of 

 all salmon species. The overall prey diversity of sockeye 

 salmon was quite low (H' = 2.74), wliich may be due in 

 part to the small sample size and advanced state of 

 digestion (mean digestion code = 2.0) of prey which 

 prevented identification to lower taxonomic levels. 



