Diets of juvenile coho salmon ( Oncorhynchus kisutch ) and steelhead trout ( Salmo gairdneri ) relative to prey availability

Abstract

Monthly diets of juvenile coho salmon and steelhead trout and the composition of the bottom and drift fauna were examined in a tributary of Lake Ontario. From June through September coho fed most heavily on terrestrial invertebrates, whereas steelhead fed primarily on benthic invertebrates. Diet overlap (Ĉ λ ) between coho and steelhead was not significant. The diet of coho was closely associated with the composition of the drift; the diet of steelhead was more closely associated with the bottom fauna. Food selection may be influenced by observed differences in distribution (riffle versus pool) of sympatric steelhead and coho salmon, but mode of feeding (surface versus bottom) may also play a role. Because of the close relationship between drift composition and diet in coho, we hypothesize that diel variation in diet will be greater in coho than in steelhead.