Food of Rainbow, Cutthroat and Brown Trout in the Cowichan River System, B.C.

Abstract

Stomach contents of 293 rainbow, 160 cutthroat and 113 brown trout were examined and analyzed according to species, size groups (5 cm.) and habitat (river or lake). For rainbows of both river and lake (4 to 50 cm. in length), insects, chiefly Trichoptera and Simuliidae, were predominant in all size groups. Fish constituted a small fraction of the food except in the winter when salmon eggs were available. River cutthroat subsisted chiefly on insects (Trichoptera) up to 15 cm., on insects and fish (Gasterosteus) up to 30 cm., thereafter largely on fish. Lake cutthroat samples did not eat fish in any number until 41 cm. long. Brown trout ate chiefly insects (Trichoptera) up to 45.5 cm., thereafter turning more definitely to a fish (salmonid) diet. The cutthroat were more piscivorous than the brown trout. A definite selection of food by the trout was indicated.