Management Implications of the Distribution and Diet of Sympatric Populations of Juvenile Coho Salmon and Coastal Cutthroat Trout in Small Streams in British Columbia, Canada

Abstract

Abstract During the late summer period of low streamflow, the habitat use and diet of sympatric populations of juvenile coho salmon Oncorhynchus kisutch and coastal cutthroat trout Salmo clarki clarki were investigated in two small coastal streams, Vancouver Island, British Columbia. In both streams the populations of salmonids consisted primarily of age 0 + fish, with coho salmon being larger in size than cutthroat trout. Partial spatial segregation occurred in both streams, with coho salmon constituting 53-91% of the salmonid biomass in pools and glides and cutthroat trout 50-88% of the biomass in riffles. Coho salmon biomass was higher in the lower reaches, while cutthroat trout biomass was higher in the upper reaches. In both streams trophic segregation was evident, with adult insects, mainly Diptera and Hemiptera, being more common in the diet of coho salmon, whereas chironomid larvae and pupae were more common in the diet of cutthroat trout.