The Importance of In-Stream Cover to Cutthroat Trout Emigration

An extensive amount of literature exists which examines the consequences of historical forest harvest practices on stream ecosystems, including fishes. However, the importance of certain aspects of physical habitat structure is not well understood for trout, especially during seasonal low-flow. Physical habitat structure in the form of in-stream cover is influenced by the riparian substrate, stream substrate and stream flow, which are factors that are impacted by forest harvest. Our objective was to provide a rigorous manipulative study in a semi-natural outdoor setting to initially address the importance of in-stream cover to trout. In our study, we examined the effect of high and low levels of in-stream cover on wild non-migratory adult cutthroat trout emigrants. We found that there were more cutthroat trout emigrants in low cover treatments than in high cover treatments with medium-sized fish emigrating more from low cover treatments. Our study indicates that in-stream cover is important to retaining fishes in stream sections. This suggests that maintaining or adding in-stream cover habitat will be critical to maintaining cutthroat trout numbers during and after forest harvest practices.