Over-winter survival and habitat use by juvenile coho salmon (Oncorhynchuskisutch) in two Lake Superior tributaries

Dramatic declines in commercial and recreational fisheries for coho salmon (Oncorhynchus kisutch) in Lake Superior have raised questions about the nat ural factors that limit their productivity. Snorkeling surveys were conduct ed during the winters of 1995-96 and 1996-97 to estimate over-winter mortal ity and determine winter habitat use by juvenile coho salmon in two spring- fed tributaries of Chequamagon Bay, Lake Superior. Results indicated high d ensities of juvenile coho salmon in pool habitats of the two streams (x = 0 .85 fish/m(2)) and high over-winter survival (>45%). Regression analyses re vealed no significant relationships between fish distribution and physical habitat variables (large woody debris, overhead cover, and pool size). No s hift in habitat use over the winter was found. These results contrast sharp ly with findings from the pacific Northwest where juvenile coho salmon gene rally occupy complex pool habitats during the winter. Although streams of t he CI-eat Lakes region are similar in many respects to Pacific streams, dif ferences, particularly in stream flow regimes, indicate that the early life history of coho salmon populations in these two regions differ dramaticall y. These observations may have important implications on the management of stream habitats in the Great Lakes.