Characteristics of Juvenile Chinook and Coho Winter Habitat

The winter habitat associations of juvenile Chinook and coho salmon were investigated over 3 winters within large glacial rivers of Southcentral Alaska, to provide information for the evaluation of the effects of hydroelectric development. Juvenile salmon relative abundance was measured during mid-winter at multiple locations representing available winter habitats. Measures of water temperature, dissolved oxygen, conductivity, pH, water depth, ice thickness, water velocity, cover and woody debris were collected at each trap location. We tested for relationships between habitat characteristics at each trap site and the number of juvenile salmon in each trap (CPUT). We then looked to see if these same relationships could be used to predict coho salmon relative abundance at larger spatial scales: specific sites and macrohabitat classification types. Juvenile Chinook and coho salmon CPUT were positively related to local measurements of woody debris, water velocity, and dissolved oxygen. However, juvenile salmon were absent from some sites and macrohabitats that had favorable habitat characteristics. We hypothesize that conditions prior to ice development or short term changes in water velocity displaced fish from potential overwintering locations with favorable habitat conditions. Therefore, accurately assessing winter habitat may require accounting for short-term adverse conditions.