Summer and Winter Habitat Selection by Juvenile Chinook Salmon in a Highly Sedimented Idaho Stream

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Abstract
Summer and winter habitat utilized by age‐0 spring chinook salmon Oncorhynchus tshawytscha was assessed in the Red River, an Idaho stream heavily embedded with fine sediment. During summer 1985, chinook salmon used habitats with water velocities less than 20 cm/s, depths of 20–80 cm, and close associations with cover (undercut banks). Densities were greater than 60 fish/100 m2. As the fish became larger they selected faster, deeper water. Eighty percent of the chinook salmon emigrated from the study sites in October when stream temperatures were 4–8°C, apparently because suitable winter habitat was not available. Those fish that remained in the study sites selected areas where submerged sedges and grasses overhanging undercut banks provided cover and where water velocities were less than 12 cm/s. After cobble substrate was added to the streambed (September 1985) beneath undercut banks and in midchannel in a glide and a riffle habitat, eight times more chinook salmon used the cobble substrate in November 1985 as compared with November 1984. Significantly more chinook salmon utilized cobble placed under banks than any other area. By March 1986, cobble piles were embedded with silt and sand, and chinook salmon densities were not significantly different from those found in March 1985.

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