Water Temperature and Velocity as Determinants of Microhabitats of Juvenile Chinook and Coho Salmon in a Laboratory Stream Channel

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Abstract
In an artificial stream channel, the distribution of juvenile coho salmon Oncorhynchus kisutch and chinook salmon O. tshawytscha at various water temperatures and average water velocities was monitored with respect to use by the fish of water velocities, cover objects, and a simulated side pond area in two successive years. In year 1, water temperature was manipulated and average water velocity was held constant. In year 2, both water temperature and average water velocity were manipulated. For both wild and laboratory-reared junvenile coho and chinook salmon, more fish were associated with cover objects (year 1 and 2) or areas of low water velocity (year 2) at 2.degree.C than at 12.degree.C. In year 2, increasing average channel water velocity increased use of cover objects by coho salmon but not by chinook salmon. Coho salmon were more associated with cover objects and were found at lower average water velocities than were chinook salmon at all water temperatures and velocities. Coho salmon apparently have a greater cover-seeking reaction to lowered water temperature and increasing water velocity than do chinook salmon. Both species increased their use of the pond area in response to low water temperature in year 1, but reduced their use of it at 2.degree.C during year 2. I conclude that low water temperatures and, to some extent, increases in water velocity may be important stimuli for microhabitat shifts often reported in stream observations of junvenile salmonids during the fall-winter transition.

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