Diel Microhabitat Preferences of Juvenile Bull Trout in an Artificial Stream Channel

Abstract

Abstract We measured day and night microhabitat preferences of age-1 juvenile bull trout Salvelinus confluentus in an artificial stream channel in early spring, and observed a significant diel shift in both microhabitat use and preference. Microhabitat variables examined were water depth, stream bottom water velocity, overhead cover, and substrate. Fish showed a stronger preference for cover during the day than at night, and generally preferred the deeper and faster areas in the channel at night compared to the daytime. The results are of importance in determining how juvenile bull trout use cover, and they suggest that maintaining or increasing rearing capacity and survival of juveniles is related to ensuring that adequate amounts of large, coarse rock substrate remain in streams. Our observations also suggest that daytime snorkeling counts of juvenile bull trout may provide inaccurate estimates of abundance because of the juvenile's extensive use of cover during the day.