Streambed substrate as refuge for O. mykiss

A flume was used to estimate the carrying capacity of streambed substrates for juvenile steelhead or rainbow trout Oncorhynchus mykiss seeking refuge from freshets. The simulated freshets had mean water column velocities of about 1·1 m s-1. The number of fish finding cover within the interstices of the substrate was documented for different substrate sizes and levels of embeddedness. The availability of suitable refuges determined the carrying capacity of the substrate for O. mykiss. For the size of the fish tested (122 mm ± 13 mm S.D.), the number of interstices with depths = 200 mm measured with a 14 mm diameter flexible plastic tube was the best predictor of the number of O. mykiss able to find cover (R2 = 0·75). Oncorhynchus mykiss seeking refuge from freshets may need deeper interstices than those seeking concealment at fall or winter base flows. The availability of interstices suitable as refuge from high flows may determine fall and winter carrying capacity.

Ligon, F. K., R. J. Nakamoto, B. C. Harvey, and P. F. Baker. 2016. Use of streambed substrate as refuge by steelhead or rainbow trout Oncorhynchus mykiss during simulated freshets. Journal of Fish Biology 88: 1,475–1,485.

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