Carrying Capacity of an Enhanced Side-Channel for Rearing Salmonids

Abstract

Two attempts were made to establish the yield of steelhead smolts (sea-run rainbow trout) (Salmo gairdneri) from a seminatural side-channel and compare it to that of the parent river. In the first, 10 000 fry were introduced to the channel which was maintained at a discharge of 0.42 m3/s. The fry, however, were largely displaced by extraneous coho salmon (Oncorhynchus kisutch), appeared unable to withstand the water velocity in winter, and were greatly reduced by infection from Cryptobia. In the second trial discharge was 0.14 m3/s. The fry tolerated this. The yield (i.e. numbers) per unit area of steelhead smolts, of mean weight 14.5 g, was 31 times that of the river; in terms of biomass it was 10 times. Channel discharge was 2.6% of the river discharge. Physical and biological factors determining smolt yield from streams are considered.