Effects of Size at and Time of Release on the Survival and Growth of Steelhead Fry Stocked in Streams

Survival and growth from age-0 fry to age-1 + parr was estimated for steelhead Salmo gairdneri stocked in two British Columbia streams at different times (May 26–October 15) and different sizes (0.2–6.0 g). Fry were released into separate sections of the two streams. Monthly mortality rates, which ranged from 15.4 to 9.6%/month, were inversely related to size at stocking and time of release. We were unable to separate the effects of size and release time because these factors were highly correlated. Daily instantaneous growth rates of early stocked, small fry (> 0.009) were much higher than those of later-stocked, larger fry (<0.002) but there were only minor differences in mean weights of age-1 + parr among release groups. In determining the best strategy for releasing fry, factors other than survival must also be considered. Costs of raising fish to larger sizes must be balanced against the costs of collecting eggs and the availability of brood stock.