Standardized seawater rearing of chinook salmon smolts to evaluate hatchery practices showed low statistical power

We examined, under standardized conditions, seawater survival of chinook sa lmon Oncorhynchus tshawytscha at the smolt stage to evaluate the experiment al hatchery practices applied to their rearing. The experimental rearing pr actices included rearing fish at different densities; attempting to control bacterial kidney disease with broodstock segregation, erythromycin injecti on, and an experimental diet; rearing fish on different water sources; and freeze branding the fish. After application of experimental rearing practic es in hatcheries, smolts were transported to a rearing facility for about 2 -3 months of seawater rearing. Of 16 experiments, 4 yielded statistically s ignificant differences in seawater survival. In general we found that high variability among replicates, plus the low numbers of replicates available, resulted in low statistical power. We recommend including four or five rep licates and using alpha = 0.10 in 1-tailed tests of hatchery experiments to try to increase the statistical power to 0.80.