Habitat-specific biomass, survival, and growth of rainbow trout (Oncorhynchus mykiss) during summer in a small coastal stream

We observed significant habitat-scale variation in the density, survival, and growth of 811 passive integrated transponder tagged rainbow trout (Oncorhynchus mykiss) enclosed for 63-68 days at natural density in 59 individual habitats (pools and riffles) in a small coastal California stream in summer 2001. The initial habitat-scale densities of trout were positively related to both depth and cover, although by the end of the experiment, the influence of cover on density was less apparent. Survival varied substantially, but with no clear relationship to any of the physical factors that we measured. Mean growth was density dependent, positively influenced by habitat depth, and also increased downstream within the 2-km study reach. The overall change in trout biomass over the experiment was also negatively related to fish density and positively influenced by habitat depth. Individual growth within habitats appeared to be unrelated to body size. The positive influences of water depth and distance downstream on trout growth in this experiment suggest that management actions that increase dry season discharge and limit aggradation will benefit salmonids in small streams.