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Response of juvenile salmonids to placement of large woody debris in California coastal streams
Large woody debris is frequently placed into streams of the Pacific Northwest in an effort to improve habitat conditions for rearing juvenile salmonids. Unfortunately, many restoration projects do not incorporate monitoring of biotic response to these activities. This project compared stream reaches and pool habitats with differing quantities of large woody debris to determine the effects of large woody debris restoration structures on biomass, size, growth, and survival of juvenile coho salmon, age-1+ steelhead, and age-0 trout in two coastal streams in Northern California from July 2004 through June 2005. No significant differences in fish response variables were detected between treatment and control reaches. However, some significant relationships between physical habitat features and fish response variables were detected. Biomass and length of age-1+ steelhead were positively related to the proportion of pool habitat, while growth was positively related to mean reach depth. Length of age-0 trout was positively related to large woody debris density during the fall, and growth was positively related to pool depth. Fish responses at the habitat unit scale were more variable, but generally indicated preferences for pools and, in some cases, cover. Overall, the proportion of pool habitat and stream depth appeared to be the most important physical habitat features influencing salmonid productivity in these two coastal streams. Although direct effects of habitat restoration were not detected in this study, these results indicated that stream restoration structures that substantially increase the amount of pool habitat and create deeper pools can positively benefit coho salmon and steelhead populations.