Investigation of the relationship between physical habitat and salmonid abundance in two coastal northern California streams

Understanding the relationship between fish abundance and stream habitat variables is critical to designing and implementing effective freshwater habitat restoration projects for coho salmon (Oncorhynchus kisutch) and other anadromous salmonids. In this study, we investigated the relationship between summer coho salmon and steelhead trout (O. mykiss) parr abundance and physical stream habitat variables in Caspar and Pudding creeks in Mendocino County, California. Relationships between summer habitat and juvenile abundance were investigated using a stratified random experimental design. Our hypothesis was that one or more of the habitat unit types and variables examined would be associated with salmonid abundance. Habitat differences were examined between the two streams, and we tested our hypotheses regarding habitat variables and salmonid abundance using a variety of statistical tools that included two-way ANOVA, factor analysis, and negative binomial regression modeling. The results indicated that juvenile coho salmon abundance was positively (proportionally) associated with slow water, water volume, and dry large-wood abundance, and negatively associated with fast-water habitat variables. Young-of-the-year steelhead trout were positively associated with water volume and dry large-wood and negatively (or inversely) associated with overhead vegetation and fast water habitats. Older age steelhead abundance was positively associated with slow water, water volume; cover habitat formed by wet and dry wood, and undercut banks. We discuss our findings relative to the use of large wood in anadromous salmonid habitat recovery programs in California coastal watersheds.