Linking Habitat Variables to Salmonid Growth, Survival, and Abundance in Two Coastal Northern California Intensively Monitored Watersheds

Understanding relationships between fish abundance, growth, and survival and stream habitat variables is critical to designing and implementing effective freshwater habitat restoration projects for salmonids. We investigated relationships between summer Coho salmon and steelhead parr abundance and physical stream habitat variables in Caspar and Pudding creeks, Mendocino County, California. Relationships between habitat and juvenile abundance were investigated using a stratified random experimental design. Our null 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 streams and we tested our hypotheses regarding habitat variables and salmonid abundance using two-way ANOVA, factor analysis, and negative binomial regression modeling.  The results indicated that juvenile Coho salmon abundance was positively associated with slow water, water volume, and large wood abundance, and negatively associated with fast water variables. Young-of-the-year steelhead were positively associated with water volume and large wood and negatively associated with overhead vegetation and fast water variables. Older steelhead abundance was positively associated with slow water, water volume; cover habitat formed by wood, and undercut banks. We discuss our findings relative to the use of large wood in salmonid habitat recovery programs in California coastal watersheds.