Juvenile Coho Salmon Movement, Habitat Use and Survival in a Coastal Basin of Southern Oregon

Juvenile salmonids display highly variable spatial and temporal movement patterns that are influenced by density dependent (e.g., competition, predation) and density independent (e.g., genetics, stream discharge, physical habitat conditions) factors.  The effects of these factors differ with fish life history stage, but will ultimately affect how salmonids utilize freshwater nursery habitats and influence their survival to smolting.  Although juvenile coho salmon movement patterns and their relationships with body mass have been previously examined, the spatial scale considered in most studies has been that of the stream reach.  In this study, we monitored the movement of PIT tagged juvenile coho salmon throughout an entire southern Oregon coastal watershed to identify the prevalent resident vs. nomadic strategies these fish may adopt and to examine possible relationships between those strategies and fish body mass, growth and survival. Specific objectives include: 1) to describe seasonal juvenile coho salmon movement patterns in a coastal basin; 2) to estimate the prevalence of each movement type; 3) to evaluate whether size and growth are related to movement strategy; 4) to evaluate whether apparent survival is affected by movement strategy type; and 5) examine the relationship between apparent survival and stream habitat variables. Results of the first year of research reveal clear differences in movement patterns exhibited by juvenile coho salmon inhabiting estuarine, tidally affected and riverine habitats.  Juvenile coho salmon with mobile strategies were larger and grew faster than sedentary individuals.  Apparent survival to smolting was greater among coho sedentary during summer than those that were mobile, but was similar between coho exhibiting mobile and sedentary behavior during winter.  These preliminary results suggest that mobile juvenile coho are not necessarily competitively inferior and represent a viable segment of stream populations.  In a broader context, variable spatial patterns reflect the capacity for plastic behavior in salmonids and the importance of maintaining diverse freshwater and estuarine nursery habitats.