Linking Life History Strategy to Environment: Using Otolith Microchemistry and Growth to Model Stage-Specific Movement of Juvenile Fall Chinook Salmon

Anthropogenic changes have significantly altered the migratory corridors and spawning habitat of Snake River fall Chinook salmon (Oncorhynchus tshawytscha). One consequence is the change in selective pressures that were formerly experienced by native populations; which for fall Chinook juveniles included fast growth and early outmigration. The population has recently undergone changes in juvenile life history expression, with a significant proportion of the population adopting a longer freshwater rearing phase, compared to a predominantly subyearling migration. Previous work has shown that these migration strategies are spatially structured within spawning areas and may be correlated with stream temperature. Additionally, modeling has indicated that the yearling life history may confer higher fitness than other life history strategies. Understanding the fitness tradeoffs driving these changes in migration strategy requires reconstructing juvenile behavior at a more detailed temporal and spatial scale than current tagging studies allow. Otoliths provide this stage-specific location and growth information based upon coupled microchemistry and microstructure analysis.  Using this information we relate performance and potential fitness consequences to the environment experienced by juvenile fish.  Results from a stage-structured movement model, parameterized with otolith and environmental data, reveal the tradeoffs for individuals adopting different migration strategies given the variability in environmental conditions.