Life Cycle Modeling Approach to Estimating in-River and Early Ocean Survival of Snake River Spring Chinook Salmon

A multiple stock life cycle model was built to reconstruct the population dynamics of six Snake River Chinook salmon populations. Juvenile and adult abundance trends were reconstructed by statistically fitting predicted juvenile and adult abundances to empirical abundance and survival data. Tributary spawning and rearing parameters were estimated for each population independently, and common main stem river and ocean survival rates were estimated in relation to environmental variables describing main stem environmental conditions, hydro system operations, and environmental conditions in the ocean. The life cycle model explicitly accounted for mainstem juvenile transportation and migration through each hydro project route of passage. Statistical model fitting results show a negative effect between a powerhouse contact index and juvenile survival through the Columbia River hydro system, and significant effects for environmental variation in the ocean. Results also indicate a delayed mortality effect, where increased powerhouse contact has a negative effect on survival in the year of ocean entry.