A model-based assessment of the potential response of Snake River spring-summer Chinook salmon to habitat improvements

The current recovery strategy for threatened Snake River Chinook salmon Oncorhynchus tshawytscha relies heavily on improvements to the quality of freshwater spawning and rearing habitat; however, the potential survival benefit from these actions is unknown. To address this issue, we created a model for predicting the early freshwater survival rates (egg to smolt) of this species as a function of five easily measured physical habitat variables and used this model to evaluate survival rates under five alternative future habitat states. Model validation showed that the predictions were reasonably accurate for individual stocks as well as for the trend in predictions across stocks. The results for the future habitat scenarios suggest that the potential for improving survival rates through habitat restoration is high for a few populations and low to nonexistent for most others while the potential for reduction in survival rates due to reduced habitat quality is great for all populations. The effects of modeled egg-to-smolt survival rate changes should be evaluated across the entire Chinook salmon life cycle to assess recovery potential.