Management strategy evaluation for salmon habitat restoration and hatchery supplementation

A primary challenge in conservation is the evaluation of management actions. For species with complex life histories, this evaluation is particularly challenging, and quantitative models are needed to understand how effects on particular life stages translate to objectives such as an acceptably low extinction risk or large abundance. We modeled the effects of increasing juvenile survival (as would result from habitat restoration) and hatchery supplementation on the achievement of recovery objectives for endangered Chinook salmon (Oncorhynchus tshawytscha) in the Wenatchee River Basin of Washington State. We evaluated these actions using simulations with a model that accounted for density-dependence operating in juvenile rearing habitat. Simulations indicated that there were compounding benefits of increasing survival in both natal streams, where juveniles are born, and in downstream areas where a portion of juveniles rear. We also found that the marginal benefit of producing more hatchery fish declined as juvenile survival improved. Simulations suggested that achieving recovery targets for abundance of spring-run Chinook salmon in the Wenatchee River would require more than a 150% increase in juvenile survival, barring increases in survival in other portions of the life cycle. Therefore, comprehensive management focusing on multiple factors affecting survival may be required to meet recovery criteria.