Exploring Reponses of Salmon to River Restoration Using Simple Food Chain Models

With the decline of salmon populations, restoration of freshwater habitats has become a key management strategy.  Yet, these practices do not always enhance salmon populations, and instead may benefit non-target species.  This may be because many restoration actions can alter the structure and function of food webs in unforeseen ways that may not favor species of concern.  Thus, understanding how salmon populations might respond to restoration efforts will require approaches that account for these critical food web interactions.  We describe a mechanism-based model that explicitly links the dynamics of freshwater food webs, salmon life cycle, in-stream physical habitat, and riparian conditions.  We used this model to explore the potential responses of salmon populations to alternative restoration strategies in a floodplain segment of the Methow River, Washington.  We provide examples of restoration actions that can have positive, negative and no effect on juvenile salmon, as well as provide potential explanations for each outcome.   Our model provides a tractable framework for exploring the consequences of different restoration and environmental change scenarios in a way that goes beyond fish-habitat relationships.  Lastly, the model can be used to provide information to generate hypotheses, plan field experiments, and ultimately guide river conservation efforts.