Combining Food Web and Ecosystem Techniques to Evaluate the Potential for Salmon and Steelhead Habitat Restoration

Fisheries professionals are often directed to use an “ecosystem approach” when assessing alternative recovery strategies for fish populations; however, the information necessary to do so is often lacking.  As a result, evaluations of most recovery actions are based on measurements of physical habitat (e.g., pool area, wood abundance, etc.), largely neglecting the food web within which target species are embedded.  In the Pacific Northwest, millions of dollars are spent annually on restoration aimed at the recovery of anadromous salmon and steelhead populations.  There is a need to develop additional techniques to evaluate the potential for these projects to succeed.  We describe a method to evaluate restoration that combines food web information with measures of ecosystem processes (e.g., food production and demand), and we describe a case study of its application.  The approach quantifies flows of energy between species within ecosystems, which can be used to quantify the strength of direct and indirect interactions, including those between fishes and their predators, prey, and competitors.  Measures of interaction strength also form the basis for evaluating the potential for any interaction (e.g., food availability or effects of a predator) to limit a given population of concern.  We are applying this approach in floodplain segments of the Methow River (Washington, USA) where the reconnection of side channel habitats has been proposed as a strategy to help recover threatened and endangered salmon and steelhead populations.  We combine estimates of fish production and food demand for all the dominate members of the fish community (both salmonid and non-salmonid), with dietary information (from gut and isotope analysis), and invertebrate food base production to create quantitative food webs for both the main channel of the Methow, and several side channels, which restoration would mimic.  This method allows us to evaluate how members of the fish assemblage compete for shared prey, and how this competition might limit production of target species.  For instance, in the Methow, over 80% of fish production can be composed of non-salmonid species, which have diets that significantly overlap with those of salmon and steelhead.  However, our results also show that dramatically different food webs can develop in side-channels with different morphologies, some of which are more favorable to the growth and survival of anadromous fish.  By including all members of the fish assemblage in a comprehensive food web approach, this method will help researchers predict outcomes, reduce uncertainty and prioritize restoration efforts.