Ecological Consequences of Pacific Salmon Recolonization after Restoration of a Migratory Corridor

Anthropogenic barriers cause multiple ecological effects including severing the link between oceans and freshwater ecosystems mediated by spawning populations of anadromous fish; however, relatively little is know regarding the ecological consequences of circumvention of these barriers for anadromous fish and their ecosystems. We applied a food web approach and stable isotope analysis (SIA) as a tool to investigate the ecological consequences of Pacific salmon recolonization after a 100-yr absence following installation of a fish ladder on the Cedar River, Washington, USA. Results from two experiments and a before-after field study allowed us to identify the functional relationship between adult salmon carcass biomass and stream food webs and the key energetic pathways by which salmon influences its food web. For example, SIA indicated a 3-fold expansion of the isotopic niche space or trophic diversity of resident rainbow trout six years following salmon reintroduction relative to before salmon even though the density of spawning adults was low. We use these combined results to suggest the magnitude of salmon fluxes necessary to affect ecosystem processes in their natal watersheds following barrier removal.