Out of the Frying Pan and into the Fire: Unintended Consequences of Interacting Conservation Interventions for Chinook Salmon in the Columbia River (WA)

Conservation management of depleted species requires understanding of dynamic processes influencing individual survival; failure to account for the interaction of selection processes and management interventions can result in unintended outcomes that undermine recovery efforts. In the Columbia River basin, various conservation and restoration efforts have largely failed to increase the production of threatened Pacific salmon (Oncorhynchus spp.) populations. Here we considered (1) how inter-and intra-annual variability in marine environmental conditions affect survival of Chinook salmon (O. tshawytscha) during their time in the ocean; and (2) how those effects depend on whether the salmon are of hatchery or wild origin, and whether they migrated to sea naturally or were transported downstream around various hydroelectric dams. We used data from more than one million fish individually-tagged from 1998-2006 to evaluate the probability of an individual fish returning as an adult in relation to its life-history, migration route, and a suite of environmental factors including river flow, water temperature, coastal upwelling, and the abundance of predator, forage fish, and prey. We found that current efforts to transport salmon downstream strongly favor hatchery-origin fish, and may hinder the survival of wild-origin Chinook. We further found that, except for select periods when river flow is particularly low, wild fish that traveled downriver through the hydropower system had higher overall survival to adulthood than their transported counterparts. We also found evidence that competition and predator aggregation negatively affects survival, and that the effects vary with fish density and a variety of climatic conditions. Our results have broad implications for conservation of salmon as well as other species in other systems, and they highlight the importance of considering the interacting effects of both anthropogenic and natural factors on the long-term viability of at-risk species.