A multispecies assessment of climate change threats to salmonids across their life cycle

During their life cycle, salmonids experience conditions in freshwater, estuarine, and marine habitats, exposing them to numerous climate change threats. The extent to which different species utilize different habitat types and habitat-specific climate change risks should result in differential overall vulnerability of these species to climate change, but most previous vulnerability assessments have focused only on particular life stages for particular species, hampering our ability to protect, restore stocks and their habitats to maximize species portfolios in river systems. We performed a life cycle-based risk assessment of climate change threats for nine species of salmonids (species within Oncorhynchus, Salvelinus, and Prosopium genera) inhabiting the Skagit River system, which is vulnerable to the panoply of climate impacts forecasted for the Pacific Northwest. The risk assessment integrated both species-specific intensity and exposure and incorporated uncertainty. We found that while climate change threats existed across all habitats inhabited by these species, the greatest threats to all species were associated with projected changes in the extremes of freshwater flow (high incubation flows, low summer flows). These results suggest that restoration strategies targeting restoration of floodplain function will be most effective for reducing the most serious threats for a broad portfolio of salmonids inhabiting the Skagit River, although other climate adaptation strategies may provide additional benefits to other suites of species.