Increasing water temperatures from changing climate and their effects on the survival of adult sockeye salmon, (Oncorhynchus nerka) on Snake River in the Columbia Basin

Abstract

As a consequence of climate change, many populations of sockeye salmon in the U. S. Pacific Northwest are now experiencing significantly warmer river conditions during their spawning migration from the ocean to their freshwater spawning grounds compared to the 30 year average. The Columbia River witnessed an extended heat wave in 2015 and low flows pushed water temperatures to 21° C, which ended up killing 90 percent of the adult sockeye salmon returning to spawn in their natal streams in the summer months. Fish passage delays at hydro-electric dams potentially compounded this effect. The purpose of this study was to determine if water temperatures had a delay effect on run-timing and potential returning sockeye salmon population mortality in the Snake River in the Columbia Basin. Run timing and delays in migration patterns were examined over the years 2014-2018 in order to notice any trends in migration patterns. Results indicated that, as water temperatures increased, so did the travel time of returning adult sockeye salmon migrating between Bonneville Dam and Lower Granite Dam. Increased water temperatures were associated with migration delays, increasing them by as much as ten days more than the average in some years. Qualitative observations of fish vigor on migrating fish through fish windows also yielded signs of fungal disease on a small number of sockeye salmon during warmer water temperature outbreaks.