Evaluation of water temperature effects on adult sockeye salmon (Oncorhynchus nerka) behavior in the Yakima River, Washington, 2019

A study was conducted in the lower Yakima River, Washington, during June–October 2019 to evaluate water temperature effects on adult sockeye salmon (Oncorhynchus nerka) behavior. A total of 60 sockeye salmon adults were tagged with radio transmitters and monitored during the study. Fourteen of the fish were collected and tagged at Prosser Dam in late June and the remainder were collected and tagged at the mouth of the Yakima River in late July. Water temperature exceeded 20 degrees Celsius (°C), conditions shown to block upstream migration of adult sockeye salmon in other river systems, from June 9, 2019 to September 15, 2019. These elevated temperatures seemed to affect the behavior of tagged fish during this study. Fish that were collected and tagged at Prosser Dam left the Yakima River within days of release and tagged fish that were collected and released at the mouth of the Yakima River failed to enter and move upstream until mid-September when water temperature decreased to less than (<) 20 °C. Monitoring sites were located adjacent to several known areas of cool-water inputs that may provide thermal refuge for fish in the lower Yakima River to determine if tagged fish spent time in these areas. Although several tagged fish moved repeatedly past these sites, most fish spent <30 minutes at any given site, indicating that fish were actively migrating past the sites rather than holding near cool-water inputs. A single tagged fish moved upstream to Roza Dam and was collected for upstream transport to Cle Elum Reservoir during our study. Additional research in subsequent years likely will be required to better understand how water temperature affects adult sockeye salmon in the lower Yakima River.