Short-term survival of fall Chinook and Coho salmon captured by purse seines in the lower Columbia River, 2017: a holding study

Co-managers of the lower Columbia River have been exploring the viability of alternative commercial fishing gears, including beach and purse seines, to allow the selective harvest of hatchery-origin fall Chinook Oncorhynchus tshawytscha and Coho Oncorhynchus kisutch salmon. The viability of purse seines as a selective fishing gear depends on the expected survival rate of released fish. In autumn 2017, the Washington Department of Fish and Wildlife implemented a holding experiment to estimate short-term survival of Chinook and Coho salmon following capture in purse seines. Treatment fish were captured by purse seines in Columbia River Commercial Fishing Zone 5 and control fish were obtained from the Adult Fish Facility at Bonneville Dam. Paired groups of treatment and control fish were held together in net pens and their survival monitored for 48 h after capture. Mixed-effects logistic regression models were developed to explore the influence of covariates including of water temperature, body size, sort time, transport time, and reflex impairment on the probability of survival. Model selection results supported simple models and none of the covariates considered were found to significantly affect survival during this experiment. Short-term (48 h) survival for adult Chinook and Coho salmon captured in purse seines was estimated to be 97.9% (94.0 – 99.3%; 95% CL) and 98.1% (85.7– 99.8%; 95% CL), respectively.