Rub, A.M., Som, N.A., Henderson, M.J., Sandford, B.P., Van Doornik, D.M., Teel, D.J., Tennis, M, Langness, O., van der Leeuw, B., Huff, D.D. 2019. Changes in adult Chinook salmon (Oncorhynchus tshawytscha) survival with the lower Columbia River amid increasing pinniped abundance. Canadian Journal of Fisheries and Aquatic Sciences 76: 1862-1873. dx.doi.org/10.1139/cjfas-2018-0290
We conducted a comprehensive mark-recapture tagging study to examine the behavior and survival of spring run Chinook salmon (Oncorhynchus tshawytscha) returning to the Interior Columbia River Basin. Our study included adult salmon returning to the Upper Columbia and Snake Rivers, two fish populations that have been protected under the Endangered Species Act for greater than 15 years. This study was prompted by concern that pinnipeds present within the estuary and lower CR during spring may be detrimentally affecting the recovery of these salmon stocks. Over a five-year period we injected adult salmon with Passive Integrated Transponder Tags as they returned to the estuary. We used these data to fit a mixed effects logistic regression model and identify covariates that influence survival to Bonneville Dam (Rkm 235). Modelling indicated sea lion exposure, the abundance of adult shad (Alosa sapidissima) within the lower Columbia River, and whether or not fish had intact adipose fins all influenced survival. Survival ranged from 0.46 to 0.80 annually over the course of the study and was lowest during the last two years.