Estimation of Survival and Run Timing of Adult Spring/Summer Chinook Salmon from the Columbia River Estuary to Bonneville Dam: A Cooperative Effort Between NOAA Fisheries and Columbia River Commercial Fishermen

Predation by pinnipeds on salmon and steelhead in the Columbia River (CR) has been identified by the NOAA Fisheries West Coast Regional Office as a severe threat to salmon recovery. Adult salmon returning to the CR during the spring are particularly vulnerable to predation because their presence most overlaps that of the transient sea lion population. In an effort to assess predation on spring/summer Chinook salmon returning to the Middle and Upper Columbia and Snake Rivers, NOAA Fisheries has been working closely with CR commercial fishermen.  Together we have marked over 1500 adult salmon within the CR estuary and measured their survival and transit time through the first 145 miles of freshwater.  After accounting for harvest and impacts from sampling gear, weighted mean annual survival ranged from 59%-90% from 2010-2015.  Lower overall survival was observed during recent years coincident with a growing sea lion population.  Within season survival has consistently been lower during periods of peak sea lion presence.  Our results imply predation is a significant source of mortality for these fish and that some fish populations may be at higher risk than others based on their behavior.