Age structure and hatchery fraction of Elwha River Chinook Salmon: 2014 Carcass Survey Report

Monitoring the recolonization of Pacific salmon and steelhead following the removal of two dams is a critical component of the Elwha Restoration Project. During fall of 2014, we collected adult Chinook salmon (Oncorhynchus tshawytscha) carcasses from the Elwha River in order to evaluate the proportion of hatchery fish, the age distribution of returning adults and the ratio of fish that exhibited stream vs ocean type life history strategies. Surveys were conducted from the base of the former Glines Canyon Dam at river km 21.4 downstream to where the river enters into the Strait of Juan de Fuca, including three tributaries. Of the carcasses sampled from the river and its tributaries (N = 302), the majority (88 %) were located upstream of the former Elwha Dam site. We also sampled fish (N = 500) throughout the season at the WDFW hatchery in the lower Elwha River. Carcasses were sampled for physical measurements, hatchery marks, scales and genetics. We sampled 797 non-jack carcasses during the sampling season, representing 18.3 % of the estimated escapement above the Elwha SONAR site. Over 96 % of the fish sampled were marked hatchery fish. Age-4 was the dominant age class (57%), and age- 2 fish (jacks) accounted for less than 1% of our total sample. All of the Chinook that migrated to the ocean as two year old juveniles were hatchery origin, and so we did not observe any stream-type life histories among unmarked fish.