Adfluvial Life History in Spring Chinook Salmon from Quartzville Creek, Oregon

Through spawning ground and snorkel surveys, we confirmed the presence of adfluvial spring Chinook Salmon Oncorhynchus tshawytscha in a tributary upstream from a high-head dam in the upper Willamette River in northwest Oregon. Spring Chinook Salmon previously had been extirpated above the dam but juvenile hatchery fish were released in the reservoir in subsequent years. In 2012, we recovered six carcasses of adfluvial Chinook Salmon adults, identified nine live adults, and recorded nine redds. Analyses of scales from carcasses revealed those fish were ages 5-6. Otolith microchemistry from an unmarked adult female Chinook Salmon did not indicate ocean residence, and no hatchery thermal marks were observed, suggesting this fish was the progeny of adfluvial adults. In 2013, we observed one live, unclipped adult and three juvenile Chinook Salmon. We conclude that adfluvial spring Chinook Salmon exist in Green Peter Reservoir and successfully reproduce. This is the first documentation of adfluvial Chinook Salmon in Oregon, and this unusual life history should be considered in the context of research, monitoring, and recovery actions pertaining to ongoing reintroduction programs for threatened Willamette River spring Chinook Salmon above dams.