Identification of Summer‐Run Chinook Salmon Spawning Areas in the Main‐Stem Columbia River Upstream of Wells Dam, Washington

Abstract

Summer-run Chinook SalmonOncorhynchus tshawytscha historically spawned in the Columbia River as far upstream as British Columbia, Canada, but the upstream extent of main-stem spawning in the contemporary Columbia River has been documented in the tailrace of Wells Dam, Washington. We utilized radiotelemetry and video monitoring equipment between 2011 and 2013 to track wild summer-run Chinook Salmon upstream of Wells Dam and document any main-stem spawning sites. Two small spawning areas totaling 3,389 m 2 were identified within 1.76 km downstream of Chief Joseph Dam and were used by spawning salmon in each year of the study. Redd deposition totaled 70, 59, and 134 redds in 2011, 2012, and 2013, respectively. When considered with tributary redd counts upstream of Wells Dam from the Methow and Okanogan rivers, main-stem spawning represented between 1.6% and 2.9% of the annual redd deposition upstream of Wells Dam within each spawning year. Redds were located in depths between 3.7 and 7 m, with spawning occurring between late October and mid-November in each year. These novel results are the first to detail main-stem spawning locations of summer-run Chinook Salmon upstream of Wells Dam and should inform population monitoring metrics, such as annual escapement and prespawn mortality estimates.