Assessment of Subyearling Chinook Salmon Survival through the Federal Hydropower Projects in the Main-Stem Columbia River

Abstract

High survival through hydropower projects is an essential element in the recovery of Pacific salmon Oncorhynchus spp. populations in the Columbia River. High dam passage survival is also a regulatory requirement under the 2008 Biological Opinion (BiOp; established under the Endangered Species Act) on Federal Columbia River Power System operation. The BiOp requires dam passage survival to be at least 0.96 and at least 0.93 for spring and summer out-migrating juvenile salmonids, respectively, and to be estimated with an SE of 0.015 or lower. An innovative virtual/paired-release design was used to estimate dam passage survival, which was defined as survival from the upstream face of a dam to the tailrace mixing zone. A coordinated four-dam study was conducted during the 2012 summer out-migration using 14,026 subyearling Chinook Salmon O. tshawytscha out-migrants with surgically implanted acoustic micro-transmitter tags. The release–recapture design consisted of 9 different release locations and 14 different detection arrays. Each of the four estimates of dam passage survival exceeded BiOp requirements, with values ranging from 0.9414 to 0.9747 (SE = 0.0031–0.0114). The virtual/paired-release design illustrated here has potential applicability wherever dam passage survival of migrant juvenile fish stocks must be estimated.

Received November 21, 2013; accepted March 13, 2014

ACKNOWLEDGMENTS

This study was prepared for the U.S. Army Corps of Engineers Portland District under a Government Order with the U.S. Department of Energy (Contract DE-AC05-76RL01830). We thank the staffs of the U.S. Army Corps of Engineers Portland District and Walla Walla District and the project personnel at McNary, John Day, The Dalles, and Bonneville dams for helping to make these studies successful.