Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 1167
Title: Passage behavior and survival for radio-tagged subyearling Chinook salmon at Lower Monumental Dam, 2005
Author/Editor: R. F. Absolon, Eric E. Hockersmith, Gordon A. Axel, Darren A. Ogden, Brian J. Burke, Kinsey E. Frick, Benjamin P. Sandford
Publication Year: 2007
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Walla Walla, Washington
Contract Number: W68SBV92844866
Pages: 40
Date: September 2007

In June 2005, an Oregon District Court ordered spill to be used at McNary Dam and the four lower Snake River dams in an effort to improve survival of juvenile Pacific salmon Oncorhynchus spp.  As a result, the U.S. Army Corps of Engineers initiated a study to evaluate passage behavior and estimate survival during the juvenile migration period for subyearling Chinook salmon O. tshawytscha, which coincided with the period of mandated spill.

For this study, we collected and tagged river run subyearling Chinook salmon at Lower Monumental Dam from 6 through 16 July 2005.  This period included the 86th through 95th percentiles of the cumulative subyearling Chinook salmon passage index at Lower Monumental Dam.  Fish were surgically implanted with both a radio and PIT tag.  We released 1,103 tagged fish into the forebay and 1,092 into the tailrace of Lower Monumental Dam.  Releases were made during both daytime and nighttime throughout the study period.

Of the 1,103 fish released into the forebay, we included only 602 in the evaluation of relative survival.  This was due to the large number of fish that were not detected by any of the telemetry arrays after release.  The fate of these fish remains unknown, but may include consumption by predators, failure to move downstream to the detection arrays, or failure to move downstream until after the life of the radio tag had expired.  Similar results were noted in 2004 for radio tagged subyearling Chinook salmon released after about 4 July during a study of passage behavior and survival at Ice Harbor Dam.

Relative spillway passage survival was estimated at 0.905 and relative dam survival at 0.722.  Estimated passage routes were 88% through the spillway, 8% through the juvenile bypass system, and 2% each through turbines and unknown passage routes.  Spill efficiency was estimated at 0.874, fish guidance efficiency at 0.832, and overall fish passage efficiency at 0.955.  Spill effectiveness was estimated at 1.53. Median forebay residence time was 3 h, and median tailrace egress time was 2 min.