Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 1168
Title: Passage behavior and survival for radio-tagged subyearling Chinook salmon at Lower Monumental Dam, 2006
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: 2008
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Walla Walla, Washington
Contract Number: W68SBV92844866
Pages: 42
Date: September 2008

We collected supplementary data on subyearling Chinook salmon Oncorhynchus tshawytscha behavior and survival at Lower Monumental Dam during 2006.  These data were collected in anticipation of installation of a removable spillway weir at the dam prior to the 2007 juvenile migration.

River-run subyearlings were collected and surgically tagged with a radio tag and PIT tag at Lower Monumental Dam from 21 June through 12 July 2006.  These dates encompassed the 85th through 93rd percentiles of the cumulative subyearling Chinook salmon dam passage index.  We released 1,143 and 959 radio-tagged fish into the forebay and tailrace of Lower Monumental Dam, respectively.  Releases were made during both daytime and nighttime throughout the study period.

Of the 1,143 fish released into the forebay, only 735 were used in the evaluation of relative survival.  This was due to the large number of fish released after 2 July, which were not detected at any of the telemetry arrays.  The fate of these fish is unknown, but may include being consumed by predators, not moving downstream to the detection arrays, or not moving downstream until after the life of the radio tag had expired.

Relative spillway passage survival was estimated at 0.943 and relative dam survival at 0.896.  Passage-route distributions were estimated at 81.4% through the spillway, 12.1% through the juvenile bypass system, 6.5% through turbines, and less than 0.5% through an unknown passage route.  Spill efficiency was estimated at 0.820, fish guidance efficiency at 0.645, and fish passage efficiency at 0.947.  Median overall forebay residence time was 2.7 h (range 0.2 139.8 h), and median tailrace egress time was 10.9 min (range 2.8 9,448.8 min).