Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 1166
Title: Evaluation of fish condition with prototype vertical barrier screens at McNary Dam, 2004
Author/Editor: R. F. Absolon, Michael H. Gessel, Benjamin P. Sandford, Gene M. Matthews
Publication Year: 2005
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Walla Walla, Washington
Contract Number: W68SBV20655422
Pages: 26
Date: July 2005

We began a study in 2004 to evaluate the effects of three prototype vertical barrier screens (VBSs) on the condition of juvenile salmonids Oncorhynchus spp. at McNary Dam.  The VBSs were designed to work at turbine loads outside the current guidelines, which specify operation within the 1% maximum turbine efficiency range, or a loading of approximately 60 MW.  Planned improvements to McNary Dam will result in operations at a loading of 80 MW or higher.

Groups of fish tagged with passive integrated transponder (PIT) tags were released into gatewells under the present (60 MW) and higher loading discharge (80 MW).  Fish were then recaptured using the separation-by-code system at the juvenile fish facility, which diverts fish based on PIT-tag code.  Recaptured fish were examined for descaling and injury, and comparisons of fish condition were made between release groups.

However, early in the study period we had to stop evaluations of the VBSs due to reports of descaling and injury to river-run fish at the juvenile fish facility when turbine units were operated at the 80-MW loading.  The prototype VBSs were left in place, but the remainder of the spring test period and the entire summer test period were devoted to determining whether descaling was occurring within the gatewell or at some point upstream from the gatewell.

To determine where the descaling had occurred, yearling Chinook salmon O. tshawytscha were released into 1) units operated at 60 and 80 MW loads, 2) units operated at both 60 and 80 MW after trash racks had been raked, and 3) A and B slots of units operated at 80 MW.  In addition, fish were collected by gatewell dipnetting and from the orifice trap on slot 6B during both 60 and 80 MW loads and examined for injury and descaling.

Subyearling Chinook salmon were PIT tagged and released in different locations in the test gatewells to determine if release location affected fish condition.  The first release compared the north and south ends of gatewells, while the second release compared the middle and north ends.  To determine whether fish condition was being affected upstream from the collection channel (at the guidance screens, gatewell, or VBS), we also collected subyearling Chinook salmon in an orifice trap at slot 6B for examination.