Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 7380
Title: Evaluation of juvenile salmonid gatewell egress using updated orifice lighting treatments at McNary Dam, 2010
Author/Editor: Gordon A. Axel, Benjamin P. Sandford, Eric E. Hockersmith, Jesse J. Lamb, Nathan D. Dumdei, J. E. Simonson, Matthew G. Nesbit
Publication Year: 2011
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon
Contract Number: W66QKZ00146663
Date: 2011

We evaluated a light ring system for illuminating an existing orifice entrance in gatewell 6B at McNary Dam during 2010.  Levels of light intensity tested were 50 lux, 300 lux, and a reference condition with lights off (<1 lux).  Groups of fish bearing passive integrated transponder (PIT) tags were released to determine whether there was a difference in gatewell egress associated with each treatment.

During each light treatment, tagged fish moved volitionally out of the gatewell, passing through the orifice and into a flume, where two monitors recorded passage sequentially.  We released fish for one light treatment per day, during both day and night diel periods, and monitored detections for each group over a 12-h period.

For each release group, we estimated mean passage time from release to first detection at the PIT-tag monitors.  Passage distribution was modeled using time-to-event methods, with three factors of week (1-6), diel period (day/night), and light treatment (300 or 50 lux or light off) and three covariates of fork length, turbidity, and turbine unit flow.  Akaike's information criterion was used to determine which set of factors and covariates were best supported by the data.

Both orifice light treatments decreased delay in the gatewell and improved egress for yearling and subyearling Chinook, sockeye salmon, and juvenile steelhead under most conditions.  Sample sizes for coho salmon were insufficient for analysis.  Differences in passage time distribution between 50 and 300 lux treatments were minimal.

The magnitude of delay between the 50 and 300 lux treatments and the reference (light off) treatment was greater for fish released in the evening than for those released in the morning, indicating that the orifice light was less effective during daytime due to ambient light.  Both 50 and 300 lux treatments provided a significant reduction in passage delay during periods of high turbidity.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Describe the relationships between human activities and species recovery, rebuilding and sustainability.