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NW Fishletter #385, Sept. 4, 2018

[8] USGS Finds Fish Surface Collectors Performance Varies Widely

U.S. Geological Survey research has found that performance varies widely for floating surface collectors used in Washington and Oregon to capture juvenile salmon and steelhead at high-end dams on their migration downstream.

These results, detailed in a new study of seven such systems, were shared with the Northwest Power and Conservation Council.

Set up in dam forebays, the collectors have been successful in some locations, and perform poorly in others, said Toby Kock, a research fish biologist at the USGS Western Fisheries Research Center.

Collectors are being used at dams throughout the region, and the study can help dam managers better understand how to increase fish collection goals, Kock told the Council in his Aug. 15 presentation.

For this study, funded by the U.S. Army Corps of Engineers, the agency reviewed operating characteristics and river conditions at Washington's Upper Baker and Lower Baker dams on the Baker River, Cushman Dam on the Skokomish River and Swift Dam on the Lewis River; and Oregon's North Fork and River Mill dams on the Clackamas River, and Round Butte Dam on the Deschutes River.

Kock said surface collectors at Upper Baker, Lower Baker, North Fork and River Mill showed 87- to 99-percent efficiency in collecting juvenile sockeye, steelhead, coho and Chinook, while the Cushman, Swift and Round Butte collectors had efficiencies ranging from 2 to 32 percent.

The study found success rates were better when higher flows went through the collectors; when collectors had lead nets to help direct juvenile fish to the facilities; when the entrance area was deep and wide; and when the effective forebay area was not too large.

Temperature can also play a role, as juvenile fish will go deeper and may pass under nets during high-temperature conditions, Kock said.

He noted modifications have already been made to some collectors, resulting in increased collection of juvenile coho at Cushman Dam, from 19 to 31 percent. Swift Dam also had an increase in coho collection, from 8 to 20 percent, and in Chinook, from 0 to 7 percent. -K.C. Mehaffey

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Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
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