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NW Fishletter #376, December 4, 2017

[5] Chum Salmon Operations Underway at Bonneville Dam

Flows to protect chum salmon spawning at Bonneville Dam started Nov. 7, a week later than planned because of the absence of chum in the area and low inflows at the dam.

Chum are now present below Bonneville Dam in the Ives/Pierce island area where they will spawn; and as of Dec. 1, 21 chum have also been counted passing Bonneville Dam.

While surveying the Ives/Pierce island area for spawning chum in early November, Washington Department of Fish and Wildlife biologists spotted Steller sea lions eating the fish near Woodward Creek, not a location where sea lions have been encountered before.

Columbia River chum are listed as threatened under the Endangered Species Act. Their returns have ranged between 1,000 and 10,000 in recent decades, with runs in the Lower Columbia Gorge population exceeding the goal of 2,000 adult chum annually. The 2016 return to the lower Columbia Gorge, near Bonneville Dam, was 3,400 chum.

The annual chum operation, dictated in a plan required by the FCRPS 2008-2014 BiOp, aims for a tailwater elevation at the dam of at least 11.5 feet but no more than 13 feet. This is the elevation range that is optimal to encourage chum spawning and protect the chum redds once they're made.

Above this elevation range, flow velocities can become too high, making it difficult for chum to spawn.

However, if water levels do rise--usually because of abundant rainfall--the chum plan, coordinated by the interagency Technical Management Team, allows dam operators to increase project outflow during nighttime hours, first up to a tailwater elevation of 16.5 feet and then, if necessary, up to 18.5 feet, because biologists believe chum are daytime spawners.

The 90 day forecast in the lower Columbia Basin is for slightly above-average precipitation. Although it's early in the season, the April-August runoff forecast is about 107 percent of normal at The Dalles Dam and 105 percent of normal at Grand Coulee.

Chum flow operations are maintained into January. -L. B.

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