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NW Fishletter #380, April 2, 2018

[15] Chelan PUD Reaches Best-Ever Lamprey Passage

The Chelan County PUD achieved a 98-percent successful adult passage rate for Pacific lamprey at Rocky Reach Dam--the best ever measured at any dam, PUD officials say.

Steve Hemstrom, the PUD's senior fisheries biologist, told Chelan PUD commissioners on March 5 that changes to the dam's fish ladder enabled the utility to basically double its adult lamprey passage rate in 2016 and 2017 compared to 2004, when less than half of the adult lamprey that started up its ladders made it past the dam.

Those changes included adding ramps to connect concrete steps in the fish ladder and putting grates over small gaps in the water intakes to keep lamprey from slipping through in places where they aren't strong enough to swim out.

Pacific lamprey are eel-like fish, a native and ancient Columbia River species that dates back 450 million years.

Brian McIlraith, Pacific lamprey project leader for the Columbia River Inter-Tribal Fish Commission, said lamprey are culturally important to the tribes that are members of the Commission, which has pushed for many years for recovery of the non-listed species. He said when the Commission started seeing declines in lamprey returns in the Columbia River main stem and then its tributaries, it sounded an alarm.

Tribes also believe lamprey are a very important biological component of the Columbia River's ecology, he said.

McIlraith said restoring adult passage is a very important piece of the overall lamprey recovery and applauded Chelan PUD's achievement. "The 98 percent--that is a very high number, and a really positive step for lamprey restoration," he said.

However, he said, some other mid-Columbia River dams still show 50-percent adult survival passage rates, which basically halves the number of adults at each barrier. In addition, large numbers of lamprey drop out of the system somewhere in the reservoirs between dams.

McIlraith said other dams have installed the same lamprey passage equipment as those built at Rocky Reach, but each dam is different. He added that he's not aware of any other dams that have reached a 98-percent passage rate. -K.C. M.

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