Passage efficiency of adult Pacific lampreys at hydropower dams on the lower Columbia River, USA

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adult, Columbia River, dams, efficiency, Hydropower, lamprey, Pacific lamprey, passage efficiency, spawning, migration, fishways, entrance, channel, upstream, Bonneville Dam, Dalles Dam, John Day Dam

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Transactions of the American Fisheries Society


Hydropower dams in the lower Columbia River may contribute to declines in thepopulations of anadromous Pacific lamprey (Lampetra tridentate) by limiting access to historicalspawning locations. To identify obstacles to migration, we documented the movements of radiotaggedadult Pacific lampreys in specific areas of fishways (entrances, collection channels,transition areas, ladders, and counting stations) at the first three dams they encounter as theymove upstream (Bonneville, The Dalles, and John Day). From 1997 to 2000, 147-299 radiotaggedlampreys were released downstream from Bonneville Dam. In 1997 and 2000, we alsomoved 50 radio-tagged lampreys each year to positions upstream from Bonneville Dam to assessthe passage success of fish that had not passed through an entire fishway (i.e., naive fish). Thepassage efficiency of lampreys at Bonneville Dam was 38-47%, and the median time required topass over the dam ranged from 4.4 to 5.7 d. In contrast, 50-82% of the lampreys passed overThe Dalles Dam in each year, and passage times ranged from 2.0 to 4.0 d. Passage efficiencywas lowest at John Day Dam, but that estimate was based on relatively few fish. After enteringthe fishways, lampreys had the greatest difficulty (I) negotiating collection channels and transitionareas that lacked attachment sites and (2) passing through the Bonneville Dam counting stations.Unexpectedly high passage success was documented in the ladders, where maximum currentvelocities could exceed 2.4 m/s. We found no evidence that lampreys released downstream fromBonneville Dam had higher passage success at The Dalles Dam than naive fish. In each year upto 60% of the lampreys made multiple entrances at the fishways, indicating that lampreyspersistently attempted to pass upstream. Dams in the lower Columbia River impede adult Pacificlamprey migration, and only 3% of the fish we tagged reached areas above John Day Dam.





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