Migration Behavior of Adult Pacific Lamprey in the Lower Columbia River and Evaluation of Bonneville Dam Modifications to Improve Passage, 2001

ii iii EXECUTIVE SUMMARY In previous years of study, we used radiotelemetry to identify obstacles to passage of adult Pacific lamprey (Lampetra tridentata) at lower Columbia River dams. Lamprey have the greatest difficulty gaining entrance to the fishways, negotiating collection channels and transition areas, and passing through count station areas at the top of the ladders. The objectives of our research in 2001 were to: 1) assess behavior, passage success, and migration rates of radio-tagged adult Pacific lamprey at lower Columbia River dams, 2) evaluate the effects of lower water velocity and structural modifications on passage of lamprey at the spillway entrances at Bonneville Dam, 3) evaluate effects of modifications to diffuser gratings (i.e., addition of plates to permit attachment of lamprey) on passage of adult lamprey at Bonneville Dam, and 4) more intensively monitor lamprey passage at the tops of Bonneville Dam ladders t