Concurrent Sessions B: Lamprey Passage - Aids to Adult Pacific Lamprey Passage at Obstacles in the Umatilla River: A Bag of Tricks

A variety of structures (e.g., hydropower dams, culverts, irrigation diversions) can delay or obstruct pre-spawning migration of Pacific lamprey (Entosphenus tridentatus). We hypothesized that low adult lamprey returns to spawning areas in the Umatilla River were caused by loss of habitat connectivity in this watershed. To identify barriers to adult lamprey passage, we conducted a 4-year radiotelemetry investigation. A total of 217 adult Pacific lamprey were implanted with radio transmitters and released in the first 55 km of the river, where there are seven low-elevation (\u3c 8 m) dams. Poor passage efficiency (\u3c 40% fitted passage probability) was recorded at four of the dams and resulted in limited escapement to upper sites. During the study, one of these dams was breached and lamprey passage efficiency immediately improved from 32 to 81% at that structure. Similarly, after water augmentation actions were taken, passage improved and migratory-phase fish exhibited a threefold increase in mean passage efficiency (from 17 to 50%). Lamprey-specific fishways have also been added at 3-Mile Falls, Feed, and Dillon dams. Structure design was tailored to the specialized requirements of each site. Our results indicate that actions to afford adult lamprey access to historical spawning areas are key to the successful restoration of this species