Low-Elevation Dams Are Impediments to Adult Pacific Lamprey Spawning Migration in the Umatilla River, Oregon

Abstract

Due to tribal concerns over the recent decline of Pacific lamprey Lampetra tridentata, a restoration program was initiated to establish a self-sustaining, harvestable lamprey population within the ceded lands of the Confederated Tribes of the Umatilla Indian Reservation in Oregon. We hypothesized that low returns of adult lampreys to spawning areas in the Umatilla River were caused by loss of habitat connectivity in this watershed. We conducted a study to determine whether the ubiquitous, low-elevation irrigation diversion dams in the main-stem Umatilla River were obstacles to adult lamprey spawning migration. Radiotelemetry was used to assess lamprey passage efficiency at seven dams located within the lowest 55-km reach of the Umatilla River. During this 4-year study, we tracked 217 adult Pacific lampreys that were implanted with radio transmitters and released downstream from the dams. Logistic regression analysis indicated that dam design, fish size, and temperature had the greatest effects on passage efficiency. Poor performance (<30% fitted passage probability) was recorded at the two lowest dams in the system and resulted in limited escapement to upper sites. During the study, one dam was breached, after which passage efficiency there immediately improved from 32% to 81%. In addition, water augmentation actions at Three Mile Falls Dam apparently contributed to improved mean passage efficiency of migratory-phase fish (from 17% to 50%). Thus, actions to improve adult lamprey access to historical spawning areas are feasible and are key to successful restoration of this species.

Received June 29, 2011; accepted February 13, 2012

ACKNOWLEDGMENTS

We thank Jakob Settle and Brandon Treloar for their help with all aspects of the radiotelemetry field effort. Howard Pennington helped with the capture and transfer of lampreys at Bonneville Dam. TeLa Branstetter maintained lampreys at the South Fork Walla Walla Facility, and Kinsey Frick managed the radiotelemetry database. Brian Burke provided help with statistical analyses. Stacy Schumacher assisted with graphics. Jeanette Howard, Doug Dey, Debbie Docherty, Celeste Reves, Brent Leonard, Helen Brandling-Bennett, Paula McAteer, Tom Ruehle, Gary James, and Julie Burke all helped with project administration. JoAnne Butzerin and Brian Zimmerman provided editorial comments to improve the manuscript. Major funding was provided by the Bonneville Power Administration.