Workmen lower a section of a prototype lamprey-passage structure into place at McNary Dam. The structure is intended to help lamprey get past the dam as they migrate.
U.S. Army Corps of Engineers
WALLA WALLA — Pacific lampreys, primitive fish that play a key role in river ecosystems, may find an easier path around McNary Dam thanks to the U.S. Army Corps of Engineers.
Engineers hope a prototype structure on the dam’s Oregon shore fish ladder will help lampreys get past the structure as they migrate up the Columbia River. Work on the project was finished late last month by Marine Industrial Construction of Wilsonville, Ore., which was awarded a $336,542 contract for the job.
In a release, Corps Project Manager Mark Smith said the foot-high flume between the entrance and exit of the McNary structure contains circle- and half-circle-shaped baffles to produce a range of reduced water velocities.
Recent studies indicate adult lampreys have difficulty entering the fish ladder. Because they move primarily along the bottom of the river, lampreys prefer lower passage routes with reduced water flows. The fish ladder entrance was set high in the water column and uses higher velocities to attract salmon and steelhead.
“We plan to conduct video monitoring to observe which velocity is preferred by migrating lampreys,” said Smith. “We anticipate this prototype structure will help us learn quite a bit about what’s best for lamprey passage.”
The passage is also fitted with detectors to help track lampreys fitted with passive identification tags.
Lampreys are important to the health of the inland aquatic ecosystem.
“As larvae, they’re the vacuum cleaners of our streams and rivers, spending the first four to seven years of their lives in freshwater, filter-feeding among the sands and fine silt,” Smith said.
As adults migrating to the ocean environment, Pacific lampreys become parasitic and feed on a variety of saltwater prey. After two to three years, they stop feeding and return to the freshwater rivers and streams to spawn.
Although not a federally protected species, lamprey numbers have “declined drastically” in the Columbia Basin during the past 30 years, said Aaron Jackson, lamprey project leader for the Confederated Tribes of the Umatilla Indian Reservation. Lampreys are culturally significant to the Pacific Northwest tribes who use the fish for food and medicine.
The fish were once common in the Snake, Clearwater and Salmon river drainages.
“We’re seeing only 4,000 returning now. There used to be millions,” Jackson said.
Tribal representatives participated in the Corps work group that was involved in the design and engineering for the McNary passage structure, the first one of its kind in the mid-Columbia River.
“We’re excited to see something like this put in the river,” Jackson said. Information gleaned from how well the McNary structure works can be applied to help design structures for other locations.
“There’s no real cookie-cutter approach,” he said. “Each dam is unique.”
Andy Porter can be reached at firstname.lastname@example.org or 526-8318.