Alanna Mayham

PORTLAND, Ore. (CN) — Pacific lamprey are making a big comeback at the Bonneville Lock and Dam in the Columbia River Gorge this fall, with returns up 170% from the dam’s previous 10-year average, the U.S. Army Corps of Engineers said Monday.

Army Corps biologists count fish as they migrate through fish ladders at mainstream Columbia and Snake river dams, all of which played a large role in the species’ decline over the last 90 to 66 years.

Since the 1990s, the scientists have worked alongside tribal and government partnerships to improve lamprey passage at the dams — an effort that appears to be paying off, considering as of Sept. 18, biologists counted 63,836 lampreys passing through Bonneville alone.

Overall this year’s lamprey passage represents a 252% jump from Bonneville’s four-year average of 41,414. The number is made all the more impressive given that biologists counted the typically nocturnally traveling species during the day — leading them to suspect this year’s return is a minimum estimate, and the number may actually reach around 165,314.

Aiding the effort was the Army Corps’ installation of a lamprey passage structure at Bonneville in addition to the dam’s current fish ladder, both of which passing lamprey use. For the traditional passing point, Army Corp biologist Kyle Tidwell explained that the agency made improvements so that lamprey can avoid strong currents, rest in areas along their journey and exit existing salmon ladders into a system with flows, angles and materials that are lamprey friendly.

The change, it appears, has made a big difference.

Help also came from funding by the Bonneville Power Administration and participation from the U.S. Fish and Wildlife Service, which, through the Pacific Lamprey Conservation Initiative, works with partners to assess lamprey populations and threats while conducting research, restoration and advocacy efforts.

But the challenge of restoring the region’s once thriving lamprey population also required the advocacy and aid of local tribes and conservationists, especially since the species are ecologically and culturally significant to the Columbia River Basin.

For instance, healthy lamprey numbers suggest positive outcomes for the region’s imperiled salmon and steelhead because they act as a buffer between the fish and predatory sea lions known to feast near the dam. From a broader biological perspective, Tidwell explained how the prehistoric fish are a good indicator of system health and system function — particularly as they have been in the river longer than any other fish, he said.

Lamprey have also historically been a culturally significant food source for indigenous tribes in Washington, Oregon and Idaho, prompting the groups to lead initiatives to help save the species’ depleting population.

About 46 years ago, four tribes with fishing treaty rights on the Columbia River came together to form the Columbia River Inter-Tribal Commission. Those tribes are the Nez Perce Tribe, the Confederated Tribes of the Umatilla Indian Reservation, the Confederated Tribes of the Warm Springs Reservation of Oregon and the Confederated Tribes and Bands of the Yakama Nation.

Together, the commission describes itself as one that provides “invaluable biological research, fisheries management, hydrology and other science to support protection and restoration of Columbia River Basin salmon, lamprey and sturgeon.”

For lamprey specifically, this involves monitoring and sustainability efforts by way of translocations, genetic analysis, local recolonization, artificial propagation and surveying the species’ accumulation of contaminants.

Along with the tribes’ leadership in lamprey restoration, this year’s increase in lamprey passage at Bonneville is also thought to be driven by ocean conditions and food availability in the Pacific Ocean, according to Sean Tackley, a northwestern division fish policy and program manager for the Army Corps.

The improvement, he said in a statement, “motivates us all to continue to what we can to help these important fish.”

Looking ahead, the Army Corps announced its biologist have begun studying downstream passage of juvenile and larval lamprey in addition to ongoing research for fish passage. The work that’s set to be initiated this year, Tidwell said, will track young lamprey and observe where they are entering the river system, approaching dams, whether they get stuck at certain points and how they move down the river.