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Environment | Flora and Fauna

A Ladder To Help Lamprey Swim Upstream

Pacific lamprey will now be able to more easily swim past the McNary Lock and Dam on the Columbia River. Dam managers have installed new lamprey passage system -– the first of its kind for the toothy, eel-like fish.

Pacific lamprey numbers have dropped dramatically in the past 25 years. No one is really sure why – but fish biologists suspect difficulty swimming upstream is partly to blame.

“Their inland distribution is certainly affected by difficult passage at mainstem dams. Either they’re not passing certain dams for a number of reasons, or the effort required to pass dams has a cumulative effect,” said Brian McIlraith, lamprey project leader at Columbia River Inter-Tribal Fish Commission.

McIlraith said Pacific lamprey numbers drop off considerably from dam to dam. He said biologists aren’t sure if that means some lamprey simply decide not to continue on to their historical range, or if they die. Biologists still don’t know much about lamprey lifecycles, like the do with salmon.

Prototype Lamprey-Passage Structure
A crane and a team of riggers lowers the new lamprey
passage system into place. Credit: Terry Zerb

What biologists do know: “Of the fish that pass Bonneville [dam] about half of those are able to make it to The Dalles. There’s a similar pattern all the way up through the Mid-Columbia and the Snake rivers,” McIlraith said.

Lamprey are an important part of Northwest tribes’ diet and cultural ceremonies. Tribal elders talk of times when rivers ran black with the eel-like fish.

A recent study showed lamprey have trouble making it past the McNary Lock and Dam on the Columbia River. The McNary Dam is the fourth dam on the mainstem Columbia River.

Now, dam managers have installed a new fish passage system 30 feet below the Columbia River’s surface. The U.S. Army Corps of Engineers had previously made smaller improvements to help lamprey pass through salmon fish ladders. Biologists said this newest passage system is designed specifically to benefit Pacific lamprey, while not hindering salmon.

Steve Juhnke is a fisheries biologist with the U.S. Army Corps of Engineers. He said lamprey don’t do well in traditional fish ladders designed for salmon. They prefer slower water flowing through the passage system than salmon. The eel-like fish can better find passage entrances when they are deeper underwater.

“It’s thought that mostly lamprey migrate closer to the bottom as they approach the hydroelectric facilities,” Juhnke said.

The McNary Dam’s lamprey passage system will also be able to monitor lamprey pit-tags. The tags help biologists track lamprey so that they can learn more about the fish’s behavior and lifecycle.

“This design is could be applied at other entrances at other [dams],” Juhnke said.

Prototype Lamprey-Passage Structure
A cross-section of the McNary lamprey passage system.
Credit: U.S. Army Corps of Engineers, Josh Davin

Other dams along the Columbia and Snake Rivers have modified fish ladders that are meant to help lamprey make it upstream. Many fish ladders at other dams are outfitted with things like smooth metal plating to help the fish move upstream.

Biologists learn from each new advance that helps lamprey more easily make it past dams, CRITFC’s McIlraith said.

“We just want to keep improving the percentage of lamprey that are able to pass these structures, and also reduce the amount of time and effort that it takes them to get through each structure,” McIlraith said. “If you can improve their entrance efficiency, if you can improve their efficiency through the ladder… Then that, in theory would allow them to migrate farther and faster.”

McIlraith said Pacific lamprey historically could migrate as far, if not farther, than salmon.

Pacific lamprey are not listed as threatened or endangered under the Endangered Species Act. Biologists are trying to recover the population numbers before the fish have to become listed.

Juhnke said a few individual lamprey will show up at McNary Dam in May. The main run will make it to the dam by early July. He said if this system works well, other dams could install a similar design.

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