Invasive sea lamprey numbers declining across nearly all Great Lakes

This story is made possible through a partnership between Interlochen Public Radio and Grist, a nonprofit environmental media organization.

Efforts to control the invasive “coiled menace” appear to be working, according to the Great Lakes Fishery Commission. To keep the momentum going amid climate impacts, experts said continued research and investment is needed.

Sea lamprey populations are down this year across almost all the Great Lakes, in line with years of slow decline of the invasive species that has harmed native fish populations.

A new report from the international Great Lakes Fishery Commission says efforts to control the invasive species are working. The Canadian-American commission, working with partners across the region, has led lamprey control efforts for more than 70 years.

“If you like fishing, if you like functioning ecosystems, if you like the Great Lakes, this is good news for all of us because it shows a much healthier set of Great Lakes with these invasive predators on the decline,” said Greg McClinchey, director of policy and legislative affairs for the commission.

Sea lamprey are eel-like creatures that latch onto and kill native fish with their suckered mouths. Efforts to control populations typically involve barriers and applying lampricides to the rivers where they spawn before they enter the Great Lakes.

In Lake Michigan, researchers estimated 20,211 adult sea lampreys in Lake Michigan, down about 1,000 from last year.

Populations in Lake Huron were at 29,602, down by nearly 15,000 sea lampreys. And Lake Superior had 29,767 of the invasive species, down more than 10,000 from the year before.

Only Lake Erie saw a slight increase of 120 lamprey, but experts said those numbers are still within their target range.

“It’s showing us that the things we’re doing are working, but also to find new and innovative ways to do even more,” McClinchey said. “The objective is to keep our foot on the coiled menace.”

The ongoing decline comes after lamprey populations boomed during the COVID-19 pandemic, when public health guidelines restricted field work.

“We saw a consequential increase in sea lamprey after that. And so this story is how they’ve closed the loop and brought it back down to the levels that we were seeing before,” said Michael Wagner, a professor of fisheries and wildlife at Michigan State University who studies sea lamprey.

The most common way to bring down populations is with lampricides — chemicals that target and kill lampreys. Other strategies include installing low-head barriers or setting traps to capture lamprey.

And FishPass, the selective fish passage project on the Boardman-Ottaway River in Traverse City, will sort and pass certain fish while keeping out invasive species like sea lamprey. Construction will finish next year.

These efforts are working, experts said. But keeping pace with the effects of climate change will require more investment and research.

From increasingly extreme floods and shifting migration patterns of the fish that lamprey attach to, “systems are becoming highly variable and less predictable,” Wagner said.

Ongoing research includes looking at ways to capture sea lamprey in open rivers instead of near dams, improving lampricides in case of evolved resistance down the line, or ways to control the species without chemicals.

Wagner said managing invasive sea lamprey opens up opportunities for other conservation work or tribal communities, like restoring native fish species or reconnecting rivers like the Boardman-Ottaway in northern Michigan.

“It’s also important to think about the impacts that manifest from that success on people whose lives, livelihoods and cultural identity are tied to the native species we find in the Great Lakes,” he said.