A parasitic invasive species threatens Great Lakes fish populations, $7B industry

The Great Lakes Fishery Commission has announced the annual sea lamprey abundances are above population targets in all five of the Great Lakes.

The Great Lakes Fishery Commission reports a significant rise in sea lamprey populations across all five Great Lakes, following relaxed efforts since the COVID-19 pandemic.

The invasive species, which feeds parasitically on fish, poses a threat to the regions $7 billion fishery.

Sea Lampreys, accidently introduced through shipping canals into the Great Lakes in 1921, use their 150-tooth-filled mouths and serrated tongues to attach to prey, killing up to 40 pounds of fish during their parasitic stage.

Before sea lamprey control, the species killed far more fish than humans did, causing considerable economic and ecological damage.

In 1958, control programs were implemented which previously reduced populations by over 90 per cent, but the pandemic halted the slowing growth in numbers in 2020 and 2021. As a result, millions of sea lamprey larvae survived, resulting in the population surge seen today.

In 2024, adult sea lamprey numbers were 8,619 higher than pre-covid averages. All five Great Lakes are above population targets with Lake Superior and Ontario seeing the largest increase. Populations in Lakes Michigan, Huron and Erie have begun to stabilize as treatment gradually resumes.

“The increased abundance in all lakes is not unexpected given significantly reduced control effort during 2020 and 2021 due to the pandemic,” said Ethan Baker, Commision chair and mayor of Troy, Michigan.

“Elevated and variable adult sea lamprey abundances should be expected over the next year or two before turning back downward.”