Report shows invasive sea lamprey abundance returning to pre-pandemic levels in Great Lakes

Ann Arbor, Mich. — The annual Status of Sea Lamprey Control report for 2025 recently has been released by the Great Lakes Fishery Commission. The report highlights that adult sea lamprey abundances increased in Lake Superior but decreased in lakes Michigan, Huron, Erie, and Ontario.

According to the report, adult indices in 2025 appear to have returned to levels seen before the COVID-19 pandemic, when lampricide treatments were limited during 2020 and 2021. The number of adult sea lampreys captured during 2025 was 37,800 adults, which is just below the three-year pre-COVID average of 38,167 (2017-2019).

Although some indices remain affected by elevated populations resulting from limited treatments during COVID, the resumption of treatment efforts indicates an encouraging shift in abundances. The decreases observed in the 2024 adult indices for lakes Huron, Michigan, Erie, and Ontario have continued into 2025.

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The report highlights the necessity of continued sea lamprey control and research into innovative control measures. Sea lampreys – native to the Atlantic Ocean – are an invasive species that have posed a constant threat to the Great Lakes ecosystem. Feeding on the blood and bodily fluids of fish, attaching to prey with a tooth-filled suction cup mouth, a sea lamprey can consume up to 40 pounds of Great Lakes fish.

Control efforts are critical to the protection, preservation, conservation, and management efforts around the basin, and the 2025 report further elucidates that lampricide treatments are highly effective in controlling sea lamprey populations.

“If we are unable to control sea lamprey populations, our native fish populations would suffer immensely,” said Earl Provost, vice chair of the Commission.

Ethan Baker, chair of the Commission, added, “The Great Lakes mean a great deal to the millions of people living, working, and recreating in the basin. This $5.1 billion industry could crash if sea lamprey populations get out of control again. No one wants to have a repeat of the early days when it was hard to find a fish without a sea lamprey wound.”

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Report details by lake

Lake Superior

Though the adult sea lamprey abundance decreased for 2025, the three-year average shows the abundance remains above target for Lake Superior. Stream-specific estimates showed the Bad and Tahquamenon rivers contributed the most to the lake-wide index estimate in 2025 (46% and 40%).

Lake Michigan: The three-year average of adult sea lamprey abundance decreased in 2025, but remains above target for Lake Michigan, but has remained relatively stable around the target level for the past 10 years. Stream-specific estimates showed that the Manistique and Big Manistee rivers contributed most to the lake-wide index estimate in 2025 (37% and 22%, respectively).

Lake Huron: The three-year average of adult sea lamprey abundance decreased in 2025, but remains above the target for Lake Huron. Stream-specific estimates showed that the Echo and Cheboygan rivers contributed most to the lake-wide index estimate (28% and 26%, respectively).

Lake Erie: The three-year average of the adult sea lamprey index decreased in 2025 and is below the target for Lake Erie. Population estimates were generated using mark-recapture data for three of five index streams.

The population estimates for Cattaraugus and Youngs creeks were modeled due to insufficient recaptures of marked sea lampreys. Stream-specific estimates showed the Cattaraugus (modeled) and Big Creeks contributed most to the lake-wide index estimate (36% and 26%, respectively).

Great Lakes Fishery Commission Report