Adult sea lamprey continue to show decreased abundances in most of the Great Lakes, according to a Great Lakes Fishery Commission (GLFC) report.
Sea lamprey control program success is measured by index estimates of adult sea lamprey abundance, sea lamprey marking rates on lake trout, and lake trout relative abundance.
To estimate sea lamprey populations, mark-recapture studies are conducted on index tributaries each year during the spring and summer.
Data for each lake provides insights into Great Lakes sea lamprey populations.
Lake Superior
The 3 year average adult index is above target and the trend has been holding steady over the past five years (2020 index not available).
The 3-year average marking rate on lake trout is above target and the trend has been holding steady over the past five years. The 2024 value was slightly higher.
The Lake Superior lake trout abundance trend has been holding steady over the past five years.
Lake Michigan
For Lake Michigan, the 3-year average adult index is above target and the trend has been holding steady over the last five years (2020 index not available).
The 3-year average marking rate on lake trout is meeting target and the trend has been holding steady over the past five years.
The lake trout abundance trend has been holding steady over the past five years.
Lake Huron
The 3-year average adult index for Lake Huron is above target and the trend has been holding steady over the past five years.
The 3-year average marking rate on lake trout is slightly above target and the trend has been holding steady over the past five years.
The lake trout abundance trend has been holding steady over the past five years.
Lake Erie
In Lake Erie, the 3-year average adult index is slightly above target and the trend has been holding steady over the past five years.
The 3-year average marking rate on lake trout is slightly above target and the trend has been steady over the past five years.
The lake trout abundance trend has been holding relatively steady over the past five years
Natural reproduction of lake trout in Lake Erie has been recently documented.
Lake Ontario
The Lake Ontario 3-year adult index is more than twice the target and the trend has been steady over the past five years.
The 3-year average marking rate on lake trout is above target and the trend has been flat over the past five years.
The lake trout abundance trend has been holding steady over the last five years.
Additional information can be found in the 2025 Status of Sea Lamprey Control report on the GLFC site.
Sea Lamprey Facts
Sea lampreys are an invasive fish that entered the upper Great Lakes accidentally through shipping canals starting in 1921.
Adult sea lampreys feed on the blood and body fluids of fish by attaching to them with a tooth-filled, suction cup mouth and file a hole through the fish’s scales and skin with a piston-like rasping tongue.
The average sea lamprey is capable of killing up to 40 pounds (18 kg) of fish during its parasitic stage.
Before sea lamprey control measures began in 1958, the species killed far more fish than humans did, causing considerable economic and ecological damage.
Sea lampreys have made the Great Lakes home, but the control program has been one of history’s biggest invasive species control success stories, reducing populations by 90% or more in most of the Great Lakes.
Despite previous control success, sea lampreys have the ability to bounce back forcefully in numbers if controls are relaxed.
Successful control of sea lamprey is crucial for maintaining popular sport fisheries in the Great Lakes.
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