The Great Lakes Fishery Commission (GLFC) announced the annual sea lamprey abundances for each Great Lake in 2024.
In it, researchers noted that populations of non-native predatory sea lampreys are above targets in all five of the Great Lakes.
The sea lamprey, a highly noxious fish, spiked in numbers when field crews were constrained in their ability to conduct sea lamprey control in 2020 and 2021.
Because of the sea lamprey’s life cycle, scientists are now seeing the ramifications of those reduced control seasons.
Recent levels of sea lamprey control give the GLFC reason to believe that sea lamprey numbers are now on the way back down.
Sea lampreys are an invasive fish that entered the upper Great Lakes accidentally through shipping canals starting in 1921.
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.
Sea lamprey abundances relative to targets are reported as 3-year averages for all lakes. According to the report, 2024 is the third year that reflected the impacts of reduced control effort due to the COVID-19 pandemic.
The number of adult sea lampreys captured during 2024 was 8,619 more than the three-year pre-COVID average of 38,167 (2017-2019). The largest increases in abundance were observed in lakes Superior and Ontario during 2023 and 2024.
Although still above target, lakes Michigan, Huron, and Erie have seen flattening trends in abundance since treatments have returned to a pre-pandemic level.
source: Great Lakes Fishery Commission
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