The Great Lakes Fishery Commission said non-native predatory sea lamprey populations spiked due to reduced control during the COVID-19 pandemic. The commission said numbers rose when field crews were constrained in their ability to conduct sea lamprey control in 2020 and 2021.
Sea lampreys are an invasive fish that entered the upper Great Lakes accidentally through shipping canals starting in the 1920s. Sea lampreys feed on the blood and body fluids of fish by attaching to them with a tooth-filled, suction cup mouth. The average sea lamprey is capable of killing up to 40 pounds of fish during its parasitic stage.
Before sea lamprey control began in 1958, the species killed far more fish than humans did, causing considerable economic and ecological damage. According to the commission, 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.
“The sustained increase in sea lamprey abundances following a lapse in annual control effort highlights the continued need for ongoing sea lamprey control and continued research into new and innovative control methods in the Great Lakes,” said Jim McKane, the Commission’s vice-chair. “Native to the Atlantic Ocean, invasive sea lampreys remain a significant threat to the Great Lakes ecosystem, and control efforts must remain a top priority for conservation and management efforts in the region. After more than six decades of successful sea lamprey control, the reduced effort during the COVID-19 pandemic shows that if controls are ceased or relaxed for even a short period of time, sea lamprey populations will rebound, and the fishery will suffer.”
According to the Commission’s 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.
A forthcoming multiagency study funded by the Commission, led by the US Geological Survey, and supported by state and federal agencies, will provide an in-depth analysis of the effect of reduced control effort during 2020 and 2021 on Great Lakes sea lamprey populations.
The story and headline have been updated to reflect that while the commission projects a decrease in population, the numbers remain high.