Officials at the Great Lakes Fishery Commission have found a resurgence in the population of sea lampreys, which represent a pernicious threat to commercial fisheries in the region. This development has been identified as a new and unusual aftereffect of reduced control efforts during the COVID-19 pandemic.
Relaxation in sea lamprey control in 2020 and 2021 has resulted in above-target numbers. In its report, the Commission 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.
But recent levels of sea lamprey control give the Commission 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, which 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. That said, sea lampreys, like a coiled spring, 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 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.
“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.”
The Commission was established by the Governments of Canada and the United States in 1955 in part as a response to the catastrophic damage caused by the sea lamprey invasion.
(Photo from Great Lakes Fisheries Commission)