Parasitic ‘Vampire’ Fish Numbers Surge in Lake Superior
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A recent report by the Great Lakes Fishery Commission (GLFC) revealed that populations of parasitic sea lampreys in Lake Superior have surged over the past four years.
This spike follows a reduction in sea lamprey control efforts during 2020 and 2021 due to pandemic-related constraints. While recent control measures are showing promise, elevated numbers are expected to persist for another year or two before trending downward.
Why This Matters
Sea lampreys, often referred to as “vampire fish,” pose a significant threat to the Great Lakes ecosystem and economy.
They feed on the blood and bodily fluids of fish, with each adult capable of killing up to 40 pounds of fish during its parasitic stage.
According to the GLFC, restricted control efforts during the pandemic may have allowed millions of larval sea lampreys to survive and parasitize “millions of pounds of valuable fish.”
Left unchecked, sea lamprey populations can decimate native fish species, causing widespread ecological and economic harm.
The mouth of a sea lamprey, full of sharp, horn-shaped teeth, makes it an efficient fish killer. Sea lamprey numbers have surged in recent years. The mouth of a sea lamprey, full of sharp, horn-shaped teeth, makes it an efficient fish killer. Sea lamprey numbers have surged in recent years. Karla Bartelt/USFWS
What Are Sea Lampreys?
Sea lampreys are invasive, eellike fish equipped with a suction-cup mouth filled with sharp teeth and a rasping tongue that bores into their prey.
Native to the Atlantic Ocean, they are not naturally found in the Great Lakes but have thrived there since their accidental introduction.
How Did Sea Lampreys Get Into Lake Superior?
Sea lampreys entered the Great Lakes through shipping canals in the 1920s. By 1958, their predation had caused devastating damage to fish populations.
Control measures, initiated in the mid-20th century, have since reduced lamprey numbers by over 90 percent, making it one of the most successful invasive species control efforts in history.
What to Know
The GLFC attributes the recent surge in sea lamprey numbers to reduced control efforts during the COVID-19 pandemic.
In 2024, 8,619 more adult sea lampreys were captured compared to the pre-COVID average of 38,167.
Lake Superior and Lake Ontario saw the largest increases in sea lamprey numbers, while lakes Michigan, Huron, and Erie showed stabilization due to resumed control efforts.
The number of sea lampreys in Lake Superior is estimated to be around 200,000. All other Great Lakes have populations below 100,000.
Two sea lamprey feeding on lake trout. Their sharp teeth and suckers allow them to rasp a hole into the side of a host fish and feed on its blood. Two sea lamprey feeding on lake trout. Their sharp teeth and suckers allow them to rasp a hole into the side of a host fish and feed on its blood. USFWS
What People Are Saying
Commission chair Ethan Baker, who is also the mayor of Troy, Michigan, in a statement: “The increased abundance in all lakes is not unexpected given significantly reduced control effort during 2020 and 2021 due to the pandemic. Control effort in 2024 continued at pre-pandemic levels, but elevated and variable adult sea lamprey abundances should be expected over the next year or two before turning back downward.
“If there was ever proof of the effectiveness of sea lamprey control, the 2020 pandemic and its effect on sea lamprey populations was it.”
Jim McKane, the commission’s vice chair, in the statement: “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.
“Maintaining consistent sea lamprey control in the Great Lakes basin is essential to sustaining the robust fishery that provides jobs, sustenance and recreation for the people of the Great Lakes basin.”
What Happens Next?
The GLFC and its partners have returned to pre-pandemic levels of control, aiming to curb sea lamprey populations over the coming years.
Future efforts include a multiagency study led by the U.S. Geological Survey to assess the long-term impact of reduced control during the pandemic.
The GLFC expects a decrease in the abundance of sea lampreys in Lake Superior at the beginning of 2025.
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