Invasive Blood-Sucking Lampreys Are About To Spawn in Great Lakes

Sea lampreys, worm-like fish with horrifying teeth, are entering their spawning season in the Great Lakes, and thanks to COVID, might emerge in larger numbers than usual.

Sea lampreys naturally live in the cold ocean waters around Canada. They lead a parasitic lifestyle, latching their sucker-like mouth to cold-blooded animals like fish and sharks and feeding on their blood and other body fluids.

Stock image: a sea lamprey with its mouth open. Sea lampreys are an invasive species in the Great Lakes. Yelena Rodriguez Mena/iStock / Getty Images Plus

Lampreys secrete an enzyme that prevents blood from clotting, in much the same way that leeches feed. In the Atlantic Ocean, their hosts are often large enough that they are not killed by being parasitized by a lamprey. In lakes, the smaller fish are killed. They rarely feed on warm-blooded creatures like humans or dogs, so while they are no direct danger to us and our pets, they have a large economical impact.

Sea lampreys are an invasive species in the Great Lakes, having gained access via human-made canals as they were previously blocked by Niagara Falls.

"Although they are a huge pest in the Great Lakes and are responsible for millions—if not billions—of dollars of damage to the Great Lakes commercial fisheries and ecosystem, they are a natural part of the ecosystem in their native range," Margaret F. Docker, co-chair on the Committee on the Status of Endangered Wildlife in Canada, told Newsweek. "They co-evolved with the host fishes, on which they feed in the Atlantic Ocean, and they aren't pests there. In fact, they are important food sources for other fishes, birds, and marine mammals."

"The problem is that lampreys eat large numbers of fish, including lake trout, lake whitefish, and ciscoes, that fisherman catch for human consumption in the Great Lakes. Canada and the United States harvested about 15 million pounds of lake trout in the upper Great Lakes each year before the lampreys invaded the lakes. By the early 1960s, after lampreys arrived in the 40s, the catch had dropped to a mere 2 percent of the previous average," said Docker.

During spawning season, lamprey numbers can increase enormously, with each female laying between 50,000 and 120,000 eggs. They usually spawn in rivers, with eggs being laid upstream, and larvae swimming downstream before embedding in the river bottom silt for around four years before they metamorphose into the adult parasite form.

Luckily, during spawning, lampreys' digestive system slows down.

"They couldn't feed if they wanted to," Marc Gaden, the communications director for the Great Lakes Fishery Commission, told CBC News. "They have only one thing in mind once they reach that spawning phase, and that's to find a mate and to spawn successfully."

Many dams were built in streams near the Great Lakes to stop the lampreys' spawning, with lampricide, a pesticide containing TFM (3-trifluoromethyl-4-nitrophenol) that doesn't harm other fish, being added to kill around 98 percent of the larvae. However, the pandemic might have inadvertently led to there being a surge in lamprey populations in 2022.

Restrictions during the COVID-19 pandemic resulted in pest control teams not being able to treat their normal numbers of streams with the lampricide, meaning that the lampreys who slipped through the net will have happily made their way into the lakes as adults.

"We're not going to really know until probably late this year or next year... the [lamprey] coming back in 2022 were survivors of the 2020 field season. We have biologists out there monitoring the spawning rate," Gaden told CBC News. "Lampreys are spawning into late June, so we will know later this year how 2020 shook out. It's reasonable to see a spike after having to defer most of the treatments."