Blood-Hungry Parasitic Sea Lampreys Invade Great Lakes, May Cause Millions of Damages

Sea lampreys are found in the cold ocean waters off the coast of Canada. They live a parasitic existence, latching on to cold-blooded animals such as fish and sharks and feeding on their blood and other bodily fluids.

In the same way that leeches feed, lampreys secrete an enzyme that prevents blood from clotting. In the Atlantic Ocean, their hosts are frequently large enough that parasitization by a lamprey does not kill them. Smaller fish are killed in lakes. They rarely eat warm-blooded animals like humans or dogs, so they pose no direct threat to people or pets. However, the worms do have a significant economic impact.

Sea lampreys are an invasive species in the Great Lakes, having gotten in through man-made after being blocked by Niagara Falls.

Pest or Food Source?

Margaret F. Docker, the co-chair of the Committee on the Status of Endangered Wildlife in Canada, explained that, despite being a major pest in the Great Lakes and causing millions of dollars in damage to the Great Lakes commercial fisheries and ecosystem, parasitic worms are a natural part of the ecosystem in their native range. She also explained that parasitic worms co-evolved with the host fishes on which they feed in the Atlantic Ocean and that the worms are not pests there. Other fishes, birds, and marine mammals use lamprey worms as a food source.

Docker pointed out that Lampreys eat large numbers of fish, including lake trout, lake whitefish, and ciscoes, that fishermen catch for human consumption in the Great Lakes. Before the lampreys infested the lakes, Canada and the United States harvested about 15 million pounds of lake trout each year in the upper Great Lakes. After the arrival of lampreys in the 1940s, the catch had dropped to just 2% of the previous average by the early 1960s.

Spawning Sea Lampreys

Lamprey populations can explode during spawning season, with each female laying between 50,000 and 120,000 eggs. They usually spawn in rivers, with eggs laid upstream and larvae swimming downstream before becoming embedded in river bottom silt for four years before metamorphosing into adult parasites. Fortunately, the digestive system of lampreys slows down during spawning.

Marc Gaden, the communications director for the Great Lakes Fishery Commission, claimed that the worms couldn't feed even if they wanted to because once they reach the spawning phase, all they want to do is find a mate and spawn successfully.

To stop the lampreys from spawning, many dams were built near the Great Lakes, and lampricide, a pesticide containing TFM (3-trifluoromethyl-4-nitrophenol) that doesn't harm other fish, was added to kill around 98% of the larvae. However, the pandemic may have unintentionally resulted in an increase in lamprey populations in 2022.

Pandemic Effect

Because of the COVID-19 pandemic, pest control teams were unable to treat their normal number of streams with lampricide, the lampreys that slipped through the net will have happily found their way into the lakes as adults, Newsweek reports.

Gaden believes there will be no way to know until late this year or early next year. He stated that the lamprey returning in 2022 were survivors of the field season in 2020. Biologists are currently monitoring the spawning rate, according to Gaden. Lampreys will continue to spawn until late June. He pointed out that a spike is to be expected after deferring the majority of the treatments.