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After 70 years, the fight to get sea lampreys out of the Great Lakes continues

A sea lamprey close up
T. Lawrence
Great Lakes Fishery Commisison
"A sea lamprey can get about the size of my forearm when they’re a fully-grown parasite," said Cory Brant of the Great Lakes Fishery Commission. ";

A number of destructive invasive species have invaded the Great Lakes in the past several decades. These non-native creatures can do significant damage to native ecosystems. Biologists work hard to control them, but it's an ongoing battle. 

Cory Brant of the Great Lakes Fishery Commission has captured the story of one particularly prolific invasive species in his new book Great Lakes Sea Lamprey: The 70 Year War on a Biological Invader.

Brant referred to sea lampreys as “the little vampires of the Great Lakes.” As that nickname suggests, the parasitic creatures can be devastating to local fish populations. 

“[Sea lampreys] swim up alongside a fish and attach themselves to the side… [They] end up wearing away scales, breaking away capillaries, and getting a pretty good blood meal,” Brant said. 

The large, parasitic fish are originally from the Atlantic Ocean. Most experts think that they first got to the Great Lakes through the Welland Canal, which was built to allow ships travelling from Lake Ontario to Lake Erie to bypass Niagara Falls. Once they made it into Lake Erie, Brant said, sea lampreys had “free range of the Great Lakes Basin.”

People initially weren’t too worried about the sea lamprey, Brant explained. From the 1920s through the 1940s, “industrial dumping, pollution, and habitat loss” in the Great Lakes meant that the fish didn’t have much to feed on.

By 1949, though, lake trout and whitefish populations — which Brant called “the bread and butter” of the Great Lakes fishery — began to plummet. The fish that did survive sea lamprey attacks looked “mangled and diseased.”

Biologists tried a range of methods to control the fish. They used basket traps, electric fences, and even brought in American eels to feed on larval sea lamprey. But none of those efforts proved effective. By the mid-1950s, Brant said that an estimated 100 million pounds of fish were killed by sea lampreys every year.

That’s when those researchers turned to a new method: poison. Specifically, a “selective toxicant” that would only kill sea lampreys, and not the native fish they preyed on.  

“It was called the ‘era of the pickle jar biologist,’ where they would essentially get tons of pickle jars, put a few lamprey in — larval lamprey, little babies,” Brant explained. “Then they’d put a few bluegills in or some other small fish [like] a few rainbow trout, and then they would add all these chemicals and see what died first.”

Nowadays, it costs about $20 million annually for the Great Lakes Fishery Commission to keep the sea lamprey population under control. They haven't been totally eliminated, but the population is around 10% what it once was. Brant argues that’s a small price to pay considering what would happen if those control efforts were relaxed.

He said that sea lampreys would make a “quick comeback," and feed on “any large-bodied fish” they could find, including lake trout, Chinook salmon, and the endangered sturgeon.

“Sea lampreys — just like zebra mussels — are major ecosystem disruptors,” Brant said. “If we let up, they make a comeback.”

This post was written by Stateside production assistant Isabella Isaacs-Thomas. 

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