Sea lamprey numbers declining in Lakes Michigan, Ontario, report shows

ANN ARBOR, Mich. - A new report on an invasive species of the Great Lakes reveals mainly good news in the fight to wrest control over the waterways from the sea lamprey.

Populations of the eel-like organism remain at near-historic lows for most of the Great Lakes, with the exceptions of some areas.

"Keeping sea lamprey populations in check is absolutely critical if we want a fishery in the Great Lakes," said Jim McKane, chair of the Great Lakes Fishery Commission in the report. "Each year, we must wage the battle anew. We cannot rest on our laurels or rely on our past success. Sea lampreys are here to stay. Fortunately, we can control their populations such that the damage they inflict on the fishery is a fraction of what it once was." 

Lamprey aren't the prettiest species that reside in the Great Lakes - in fact, they take on the appearance and behavior similar to that of a vampire. Acquiring their food by latching onto other fish, they remain there for 12 to 18 months. Since wiggling their way to the Great Lakes Basin via manmade shipping canals and lacking any predator, they have wreaked havoc on the region's fisheries. 

Since funding and resources were diverted toward reducing their impact however, the Great Lakes Fishery Commission has achieved monumental success. Before control efforts were put in place, sea lamprey killed an estimated 103 million pounds of fish every year. That number has been reduced to less than 10 million pounds of fish per year.

On Tuesday, the commission reported that Lakes Ontario and Michigan saw lamprey numbers below the target number, Lake Huron was at or just above the target, and Lakes Superior and Erie came in above target but numbers were "holding steady." Communications Director Marc Gaden said the signs were "very encouraging."

"(For) Superior, the lamprey are above target, but its trending downwards and the fishery has done intensive treatment this year," he said.

For reducing lamprey numbers, researchers are often firing at a moving target. A lampricide, which is applied to the lamprey larvae at locations where the species likes to spawn, was placed at areas in Lake Superior in 2016. For reasons that aren't entirely understood, treatment results were mixed. One of the reasons numbers could be higher than their target mark is because lamprey populations can benefit from improved conditions among other fish populations. More food means a better chance of succeeding. Which is why researchers went through another lampricide spraying in 2019. 

A curious find embedded in the report shows that despite increased numbers of sea lamprey, the number of wound rates on fish where the invasive species attach themselves is showing signs of declining. Researchers aren't sure why.

And then there's Lake Erie, arguably one of the most productive lakes in the world still dealing with a major sea lamprey infestation.

"Lake Erie has been above target since the mid-2000s. When I say above target, it was way above target," Gaden said. "The problem is, they are coming from outside Lake Erie."

Lake Erie doesn't have many hospitable places for lamprey to survive and thrive - which is why scientists were confused to see their numbers rise in the mid-2000s. After intensive treatments didn't work, Gaden said researchers began to suspect Lake St. Clair may be the offender, offering enough habitat for the lamprey to breed, as well as the conduit to a major source of food.

However, just like with Lake Superior improvements to habitat, major restoration efforts in Lake Erie and tributaries that lead into the water body have promoted the growth of several fish species. But that also means the lamprey have enough food to sustain themselves. 

Jack Nissen is a reporter with Fox 2 Detroit. You can reach him at (248) 552-5269 or at Jack.Nissen@foxtv.com