Once near extinction, lake trout are officially recovered in Lake Superior

• Lake Superior lake trout are officially recovered, officials say
• The news comes seven decades after invasive species and overfishing nearly wiped them off the map
• Keeping the population stable will still require regular efforts to control sea lamprey

Seven decades after overfishing and invasive species nearly wiped them off the map, Lake Superior’s lake trout population has finally recovered.

That’s the conclusion of a binational group of tribal, US and Canadian species managers, who announced the milestone Wednesday in light of data that shows the self-sustaining population today is roughly as big as it was in the 1930s, before overfishing and invasive sea lamprey devastated the fish.

The group, known as the Lake Superior Committee, celebrated the recovery as testament to the progress that can be achieved when competing interest groups set aside their differences to work toward a common goal.

The recovery announcement may not be all that surprising to Lake Superior anglers — the local lake trout have been doing well for quite some time.

“It’s probably been 20 years that we’ve been in a pretty decent place,” said Dave Caroffino, a fisheries biologist in the Michigan Department of Natural Resources and vice chair of the Lake Superior Committee. 

But recent analyses of fish population data allowed species managers to officially declare victory. 

It’s a massive turnaround for a fish once on the brink of extinction. Amid fishing pressure and the proliferation of lamprey that arrived in the Great Lakes via human-made shipping canals, annual harvests plummeted from historic averages of about 4 million pounds to just 210,000 pounds in 1964.

“They were on the edge of disappearing,” said Bill Mattes, Great Lakes section leader for the Great Lakes Indian Fish and Wildlife Commission and chair of the Lake Superior Committee. 

“Managers felt the fishermen might as well fish, because they're going to be gone anyway.”

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The crisis led the governments of the US and Canada to form the Great Lakes Fishery Commission, a body tasked with reining in overfishing and finding a way to control sea lamprey.

The game-changer: A 1958 discovery that the chemical compound 3-trifluoromethyl-4'-nitrophenol, or TFM, was capable of killing lamprey without significantly affecting other species. For decades since, rivers throughout the Great Lakes have been regularly treated with the chemicals.

Stricter fishing regulations and a hatchery-raised fish stocking program also aided the  recovery, eventually allowing naturally reproducing fish to repopulate the lake. 

What happens now

Seven decades may seem like a long time, but to Mattes, the lake trout recovery has been remarkably swift. The average lake trout doesn’t begin reproducing until it’s about 9 years old and lives to age 40. That means it’s only been five generations since the collapse. 

Today, there’s no need to regularly stock lake trout in Lake Superior. But regular lampricide treatments will remain necessary.

“We've been able to drive [lamprey] down to 10% of their non-controlled level, but that 10% still takes a significant number of fish,” Mattes said. “So we need to keep that control up.”

Today, fishery managers estimate Lake Superior’s self-sustaining trout population is at least as large as it was in 1938, before sea lamprey arrived. Populations in the other four Great Lakes are not so robust. 

Lake Trout recovery efforts are still ongoing in lakes Michigan, Huron, Erie and Ontario, with some encouraging signs in parts of lakes Michigan and Huron. But those lakes also contend with invasive mussels and alewives that can’t gain a foothold in Lake Superior’s frigid waters. 

It’s unclear whether lake trout can thrive despite the onslaught. But Mattes said there’s reason to hold out hope.

“Lake trout are very resilient species,” he said. “If given the chance, they can do well.”