A fish that was nearly wiped out of the Great Lakes is on its way to a full recovery now in Lake Huron. Lake trout are suddenly doing what biologists have been trying to get them to do for more than 40 years: make babies. The change might mean a more stable and resilient ecosystem in the future.
Jim Johnson didn't think he'd see the day when lake trout recovered in Lake Huron. Johnson runs Michigan’s Fisheries Research Station in Alpena. He’s been working on the lake for 25 years and for most of that time it looked hopeless.
"I felt we were so completely stymied by one thing after another after another," he recalls. "The litany of challenges working against the reestablishment of a self-sustaining lake trout population seemed insurmountable."
The federal government has hatched almost 100 million lake trout since 1972 and put them in Lake Huron, but those stocked fish couldn’t seem to reproduce, until recently. Among the persistent problems were invasive species like sea lamprey and alewives, both from the Atlantic Ocean.
Lampreys are parasites, they decimated the lake trout fishery back in the 1940s. The eel-like fish has since been controlled with a chemical discovered in the 1950s but the St. Marys River has been a challenge to effectively treat.
A diet of alewives makes a lake trout sterile and this has been the decisive factor. Alewives also eat lake trout fry. Alewives had their own problems about 10 years ago and disappeared from Lake Huron. Then everything changed.
Jim Johnson says now lake trout don’t need much more help from hatcheries.
"The end of stocking is in sight for the main basin of Lake Huron."
True apex predator stands up
Lake trout arrived in the Great Lakes just after the glaciers receded and adapted to cold and empty waters. So they’re perfectly suited for the lakes. They have a long lifespan and will search every corner of the lake for food and if there’s no food available they’ll just stop growing.
Ellen Marsden, a fish biologist at the University of Vermont, says there are lake trout in northern Canada that have evolved quite differently.
"The lake trout that we know and love are big, piscivorous and fast growing," Marsden says. "There are also lake trout that are mature and could be 25 years old at half the size our lake trout are and they’re feeding on plankton."
No lake trout in the Great Lakes feeds on plankton but Marsden says that shows how adaptable the fish genus salvelinus is.
"Even Darwin knew this group as a highly flexible group," she says.
The prospect the lake trout returning to the top of the food web is an exciting one for scientists. This is already the case in Lake Superior but Lakes Michigan and Huron have been dominated by salmon from the Pacific Ocean for most of the last 50 years. Salmon were introduced to create an exciting sport fishery but Jim Johnson says the exotic fish couldn’t withstand recent and dramatic changes in Lake Huron’s ecosystem and died off.
"People tended to think of the Chinook as an apex predator," he says. "But they don’t meet these criteria of what an apex predator needs to do and that is to adapt to changing situations and still be there after a crisis."
Johnson says native fish like lake trout and walleye are filling the void created by the salmon’s demise in Lake Huron. He expects the lake to be a more stable ecosystem in the future and less expensive to manage since it won't need to be stocked with millions of hatchery fish annually.
His staff will make a recommendation next month about future stocking efforts for Lake Huron.
This video footage was taken by researchers at the University of Vermont. These lake trout are spawning in Lake Champlain.