HYDE PARK — Some are cheering the potential demise of two invasive species in Lake Michigan, hoping the lake can now return to its natural state.
But scientists say that is impossible.
Lake Michigan has been almost exclusively a man-made ecosystem for nearly a century, according to the fisheries biologists charged with stewardship of the lake.
It's true that invasive alewives from the Atlantic Ocean and their predators, Chinook salmon from the Pacific, are in a battle to survive in the lake as their numbers continue to veer towards collapse.
New openings in the food web could mean a resurgence in native lake trout and walleyes, but biologists warn against thinking that would make the lake any more “natural” than it is now.
Sam Cholke says nearly all of the lake's ecosystem isn't natural:
Lake Huron experienced a collapse in the number of alewives and salmon in 2003 and has since seen an increase in lake trout, but fisheries experts are quick to point out the lake trout are there because state fisheries put them there.
Randall Claramunt, a fisheries biologist with the Michigan Department of Natural Resources, said the trout population in Lake Michigan would not survive on its own.
They exist — and would only continue to exist after a possible collapse in the salmon population — because of massive efforts by state fish nurseries to breed millions of trout and release them into the lake every year.
Claramunt said biologists have some limited control over the predators in the lake, but it’s what’s happening to the bottom of the food chain that has handed ownership of the lake’s ecosystem over to man.
“We control the top-down, but not the bottom-up,” Claramunt said. “Can we restore balance to a system that we pretty much destroyed and make it sustainable?”
The biggest sign of the man-altered state of Lake Michigan today is the pristine clarity of the water.
Invasive quagga and zebra mussels from Eastern Europe were brought into the lake as stowaways on freighters and have rampaged across the lake in the last 15 years, filtering millions of gallons of water so that it now appears crystal clear, according the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory.
Quagga mussels now appear in densities as high as 35,000 per square meter, and they have completely decimated the bottom of food web in the lake, according to NOAA.
The mussels gobble up nearly all of the microscopic phytoplankton during their spring feeding and the native crustaceans that once fed on that plankton have disappeared from the lake, according to biologists.
Steve Pothoven, a fishery biologist at Great Lakes Environmental Research Laboratory, hesitated to say crustaceans like diporeia are extinct in the lake, but he said their numbers are now too small to effectively measure.
“They have disappeared and they were full of fat and everything ate them,” Pothoven said. “It’s hard to figure out exactly why now because they’re gone.”
Alewives became a pestilence in the lake in the 1960s because they liked diporeia so much, making up the bulk of their diet until invasive mussels were introduced, according to Pothoven.
It’s tempting to think that a mass die off in 1967, when a billion pounds of dead alewives were pulled from the lake, was Mother Nature restoring balance. But the fish died because of man-made pollution on the southern tip of the lake that allowed blue-green algae to bloom, which made the water so toxic that dogs that drank from the lake died of convulsions, according to news reports from the time.
States introduced Chinook salmon to the lake as the first predator of the alewives in 1967, an experiment that was successful for decades but is now close to running out of control.
But all the predators in the lake — brown trout, lake trout, rainbow trout, Coho salmon and Chinook salmon — all exist only because state fisheries stock the lake every year to bulk up the populations.
Still, there are signs of hope — although maybe not of some return to the primordial ecosystem of Lake Michigan — but of balance.
Pothoven said rainbow smelt runs have increased in numbers near his station in Muskegon, Mich.
Though smelt are also not native, escaping into Lake Michigan from an infestation in Crystal Lake in 1926, they are a key part of the lake trout diet, according to the University of Wisconsin Sea Grant Institute.
Lake trout still face challenges, though, from parasitic sea lampreys, an eel-like fish that snuck into the lake through the Welland Canal around Niagara Falls from the Atlantic Ocean in 1936. Native whitefish, catfish, walleye and chubs have also been ravaged by sea lampreys, according to the Great Lakes Fishery Commission.
Scientists said it’s still possible to find a balance in the lake’s ecosystem, but it’s foolish to think the lake can ever return to the way the lake was more than a century ago.
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