3 days ago
Scientists race to save Lake Michigan whitefish as invasive mussels, warming waters are wiping out population
Sitting by a dock near the northern tip of Door County, Wisconsin, Charlie Henriksen looked out at the surrounding waters, where Green Bay meets Lake Michigan.
'Our dock is 5 miles from what used to be the greatest fishing in the Great Lakes,' Henriksen said.
The lifelong Wisconsinite has run his commercial fishing business, Henriksen Fisheries, for over 37 years, and has been fishing in this area for 50. For much of his career, Henriksen said fisheries in Green Bay and across Lake Michigan, including his, were anchored by the lake whitefish — a species of freshwater fish native to the Great Lakes.
Yet as climate change and invasive species threaten the whitefish's reproductive patterns, experts say the species is at risk of disappearing entirely from Lake Michigan in the next few years.
'(The decline) kicked the business in the head. It was just devastating,' Henriksen said.
From salted whitefish exports that poured out of Chicago's harbor in the late 1800s, to whitefish dinners in northern Michigan and Wisconsin, to their integral role in some Anishinaabe creation stories, they've been a cultural and culinary cornerstone of the region for thousands of years. They're also a major economic engine for fisheries across the Great Lakes, which bring an estimated $5.1 billion to the region annually.
Today, whitefish populations have dwindled to between 1% and 10% of their historic highs, according to Jason Smith, a biologist with the Bay Mills Indian Community in Michigan's Upper Peninsula. While the decline has been steady over the past 15 years, Smith said it's getting to the point where there are hardly enough fish to sustain commercial fishing in northern Lake Michigan.
Now, researchers across the Great Lakes are racing against time to restore whitefish populations — and figure out why these Lake Michigan fixtures are still thriving in a few small pockets of the Michigan and Wisconsin coastlines.
'Even in the leanest times of whitefish, that relationship between the people and Atikameg always continued,' said Smith, referring to the word for whitefish in the Indigenous Cree language. 'Really, the reason I do this work is to make sure that that relationship continues.'
One of the main reasons for their decline lies in plain sight. While Lake Michigan's floor is flat and sandy in most places, much of the lake bottom today is carpeted in the shells of quagga mussels. This invasive species, along with zebra mussels, another invasive mussel, were first found in the Great Lakes in the mid-1990s. Both species are filter feeders, meaning they absorb phytoplankton and zooplankton, which young whitefish rely on as a source of food and nutrients.
'How nutrients transfer through the food web has kind of been cut off and altered by mussels,' said Will Stacy, a biologist with the Illinois Department of Natural Resources. 'They blanket the bottom in a lot of areas, and they filter out a lot of that primary production.'
Over the past 20 years, these two species have expanded across much of the Great Lakes, filtering plankton and other nutrients out of the water. When zebra mussels first appeared in the lake, whitefish were able to adapt, moving deeper below the surface where nutrients were still plentiful. But when quagga mussels started to spread, local fishers noticed that whitefish began to struggle.
'The quagga mussels changed everything, for everything in the lake,' Henriksen said.
National Oceanic and Atmospheric Administration scientists estimated about 300 trillion mussels covered Lake Michigan in a 2015 count. Without plankton to support the bottom of the food chain, it's become harder and harder for whitefish to reproduce and sustain their offspring.
'The population is just more and more dominated by older fish,' said Jared Homola, an assistant professor in Michigan State University's department of fisheries and wildlife. 'It's what we call recruitment failure, when reproduction is failing. If the whitefish are successfully reproducing, the young just aren't surviving to be able to reproduce themselves.'
Whitefish populations have suffered from invasive species in the past. During the 20th century, the invasive sea lamprey was introduced to the Great Lakes. This species preyed directly on lake whitefish, leading to sharp declines in the 1960s and '70s.
Along with state and federal agencies, the Great Lakes Fishery Commission, which works with both Americans and Canadians to manage commercial fishing in the lakes, launched efforts to control sea lamprey populations. They've reduced the species' population by an estimated 90%. By the turn of the century, whitefish had rebounded to their 'highest ever abundance,' Smith remembers.
Today, though, the threats to whitefish are much harder to control — and are receiving much less funding. The EPA's Great Lakes Restoration Initiative funds several invasive mussel research and control projects. In 2023, federal agencies put a total of $1.6 million toward GLRI-run mussel projects. Their main invasive mussel research project has gotten a total of $2.45 million in federal funding since it started in 2015.
In comparison, the Great Lakes Fishery Commission budgets over $20 million annually toward sea lamprey control, with a smaller slice of funding also coming from Canada. Agencies that partner with the commission on lamprey control were targeted by Donald Trump's administration earlier this year, but after some delays, the program is back on track.
Funding for mussel restoration projects has remained intact under the Trump administration, according to Erika Jensen, executive director of the Great Lakes Commission.
Given the scope of the mussels' impact on the food chain, Smith said it can also be harder to pinpoint effective ways to combat their spread.
Typically, when fish populations run low, local authorities can gradually restock fish, raising fish in hatcheries and introducing them to the lake to supplement the population. But this, Smith said, is an 'ecosystem-driven decline.' Even if new fish are introduced to the lake, it doesn't address the root of the problem: less nutrients in the water column to support whitefish larvae.
'The easy levers to pull, like harvest stocking, all of those sorts of things are really not super helpful in this situation,' Smith said.
These shifts in the food chain are also coupled with another threat to the lake ecosystem: warming temperatures. Whitefish and other native species typically lay their eggs in nearshore reefs in the fall. As the eggs incubate over the winter, ice cover along the Great Lakes coastlines helps protect them from winter storms and UV radiation until they hatch in the spring.
But over the past 50 years, surface water temperatures in the Great Lakes have consistently increased. In Lake Michigan, the coldest lake surface temperatures recorded each winter averaged 43% warmer from 1970 to 2022 than they were averaging from 1941 to 1970, according to a recent study produced by the University of Michigan. With warmer lake surface temperatures comes less ice cover — and less protection for whitefish larvae.
'If these fish were simply adapted to hatching in a very sheltered environment, and then all of a sudden, due to climate change, there's no longer ice cover, and they're getting that direct sunlight as a very small, fragile larvae, it seems like it's maybe causing higher mortality,' Stacy said.
In Illinois, it's hard to track this trend in a definitive way. Lake whitefish are generally few and far between in southern Lake Michigan. That's been the case for several decades, even before zebra and quagga mussels were introduced to the lake, Stacy said. When Illinois' commercial fisheries were still active, whitefish catches in the region were simply lower than their counterparts in Wisconsin and Michigan. The state ceased all commercial fishing in the 1990s.
Farther north, Smith said there are still a few spots, such as Wisconsin's Green Bay or the St. Mary's River that connects lakes Superior and Huron, where zooplankton levels are high enough to sustain whitefish populations.
'The northern bay seems to be, not completely, but somewhat in lockstep with Lake Michigan,' Henriksen, the Green Bay-based fisherman, said of whitefish populations in the area. 'But the southern bay is its own little world, and it's thriving.'
By establishing strict quotas on how much whitefish local fishermen can catch, the Wisconsin Department of Natural Resources and other local authorities have helped preserve at least part of the whitefish population in the nutrient-rich waters.
Still, Henriksen said, it's not quite enough.
'There's no way that we could acquire enough quota in the lower bay to produce at the levels we produced when there was a lot of fish in the northern bay and in Lake Michigan,' he said. 'So we've made some adjustments.'
At MSU, Homola and his team are testing out a method called close-kin mark-recapture to more accurately track whitefish populations. Through this strategy, researchers use fish tissue samples to identify individual fish that are related. Based on the number of parent-offspring pairs or 'family groups' they find in their data, Homola said they can calculate how many total fish are in a population.
Currently, most Great Lakes agencies estimate whitefish populations based on the amount of whitefish caught in surveys. But Homola noted that this becomes far more difficult as whitefish populations shrink.
'The fewer lake whitefish there are, the more important it is to know how many there are,' he said.
Smith and other researchers at tribal fisheries are also working on incubating whitefish eggs in tributaries of Lakes Michigan, Huron and Superior. Nutrients are typically more abundant in rivers, so by introducing them in these more stable habitats, Smith said they're hoping to give young whitefish 'a chance to keep going.'
Other Indigenous researchers with the Sault Tribe of Chippewa Indians are raising Atikameg, or whitefish, in natural ponds. Last year, they released over 45,000 whitefish into the waters around the eastern end of the Upper Peninsula.
These methods are meant to serve as a 'bridge' to rehabilitation, Smith said. In the past, government-run fish restocking projects have relied heavily on man-made hatcheries, leading to a lack of genetic diversity in fish populations.
'I don't think any of us are thinking about restocking hundreds of millions of fish through this method,' he said. 'What we're trying to do is make sure that that wide variety of genetics continues.'
