Lake whitefish are the most important commercial fish species in Michigan.
But in the last decade, state biologists say fishers are harvesting about a third of what they used to get. The catch dropped to 1.7 million pounds last year, down from five million pounds in the early 2000s.
Agencies across the Great Lakes are trying to learn more about the population decline.
Field research on the beach
Dave Caroffino and his team have arrived at a beach in Leland on Lake Michigan. Caroffino is a fisheries biologist for the Department of Natural Resources.
He and his team have brought a long net, or seine.
“So, once we find a decent spot we spread our beach seine out. It’s 150 feet long,” he says. “We stretch the net out and then just kind of sweep it to one side, and we kind of go parallel to the beach as far as we can.”
They’re here to catch juvenile whitefish.
Caroffino says lake whitefish are by far the most important commercial fish species in the Great Lakes, and a decline in the population is a big deal for fisheries, tourism and the economy.
“We might think that ‘well, we’ll just switch to something else,’ but there isn’t enough of anything else that you can just switch to,” he explains.
Commercial fisheries are already dealing with the decline, catching fewer fish and adjusting their business models.
The culprit? An invasive species
Fisheries biologists say the main reason whitefish are declining is because of changes in the food web.
Caroffino says, basically, invasive mussels – particularly quagga mussels – are blanketing the bottom of the lakes.
“Quagga basically filter nutrients out of the water, which don’t allow phytoplankton and zooplankton to really abound,” he says.
Juvenile whitefish eat zooplankton. So when there are fewer zooplankton, it’s harder for young whitefish to survive.
Scientists say climate change might also be hurting whitefish, and lake trout are eating some of them, but the mussels are the main culprit.
Erik Crissman, a fisheries technician, is helping Caroffino pull the net back in.
“Now we’re just going to work our way in. He’s going to pull it in from that end. I’ll pull it in on this end,” say Crissman.
They pull the net up onto the beach. There are small fish hopping around. They’re about the length of a toothpick. There are also a bunch of algae.
More than 10 state, federal, and tribal agencies are surveying spots like this in Michigan, Wisconsin, and Canada, and they’ve been doing it for the past five years.
The goal of these surveys is to help biologists predict harvest numbers in the future and figure out what’s affecting the fish at each site.
“Recognizing that we can’t flip a switch and change Lake Michigan, we’re trying to figure out what can we do – what’s our small part to understanding what’s going on,” says Caroffino.
Then – Caroffino says – they’ll be better at managing the Great Lakes for whitefish.
Huddled on the beach, they measure the whitefish to see if they’re getting enough food to grow and survive.
All in all, they catch 15 juvenile whitefish in this haul. Caroffino says he didn’t have high hopes for this year.
“Really, overall the biggest surprising thing for me this year is that we’re catching decent numbers of fish in many areas,” he says.
He says that hasn’t happened since 2015. Caroffino doesn’t know why this year has been better, but he says he should know more in September.
That’s when all the agencies’ survey results will be combined.
Caroffino wants one thing to be clear: whitefish aren’t going away.
“No sounding the alarm here. Whitefish will always be a part of the Great Lakes ecosystem,” he says.
But he says there just might be fewer fish to catch and eat in the future.