Agencies investigating whitefish decline in the Great Lakes

Aug 28, 2018

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.

 

Dave Caroffino, a fisheries biologist for the Department of Natural Resources, has arrived with his team at a beach in Leland on Lake Michigan. They've 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 at the beach to catch juvenile whitefish.

 

DNR fisheries technician Eric Crissman pulls a 150-foot net out into Lake Michigan. Over 10 state, federal and tribal agencies are surveying juvenile whitefish populations to learn more about their declining numbers.
Credit Morgan Springer

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 mussel behind the decline

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," says Caroffino, "which don’t allow phytoplankton and zooplankton to really abound."

Juvenile whitefish eat zooplankton. So, when there are less 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.

 

State biologists (from left to right) Eric Crissman, Dave Caroffino and Courtney Weldon work to capture juvenile whitefish in a 150-foot net. State, federal and tribal agencies have been conducting surveys like this for the past five years.
Credit Morgan Springer
State biologists search for whitefish in the algae. They measure the fish and bring them back to the lab for genetic testing.
Credit Morgan Springer

Erik Crissman, a fisheries technician, helps Caroffino pull the net back in and up onto the beach. There are small fish hopping around. They’re about the length of a toothpick. There’s also a bunch of algae.

 Survey goals

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 better understand 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, he says, they’ll be better at managing the Great Lakes for whitefish.

 

In the early 2000s, commercial fisheries in Michigan were harvesting around 5 million pounds of lake whitefish. In 2017, they only harvested 1.7 million pounds. Scientists say invasive mussels are changing the food web and leading to the decline in whitefish populations.
Credit Morgan Springer

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.

 

Fisheries technician Eric Crissman hauls a 150-foot net down the beach in Leland, Michigan. Juvenile whitefish surveys like this are happening in Michigan, Wisconsin and Canada.
Credit Morgan Springer