The Environment Report
6:00 am
Tue October 1, 2013

Great Lakes fish on a diet

The second story in our series, "In Warm Water: Fish & the Changing Great Lakes."

Scientists say one way climate change is harming the Great Lakes is by warming the water too quickly in the spring.

That warm-up can decrease food for tiny creatures in the lakes--the creatures that game fish like trout and salmon eat.

Leaner meals

As his small research boat zooms near the breakwater in Milwaukee, scientist John Janssen looks at the monitor in the boat's dashboard and reads the Lake Michigan surface water temperature.

Janssen has paid a lot of attention to water temperatures in the nearly 40 years he's been studying the Great Lakes.

For more than a decade, he's been at the University of Wisconsin-Milwaukee. Janssen and other scientists have noticed that all the Great Lakes have tended recently to warm earlier in the spring. He says in deeper water lakes like Michigan, Superior, Huron and Ontario that's an especially vital change that affects the lake food web.

“With the faster warming up, there's not as much time for the phytoplankton to grow, and as a consequence there's not as much food to feed the zooplankton that feed on the phytoplankton and there's not enough food for the little baby fish, so you can't support the big fish that people love to catch," he says.

Janssen says the big fish like whitefish, brown trout and salmon might not grow as much.

But scientists say climate change is complex, and brings many things, including more frequent heavy rainstorms. Janssen says the big storms wash nutrients off the land, and into the Great Lakes.

That might provide a bit more food for the little critters at the bottom of the food web, but Janssen says anglers might still have to get used to catching smaller fish.

Will the fishing change?

Jason Woda fires up the engine on the Trophy Hunter, the charter fishing boat he operates in Milwaukee. Woda's been in the business for 14 years, helping anglers reel in trout and salmon. He's not a denier of climate change, but says the faster warming of Lake Michigan hasn't made much of a difference to his business.

“I don't see it changing a lot. Everything is kind of controlled, everything has a check and a balance as far as food and forage base, biomass and the number of fish we put in. There's a whole bunch of checks and balances there," Woda says.

The fishery is heavily managed, but the lakes are not in balance. Invasive species have shaken up the food web, and now, climate change is encouraging some anglers to adapt.

Step inside the cold water fish hatchery run by the Keewenaw Bay Indian Community in northern Michigan and you see dozens of small brook trout swimming in the tanks.

The tribe has also has added ponds for rearing walleye, because under climate change walleye might do better than trout, at least near the Keewenaw Peninsula along Lake Superior.

Hatchery manager Evelyn Ravindran says a reduced trout population would be a cultural and economic loss for the tribe.

"For the commercial fishery, it'd be pretty devastating. People, they have their traditional fishing ground. They have activities -- bringing your children out to those grounds where you grew up fishing -- those are strong traditions people would be really hurt to see disappear,” she says.

The feel of the wind and look of the water along Superior, Michigan and the other Great Lakes will continue to be familiar. But scientists say a changing climate will make things challenging for today's fish populations.

Related program: