What’s Tipping the Scales Toward More Bass, Fewer Walleye in Wisconsin Waters?

by Sydney Widell
For walleye and other northern Wisconsin fish, a warming climate may mean smaller populations and shrinking ranges, said Center for Limnology Director, Jake Vander Zanden, in a lecture Wednesday.
Addressing a crowd of homeowners and area fisherman at the Nicolet Area Technical College, Vander Zanden illustrated the way warming lakes, among other factors, are already sending walleye and other cold water fish into decline.

Jake Vander Zanden.

Walleye prefer colder water, so warming northern lakes could be one reason walleye ranges are shrinking, Vander Zanden said. He contrasted that trend with growing numbers of largemouth bass, a fish that is more tolerant of warmer water.
“Warming temperature seems to be a pretty major factor in shifting the balance toward largemouth bass,” Vander Zanden said. “These projections are difficult to do, but they give us a sense of what we might expect for our fish communities.”
The area’s shifting bass and walleye populations are only passengers of other ecological changes, Vander Zanden said. As their lakes warm, other cold water fish, like lake herring and perch, stand to loose ground — or in their case, water — as well.
Warming lakes may not be the only factor driving the population turnover, though.
Unpublished data collected by Vander Zanden’s graduate student Holly Embke indicate that direct human activities like fishing also play a role in tilting the scales against walleye and towards bass, Vander Zanden said.
“People fish walleye with the intent of harvesting. They’re amazing in the frying pan,” Vander Zanden said. By comparison, it’s rare to find anglers in Wisconsin who keep bass for table fare, meaning more bass are tossed back into the lake to continue to live and reproduce while their walleye counterparts are destined for a dinner plate.  
Vander Zanden acknowledged the possibility of other factors, like competitive interactions between the species and habitat loss as other stressors that could be contributing to declining walleye numbers amid surges in bass populations.
“Some of these other factors are changing as well, but warming temperatures combined with differential exploitation is really what’s shifting our communities more towards bass,” Vander Zanden said. “But it’s an area that’s not fully understood.”
Holly Embke counts fish as part of a study on a northern Wisconsin lake. Photo: Riley Steinbrenner

Embke’s upcoming research aims to answer some of those questions by explaining how different stress factors interact with each other. Vander Zanden hopes that her research will trace the perimeters of a “safe operating space” for cold water fish, or the conditions where vulnerable species can continue to exist despite different combinations of stressors.
“This is a concept that we’re trying to frame to any natural resource that may have different stressors.” Vander Zanden said. “If we see one stressor is coming on that we can’t really do anything about, we can find different ways to minimize the impact of other stressors.”
Vander Zanden’s lecture was the final installment of the “Our Changing World” series, a program co-sponsored by the Nicolet College Sustainability Professional Learning Community and the Oneida-Vilas Chapter of the Citizens’ Climate Lobby. The program explored specific, local climate change impacts and provided a community platform to discuss those issues.

Sydney Widell is the Center for Limnology’s Summer Science Communication Intern up at Trout Lake Station. Stay tuned from more dispatches from her summer up north!