Bass Set to Win, Walleye Lose Under Warming Projections

Walleye. Photo: Gretchen Hansen

Following up on our call for political officials in Wisconsin to start taking climate change seriously, here is a post originally published in September of 2016 about one of the potential impacts global warming will have on Wisconsin and Midwest lakes. For more, check out the researchers’ amazing website!

Climate change is predicted to alter sport fish communities in Midwestern lakes, according to a new study that related water temperature to suitability for walleye and largemouth bass in over 2,100 Wisconsin lakes.
Walleye populations have been declining and largemouth bass populations have been increasing in lakes across Wisconsin for the past 30 years. These changes are cause for concern for many anglers and policy makers; freshwater fishing in Wisconsin is valued at over $1.5 billion, and walleye are the preferred species for many anglers.
Researchers identified characteristics of lakes where walleye or largemouth bass were most likely to thrive. Both species were strongly influenced by water temperature; walleye populations thrived in cooler, larger lakes, while largemouth bass were more abundant in warmer lakes.
“Generally this means that lakes that are best for walleye are not the best for largemouth bass, and vice versa” said study author Gretchen Hansen, former Wisconsin DNR Research Scientist currently with the Minnesota DNR. “Going forward, we predict that many Wisconsin lakes are going to become more suitable for largemouth bass, and less suitable for walleye”.

Gretchen Hansen.
Minnesota DNR research scientist, Gretchen Hansen.

The suitability of individual lakes for supporting walleye and largemouth bass was based on a computer model that estimated daily water temperatures from 1979-2014 for thousands of lakes using information on lake size, depth, water clarity, and historical weather. “We don’t measure water temperature in many lakes”, said co-author Jordan Read, who works at the U.S. Geological Survey. “Modeled lake temperatures can fill the gaps and provide fisheries managers and researchers with a full historical record of water temperature for each of these lakes.”
Future lake temperatures were also predicted for the 2,100 lakes using mid- and late-21st century climate projections. The study authors emphasized the diversity of lakes in terms of how they will respond to climate change. “Wisconsin’s lakes are going to get warmer in the future, but how much warmer they will get varies among lakes” emphasized study co-author Luke Winslow of the U.S. Geological Survey.
By accounting for variability among lakes in how they respond to climate change, researchers estimated how individual lakes and their fish communities were expected to respond to future warming.
The percentage of lakes likely to support natural reproduction of walleye was predicted to decline from 10% to less than 4% of Wisconsin lakes by mid-century. At the same time, the percentage of lakes with conditions conducive to high largemouth bass abundance was predicted to increase from 60% to 89% of lakes by mid-century.
Notably, when projected changes are considered in terms of total lake area, the story is more optimistic.  The percentage of lake acreage likely to support natural reproduction of walleye was predicted to decline by a much smaller amount, from 46% to 36% by mid-century. “Walleye populations in large lakes appear to be more tolerant of warming than walleye populations in small lakes” explains Hansen.  The authors emphasized that focusing management resources to protect walleye and their habitat in these lakes is essential.
The study predicts improved conditions for largemouth bass in over 500 lakes that are not currently suitable for either species, representing expanded fishing opportunities for bass anglers. The percentage of lake acreage with conditions conducive to high largemouth bass abundance was predicted to increase from 28% to 85% by mid-century.
The research team continues to pursue the question of how fish communities in lakes are likely to change in the future, with current work focused on expanding their analysis to include lakes in Minnesota and Michigan.
The study was funded by the Department of Interior Northeast Climate Science Center, with additional support from the National Climate Change and Wildlife Science Center, and the Wisconsin DNR Sport Fish Restoration funds.
The findings were published in the journal Global Change Biology, available open access at . Learn more by visiting, where you can read more detailed information about the study’s findings, and examine predictions for individual lakes throughout Wisconsin with an interactive map.