Natural walleye lakes could be a rarity in Wisconsin by mid-century, thanks to climate change, a new study warns.

And the largemouth bass shall inherit the warmer waters — and flourish, the government-funded study further predicts.

By as soon as 2040, a mere 4 percent of Wisconsin lakes might be able to support naturally sustained walleye populations — a 60 percent reduction from today — while the number of lakes conducive to high-abundance largemouth bass populations could rise to 89 percent, up from 60 percent today, according to the study, co-authored by researchers from state and federal agencies. The study was published Thursday in the scientific journal Global Change Biology.

In other words, walleye fade, and largemouth bass take over.

Such a transformation would strike at the core of Wisconsin’s piscatorial identity, which cherishes the flaky flesh of walleye above all others — and supports a $1.5-billion freshwater fishing economy.

The bass-walleye transformation isn’t new. For 30 years, researchers have watched traditional walleye lakes become bass-dominated lakes, often to the chagrin of anglers and cabin owners. The root cause is not known for certain, but it correlates with lakes getting warmer as summers have grown hotter and winters have become shorter and less severe, said Gretchen Hansen, the study’s lead author. The warming climate is a likely culprit because biologists have long established that in similar lakes, walleyes dominate in cooler waters and largemouth bass in warmer waters.

“We don’t know for sure what the causal mechanism is there, but it’s the best correlation we have,” said Hansen, a former research scientist with the Wisconsin Department of Natural Resources now working with the Minnesota DNR. “I do think that given trajectories of climate change, it’s pretty clear that will will have fewer lakes with walleye.”

Hansen, as well as co-authors Jordan Read and Luke Winslow of the U.S. Geological Survey, ran computer models to see what would happen if temperatures continued to warm under one of the most-dire climate prediction models.

“This is pretty much the worst-case scenario,” Hansen said. “It might not be this bad. A lot of people argue for using worst-case scenarios because if you can plan for that and things are less severe, then you’re better off. And we do still predict places (85 lakes) where walleye will be OK (through 2089). Those should be the highest priority lakes to protect.”

Of some comfort to walleye anglers might be that not all lakes respond the same to warmer temperatures, and walleyes in large lakes seem to be able to succeed in warmer temps than smaller lakes. As a result, the total acreage of natural walleye waters wouldn’t fall as drastically as the number of lakes, according to the study.

The group created an interactive map that allows viewers to zoom in and out of Wisconsin, examining how regions and even individual lakes might change in the future if water temperatures climb as predicted.

Several years ago, the state embarked on an ambitious plan to try to stock its way out of the walleye-bass “flip” by expanding hatcheries and stocking more and larger walleyes in lakes where the fish had once dominated without human intervention. It’s too early to tell if it’s working, and Hansen said her study doesn’t ponder whether predicted bass-dominated lakes could still host an entirely stocked population.

The study also didn’t examine waters in neighboring states Minnesota and Michigan, where scientists aren’t sure if the walleye-bass flip is also happening. The authors intend to study that next.

“There are different types of lakes in parts of Minnesota, but in general, you wouldn’t think the fish or the climate would change at the state line,” Hansen said.