The most popular target for Wisconsin anglers, the walleye, is facing mounting pressures from overfishing, climate change and dwindling habitats.
In a study published this week in the Proceedings of the National Academy of Sciences, UW-Madison graduate student Holly Embke found 40 percent of walleye populations in the state are “overharvested” — nearly 10 times higher than the standard estimate based on abundance alone.
“We wanted to take a more nuanced approach and ask not only how many fish are in a lake but also consider how fast they’re growing, how big they are, and how many are produced every year,” Embke said.
Polling has found around half of the state’s residents fish, and hundreds of thousands of out-of-state anglers come to Wisconsin’s waters each year. An American Sportfishing Association report found recreational fishing contributes $1.9 billion to the state’s economy and sustains more than 13,000 jobs.
Nearly three decades ago, the state DNR and the Great Lakes Indian Fish and Wildlife Commission set walleye harvest limits for both recreational fishing and tribally protected activities. The management plan created in the late 1980s was based on fish abundance, using walleye population estimates to set a maximum harvest level of about 35 percent of adult walleye in any lake. The actual rate of depletion was thought to be less than half that level.
Study co-author Steve Carpenter, director emeritus of the UW-Madison Center for Limnology, said those regulations “worked for a long time … and then they stopped working.”
A release from the university shows annual walleye production in many Wisconsin lakes has decreased by more than a third in the past few decades. Plus, walleye stocks now take longer to replenish themselves.
Study authors measured how walleye biomass had changed over a 28-year period in 179 lakes, comparing walleye production to the total harvest for those lakes. In addition to the new findings on overfishing, they also found “great variation” in production between lakes, meaning some can sustain higher levels of fishing than others.
The release shows more than 1 million recreational anglers account for about 90 percent of walleye harvested in the state, while the other 10 percent are caught by around 450 tribal members using spears.
The DNR has changed certain fishing regulations to protect populations, as well as stocking hatchery-raised fish in lakes where walleyes are struggling the most. But state walleye populations haven’t improved.
Factors identified in the study include lakefront development edging out shorefront habitats, as well as warming waters in Midwest lakes due to climate change.
“Nature has changed,” Carpenter said. “The climate now is different from what it was in the 1980s, and it’s not going back. That means habitat is decreasing and, on average, walleye stocks can’t take the harvest levels they have seen.”
According to the study’s authors, those factors along with the newly identified overfishing of walleye underline the need for updated regulations that reflect the struggling walleye population.