by Adam Hinterthuer – Walleye are a culturally and economically important species of game fish across the Midwest, and a species that is struggling to adapt to warmer lakes. As scientists, fisheries managers, Tribes and anglers all work to protect walleye populations, a new study has taken the discussion into the weeds.
Specifically, the study asked, what’s the relationship between walleye survival and aquatic plants?
The answer to that question is contained in an article published November 15 in the journal, Fisheries Research.
Beds of aquatic plants are often important fish habitat in a lake, especially for young fish looking to find cover to avoid predators and structure to find food. This study set out to look at how vegetated habitat in a lake impacted walleye recruitment – or the survival of young walleye through their first summer. What they found, says lead author, Bobby Davis, is that it’s complicated.
“Recruitment was highest in lakes with a moderate amount of aquatic plant habitat, but suffered once there got to be too many,” Davis says.
Davis, a professor at Young Harris College, was a postdoctoral researcher at the UW-Madison Center for Limnology during the study and worked with a group of researchers from the University of Minnesota and the Minnesota and Wisconsin Departments of Natural Resources. The researchers looked at roughly two decades worth of data on walleye recruitment and plant communities for 200 lakes across Minnesota and Wisconsin.
That data suggests, Davis says, that when it comes to making it through their first year of life, walleye have a sort of “Goldilocks” kind of preference for plants.
In other words, walleye recruitment responded positively to the presence of beds of nearshore plants until there got to be too much of a good thing. The researchers observed successful walleye recruitment most frequently when 40-60% of the lake’s nearshore waters had vegetation. Any more, and recruitment suffered. Walleye especially struggled in smaller lakes with lots of plants.
This finding aligns with general patterns of fish distribution and habitat preferences, as fisheries researchers know that walleye and other fishes in the percidae family are most abundant in rivers and rocky, open water lakes, while centrarchid species like bluegill thrive in lakes with abundant aquatic plants.
But it’s not simply a case of “less plants equals more walleye,” cautions Zach Feiner, a co-author of the paper and a research scientist at the Center for Limnology.
“Plants are more like a signal for a suitable walleye lake,” he says. “Once you get to very vegetated lakes, the overall environment is not conducive for walleye. Those lakes tend to be smaller, warmer, and shallower, which are all conditions that we know don’t lend themselves to healthy walleye lakes.”
Feiner notes that studies that have shown that walleye larvae and juveniles are less efficient foragers in complex environments. So, “while it might be good to have some plant cover to hide in,” he explains, “if there’s too much vegetation, that actually decreases their foraging ability and then they don’t grow and survive as well.”
Feiner hopes that their study can help add some perspective when it comes to walleye management across a landscape level.
“This could add to our toolbox of knowledge and help us prioritize stocking and other walleye management decisions,” he says. As the climate – and our lakes – continues to warm, identifying the places where they are more likely to be resilient to these changes is important.
“We have limited bandwidth and management hours,” Feiner says, “so this could help us identify lakes where we don’t need to invest our resources for walleye from the lakes where the plant community is “just right” and our management efforts are more likely to pay off.”
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Full Article in Fisheries Research available here: https://www.sciencedirect.com/science/article/abs/pii/S0165783625003327?dgcid=author
Media contact: hinterthuer(at)wisc(dot)edu OR zsfeiner(at)wisc(dot)edu