New study could explain Lake Mille Lacs' declining walleye population

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Walleye populations in Lake Mille Lacs have declined dramatically over the last two decades, and a new study highlights why it’s happening. 

University of Minnesota researchers say the clarity of the water started getting better when zebra mussels showed up in 2005. Meanwhile, the walleye population continued to decline.

“The biggest jump in clarity were well before zebra mussels were established,” said Gretchen Hansen, an assistant professor at the U of M. Hansen previously worked for the Minnesota Department of Natural Resources.

Hansen’s study, published in the journal “Ecosphere,” firmly links what’s been suspected by many. As Mille Lacs cleared, the walleye population dropped. The data all lines up because their habitat--darker water--shrunk.

“It can raise the temperature, but in the case of walleye, they don’t like bright light. They don’t like clear water, so just the clarity itself can impact walleye habitat,” she said.

It’s still not known exactly the reasons for clearer water, but this research has developed ways to measure a lake's clarity and calculate an effect on walleye population. From that, researchers can figure out limits that should be used to boost them back up.

“I would say the long term implications are more just the idea of looking at habitat and changing conditions and tying our harvest conditions to those changing conditions, in order to adapt and sustain walleye fisheries in the long term,” Hansen said.