Walleyes thrive in darker water thanks to their low-light vision that allows them to outcompete other predator species for food. Therefore, harvest has to respond to avoid over-exploiting walleye under new habitat conditions.”

“Because Mille Lacs is fairly shallow and uniform in depth, the walleye cannot retreat to deeper water as they can in some clear lakes and the lake can support fewer walleye. “As the water has gotten clearer in Mille Lacs, the area of the lake with suitable walleye habitat has gotten smaller,” said Hansen, assistant professor of fisheries, wildlife and conservation biology at the U. Water clarity was around 6 feet from the 1930s, the earliest records, to the early 1980s. That’s probably due to a reduction in human-caused pollution like fertilizer runoff and better septic systems and sewage treatment along the lake.Īfter zebra mussels arrived in 2005, they filtered even more nutrients out of the lake, making it even clearer. Hansen said the lake’s water clarity jumped dramatically in the 1990s, even before zebra mussels invaded the lake.

It’s not that the water is gone, it’s just too light and too bright for walleyes to thrive, said Gretchen Hansen, a University of Minnesota assistant professor who headed the research.

That was the finding of a University of Minnesota study published Tuesday, May 7, in the journal Ecosphere that found the now years-long decline in walleyes in the big lake is being spurred by that reduction of suitable habitat. DULUTH - The amount of usable walleye habitat in Mille Lacs Lake has declined dramatically in recent decades because the big central Minnesota lake is getting much clearer, likely due to a reduction in human-caused pollution and an invasion of zebra mussels.

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