U of M-led panel completes Mille Lacs Lake walleye management review

January 16, 2015

A nationally recognized University of Minnesota fisheries professor and colleagues from other universities in the U.S. and Canada have completed an independent review of the Minnesota Department of Natural Resources’ management of Mille Lacs Lake. They confirmed that low survival of young walleye is most likely responsible for the decline in the 132,000-acre lake’s walleye population.

“Our independent review of DNR management of Mille Lacs reached similar conclusions as the agency,” said Paul Venturelli, a quantitative fisheries ecologist at the university. “Mainly, more walleye are not surviving their first three years of life. It is unlikely that recreational or sustenance harvest is a root cause of this problem.”

The DNR asked the panel in early 2014 to review past and current management practices as part of an effort to increase the lake’s walleye population as quickly as possible. After collecting data from the DNR, the panel worked independently of the agency to come up with conclusions and make recommendations for Mille Lacs walleye management.

 “The DNR opened up its books for our panel as we worked independently to examine the data and factors that may have contributed to the decline, and made recommendations to the agency about future actions that it could take involving data collection, research and management,” Venturelli said.

In addition to evaluating hypotheses about the walleye population decline, the panel made the following recommendations:

  • Revisit the methods used to determine annual target harvest levels.
  • Set conservative harvest regulations until the population improves or the lake’s system is better understood.
  • Determine the potential effect of cormorants on the walleye population and, if necessary, implement cormorant management.
  • Manage fish that prey on young walleye (northern pike, smallmouth bass and larger walleye) in ways that benefit young walleye survival.
  • Continue intensive fish population monitoring and other forms of data collection.
  • Avoid walleye stocking. Natural reproduction in Mille Lacs is already very high. Rather, the problem appears to be low survival from the first winter to approximately the third fall. Stocked fish would suffer the same fate and could exacerbate the problem by helping to sustain predator populations.

“The causes of the decline in survival are complex because of many direct, indirect, and interacting factors. But I think that we succeeded at narrowing the focus of the discussion,” Venturelli said.

According to Venturelli, the decline in the survival of young walleye started in the late 1980s,  well before the fishery began to decline around the year 2000.

“And yet the population has been reproducing at high levels throughout this period and into the present,” Venturelli said. “The young just aren’t making it through. This is likely the result of walleye predation, and to a lesser degree, recent predation by pike and cormorants.”

Possible explanations for higher predation include fewer tullibee for larger walleye to feed on, improved water clarity and quality since the Clean Water Act of the 1970s and the possible effects of invasive species.

Don Pereira, Minnesota DNR chief of fisheries, thanked the group for their efforts on behalf of the improving Mille Lacs walleye fishery.

“While it would have been helpful if the panel could have identified a significant problem or approach to address the issue that we might have missed, it is reassuring that the panel’s findings indicate that we are on the right track for understanding and ultimately addressing the walleye decline,” Pereira said.

Venturelli presented the panel’s work at the DNR’s annual roundtable with stakeholders today.  To read the panel’s full report, see http://z.umn.edu/millelacswalleyepanel.

Other panel members were Jim Bence and Travis Brenden of the Quantitative Fisheries Center at Michigan State University; Nigel Lester, Ontario Ministry of Natural Resources and the University of Toronto; and Lars Rudstam, Cornell University and Oneida Lake Field Station.

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