Mille Lacs/Cannibalism

[Lee Borgersen]

   Cannibalism and water clarity to blame for decline in Mille Lacs Walleye



 

Posted: Thursday, January 29, 2015 



Blue ribbon panel study and report release by U of M

The decline in the walleye population of Mille Lacs Lake is unlikely due to over harvesting by angling or netting according to a recent report released by the University of Minnesota blue ribbon panel. Rather the decline points to decreased survival of young walleye.

The panel consisted of the following: Paul Venturelli, Department of Fisheries, Wildlife and Conservation Biology at the University of Minnesota, Jim Bence and Travis Benden of Department of Fisheries at Michigan State University, Nigel Lester of the Ontario Ministry of Natural Resources and the University of Toronto, and Lars Rudstam of Cornell University and Oneida Lake Field Station. The DNR opened their books to the panel for complete review and recommendation of future data collecting and management of Mille Lakes Lake walleye.

The panel studied several hypotheses and agreed the decline in the Mille Lacs walleye began around 2000, which corresponded to a period of considerable change for both the walleye fishery and the lake itself, according to the report. The changes in the fishery occurred against a backdrop of lake changes related to water quality, trophic ecology and invasive species.

The most significant finding in the study, according to Rick Bruesewitz of the Minnesota DNR Aitkin Fisheries, is the decreased survival rate of the young fish.

The panel found the survival age of the 1-, 2- and 3-year-old walleye has been declining since 2000 and that this decline is potentially due to cannibalism by larger walleye, and predation by northern pike, small mouth bass and cormorants.

The potential increase in cannibalism may be due to a combination of many large adult walleye and fewer lake cisco. One hypothesis is that Mille Lacs walleye once preyed heavily on lake cisco that are no longer available therefore the walleye resorted to cannibalism, even though many yellow perch are available.

The decline in Mille Lacs Lake walleye may also be due to changes in the environment of the lake itself. Of major significance is the water clarity. Due to the Clean Water Act of the 1970’s, nutrients that were once pumped into the lake via septic systems and run-off are no longer being pumped into the lake. The water is cleaner and clearer now than it has ever been. Zebra mussels and spiny water fleas could also be altering the nutrient pathways.

Based on the findings of the panel, it is their recommendation that the DNR revisit the harvest policy. Recreational and subsistence fishing mortality is unlikely to be the direct cause of the decline of walleye, the report states. In other words, the decline in walleye population is not a result of over harvesting by anglers or Native American netting. Management of the number of walleye harvested is however, the only driver of walleye management that can be controlled. 

“If fishing levels were not reduced due to emergency regulations, it is possible that spawning stocks could decline to levels from which they might not easily recover,” the report states.

The future of Mille Lacs walleye may also depend more on how other species are managed. Loosening the limits of northern, a major predator of the young walleye, is a step in the right direction, according to the report.

The Panel also stated clearly it does not recommend walleye stocking in Mille Lacs Lake. Natural reproduction is not the problem and restocking with young walleye would only add to the cannibalism rate.

The full 31-page report can be read by going to: http://z.umn.edu/millelacswalleyepanel

[snow1]

Oh yeah that's it...nothing like grabbing straws...