Understanding Mille Lacs Lake


What is happening at Mille Lacs Lake?


The aquatic system is undergoing significant change, including a declining walleye population. The vast majority of walleye that hatch do not survive to their third autumn in the lake. The DNR has initiated unprecedented actions in response to this unprecedented change. The agency wants to increase the walleye population as quickly as possible with minimal impact to the local community.



Why is this happening?


While state and tribal fisheries management has played a role in the decline, the persistent problem of promising walleye year classes that disappear year after year also is linked to system change. Changes include increased water clarity that benefits sight-feeding fish; the introduction of zebra mussels, Eurasian watermilfoil and spiny water fleas; significantly higher populations of northern pike that prey on walleye; a changing zooplankton community that may be altering the aquatic food chain; and declines in certain forage species, including tullibee.



What is the DNR doing?


As part of a multi-pronged systematic approach to improve the walleye population, DNR convened a blue-ribbon panel of national fisheries experts to review past and current management practices. These experts reviewed and confirmed the DNR's work and offered recommendations. The agency now is in the process of creating a new fisheries office to focus exclusively on Mille Lacs, assigning a new Mille Lacs project leader and providing more staff support for monitoring and technical analysis.



What will this mean to anglers?


The agency will continue to implement regulations that protect young walleye. The2013 year class is the first strong year class the lake has produced since 2008. The 2013 year class and upcoming year classes need to be protected to ensure there is adequate spawning stock in the future. Currently, there is adequate spawning stock, more than enough egg production and abundant fry production.



Anything else planned?


DNR is exploring new and innovative ways to engage citizen input on future management decisions; considering any feasible methods to manage aquatic invasive species; continuing discussion and cooperation with tribal natural resource managers; and supporting a Mille Lacs tourism marketing initiative with Explore Minnesota Tourism.



    A Changing Lake

    Water clarity


    Water clarity has nearly doubled since the mid-1980s. Improvement began about 25 years after the implementation of the federal Clean Water Act in the early 1970s. Zebra mussels were first discovered in Mille Lacs in 2006. They did not exist in great numbers until 2011. Improved water clarity has been linked to young-of-the-year walleye moving offshore at smaller sizes and may also benefit sight-feeding fish that prey on walleye and perch.

    Underwater photo of Mille Lacs Lake bedrock before zebra mussels.
    Underwater photo of Mille Lacs Lake bedrock after zebra mussels.

    Underwater photos taken before (left) and after (right) zebra mussels infested Mille Lacs Lake. Note the difference in water clarity.



    More predators


    Northern pike and smallmouth bass populations have risen significantly since the early 1990s. In 2013, the northern pike population increased to the highest level ever observed. The 2013 smallmouth bass population was the second-highest ever recorded. Populations of black bass (smallmouth and largemouth) have been on the increase throughout Minnesota and Canada.



    Aquatic invaders


    Mille Lacs now contains zebra mussels, spiny water fleas and Eurasian watermilfoil. While it's unknown exactly what implications these infestations are having, it's suspected the increase in milfoil is providing more ambush cover for northern pike. Water clarity also allows more aquatic vegetation, some of it invasive, to grow at deeper depths and in more dense stands.

    Underwater photo of native Mille Lacs Lake mussel after zebra mussels.
    Underwater photo of native Mille Lacs Lake mussel before zebra mussels.

    Before zebra mussels infested Mille Lacs Lake, cadis fly, snails and other native organisms co-existed with native mussels (left). Now, zebra mussels attach themselves to native mussels, displacing those symbiotic organisms. Native mussels, now with restricted feeding openings and competing with zebra mussels for the same microscopic food, eventually starve to death (right).




    Food competition


    First detected in 2009, spiny water flea numbers have fluctuated but show no signs of declining. Spiny water fleas have a negative impact on the native zooplankton community by directly competing with small fish for food and altering the historic aquatic food chain.



    Fewer tullibee


    The most prominent change is a decline in tullibee, likely the result of warmer water temperatures. A decline in tullibee is likely negatively affecting walleye in Mille Lacs, especially larger walleye. Walleye grow significantly faster when they are able to feed on tullibee because it is higher in calories than other prey species, including yellow perch. In recent years, however, production of juvenile tullibee has been strong.



      Fish management

      What is DNR's short-term approach to walleye management?


      The future of Mille Lacs Lake walleye fishing will depend on what the lake's new equilibrium is – an aspect of the lake that clearly is changing and a subject about which there is still much for fisheries biologists to discover. In the short term, DNR will set fishing regulations conservatively based on the need to protect the current population of spawning walleye and fish that hatched in 2013.



      What is DNR's long-term approach to walleye management?


      After the fisheries walleye population recovers, the state and the bands will implement a new harvest policy that:

      • Spreads walleye harvest over a broader size range
      • Considers size, age and sex composition when establishing harvest levels
      • Relates safe harvest levels to changing lake productivity




      How will other fish species be managed?


      Mille Lacs Lake remains a world-class fishery for northern pike, smallmouth bass and muskellunge. Partly to provide angling harvest opportunities and partly to manage northern pike predation on young walleye, DNR will continue to implement liberal fishing regulations that have minimal impacts on the lake's population of northern pike and smallmouth bass.



      How does tribal netting impact Mille Lacs' walleye population?


      Survival, not reproduction, is the problem with Mille Lacs' walleye population. While harvest of walleye – either by netting or sport fishing – can remove spawning stock, neither has contributed to the present walleye decline. Reproduction remains strong in Mille Lacs but survival of young fish has not. DNR's population sampling work proves this, and a blue-ribbon panel of national and international fisheries experts confirmed the results.



      How is the walleye change in Mille Lacs Lake different than Red Lake?


      Both lakes suffered a change in the walleye population. The Red Lake change occurred in the 1990s due to overharvest and illegal fishing, reducing the amount of walleye that could spawn each spring. In Mille Lacs Lake, an adequate number of spawning fish continue to produce strong hatches but not enough young walleye are surviving to maturity. Because of this lack of survival, implementing regulations that protect young fish so more can mature to spawning age is a crucial aspect of managing to prevent a similar change in Mille Lacs' spawning population.



        Blue-ribbon panel

        The panel


        Mille Lacs Lake is famous for walleye fishing. Since about 2000, walleye have been in decline. In early 2014, the Minnesota Department of Natural Resources asked a five-member panel of national and international fisheries experts to determine why and recommend future actions. The panel operated independently from DNR and issued a detailed report in January 2015.



        The data


        The panel looked back before 1999, when walleye numbers were higher in the lake, and compared then to now. What did they look at? Data from then and now describe the lake's walleye populations, predators, competitors and prey, as well as other factors like water quality, invasive species and the tiny organisms that live in the lake.



        The decline


        When the decline in walleye began around 2000, Mille Lacs Lake was changing. These changes affected virtually everything that lives in the lake. Fishing regulations and management also were changing but these changes affected a comparatively small portion of what lives in the lake.



        The findings



        • Since 2000, other fish – including other walleye and possibly cormorants – are eating young walleye in numbers that contribute to the overall decline.
        • Significantly fewer walleye that are one year old aren't surviving through their second and third summers.
        • Overfishing, including tribal netting, has not led to a decline in the number of walleye that are old enough to reproduce in the lake.
        • Female walleye are naturally producing enough eggs because there has been no declining trend in the number of walleye that hatch each year.




          Fall assessment

          What is the fall assessment?


          A fall assessment occurs every September on each of Minnesota's large lakes, which are defined as the 10 largest lakes with naturally reproducing walleye populations. Data collected during each lake's assessment is used to help make statistically accurate fish population estimates and determine fishing regulations. Minnesota's large lakes are Cass, Kabetogama, Lake of the Woods, Leech, Mille Lacs, Pepin, Rainy, Red, Vermilion and Winnibigoshish.



          How is data collected on Mille Lacs?


          As shown on the map below, sampling during the annual fall assessment on Mille Lacs is done using a variety of methods, in multiple places and at multiple times. These different methods and multiple samples provide more comprehensive data that allows more accurate population estimates to be calculated.

          Move your mouse over the map's legend to see sampling sites
          Mille Lacs Lake Sampling
          Move your mouse over the map's legend to see sampling sites


          Mille Lacs Lake electro fishing sitesMille Lacs Lake water quality/zooplankton testing sitesMille Lacs Lake 2014 trawling sitesMille Lacs Lake pike gill net sitesMille Lacs Lake standard gill net sitesMille Lacs Lake forage gill net sites


          What fish and age groups are targeted?


          An assessment is designed to look at a lake's entire population of fish. Fish of all sizes and many species &endash; even those that commonly serve as food for larger fish – are caught using multiple methods, counted, weighed, studied and tested.



          What do assessment results reveal?


          Analyzing data collected shows population trends and relative sizes of fish within those populations. Stomach contents of netted fish can reveal their prevailing or preferred diet. Scales and otoliths (a fish's inner ear) show age. The physical condition of fish can provide information on fish health and disease.



          What other factors are sampled during an assessment?


          A number of water samples, some of which are collected in the fall, are analyzed as part of an annual assessment. Analysis conducted on water samples include temperature and oxygen profiles; alkalinity, dissolved solids, phosphorus and chlorophyll; water transparency; and zooplankton.



          What happens to the remains of netted fish?


          Edible fish are made available to approved charitable organizations, which utilize those fish for food. Fish that are not edible are used to create compost that helps fertilize trees grown in DNR nurseries.