A brief history of Lake Mitchell fish stocking and the walleye fishery Written by Mark Tonello MDNR fisheries biologist. Summarized by Dave
The first documented fish stocking of Lake Mitchell took place in 1874, when lake whitefish were stocked. Other stockings in the 1800s included Chinook salmon, lake trout, smallmouth bass and walleye. The shallow warm nature of Lake Mitchell makes it unsuitable for cold-water species like trout, salmon,and whitefish. Walleye and smallmouth bass were again stocked in 1909 and 1910. From 1929-1940 intensive stockings of bluegill, yellow perch, and emerald shiners were made.
The Lake Mitchell fish community has undergone major changes in the last thirty years. Largemouth bass have become abundant while the once self-sustaining walleye fishery now requires stocking to maintain. No walleye stocking was done between 1940 and 2004. Walleye reproduction declined noticeably in the late 1990s. A 2012 survey noted only one fish dating from an unstocked class, all other fish fish were stocked. Clearly stocking plays a major role in the Lake Mitchell walleye fishery, although, even with stocking, the walleye population is much smaller than it was in the 1980s and early 1990s.
The exact reason for the lack of walleye reproduction is unknown, it may have something to do with the recent abundance of largemouth bass. Almost seven times more largemouth bass were taken in the 2003 net survey than were found in the 1993 nets. Studies show that largemouth bass prey on juvenile walleye, which may have an effect on the walleye population.
Fish growth may also have an effect. In 1980 and 1988, most fish species in Lake Mitchell were growing faster than the state average. However, starting in 1993, growth rates began to diminish and by 2012 only two species, walleye and smallmouth bass were growing faster than the state average. The decline in growth rates among other species may be due to reduced numbers of walleye, a major predator of panfish. The increased number of panfish may create more intraspecific competition among panfish species, leading to slower growth.
Another plausible explanation is the loss of mayflies that has occurred in both lakes. Mayflies are an important food item for many fish species. Although a few flies hatch every year, the last significant hatch occurred in 2001. Although the exact reason for the disappearance of mayflies is unknown, it may be linked to copper sulfate, which is known to negatively effect invertebrate populations and mayflies, in particular. Lakes Cadillac and Mitchell were treated with large amounts of copper sulfate to prevent swimmer's itch until the practice was discontinued in the mid-1990s.
In the early 1990s Eurasian water milfoil (EWM), an invasive aquatic weed became prevalent first in Lake Mitchell and later in Lake Cadillac as well. The plant has been held at bay in the lakes due to annual chemical treatments of 2, 4-D, but the presence still poses a problem. Typically the plant survey done in Lake Mitchell in May finds about 300 acres of milfoil which is chemically treated in June. If untreated, over time, EWM would undoubtedly dominate much of Lake Mitchell creating negative effects on fish populations. In 2010 hybrid milfoil appeared and is now the predominant form of milfoil in the lake. The hybrid plant is more resistant to treatment and requires higher dosages to kill the plant. The vast increase of aquatic plants in Lake Mitchell that has occurred over the last twenty years has resulted in much more silt covering lake bottom that was once gravel and sand. Yellow perch, walleye, and smallmouth bass favor hard bottom habitat and the loss of that may have contributed to the decrease in the numbers of these fish in Lake Mitchell.
Mark Tonello, the MDNR fisheries biologist, who prepared this report recommends that since surveys have shown no signs of natural reproduction in walleye since 2003, stocking in Lake Mitchell should continue at a rate of 50/acre (130,000 fish) every other year. Since a full complement of walleye was stocked in 2012, the next should occur in the spring of 2014.
What lakeshore property owners can do to preserve the fishery
According to Tonello's report, there are some things that lakeshore residents you can do to preserve the fishery. Nearly 75% of the shoreline contains seawalls or riprap and many lawns are mowed right down to the water's edge. This results in loss of native vegetation that holds back erosion and catches runoff of lawn fertilizers into the lake. Applying fertilizers containing phosphorus to lawns puts nutrients into the soil that, if allowed to leech into the water, will stimulate growth of aquatic plants. Allowing native plants to grow along the shoreline in a green belt will provide habitat for amphibians and invertebrates. If shoreline erosion seems imminent, then riprap rather than seawalls should be used and native vegetation should be permitted to grow in front of the barrier. Tonello's report, in its entirety, is found on our websitewww.lakemitchell.org