Mukooda Lake Genetics Research
By Kevin Peterson, DNR Fisheries
Mukooda Lake is located near Crane Lake, Minnesota within Voyageurs National Park and is one of a handful of lakes in the area that contains lake trout. Lake trout typically inhabit the deep, cold, clear lakes of the Canadian Shield. With a surface area of 754 acres and a maximum depth of 78 feet, Mukooda Lake has the physical and chemical characteristics needed to support lake trout. Mukooda has an unusually diverse fish community which also includes walleye, northern pike, smallmouth bass, largemouth bass, and black crappie. Most of these fish were present in the initial fisheries assessment that was done in 1969; however black crappie, bluegill, green sunfish, black bullhead and burbot have all found their way into Mukooda Lake in recent years and could now be competing with the native lake trout.
The Minnesota Department of Natural Resources (DNR) has a history of stocking lake trout in Mukooda Lake that dates back to 1942. Since 1988, all lake trout that were stocked had a fin clipped so they could be later identified in fish population assessments. The presence of stocked (clipped) fish in subsequent investigations ranged from zero to as high as 50 percent. A winter creel survey of anglers completed in 2002 revealed relatively few stocked fish among the angler’s catch; only four of the 57 fish examined by the creel clerk had clipped fins. This low contribution of stocked fish to the anglers catch caused DNR fisheries managers to reevaluate their stocking efforts on Mukooda Lake. Questions also arose about the continued presence of unclipped fish. Could these fish be remnants of the original lake trout population that were present before the stocking program began?
Fisheries Managers turned to Dr. Loren Miller, a DNR Research Scientist who maintains a genetics lab at the University of Minnesota to help answer these questions. Fortunately, a good collection of scale samples had been preserved from earlier investigations and Miller was able to obtain genetic material from these structures. With help from Voyageurs National Park, additional samples were collected and sent to Miller’s lab for analysis. Using DNA fingerprinting methods like those seen on crime shows, Miller was able to determine the genetic background of each individual fish that was sampled. The results were surprising. In spite of decades of stocking lake trout in Mukooda Lake, the unclipped fish had a genetic makeup that was very different from any of the stocked fish. In other words, the fish that were raised in a fish hatchery have had poor reproduction and there has been little if any mixing between them and the fish that were present when stocking began. With this new information in hand, the Minnesota DNR suspended lake trout stocking in Mukooda Lake in 2010.
When you consider all the stressors the lake trout of Mukooda Lake encountered, including competition from stocked fish, new species introductions, and climate warming, it is remarkable they have persisted all these years. Minnesota may be the land of 10,000 lakes, but only about one hundred of these lakes have populations of lake trout. Many of these lakes face the same kind of threats from invasive species and loss of habitat due to climate warming. Research on the unique lake trout of Mukooda Lake is ongoing and may provide clues as to how other populations may be able to survive under similar conditions. DNR Fisheries Managers, Voyageurs National Park Biologists and Research Scientists will continue working together to monitor the population and develop appropriate management strategies. One thing seems clear; this unique genetic strain of lake trout in Mukooda Lake is a valuable resource that deserves protection.