The call for more modern diet studies on muskies is being answered, and Lake Miltona in Douglas County is part of a project that will take a close look at the big game fish’s primary prey in some Minnesota lakes.
Kamden Glade is a 25-year-old graduate student at Bemidji State University who is in charge of gathering most of the diet data. The Minnesota DNR and Bemidji State University have a contract to complete the project, with Brian Herwig of the Bemidji DNR office and Jeff Reed of the Glenwood office leading the overall research.
The work is scheduled to look at 11 bodies of water in Minnesota. Seven of those lakes hold muskies, but northern pike, largemouth bass and walleyes are also a part of the study that is designed to do a wide-ranging diet overview of some of the state’s most popular predatory fish and see how the species are co-existing in Minnesota waters.
“We’re taking diets from muskies, northern pike, walleye and largemouth bass in all the lakes so that we’re able to compare diets between lakes and between seasons,” Glade said. “Then we have (four) reference lakes too to see if there’s any kind of significant difference in walleye, pike and largemouth bass diets in lakes that do or don’t have muskies in them.”
Miltona, Little Boy (Longville), Bald Eagle (East Metro), Ten Mile (Hackensack) and South Center (Chisago) Lakes were sampled in 2019 during the spring, summer and fall seasons. Other muskie lakes that are scheduled to be sampled for the study include Bemidji and Shamineau (Little Falls) in 2020 and North Star (Grand Rapids) and Pelican (Fergus Falls) in 2021. Lakes without muskies in the study are Ten Mile, South Center, Grace and Deer (Bemidji).
The COVID-19 pandemic is likely to stop spring sampling in 2020, but Glade said they are hopeful that sampling not done this year could be rescheduled to 2021. The work is scheduled to be completed in the fall of 2021 with final publication of the results following that.
A close look at Miltona
Glade has not analyzed all the numbers from every lake that was sampled in 2019 due to the study being ongoing, but he has taken a hard look at the data from Lake Miltona.
Most of the muskies that are sampled are captured through electrofishing at night. Researchers also looked at the diets of fish on Miltona by going along with crews from the Glenwood Area Fisheries department during netting surveys in 2019.
Diet samples are taken from muskies by placing a small piece of clear tubing through the fish’s mouth and into the back of its stomach. Water is then slowly pumped in before pressure builds enough to cause the fish to regurgitate any stomach contents. Some fish sampled had nothing in their stomachs due to not feeding recently.
“Overall, we had a 67% full stomach rate on muskies throughout all seasons, which is actually quite a bit better than most of the other studies that I’ve seen,” Glade said.
From Miltona, 29 muskies were sampled with full stomachs in the spring, compared to two in the summer and 15 in the fall. The contents ranged from easily identifiable species that had just been eaten, down to matter that was nothing more than bones or a small piece of tissue.
“Some of those you can identify the species based on the bone structure,” Glade said. “Beyond that, we’re working with Dr. Loren Miller from the University of Minnesota and the Minnesota DNR. He’s a geneticist. He’s able to take a little chunk of flesh from a diet and he can do genetic barcoding on that chunk of flesh and tell us what species it was.”
The preliminary numbers on Lake Miltona showed that yellow perch made up the largest percentage of the muskie’s diet by numbers.
“Largemouth bass were a fairly important diet item for them as well,” Glade said. “They had a decent amount of bullheads there, and also some crappie and bluegill. Then white suckers were also important for them.”
Yellow perch came out to about 65% of the total diet items by number for Miltona muskies, but that is not the only thing researchers look at when assessing diet studies.
Percentage by mass, the total mass of one prey species divided by the total mass of all prey species present, is also an important factor. Yellow perch made up about 8% of the muskies’ diet by mass on Lake Miltona.
That’s because muskies will commonly feed on larger prey. One muskrat, one ring-billed gull, 11 northern leopard frogs and two northern pike were found in muskies on Miltona. A couple of bowfin, commonly known as dogfish, were also found.
“They’re not eating extremely frequently, but when they do eat they’re eating some fairly large diet items,” Glade said. “We had a couple muskies from Miltona that had white suckers in their stomach that were at or over 20 inches in length.”
Co-existing with other game fish?
A total of three walleyes were found in muskies on Lake Miltona. That made up less than 1.5% of the muskies’ diet by number and less than 2% by mass.
“It’s definitely not like they were targeting walleyes,” Glade said. “We expected to see some. I was kind of surprised we didn’t see more, just based on how often we saw muskies and walleyes in the same areas when we were sampling.”
Researchers for the study are using an overlap metric to analyze how the predator species are competing for limited resources within a lake. That overlap metric is accumulated by looking at each species’ diet as it relates to percentage by number and by mass.
“It gives a number between zero and one. For muskies and walleye, that was about 0.23, so definitely low,” Glade said. “Anything below 0.4 is considered low overlap. So it’s definitely looking like at least on Miltona they are not competing for the same resources too much.”
Yellow perch are an important prey species for all the game fish, but the low percentage by mass that perch accounted for in the muskies’ diet made for that low overlap with walleyes.
Northerns surveyed on Miltona had a diet of yellow perch that consisted of almost 70% by number and 40% by mass. Largemouth bass also had nearly 40% by mass of yellow perch, and walleyes relied on perch for their diet at 40% by number and about 60% by mass.
Walleyes, northern and bass exist in the lake at much higher densities. Miltona is managed as a trophy lake for muskies, and fingerlings are stocked at low numbers in order to create better opportunities for fish measuring 50-plus inches.
“I haven’t really analyzed the numbers from a lot of the other lakes, but just from looking at Miltona, there was a lot higher chance of overlap between the other three species than muskies had on any of the other three species,” Glade said. “For instance, walleye had a relatively high overlap with both pike and largemouth bass. That was a little interesting to see, but not entirely unexpected. The muskies had relatively low overlap with all three of the other species.”
Sampling is completed on Lake Miltona, with more lakes left to look at across Minnesota over the next two years. The end result should be some modern research that can help guide management decisions on Minnesota waters.
“If there is a significant shift in diets when we’re stocking muskies, maybe that is something we need to look at a little closer,” Glade said. “If there’s not, that also gives managers important information they’re able to continue stocking or increase stocking and have scientific data to back that up instead of anecdotal observations.”