ALEXANDRIA, Minn. — Minnesota's Department of Natural Resources has done surveys on muskies on Lake Miltona for years, but additional work that started in the spring of 2019 should paint a clearer picture of how the trophy game fish is doing in one of Minnesota’s premier muskie-fishing destinations.

The DNR started a two-year study last spring that implemented the use of microchips on muskies in Lake Miltona, about 15 miles north of Alexandria in Douglas County.

The microchips, are also known as passive integrated transponder tags, or PIT tags. The PIT tags, a little larger than a grain of rice, are planted just under the skin of muskies. When a tagged fish is recaptured, the PIT tag will allow the DNR to clearly identify the muskie and gather important data from that fish.

“Our main objective is to get a population estimate,” Glenwood Area DNR Fisheries Specialist Nick Rydell said. “Really determine how many muskies are in Miltona. Some underlying objectives are to get some ideas on age and growth in the future using PIT tags and also evaluate the size structure. What kind of size distribution of fish do we have in the lake?”

A Passive Integrated Transponder tag, shown here, is slightly bigger than a grain of rice. Placed just under the skin of the muskie, the tag will continue to work and help the DNR track data on each individual fish throughout its entire lifespan. (Contributed photo)
A Passive Integrated Transponder tag, shown here, is slightly bigger than a grain of rice. Placed just under the skin of the muskie, the tag will continue to work and help the DNR track data on each individual fish throughout its entire lifespan. (Contributed photo)

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The data gathered through the use of PIT tags will ideally give the DNR a better idea of their management strategy in the lake going forward.

“Do we need to possibly decrease stocking? Or do we need to up our stocking and increase the number of fish?” Rydell said. “Miltona is kind of managed as a trophy fishery, so we kind of want that lower density of fish in there so we are getting these fish over 50 inches.”

How the study works

The DNR fisheries staff used a period of 10 days after ice out last spring to catch and tag as many muskies as it could on Miltona.

Sampling of the fish needs to be done in the spring of the year when the muskies are going through their spawning ritual in shallow water. That tends to be when water temperatures reach the upper 40-degree range.

Large-frame trap nets that extend 100 feet from shore are used along shorelines throughout the lake. Workers check these nets every day. Muskies that are caught have measurements taken for length and weight, along with PIT tagging them before the fish swims free again.

Electrofishing at night was also done in order to increase the sample size. This required a spot-and-stalk approach with the use of a spotlight. Once close enough to the fish, an electric current is applied to stun the muskies just enough to get a net under them before they are placed in a holding tank on the boat where the tag is placed and measurements are taken.

“Based on how many fish we PIT tagged the year before, we’ll come back this spring and based on the ratio of fish that have tags versus those that don’t, we can estimate the total number of muskies in the lake,” Rydell said.

The tags do not allow the DNR to track the muskies on a daily basis to gather specific information such as their preferred habitat at different times of the year, but it can help paint a picture of how far the fish are moving within the lake.

“We captured one female that was tagged on the north end of the lake by Tamarac Bay,” Rydell said. “Then two days later, we recaptured it and it was all the way on the south side of the lake. They seem to move quite a bit even within that spawning period.”

What the numbers say

The DNR tagged a total of 116 Miltona muskies last spring.

Ten of those were sub-adults under 30 inches in length, and 106 of them were adults measuring 30 inches or greater. The biggest fish caught and tagged in 2019 measured 52.8 inches.

“The biggest we’ve ever sampled was a 53.6-inch muskie in 2015,” Rydell said of Miltona. “I’m sure there are 55-inchers in there. We’ve heard reports from anglers claiming they’ve caught 55-inch muskies, and I don’t doubt it. Typically, anglers are targeting bigger fish, so they’re more likely to catch one than we are in our sampling.”

Lake Miltona is designated as a premier muskie fishery in the state, and the numbers tend to show that too. Rydell said any muskie measuring 42 inches or more is categorized as a memorable-class fish. About 55% of all the muskies captured last spring fit that category. About 10% of the fish tagged were 50 inches or greater.

The DNR will complete the two-year tagging project this spring when it surveys more muskies. Data will be collected from any fish that are recaptured from 2019 and additional tags will be placed into any fish that do not have tags in them.

“That will give us additional age and growth data if we recapture those fish in future surveys, which Miltona is on roughly a four-year cycle at this time,” Rydell said. “A PIT tag will continue to work for 75-plus years, or in this case, the entire lifespan of the fish. They don’t have an internal battery and are activated by the scanner, so they never run out of power. This makes them really reliable, even over long time frames.”

Rydell said statewide averages for muskies show that a 50-inch fish is typically around 17 years old. It often takes about 10 years for a muskie to reach 40 inches.

“Lifespan is kind of dependent between males and females, but generally if you have a muskie that is pushing upper-teens, that is getting toward the end of its life cycle,” Rydell said. “Rarely does a muskie live past 20 years.”