How do wildlife officials count the fish in Minnesota's lakes?
Anglers are counting down the days to May 10 after the Department of Natural Resources announced you can keep two walleyes daily on Lake Mille Lacs this year.
Given the high numbers for the prized catch, we wondered: How does the DNR count fish in lakes? Good Question. Our Jeff Wagner tackles how they tally up a total.
Many Twin Cities lakes remain frozen but fragile. It's the tricky time of year when ice is too thin to fish on but thick enough to block boats. From smaller lakes like Phalen to the massive ones like Pepin, anglers on the shoreline are showing true patience ahead of the fishing opener.
"It's a transition period and actually for some fish it's a little bit of a rest period," said Brad Parsons, DNR fisheries section manager.
He's anticipating a big year for Lake Mille Lacs after walleye restrictions were loosened.
"Right now, we estimate there are about 800,000 walleyes larger than 14 inches in Mille Lacs," he said.
That's a massive number to keep track of, but the DNR has a system.
How does the DNR count fish in lakes?
"There's a variety of ways depending on the lake. A lake like Mille Lacs, we actually have what we call population estimates," he said.
It starts with using gill nets to catch them, then tagging them. The tags are about 4 inches long and the width of a spaghetti noodle.
"We can put them in the fish in between the dorsal spine," he said.
Tens of thousands of walleyes in Lake Mille Lacs are currently tagged, some for several years. Parsons said they can learn a lot from a long-lived fish. Tracking their weight, growth, and age speaks to a lake's health.
"It's that ratio of the fish that we (tagged) to the total number of fish that we catch that tell us the number of fish that are in there," he said.
Counting walleye on Mille Lacs happens every five years — a massive job including help from tribal nations.
"Our gill nets are really targeting pike and walleye and perch, whereas we have trap nets and those are more effective for things like bluegills and cropies. And bass are hard to catch with any net," he said.
Because of the difficulty of catching bass, the DNR turns to electrofishing. That's when they use a current in the water to temporarily stun the fish, making it easier to count and weigh them before they're back to swimming.
Does the DNR count fish in all of Minnesota's "10,000" lakes?
"We actively manage about 6,000 of our lakes," said Parsons.
Beyond catching fish themselves, the DNR relies on anglers to help them keep track of numbers through surveys during the season.
The questions include how long someone has been fishing, how many fish they caught and how many fish they released. Surveys on Mille Lacs and other popular walleye-filled lakes will start up later in the spring.
It's a multi-faceted approach that people count on before dropping a line.
"Somebody told me once, managing fish is like managing a forest where the trees are invisible and they're moving around," he joked. "That's what makes it challenging but really interesting at the same time."
Parsons said the DNR stocks 1,100 lakes with walleye in Minnesota but the fish can be found in about 2,000 lakes.
