LAKE MILLE LACS, Minn. (FOX 9) - In a first of its kind walleye study on Lake Mille Lacs, researchers with the Tribal DNR are hoping adult walleye will help tell the story of why Minnesota’s most coveted fish from arguably the greatest walleye fishery in the world has struggled to recover.
In 2014, the Minnesota Department of Natural Resources discovered through a study on fish diet that mature walleye, those over 18 inches, were eating their young at alarming numbers.
“Walleye will always eat walleye,” said Carl Klimah, a Tribal DNR fisheries biologist. “It’s part of their survival. The issue is walleye usually don’t eat their young to the point where the population starts to go down.”
In 2018, the Tribal DNR took on the mystery, launching along with the U.S. Fish and Wildlife Service a Walleye Telemetry Study - a high-tech fish spying project. Over the course of several months, researchers stunned 140 walleye, a mix of adults and juveniles by sending a mild current through the water. They surgically implanted electronic tags into the walleye before releasing them back into Mille Lacs.
Unlike other fish-shocking studies that really just counted walleye, this project looks for answers by studying fish behavior both in the lake and in the lab.
The biologists track the fish back at the lab. On a map, each dot indicates the placement of acoustic receivers throughout Mille Lacs. There are 61 total high tech underwater listening devices, each recording water temperature and light penetration. The device notes when a tagged walleye swims by. A circle around each receiver indicates the half-mile range tagged fish can be detected.
“It’s a big study and we hope to have big results, so we can figure out what’s going on in this lake,” said Klimah. “We need to figure out why those juveniles are disappearing.”
The answer may be something scientists call “The Squeeze Theory” brought on by invasive species like zebra mussels that feed on plankton. Less plankton means clearer, “warmer” water, something walleye don’t like.
“Because there is so little cool water, the adults and juveniles will start to overlap, squeeze into the remaining space to the remaining habitat and as a result they start eating each other,” said Klimah.
Clearer water means there’s more sunlight penetrating deeper, thus creating warmer water. That results in more areas of the lake that are too warm for walleye. That scenario squeezes more fish, large and small, into limited areas closer to their optimal water temperature of 68 degrees. As walleyes stack up in fewer and fewer pockets of the lake, adults begin to cannibalize their young out of convenience.
In what is a very big scientific undertaking, the whole telemetry project is a commitment to tribal members who rely on the lake and all other sportsmen who also hold this iconic fish in great esteem.
“The importance of the walleye or ogaa as we call it here in Mille Laces is pretty critical,” said Bradley Harrington, Tribal DNR Commissioner. “Not just to our physical sustenance, but also to our spiritual health as well … There’s a story that goes back that talks about the gifts given by the creator to the Anishinaabe people and walleye being one of them as one of the animals that agreed to provide life to the Anishinaabe.”
Over the next month, tribal biologists will retrieve the fish spying receivers from the lake, compile the data and offer the results to other scientists. Tribal members say projects like this empower sovereignty among the Ojibwe and set a path for more research with the ultimate goal of fixing the walleye population on Mille Lacs for all people.