Mille Lacs Lake

Walleye lakes

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Walleye population research

April 2016 egg take video May 2016 fry release video

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Fisheries biologists have completed the second step in a research project that will provide information about the number of Mille Lacs Lake walleye hatched in the wild. Unlike conventional stocking efforts, fry were hatched in St. Paul from eggs captured in Mille Lacs and released back into Mille Lacs in early May. Normally, fry stocked into a lake come from eggs captured in a different lake.

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Trap nets are set along rocky shorelines, the preferred habitat of spawning walleye.
A lead net funnels fish to the circular net where fish are trapped and held uninjured until release.
Workers pull up the circular end of the net where fish are trapped.
Fish caught inside a trap net.
Using a long-handled net to safely remove fish from the trap net.
The hand net is removed so fish can be sorted and transferred to a holding tank.
Walleye in the hand net.
Walleye from the hand net are dumped into holding tank
Fish not wanted, such as this northern pike, are carefully released.
A boat dock is used to stage the fertilization line.
Fish are transferred from boats to the holding tank.
Fish are transferred from boats to the holding tank.
Fish are transferred from boats to the holding tank.
Fish are transferred from boats to the holding tank.
A tank holding female walleye.
Females are squeezed and their eggs collected in a bowl.
Males are squeeze and their milt is collected in the same bowl. Two males are used to fertilize the eggs from every female.
Water is poured into the egg and milt mixture as it is gently stirred. This mixing is when actual fertilization occurs.
Bentonite clay is mixed with water. Several scoops of this mixture are added to the egg bowl to help reduce the clumping of eggs. Clay particles in the water simulate the rocks to which eggs normally would cling.
After several minutes of mixing, the egg mixture is poured into a screen sieve.
Sieve holes are small enough to allow particles of clay to wash away but not the fertilized eggs.
Eggs are gently poured into a cooler filled with water.
Eggs are left to water-harden for about two hours. As they rest, eggs expand about two to three times their original size.
Hardened eggs are transferred to a cooler of fresh, clean water for transport to the St. Paul hatchery. To prevent the spread of any invasive species, water used for egg transport is brought to the site, not collected from Mille Lacs Lake.
Walleye eggs hatch in DNR's St. Paul hatchery.
Hatched fry, water, the antibiotic for marking and air were packaged into five-gallon containers for a safe trip from St. Paul back to Mille Lacs Lake.
Walleye fry alive and swimming inside a container.
Eric Jensen, large lake specialist for Mille Lacs, returns these walleye fry back to the lake where the eggs originated.
These walleye fry will be about 3 inches long in September when electrofishing and netting begins for the fall assessment.

To differentiate fish from those released and those produced in the lake by natural reproduction, fry hatched from captured eggs will be marked with oxytetracylcine (OTC), a common antibiotic that places a mark on the fish's ear bone. Young fish caught this fall by electrofishing and in assessment nets will be examined for these marks.

The marks allow fisheries biologists to estimate critical parameters of the wild fish, including natural hatch rate and numbers of naturally reproduced fry, as DNR has done in several other Minnesota lakes including Leech, Vermillion, Ottertail, Winnibigoshish and Red.

Stocking is not needed because Mille Lacs has enough spawning walleye. But data collected and analyzed as part of this research project can be used in a worst-case scenario if a time comes when there are not enough walleye to spawn.

Video archive

2015 Assessment

September 2015 Update

September 2015

2014 Update

April 2016 Update

August 2014