DNR researcher studies fish gene pools to repopulate state lakes

It wasn't too long ago when North American fish-­stocking programs operated on the premise that a species was a species.

If the muskies Minnesota needed in a given year came from Iowa, so be it. If other muskies needed for stocking were reared in Wisconsin, fine. At times they were both released into lakes stocked since the 1950s with a strain of muskies taken from Voyageurs National Park.

Then along came DNA fingerprinting and fish genetics — a thriving science at the Department of Natural Resources thanks to a molecular biologist who grew up hunting ducks around Eagan, Burnsville and Rosemount in the 1970s.

As the DNR's fish chromosome answer man, Loren Miller is as busy with Minnesota fisheries questions as he's ever been. During 20 years as the state's go-to fish population geneticist, he has stepped in to protect Lake Superior steelhead from unwanted crossbreeding with Kamloops. He's also discovered eight distinct strains of walleyes in the state, and determined that hatchery-supplied coaster brook trout weren't contributing to North Shore populations.

His research has covered the reproductive success and failure of stocked lake trout, brook trout and walleyes. And in lakes that have been stocked over time with various strains of the same species, he's become adept at discerning which of those fish are best at reproducing.

"Some stocked fish live long enough to be caught, but they don't enhance the reproductive value," Miller said in a recent interview.

Take Lake Sarah in Murray County, northwest of Windom. Minnesota spent years stocking it with walleyes taken from productive northwoods walleye fisheries such as Lake Vermilion and Cutfoot Sioux. In fact, because those northern lakes were good sites for egg collection, Sarah was lumped in with them as part of the same genetic management unit.

His recent genetics data showed that most if not all of the current walleye ancestry in Lake Sarah comes from what the DNR calls the Lower Mississippi Strain of the state fish.

DNR resource managers now have made Lake Sarah an egg-take source of its own. In 2016 and 2017, ripe females from the lake produced a stockpile of eggs that the DNR fertilized and raised into walleye fry. In 2016 alone, the put-back to Lake Sarah was 253,676 walleye fry and the remainder were stocked into nearby waters.

"We knew Sarah had a naturalized population and gene testing showed how distinct it was," Miller said. "It'll be interesting now to see if we get natural reproduction in some of these lakes."

Miller, who graduated from Burnsville High School in 1982, said his love for the outdoors began more with hunting than fishing. When Gerald Ford and Jimmy Carter were in the White House, he wouldn't think twice about walking through his neighborhood with a shotgun in hand, en route to river bottoms where ducks could be ambushed. He remembers waking up at 2 a.m. on certain days to nab choice parcels of public land for waterfowl hunts with classmates.

Even today, as the owner of recreational land near Lonsdale, Miller said he's more apt to take after wild turkeys and pheasants in southern Minnesota than he is to fish. He said he hardly has enough time to do both.

His cramped office and small lab for decoding fish DNA is located on the U's St. Paul campus. His paychecks come from the DNR.

Miller said the DNR's decades-old trove of fish scales — collected in little brown envelopes for purposes of aging fish populations across the state — have been instrumental in a lot of his work by providing DNA samples for tracking the ancestries of fish.

And while it was a breakthrough for him to identify eight distinct genetic ancestries in walleyes — including a nearly pure family of walleyes in Mille Lacs — he sees advances coming in DNA fingerprinting that could allow him to differentiate biological traits among the various strains. He gets asked about that a lot.