The New Old Trout

For decades, the Minnesota Department of Natural Resources has raised and released brook trout to maintain and restore trout populations in Minnesota’s stream-rich Driftless region. Last August, for the first time, the trout it released were exactly the right trout.

Brook trout are the only native salmonid species in southeastern Minnesota. They were nearly wiped out by land-use practices of the early to mid-1900s, which raised the temperatures of many Driftless streams and polluted them with nutrients and sediment.

In recent decades, stream water quality has improved as land-use practices have evolved, and DNR stocking programs have helped restore brook trout to many Driftless streams. But until now, the stocked fish have been a genetic mixture of local, native brookies and hatchery strains from other parts of the country.

This new strain of brook trout, dubbed MN Driftless, is the product of genetic research and good timing. Through the early 2000s, DNR researchers sampled the genetics of brook trout in the Driftless and identified a lineage of “heritage” brook trout in some small headwaters streams that didn’t share ancestry with the brook trout that had been stocked in the area. This suggested that these were remnant populations of native Minnesota trout. Their study was published in 2015. (See “Brook Trout Stronghold,” March–April 2018.)

That same year, floodwaters contaminated the DNR’s brook trout hatchery system, bringing in disease that killed the hatchery’s brood stock trout, the adult fish whose offspring are stocked in streams. The disease outbreak, while not exactly a good thing, presented a unique opportunity, says Melissa Wagner, Lanesboro area fisheries supervisor.

“It was actually critical in making action happen,” she says. “We didn’t have a strain we were going to be able to stock.”

In 2016, DNR fisheries teams returned to streams identified in the 2015 study, harvested brook trout eggs and milt, and began to build a new brood stock population at the Peterson State Fish Hatchery, a process that took several years. By using local, native fish in their hatcheries, Wagner says, fisheries managers can have more confidence in the success of stocked trout. “These populations have already persisted this long in this particular area,” she says. “Whatever characteristics have helped them to persist—our confidence in this strain is built on that.”

In 2023, 14 streams received MN Driftless fingerlings, and they will get more over the next two years. If the fish do well, Wagner says, the DNR will stock more waterways, especially streams that have improved water quality but lack trout.

“Sometimes there’s no other fish that prefer these really cold waters,” Wagner says. “You’ve got invertebrates that are doing their thing, you’ve got the plants,” but no trout.

“It’s about getting the historic ecosystem reestablished.”