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For years, low-flying pilots in stripped-down airplanes built up one of the strongest trout fisheries in the country by dumping hundreds of thousands of fish into Minnesota lakes at about 100 mph.

Remarkably, when dropped from 100 feet in the air — high enough to keep the fish from skipping across the water — about 80% of the brookies, rainbows and brown trout prized by anglers would survive the fall, swimming away to repopulate dozens of Minnesota’s coldest, deepest and most remote lakes.

This fall, for the first time, nearly 100% of the trout stocked from the air survived.

That’s because Brad Maas, one of the DNR’s most experienced pilots, was able retrofit a helicopter with the water tanks holding the trout. By using the helicopter rather than the DNR’s airplanes, pilots were able to safely and gently drop the fish while hovering a few feet above the water.

Because of the helicopter’s success, the DNR may never use airplanes to stock fish again, said Capt. Christopher Lofstuen, chief pilot for the Minnesota Department of Natural Resources.

“I think we have a better mouse trap now,” he said.

The DNR stocks about 500,000 trout a year that it raises in hatcheries across the state along with walleye, northern pike and a number of other species. It pays for the effort with money collected from trout stamps sold to anglers, which have been selling at record highs for each of the last five years.

While most of the fish are trucked in and released on shorelines, a few dozen trout lakes in northern Minnesota are too remote. It would cost too much for the DNR to truck in trout to lakes in Voyageurs National Park, for instance, and in many parts of the Superior National Forest, so instead, they bring the fish to small airfields in Ely and Grand Marais, and pilots take care of the rest.

Other wildlife agencies in North America have been dropping fish from airplanes for years as well, including in hard-to-reach places in Ontario and over the Rocky Mountains in Utah and Wyoming.

Only in the last few years have many of these agencies been switching to helicopters.

The big reason the change has come so slowly is the cost, Lofstuen said.

“A helicopter is a lot more expensive to fly than a fixed wing,” he said.

But it remains to be seen if the helicopters will be more expensive than the airplanes in Minnesota.

In the first two stocking runs in the helicopter, Maas — the pilot who engineered a way for the holding tank to fit in the back of the DNR’s helicopter — was able to release 21,000 trout in eight lakes inside Voyageurs National Park. The bill was about $6 per pound of fish. The DNR’s airplanes would, at best, only have been able to do half of that work at a cost of about $4 to $5 per pound, Lofstuen said.

And about 20% of the fish released from the planes would have died.

“So when you compare the price per pound in viable fish, it ends up a little more expensive with a helicopter but not much,” he said.

But the biggest advantage of the helicopter is safety.

To make room in the airplanes for trout tanks holding hundreds of pounds of fish and water, pilots need to strip them of almost everything else. Even carrying just the bare minimum of 30 minutes of extra fuel, the planes are loaded to their absolute limits. And that leaves very little room for error or turbulence, Lofstuen said.

When the wind whips off Lake Superior, it quickly gets dangerous for pilots over Voyageurs or the Boundary Waters Canoe Area Wilderness. One plane carrying trout was blown upside down by the wind before the pilot was able to recover. In one case, an entire load of fish was dumped on the runway after a mechanical failure on takeoff, Lofstuen said.

Helicopters, meanwhile, can carry greater weight in stronger winds with much less stress on the aircraft or the pilot.

“Wildlife research flying is already some of the most dangerous flying you can do,” he said. “So when we started looking into using helicopters we had to ask, is it worth the risk [in fixed-wing airplanes] just for fish?”

Greg Stanley • 612-673-4882