Every fall, residents in the Knife River valley northeast of Duluth see the helicopter. It flies low over their land. Some of them wonder why a helicopter would be flying so close to the ground and so slowly. They might wonder if it’s on some military mission, sniffing out potential trouble perhaps.
But that isn’t the case.
Inside the helicopter, along with a pilot, is a fisheries biologist looking for beaver dams. The Minnesota Department of Natural Resources conducts the flight one day each fall in the name of fisheries management on main branches of the Knife River on the North Shore.
The fisheries biologist notes the location of beaver dams for removal that fall or the following spring, said Deserae Hendrickson, DNR area fisheries supervisor at French River.
“Typically, the goal is to remove all the dams,” Hendrickson said, “and you have to remove the beavers before you remove the dams.”
Fisheries biologists say beaver dams and the ponds they create are harmful to the Knife River’s rainbow and brook trout fisheries. But some residents say beavers belong in the landscape and that their ponds provide important benefits to wildlife and to streams.
Problems with dams
After each fall’s flyover, the DNR contracts with federal trappers from the U.S. Department of Agriculture’s Wildlife Services division to trap the beavers and remove dams on public land. The trappers also seek permission from landowners to remove beavers and dams on private land.
Impoundments created by beaver dams are considered detrimental to the Knife River’s migratory rainbow trout and resident brook trout populations, Hendrickson said. Beaver ponds warm the stream’s water, and trout do not fare as well in the warm water that flows on downstream. Stream temperatures can be as much as 10 to 15 degrees higher downstream of a beaver pond than upstream, Hendrickson said. Some juvenile rainbow trout, the progeny of Lake Superior’s migratory steelhead, leave the stream early if conditions aren’t right. They are more vulnerable to predation when they down-migrate prematurely.
Beaver dams also block the upstream migration of spawning rainbow trout, and beaver ponds can trap juvenile fish, which can die as the water warms.
Beaver ponds on the Knife River system cover an average of about 10 acres each, Hendrickson said. The ponds flood the land, killing trees that once shaded cool, healthy streams, DNR fisheries officials say. After a pond is abandoned by beavers, grass—often non-native reed canary grass—replaces what was once a healthy forest.
“After a dam is gone, there can be long-term impacts to that riparian (streamside) corridor and a failure of trees to re-establish on their own,” Hendrickson said. “It can take decades.”
In the past five years, from five to 43 beavers were trapped per year on the main branches of the Knife River, Hendrickson said. Over the same period, from six to 43 dams were destroyed annually. One beaver colony might build several dams.
As recently as 2008, when trapping was done on tributaries as well as the main branches of the Knife, 143 beavers were trapped and 99 dams destroyed, according to the DNR.
Anglers, especially members of the Lake Superior Steelhead Association, generally support the effort to remove the dams and beavers.
“The reality is, we have to have some beaver management for the unnaturally high populations we as humans have created by how we’ve managed the riparian forest,” said Craig Wilson, president of the LSSA.
But a group of about 30 Knife River residents called Advocates for the Knife River Watershed opposes the removal of beaver ponds, said Corlis West, who is chair of the organization’s board.
“There are a lot of people in our organization who really value the beaver ponds as something that attracts wildlife and increases biodiversity,” West said. “Not just beavers, but for moose and mink and waterfowl and frogs and turtles.”
North Shore resident John Green, a retired University of Minnesota Duluth geology professor, says beaver dams play an important role in the landscape.
“They provide special habitat,” Green said. “They’re wildlife magnets for breeding and migrating birds. All kinds of wildlife like them, and people enjoy those.”
Beyond that, Green said, the dams help control runoff after big rains, helping prevent erosion downstream.
“But it’s more than just the erosion of the banks,” Green said. “It’s all the essential critters in the food chain in the streambed too, that provide sustenance for the fish—and each other. It’s a more sustainable and diverse ecology all around with the beaver ponds.”
While Knife River watershed residents can refuse to allow trappers on private land, in at least two cases, West said, beavers have been trapped without landowner permission. Warren Peterson of Duluth Township said he had beavers trapped two or three years ago after he had denied permission to federal trappers to trap on his property. He doesn’t know who trapped the beavers. The dam was not destroyed when the beavers were trapped, he said.
“It was kind of sad,” Peterson said. “There were nice, big ponds back there. Water’s life. There were birds every spring—blue herons, all kinds of ducks and geese, animals feeding back there. It was beautiful.”
Hendrickson maintains that trappers working under the DNR’s authority do not trap without landowner permission.
“About 20 percent of the landowners deny us permission,” she said. “They don’t want us to trap on their land. We respect that.”
Dan Croke of Normanna Township formerly trapped beavers in the Knife River watershed for the federal government but decided to quit. He said he believes the DNR is taking too many beavers in the area.
“It seems like the whole Knife River valley is being managed just for steelhead and trout,” Croke said. “It’s my impression that beaver have been totally eradicated in the whole Knife River valley, over 200 square miles.”
Hendrickson disputed that notion. She said aerial surveys from 2015 showed that 187 beaver dams remained on Knife River tributaries where no DNR-authorized trapping was occurring. It’s impossible to know for sure how many of those dams represent active beaver colonies, Hendrickson said.
“The majority are likely to be active,” she said, “but there is no way to tell for sure from the photos. … We have by no means eliminated beaver from the watershed.”
Croke and members of the Advocates for the Knife River Watershed say that removing beaver dams in upstream areas of the Knife leads to more erosion downstream.
“Any time you get a 1- or 2-inch rain, there’s nothing holding that water back,” Croke said. “All that water flushes down in one big surge and takes out the river banks below.”
Beaver trapping and beaver dam removal is an ongoing challenge, Hendrickson said, because juvenile beavers are booted out of family lodges on tributaries each year and must establish new territories. They often relocate from those tributaries and build new dams on main branches of the Knife, Hendrickson said.
Miles of habitat
The Knife and its many tributaries form the most extensive system of any trout stream on the Minnesota shoreline of Lake Superior. The system accounts for 95 miles of 180 miles of water available to trout and salmon on the entire North Shore. The Knife supports the largest run of steelhead—Lake Superior’s migratory rainbow trout—on the shore. Steelhead, though not a native species, were first stocked in Lake Superior in 1895.
Some opponents of beaver trapping on the Knife say the DNR responds too readily to pressure applied by the Lake Superior Steelhead Association. Hendrickson said the Knife is a priority for beaver control because it represents so much of the North Shore’s spawning and rearing area for migratory trout.
“A lot more of (Knife River management) is driven by the fact that this is the right thing to do,” she said. “There are lots of other trout streams up and down the shore where we’re not doing anything. The Knife ends up being a priority by virtue of the number of miles accessible to anadromous (migrating) fish.”
Of 2,093 miles of designated trout streams and tributaries in the Lake Superior watershed in Minnesota, beaver control is done by the DNR on about 6 percent, she said.
The steelhead association has hired trappers to remove what it calls “isolated problem beavers or dams on the Knife that the DNR either didn’t get to or wouldn’t remove,” said the LSSA’s Wilson. That trapping was done by permit from the DNR during regular trapping seasons, Wilson said.
Beaver trapping and dam removal is just one aspect of ongoing action by several agencies and organizations to improve trout habitat in and along the Knife River. In recent years, efforts have been made by those entities to regenerate the forest along the Knife and its tributaries.
The Lake Superior Steelhead Association has sought and received $1.8 million in grants from the Lessard-Sams Outdoor Heritage Council, which recommends legislative expenditures of Legacy funds generated by state sales taxes. Some of that grant money has been used by the LSSA to buy and plant thousands of trees along the river. None of that money has been spent for beaver control, LSSA’s Wilson said. The reforestation effort will take a long time, he said.
“You plant a tree on a North Shore watershed, and you catch a steelhead behind a rock 100 years later,” Wilson said. “It takes a century to replace what you’ve lost.”
Minnesota Trout Unlimited also supports efforts to restore the Knife River watershed and its fishery, said state director John Lenczewski. That includes beaver trapping and dam removal.
“The single-species (forestry) management we’ve had in the watershed has been for aspen,” Lenczewski said. “So the beaver populations are unnaturally high. The problem is, they’re a hindrance to restoring the forest. One good (beaver pond) flooding in an area you’ve been trying to restore, and it destroys all your work.”
The Advocates for the Knife River Watershed also have lobbied for reforestation, for larger buffers along waterways during logging operations and for efforts to reduce streambank erosion during periods of high water, West said.
Dave Zentner of Duluth, an Izaak Walton League member and former national president of the organization, says the conflict over the beaver issue is “a classic example of a fight we don’t need.”
“I think strong beaver management is very important,” Zentner said, “but we need to look at the specific site. Is the theme ‘beaver,’ or is the theme ‘brookies and steelhead?’ Given that watershed, I think we should give more emphasis to the fishery. But with the various branches in the system, I don’t know if you need to take the beaver out of every tributary.”
He urged a broader discussion, what he calls a more holistic approach to stream projects, in which the expertise of hydrologists, fisheries biologists, foresters and transportation officials all are considered in managing a watershed.
A final draft of the DNR’s revised Lake Superior Fisheries Management Plan is expected soon. The plan was last revised in 2006. Habitat management, including beaver trapping and removal, is expected to be included among management strategies on the Knife River in the revised plan, as it is in the current plan.