Published April 18, 2010, 12:00 AM

Fishers establish population in northeastern N.D., study concludes

For the first time in a century, it appears fishers have established a population west of the Red River, researchers say.

By: Brad Dokken, Grand Forks Herald

Fisher sightings have become more common in northeastern North Dakota, and findings from a recently completed research project suggest the fur-bearing mammals aren’t just stragglers from Minnesota.

For the first time in a century, it appears fishers have established a population west of the Red, researchers say.

“North Dakotans have an animal that hasn’t been there for 100 years at least,” said Tom Serfass, an associate professor of biology at Frostburg State University in Maryland who oversaw the fisher study through a partnership with the North Dakota Game and Fish Department. “It’s very unusual what we’re seeing. Based on the literature for this animal, no one would have thought this to be fisher country.”

Members of the weasel family, fishers generally are associated with heavily forested areas of northern Minnesota and Canada. But within the past decade, they’ve been showing up with growing frequency along rivers such as the Turtle, Red and Pembina, which apparently have adequate habitat to support at least limited fisher populations.

Seeking proof

In an effort to learn more about the frequency of fishers and where they’re living, Maggie Triska and Steve Loughry, two graduate students at Frostburg State, spent the summers of 2008 and 2009 documenting fisher sightings with digital cameras and “track plates” — pieces of aluminum placed in mailboxes and covered with soot or contact paper. The track plates also are baited to attract animals.

The first year, Triska and Loughry, along with another grad student, Steve Pepper, set cameras and track plates at 184 sites along the Red River and several tributaries, mainly north of Grand Forks.

The researchers detected fishers at 54 of those sites.

Last year, the students expanded the focus by setting trail cameras and track plates farther south along the Red River and west throughout upstream reaches of the Sheyenne River, plus a handful of forested sites in the Turtle Mountains and near Devils Lake.

They also sampled locations north of Grand Forks that had produced fisher sightings the previous year.

According to Triska, a Wilton, N.D., native, the researchers documented fishers at 78 of the 172 test sites last year, but the vast majority came from Grand Forks County and north. South of the Goose River, she said, the number of fisher sightings dropped considerably.

“The strong spots from 2008 held steady,” she said.

Otter offshoot

According to Serfass, the fisher study was an offshoot of a two-year otter project Frostburg State launched in northeastern North Dakota in 2006. Serfass is an authority on otters who served as North American coordinator for an international group focused on otter research, and Frostburg State has partnered with the North Dakota Game and Fish Department to study the two species using funding from a State Wildlife Grant.

The U.S. Fish and Wildlife Service funds the grants program to help states study species of special interest or concern.

Triska’s focus during the fisher study was to look at the effects of flooding on fisher distribution and develop a model to predict where the species might expand in the future. Loughry, meanwhile, looked at the effectiveness of trail cameras and track plates in documenting fishers. He also looked at the habitat types that were most conducive to detecting the animals.

Serfass said the students documented fishers in places the animals weren’t supposed to be — at least according to the computer models.

“We don’t know if that’s the result of this new population, and they’re occupying areas they won’t be when they settle in or whether the models are just not predicting what’s going to happen,” Serfass said. “They may not have had enough time to expand into some of the potential areas.”

But the models did show that fishers someday could colonize along the Sheyenne River, even though they weren’t widely documented during the fieldwork, Serfass said.

Another finding: “It appears the upper part of the Pembina River is being colonized pretty rapidly,” Serfass said.

Loughry said trail cameras provided indisputable proof of fisher sightings — it’s hard to argue with the image of a fisher in the flesh, after all — but the track plates also were effective at determining whether fishers were at a particular site.

The gear also detected fishers in both large and small blocks of habitat, Loughry said, something he didn’t expect.

“I thought they’d be in large patches more often, but as far as the northeast (part of the state), it seemed our detections occurred pretty much everywhere,” he said.

How many?

So how many fishers roam the wilds of North Dakota? Loughry said it’s difficult to estimate, based on the number they detected during their research.

“We don’t know if we’re seeing the same individual at a lot of sites,” he said. “With the landscape so linear, one male fisher could be covering miles.”

As a result, Triska said she looked at habitat potential and literature from other regions to develop an estimate. Based on the different habitat scenarios, Triska estimates North Dakota’s fisher population at about 250, a number she adds is far from definite.

“The numbers predicted under various scenarios were in the low hundreds, and a state like Minnesota has population estimates (based on trapping data) around 12,000,” said Triska, who recently defended her graduate thesis on the fisher project. “So, the population in North Dakota is likely very small and restricted by available habitat.”

Besides fishers, the grad students documented the presence of pine martens in the Turtle Mountains, Serfass said, something the researchers didn’t expect.

“We didn’t know they were there,” he said.

What’s next

With the fisher study now complete, Serfass said he’ll shift gears to a study of otters along the Missouri River basin in western North Dakota, which also will be funded by a State Wildlife Grant. No follow-ups to the fisher study are in the works at this point, Serfass said, but given the chance, he said he’d like to put radio collars on some of the animals.

In the meantime, he said, fishers in North Dakota appear to be here to stay — at least in the northeastern part of the state. Before the research project began, that would have been speculation, at best.

“I would say from the distribution that Maggie and Steve were able to delineate, that it’s very unlikely that this is a temporary occurrence,” Serfass said. “The population structure itself over time — that we don’t know. But unless things change dramatically, I would say this animal is re-colonizing and they’ll stay in the state.”

Dokken reports on outdoors. Reach him at (701) 780-1148; (800) 477-6572, ext. 148; or send e-mail to bdokken@gfherald.com.

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