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Wide-ranging muskrat mystery may finally get look

| Saturday, Feb. 18, 2017, 11:30 p.m.

Brian Mohn made what should have been a startling admission.

The silver-haired Hamburg resident, president of the Pennsylvania Trappers Association, said his take this past season was notable for one omission.

“This is the first year since I was 12, and I'm not going to tell you how old I am, that I did not catch a single muskrat on my trap lines,” Mohn said.

He's likely not alone.

Muskrats — once the staple of every trapper's take, and the furbearer that perhaps got more trappers started than any other — are in decline.

“I know it's something we've been hearing more about,” said John Windau, spokesman for the Ohio Division of Wildlife.

Their troubles are of the long-term variety, too, added Harry Spiker, game mammals section leader for the Maryland Department of Natural Resources. Though muskrats have started to get more attention in the last five to 10 years, something began happening to them much further back than that. He said populations started their downward trend perhaps 30 years ago.

It's been a steady decline ever since, he added.

“It's not like they're going to go extinct any time soon, or even go on the endangered species list. But it's been going on long enough that we're comfortable saying there's a decline,” Spiker said.

“It's region-wide thing, all up and down the East Coast, if not further.”

Indeed, researchers with McGill University in Montreal are even looking into muskrat declines in the Northwest Territories, near the Yukon.

The numbers in Pennsylvania are an example of just how things have changed. While the number of Keystone State muskrat trappers has remained relatively stable, harvests have not. Trappers took more than 720,000 muskrats in 1980. That fell to about 300,000 in 1990, 178,145 in 1994 and just 66,397 in 2015.

Exactly what's going on with the species is a mystery.

“It's still kind of the number one question in furbearer management,” said Matt Lovallo, game mammals section supervisor for the Pennsylvania Game Commission.

There are a lot of possibilities.

One might be tied to rainfall. There's been a “real dramatic, kind of persistent change” in how much rain falls and when, Lovallo said.

In decades past, rainfall episodes tended to be more frequent but of lower intensity, he said. These days, they're less frequent, but often more violent.

That might be playing havoc with muskrats, which often build dens in the banks of creeks and rivers, Lovallo said.

“That probably has a pretty dramatic effect,” he said.

Other factors could be in play, too, Spiker said. Populations of raptors and even raccoons — both of which will prey on muskrats — have increased, for example, he said.

Chemicals in the water could be an issue, too.

According to information from Windau, Susie Prange, furbearer biologist for the Ohio Division of Wildlife, looked at 592 muskrat carcasses donated by Ohio trappers. They were examined for a number of things, including chemical contaminants.

Forty of 41 tested for metals had moderate to severe levels of contamination. Three showed exposure to 17 or 18 different elements.

“Such metal contamination can have negative effects on health, survival and reproduction,” she wrote in an article for the Ohio State Trappers Association magazine.

Muskrats, like rabbits, are prolific breeders, Spiker said, capable of producing multiple litters — sometimes as many as four a year — each of five to eight young.

Lovallo, though, said that in Pennsylvania at least, the ratio of young muskrats to adults in harvests has remained stable or even increased over time. That to him “kind of rules out the idea that something might be happening reproductively.”

Spiker wonders if the problem might be something habitat related.

Their numbers remain strong in the Chesapeake Bay region, he said. That's long been their stronghold.

But every farm pond and creek used to be home to at least a few of the furbearers, too, he added. That's no longer true.

“Where we really don't see them is in that secondary, tertiary habitat,” he said. “We just don't see them in all the places we did 30, 40 years ago.”

Game Commission biologists are hoping to find clues to the mystery soon. Lovallo said they're seeking funding to do a muskrat research project that would involve going into muskrat dens and tagging some — with radio transmitters or pit tags like those sometimes implanted in pets — to track their movements and monitor survival. They hope to begin perhaps as soon as this fall.

In the meantime, the mystery will remain unsolved.

“Being that this is such a long-term trend, there are just so many variables,” Spiker said. “That makes it so hard to pin down.”

Bob Frye is the Tribune-Review outdoors editor. Reach him at 412-216-0193 or See other stories, blogs, videos and more at

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