This hole in the bank of a farm pond in Wyoming County is being used as a den by muskrats. Muskrats prefer to burrow into earthen banks for cover, but the placement of riprap along streams and rivers for flood control has limited the places where the furbearers can live.
Tom Venesky/the times leader
It’s the perfect oxymoron: cleaner water in Pennsylvania streams, river, lakes and ponds might actually be harming a once-common aquatic furbearer.
That’s what might be happening to the muskrat, as populations have virtually disappeared in some parts of Pennsylvania as well as the eastern part of North America.
“Muskrats were the number one furbearer at one time, but all that has changed now,” said Tom Hardisky, a furbearer biologist with the Pennsylvania Game Commission.
The change became noticeable in the early-1990s when muskrats began disappearing from the ponds and streams they traditionally inhabited, Hardisky said. While the northwest and western regions of the state still hold strong muskrat populations, the decline is hitting hard in Northeastern Pennsylvania and spreading into New England and several Canadian provinces, including Nova Scotia, Prince Edward Island, New Brunswick and Quebec, according to Hardisky.
“In Northeastern Pennsylvania, where I grew up, muskrats have basically disappeared from many areas, and I haven’t seen a comeback,” Hardisky said. “Farm ponds are the only areas in the northeast where there are still some muskrats. In the rivers and streams it’s way down.”
Reasons for the decline are still being tossed around by biologists, but disease, at least in Pennsylvania, has almost been completely ruled out because populations usually rebound a few years after an outbreak occurs.
Hardisky said impacts of heavy metals or pesticide contamination also don’t seem to be factors either.
Predation is a partial factor, he added, as muskrats are a popular prey species for great-horned owls, red-tailed hawks and mink.
Still, increased predation might be pointing biologists to the main reason why muskrat populations are plummeting.
“The cause of high predation goes back to habitat,” Hardisky said. “It goes back to streambank conditions.
“It all has the symptoms of a bigger problem – environmental changes. One of those changes is cleaner water.”
In the past, when runoff from farms and residential areas was discharged directly into waterways, the increased nutrient load caused vegetation along streams and rivers to flourish. In turn, muskrats benefited from a lush food source and thick cover.
Also, before flood control measures resulted in the banks of streams and rivers being covered in riprap, those shorelines were generally dirt and muskrats were able to easily burrow and make dens. Today, the riprap, which is large stones, prevent muskrats from burrowing and prohibits vegetation from growing on banks.
“Riprap is great for channeling streams, but it’s not great for muskrats,” Hardisky said. “And water quality is a tough factor to address. Allowing runoff is something we’ve been discouraging for years, but it’s very possible that’s what muskrats need. A lot of the sloppy things that used to be done in the past really benefited muskrats. It’s crazy.”
Hardisky compares the muskrat decline to that of wild pheasants in Pennsylvania decades ago. With pheasants, the loss of farm habitat complete with plenty of brushy hedgerows caused the gamebird to decline drastically.
“It’s very similar to what’s going on with muskrats,” he said. “A steady decline.”
Obviously, directing more dirty runoff into waterways to increase muskrat populations isn’t feasible, but that doesn’t mean biologists are ready to give up on the once prolific furbearer.
Hardisky said he has yearned to do a muskrat study in Pennsylvania, but it would be a large undertaking and funding isn’t available. But in Prince Edward Island, wildlife biologists are conducting a comprehensive muskrat study looking at numerous possible factors for the population decline. The results of the study might shed light on the muskrat decline in other areas, including Pennsylvania.
“Maybe this study will give us something to focus on here,” Hardisky said. “Right now, it’s wide open.”
With muskrat numbers down, trapping season could be shortened
Muskrats are the nation’s most abundant furbearer species and have long been considered the backbone of traplines in Pennsylvania. But with the population decline, it’s possible that the trapping season for muskrats in Pennsylvania could be shortened, according to Tom Hardisky.
Currently, trappers in Pennsylvania can trap muskrats from Nov. 20 to Jan. 9, 2011. In 2008, according to the PGC’s harvest estimates, trappers took 74,059 muskrats, a sharp decline from a high of 216,066 in 1997.
Still, while a season reduction is a possibility, Hardisky said it’s not the answer to solving the muskrat decline.
“The solution isn’t really to knock back the season, it’s to improve the habitat,” he said. “We really need to attack the problem. If it gets worse and there continues to be fewer places where a new trapper can find muskrats, it will definitely impact the future of trapping.”
Hardisky did advise trappers pursuing muskrats that as their success rate drops dramatically at a particular location, to move on to another area.
“You don’t have to get every last one. Leave a few there to reproduce for next year,” he said.
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