Rat Poison from Illegal Pot Farms Threatens Cat-like Fishers

First Posted: Jun 28, 2013 12:39 PM EDT

It turns out that fishers, the weasel-like creatures that specialize in eating porcupines, may be in trouble--from pot. Scientists have discovered that rat poison used on illegal marijuana grows are killing fishers in the southern Sierra Nevada which could mean devastating consequences for this species.

Fishers, otherwise known as fisher cats, are only found in North America. Although this species historically ranged through the forests of Canada and the United States, it now only inhabits parts of its range today. Currently, this species is being threatened by hunting and forest habitat loss due to logging and road building. Yet it turns out that they might now face a new danger: rat poison.

Previous studies showed that rodenticides were being found in the tissues of fishers, yet scientists hadn't pinned down exactly where these poisons came from. This new study, though, shows exactly how fishers are being killed.

The scientists radio-tracked the fishers, examining exactly where they went. In the end, they found that female fishers who live in areas with a higher number of marijuana sites had more exposure to rodenticides and, subsequently, lower survival rates. With that said, it's not likely that legal marijuana sites are at issue; more likely it's the illegal grows. The fishers didn't venture into rural, urban or agricultural areas where rodenticides were used legally; this means that illegal applications are to blame.

"Exposure of wildlife to pesticides has been widely documented, but this is a fundamentally different scenario," said Kathryn Purcell, wildlife biologist, in a news release. "In marijuana cultivation sites, regulations regarding proper use of pesticides are completely ignored and multiple compounds are used to target any and all threats to the crop, including compounds illegal in the U.S."

Not all of the fishers have died from directly consuming flavored rodenticides. Others have died due to a more limited exposure. Yet even this limited poison may have predisposed the animals to dying from other causes--such as reducing their ability to heal from injuries and causing brain damage.

"By increasing the number of animals that die from supposedly natural causes, these pesticides may be tipping the balance of recovery for fishers," said Craig Thompson, a PSW wildlife ecologist, in a news release.

The findings have major implications for this species, which are a candidate for listing under federal, Oregon and California endangered species acts. Needless to say, regulations need to be put into place to control these pesticides more closely--especially when it comes to illegal applications.

The findings are published here.

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