ALBANY, Calif., Nov. 4 (UPI) -- The growth of illegal marijuana farming Northern California is threatening forest-dwelling fishers, a rare member of the weasel family.
Increasingly, the remote forests of both public and tribal lands are serving host to illegal marijuana farms, clandestine pot fields planted and cultivated in secret. To keep wildlife from eating their crops, farmers scattered rat poison around their patch of plants, putting a range of animals in harms way. Fishers have been especially affected.
A new study by researchers with the U.S. Forest Service found fishers in Northern California were five times more likely to die from poisoning than their counterparts in southern Sierra Nevada, where the climate isn't as conducive to remote pot farming.
The fishers studied were trapped and outfitted with a satellite tracker collar. When the collar stopped moving, researchers went to retrieve the deceased fisher.
Of the 167 fisher deaths documented by Forest Service scientists, 10 percent were caused by rat poisoning. Some 85 percent showed evidence of exposure to rat poison, and more than half had been exposed to multiple kinds of poison.
Male fishers were 13 times more likely than females to be exposed to rat poison, as they're more active during the spring when farmers are especially liberal with the use of poisons and pesticides.
"We know that a 10 percent change in mortality rate is enough to determine whether fishers in California are able to expand their population size or not," study author Craig Thompson, a research wildlife ecologist at the Pacific Southwest Research Station, said in a press release. "Now we know that rodenticide poisoning alone is enough to keep fisher populations suppressed in the state, even without accounting for the fact that low doses of these poisons also cause the animals to be lethargic and susceptible to disease, which in turn increases the potential for other sources of mortality."
Thompson and his colleagues, who published their findings in the journal PLOS ONE, say more needs to be done to end the clandestine farming and diminish the threats to wildlife.