The population of mammals called fishers in Sierra Nevada has become increasingly endangered. The latest threat comes from illegal marijuana growing sites and their use of rat poison. Rodenticides are scattered around marijuana farms to deter pests, enhanced with flavor such as bacon, fish, and peanut butter, which attracts animals other than rats.
The study, published in the journal PLoS One, shows that an increasing number of fishers are being exposed to and dying from a variety of rodenticides. The research examined the death of 167 fishers between 2012 and 2014 and found that 10 percent of deaths are directly connected to marijuana growing sites. They also found that the rate of exposure to rat poisons rose from 79 percent to 85 percent over that period of time.
Necropsies have confirmed as many as six types of rodenticides in one animal. The most dangerous substances found in the fishers were anticoagulant rodenticides (ARs). These poisons stop mammals from recycling vitamin K; a deficiency in vitamin K creates blood clots and coagulation problems that can prompt uncontrollable internal bleeding. Of all the poisoning cases, 69 percent were in the spring, which is when the fishers mate and raise their young.
"We're showing that it's not getting better," said Mourad Gabriel, lead author of the study, in a statement. "Fishers are the flagship species. We have to think of so many species, like Sierra Nevada red foxes, spotted owls, martens – they all are potentially at risk. This is essentially going to get worse unless we do something to rectify this threat."
West Coast fishers are mid-sized weasels living in the isolated forests of California, Oregon, and Washington. As of 2015, the Sierra Nevada population includes about 250 individuals, with the species listed as threatened under the California Endangered Species Act.