Fishers are reclusive forest-dwellers, a bit larger than their weasel cousins. They are a candidate for the endangered species list. California fishers live in small isolated groups in the southern Sierra, in Yosemite forests and parts of Northern California.
Researchers tested 58 carcasses of fishers they monitored on public lands. Nearly 80 percent had been exposed to rat poison.
Ecologist Mourad Gabriel says his team was confused how fishers living far from urban or agricultural areas were being exposed to rat poison:
GABRIEL: "But law enforcement would inform us that where these particular fishers were, they had dismantled several marijuana grow sites. And at these grow sites was up to 100 pounds of rodenticide."
Gabriel says the majority of the fishers were poisoned by eating rats or mice that consumed the food-flavored poison. He says this means other species like red fox, spotted owls, wolves and wolverines may also be at risk.
And, even at non-fatal levels, the rat poison could harm the fishers by making them tired and slowing their reaction time, which makes them vulnerable to predators.