Scientists at UC Davis say illegal marijuana farms could be harming a rare California mammal. High doses of rat poison, commonly used by pot farmers, are showing up in Pacific fishers.

Fishers are a weasel-like animal found in California’s secluded forests.  The species is currently being considered for protection under the Endangered Species Act.

UC Davis researcher Mourad Gabriel analyzed the bodies of dead fishers, he was surprised by what he found. "Almost 80%, basically 79% of fishers in California were exposed to this particular toxicant, rodenticide," says Gabriel.

Most of the fishers had been tracked with radio collars, so Gabriel knew they hadn't gone into inhabited areas. That pointed to illegal marijuana farms as the source.

"As many ecologists or biologists who work extensively in the field in California know, you do run into these grow sites almost at a constant basis. There’s one documentation of close to a hundred pounds of rodenticide were distributed at one grow site," says Gabriel.

That could also be putting other animals in the ecosystem at risk, like spotted owls and Sierra Nevada red foxes.