By Andrew Becker, California Watch

Toxic chemicals used to rid rodents from illicit marijuana gardens in the Sierra Nevada range and elsewhere in California may have inadvertently poisoned dozens of vulnerable weasel-like mammals called fishers, according to a new study released this month.

Biologists from UC Davis, the nonprofit Integral Ecology Research Center, and state and federal land agencies found that nearly 80 percent of a sample size of fishers found dead in the wild were exposed directly or indirectly to anticoagulant rodenticides – rat poison. They point to illegal marijuana cultivation as a likely culprit for the introduction of the chemicals to remote areas where the animals live.

Fishers are members of the weasel family and formerly ranged across the northern forests of North America. But logging and fur trappers lured by their once-valuable pelts drove the fishers’ numbers down, wiping them out in some parts of the United States. The sample group of the rare animals, which could be listed for protection under the Endangered Species Act, were found over a five-year period ending in 2011 in Northern California and in the southern Sierra Nevada range. Some of the dead animals were found in remote wilderness areas with no roads or campground access.

The study, which documented exposure to such poisons in fishers for the first time, raises questions about the threat to other rare forest predators, such as the Sierra Nevada red fox, wolverine, gray wolf and various owl species. It also raises questions about the long-term environmental impacts from marijuana gardens treated with the poisons, which have become increasingly toxic as rodents build resistance to the chemicals. Nearly all of the fishers that died after coming into contact with the anticoagulants were exposed to highly toxic versions of the chemical.

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