Rat poison used on illegal marijuana grows is killing fishers in the southern Sierra Nevada, according to a recent study conducted by a team of scientists from the U.S. Forest Service's Pacific Southwest Research Station (PSW), University of California, Davis, University of California, Berkeley, and the Integral Ecology Research Center.
A previous study published last summer by the research team documented that rodenticides were being found in the tissues of the cat-sized, weasel-like critters which live in rugged portions of the southern Sierra Nevada. The authors speculated that the most likely source of the poisons was the illegal marijuana grows found throughout the Sierra Nevada. This new study solidifies that link, documenting that female fishers who live in areas with a higher number of marijuana sites had more exposure to rodenticides, and subsequently had lower survival rates.
The findings concern scientists because the fisher is a candidate for listing under federal, Oregon, and California endangered species acts, and is considered a sensitive species in the western United States by the U.S. Forest Service. The researchers deduced that illegal marijuana grows are a likely source of the poison, because the fishers in this study were radio-tracked and many were not observed venturing into rural, urban or agricultural areas where rodenticides are often used legally.
Illegal marijuana cultivation on public lands is widespread, and some growers apply large quantities of numerous pesticides to deter a wide range of animals and insects from encroaching on their crops.
While the exposure of wildlife to rodenticides and insecticides near agricultural fields is not uncommon, the amount and variety of poisons found at the illegal marijuana plots is a new threat.