Illegal marijuana cultivation threatens endangered wildlife

Published on
information-circle This article is more than 3 years old

The fisher, an endangered member of the weasel family native to California forests, seems an unlikely casualty of the gradual erosion of prohibitions on marijuana use in the United States.

Years of habitat loss and trapping have decimated the west coast fisher population, making it a candidate for listing under the federal Endangered Species Act.

Yet, a new threat to the imperiled fisher has emerged in recent years. Wildlife ecologists have attributed multiple fisher deaths to anticoagulant rodenticide exposure at illegal marijuana farms hidden on public and tribal lands in California.

Demand for marijuana has exploded now that nearly half the United States and the District of Columbia have decriminalized marijuana use for medical or recreational purposes. Mourad Gabriel, PhD, a wildlife disease ecologist working in California, says his state has become a magnet for people looking to cash in on this emerging market.

Anticoagulant rodenticide bait pellets at an illegal marijuana cultivation site in fisher habitat (Courtesy of Mourad Gabriel, PhD)

“What we’re seeing right now in California is our natural resources are being decimated. People are flocking to California to grow marijuana because it has millions of acres of free public land and free water,” said Dr. Gabriel, who spoke on the issue July 26 at the AVMA Annual Convention in Denver.

Dr. Gabriel is executive director of the Integral Ecology Research Center, and he has been studying threats to two California fisher populations for the past six years. In 2012, he and his colleagues reported that toxicology screening of 58 fisher carcasses revealed 46 had been exposed to anticoagulant rodenticides. Of those animals, 96 percent had been exposed to one or more second-generation AR compounds.

No spatial clustering of rodenticide exposure was detected, suggesting the contamination was widespread throughout the fisher’s forest habitat. Illegal marijuana cultivation sites were found to be the source of the rodenticide, which growers use in excess to protect the plants.

Dr. Gabriel noted the first confirmed intentional poisoning of a fisher was identified at an illegal marijuana site in Northern California in 2013. Hot dogs laced with a carbamate insecticide had been strung around the area. Necropsy and toxicology screening showed the fisher had died as a result of ingesting poisoned hot dogs.

In addition to fishers, Dr. Gabriel said, bear, fox, and other native wildlife carcasses are regularly discovered at these illegal cultivation sites, which are known as “death ring zones.” The ecology of these forested areas is further damaged by clearcutting, water diversion, and the use of massive amounts of high-grade fertilizer, a mean of 2,000 pounds per site, he added.

“Clandestine (activity) involving wildlife isn’t something we’re used to in North America, unlike in Africa, where illegal activities such as poaching for ivory and bush meat are very well-established,” Dr. Gabriel observed.

He said more research is necessary not only to determine the scope of this environmental and ecological problem but also to inform government agencies, wildlife managers, policymakers, and the public. Funding to decontaminate these sites is limited, with most coming from private donors, according to Dr. Gabriel, who wants to see more support for such efforts.

Related JAVMA content:

Veterinary marijuana? (June 15, 2013)