California’s Illegal Pot Farms Are Killing Rare Animals

Pacific fishers, an endangered type of weasel, are being poisoned by toxic rodenticides used by marijuana growers.
A Pacific fisher. (Photo: Bethany Weeks via USFS Region 5)
Nov 4, 2015· 2 MIN READ
John R. Platt covers the environment, wildlife, and technology and for TakePart, Scientific American, Audubon, and other publications.

Are some Californians unintentionally killing wildlife every time they toke up?

Marijuana may be all but legal in California, but the same thing can’t be said about every pot farm. In 2014, police conducted 250 raids of illegal pot farms on public land in the state, destroying more than 600,000 plants in the process.

These “trespass growers” chop down trees, bulldoze native plants, divert streams and other sources of water, and perhaps worst of all, litter their plots with deadly rodenticides designed to protect their cash crops from hungry wildlife.

An imperiled species is taking the bait. New research published Wednesday in the journal PLOS One finds that an increasing numbers of Pacific fishers—a cat-size type of weasel—are being exposed to or are dying from rodenticides found at these trespass pot farms. The fishers either eat the poison or kill rodents that have consumed the toxins. Either way, they die or become weakened and less able to survive.

(Photo: USFS Region 5)

Fishers are not unique to California, but their population in the Pacific Northwest was nearly wiped out decades ago by logging in their old-growth-forest habitats. Today, two remote populations survive in California. Earlier this year the state declared one of those two populations endangered.

This is the second study of fisher deaths related to marijuana farms. The first, published in 2012, found that 79 percent of dead fishers had been exposed to rodenticides. The new study, which covers 2012 to 2014, finds that the number has increased to 85 percent. One animal’s body contained six rodenticides.

The increase was surprising, said the lead author of both papers, Mourad W. Gabriel, executive director of the Integral Ecology Research Center. “The 2012 paper generated a significant amount of public and media response,” he said. “I thought that private growers or illegal trespass growers may have gotten the message that this is a concern.”

RELATED: Your Pot Habit Is Contributing to a Guacamole Crisis

That doesn’t appear to be the case. Illegal pot farmers have changed their growing strategy in a way that’s worse for wildlife. Gabriel said growers in 2012 tended to keep all their plants clumped at a single site on public land. “Now it’s 10 plots of 300 plants spread over a half a mile, with multiple toxicant loads spread over the space,” he said. This minimizes the grower’s risk of getting caught while increasing the risk that wildlife will be exposed to the rodenticides.

Making matters worse, most of the sites that law enforcement officials find and destroy are not adequately cleaned up, meaning the toxic threat remains after the growers are gone. “What we’re finding is that only between 15 and 20 percent of all eradicated grow sites are fully remediated,” Gabriel said. “We have this historic backlog in addition to all of the new sites that are being cultivated.”

Conservation groups said this new data may help fishers in the long run. “It makes for a stronger case that fishers need protection,” said Noah Greenwald, endangered species director at the Center for Biological Diversity, which has petitioned to list the fisher under the federal Endangered Species Act.

The government agreed in 2014 to consider protecting the Pacific fisher. A final decision is due next year.