Marijuana Growers and the Death of Fishers

Using harsh rodenticides, marijuana growers in California are threatening fishers, a critical umbrella species, on the Hoopa reservation and national forest land.

Tire Full Of Weed

"I'm not focused on the pot plants," Gabriel says. "What makes my blood boil is the environmental damage being done on public land."

Photo By H. Lee

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Hiking through the northern California woods in the course of doing his job, Mourad Gabriel frequently encounters angry men who are unhappy to see him. They’re marijuana growers, illegally using federal and tribal lands in remote, hard-to-reach locations. And their reactions to seeing him may range from yelling at him to brandishing their pistols or Kalashnikov rifles and posting his home address on a cannabis blog—along with the ominous observation that “snitches end up in ditches.”

Gabriel isn’t with the Drug Enforcement Administration or any other law enforcement agency. He’s a wildlife disease ecologist nearing the completion of his doctorate at the University of California, Davis, who has spent a decade studying fishers—furry, elegant predators the size of large house cats. Fishers once roamed our northwestern forests in abundance, but their numbers have dwindled dramatically in the region. Now Gabriel, 38, believes he has unlocked the mystery as to what’s keeping this species from bouncing back. And his discovery, alas, is what has outlaw pot growers reaching for their guns (or computer keyboards).

“I’m not focused on the pot plants,” Gabriel says. “What makes my blood boil is the environmental damage being done on public land.”

Hit hard by fur trapping and the logging of the forests they favor, fishers had all but vanished from their historic range by the early 20th century. Gabriel describes them as an “umbrella species,” meaning that they tend to be good indicators of their ecosystem’s overall health. By studying the remaining fishers closely, biologists can get a sense of how other members of their ecosystem are faring.


In 2004 Gabriel was engaged in a study of predators on land owned by the Hoopa tribe in northern California’s Humboldt County. To his surprise, the fisher population on the reservation had declined precipitously in the years since a survey was made in the 1990s. Gabriel knew that fishers need mature forest to survive: they rest and raise their young inside the cavities found in the trunks of very old trees. The reservation still boasted plenty of ancient oaks, chinquapins, and Douglas firs. Why, he wondered, weren’t more fishers living there?

“Some of the fishers we were radio-tracking had died of rodenticide poisoning,” Gabriel recalls. “I couldn’t imagine how that had happened, since fishers live far from cities or farm fields.” He made the connection to industrial-scale marijuana farms after some members of the Hoopa tribal police showed him photos of grow sites they had dismantled after raids. Pesticide containers were scattered across the landscape, their poison baits marked with countless scratches made by the gnawing teeth of mice and rats. The pot growers, it soon became clear, were spreading large amounts of rodenticide around their plants to protect them from tiny pests. The rodents were living for several days after eating the poison—just long enough to be preyed on by fishers.

Gabriel began to document the stunning quantities of rodenticide that were peppering the 144 square miles of the Hoopa reservation. On one grow site near the reservation, 90 pounds were discovered. He calculates that 10.5 pounds (the amount he found at one of the first sites he studied) is enough to kill 12,542 deer mice or 1,792 wood rats—and anywhere from 5 to 28 fishers. Over the next eight years, on both Hoopa and national forest land, the rodenticide-linked casualties kept piling up.

In addition to legal pesticides that are already in wide use, significant amounts of banned pesticides, including DDT and carbofuran, have been found at abandoned sites. Gabriel has also seen signs of illegal clearcutting and stream diversion. “No law seems to sway these individuals,” he says.

His research has led him to conclude that the same rodenticides killing fishers pose a grave threat all the way up the forest food chain. If the problem is left unaddressed, he says, the result could be a biologically devastated forest—one where no fisher or bobcat hunts and no bird sings. As he continues with his research, he has also begun collaborating with a group that works to clean up contamination at dismantled grow sites.

“The rogue pot industry is a human problem,” he says. “And we’re going to need a human solution.”

Sharon Levy spent a decade working as a field biologist in the woods of Northern California before taking up science writing full time. This story was originally published in the Winter 2012/2013 issue of OnEarth.