Marijuana Growers and the Death of Fishers

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

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

“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

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

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 

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