Increasing Number of Threatened Species Dying of Rodenticide Poisoning From Marijuana Grows

A fisher dying of rodenticide poisoning.

Press release from UC Davis:

Mourad Gabriel of Integral Ecology Research Center stands amid an illegal marijuana grow site in Northern California. Gabriel led research with UC Davis connecting rat poison at such sites to the deaths of fishers, weasel-like mammals proposed for federal listing as a threatened species. Credit: Mark Higley/Hoopa Valley Tribal Forestry

Mourad Gabriel of Integral Ecology Research Center stands amid an illegal marijuana grow site in Northern California. . [Photo Credit: Mark Higley/Hoopa Valley Tribal Forestry]

The situation is growing worse for fishers being poisoned by rodenticides on illegal marijuana grow sites in California, according to a study by a team of researchers led by the University of California, Davis, and the Integral Ecology Research Center, based in Blue Lake, California.Fishers are midsized weasels that live in isolated forests of California, Oregon and Washington. The West Coast fisher population was proposed for federal listing as a threatened species in late 2014. In 2015, the southern Sierra Nevada population was listed as threatened under the California Endangered Species Act.The study, published Nov. 4 in the journal PLOS ONE, shows that increasing numbers of fishers are being exposed to and dying from greater varieties of rodenticides found at trespass pot farms.Fishers most affected live in the Sierra Nevada range near Fresno and in forests stretching from Humboldt County to Redding in Shasta County.

The study was led by Mourad Gabriel, who began the research as a doctoral student with the UC Davis Veterinary Genetics Laboratory and is now director of the nonprofit IERC.

‘It’s not getting better’

Gabriel’s studies in 2012 and 2013 were the first to link rat poison and illegal marijuana farms to fisher deaths, bringing broad attention to the issue.

In the 2012 study, Gabriel recorded four fisher deaths in five years due to rat poisoning from illegal marijuana grows. This new study examined the deaths of 167 fishers, with 129 of them suitable for necropsies. The study found that, between 2012 and 2014:

  • Eight more poisoning deaths occurred, a 233 percent increase in the annual rate of poisoning deaths over the 2012 study.
  • 69 percent of all poisoning cases were in the spring, when fishers mate and raise their kits.
  • Exposure rates to rodenticides rose from 79 percent to 85 percent.
  • Necropsies confirmed as many as six different rodenticides in one animal. Some of the chemicals found were considered safer alternatives to other commercially available rodenticides, but they nonetheless killed fishers.

For the full study period, 2007-2014:

  • Predation caused the majority (70 percent) of fisher deaths, but rat poisoning connected to marijuana grow sites accounted for 10 percent of fisher deaths.
  • An additional fisher from 2008 was reclassified as a poisoning death, bringing the total number of poisoning deaths between 2007 and 2014 to 13.

“We’re showing that it’s not getting better,” said Gabriel. “Fishers are the flagship species. We have to think of so many species, like Sierra Nevada red foxes, spotted owls, martens — they all are potentially at risk. This is essentially going to get worse unless we do something to rectify this threat.”

Most fishers exposed to rat poison


This fisher, brought to UC Davis for a necropsy, was poisoned by anticoagulant rodenticide (rat poison) found on an illegal marijuana grow site in Northern California.

The necropsies were conducted at the California Animal Health and Food Safety Laboratory System, or CAHFS, which is part of the UC Davis School of Veterinary Medicine.

“We’re sort of a one-stop shop with a tremendous resource of people and broad array of tests that can be brought to bear about why an animal died,” said co-author Robert Poppenga, a professor and veterinary toxicologist with CAHFS. “The thing that intrigued us early on was the detection of anticoagulant rodenticides in these fishers. They’re out in the middle of nowhere. Yet, based on post-mortem testing, more than 85 percent have ARs in their system.”

Anticoagulant rodenticides inhibit the ability of fishers and other mammals to recycle vitamin K. This creates a series of clotting and coagulation problems, which can lead to uncontrollable internal bleeding.

The poison, which is often enhanced with bacon, fish and peanut butter “flavorizers,” is scattered around illegal marijuana grows in remote sites to deter pests from the crop.


This is the amount of rat poison found at just one illegal marijuana grow site in Northern California.  [Photo provided by Mourad Gabriel]

Team effort

The research team included seven additional UC Davis scientists, as well as researchers from Hoopa Tribal Forestry, U.S. Forest Service-Pacific Southwest Research Station, Wildlife Conservation Society, UC Berkeley, Humboldt State University, and California Department of Fish and Wildlife.

Funding for the study came from IERC, UC Davis CAHFS, Hoopa Valley Tribal Forestry, United States Forest Service, National Park Service, United States Fish and Wildlife Service, California Department of Water Resources, California Department of Fish and Wildlife, California Department of Forestry and Fire Protection, The Sierra Nevada Conservancy, Sierra Nevada Adaptive Management Project, and the Bureau of Indian Affairs.

Additional information:

Earlier Chapter: How Some Growers Are Killing Fishers



  • This boils my blood. I’m not against growers, just ignorance. Make trespass grows a priority and focus on public and timber land. And when you do bust the garden, make sure to get the perps as well. I bet the amount of rodenticides found on private property is pretty low. I would love to point to a specific group of people, but I will keep that thought to myself.

    • Hey KMUD!!!! This is on you!!!! Marijuana this and Marijuana that. We have scum coming to the Emerald Triangle from every nook & cranny who do not value nature or our quality of life. You people are so focused on a particular niche/group and because of this we see this outcome. Your focus on MARIJUANA ONLY has been a detriment to our local businesss, community cohesion, non-profits, social network and and way of life.

  • Six different rodenticides in one animal!! That is unacceptable. We need to stop using this toxin and leave the wildlife alone! Fishers and martens have enough problems without people making it worse.

    • Every grocery store or food counter uses rat poison, it’s what’s in those black boxes with the hole in them. Heck, it’s in tap water as well, fluoride….

      Fukushima has killed off more wildlife than some Isis growers in Toyota trucks.

      That said, stickey traps work great.

  • Please authorities put your ppt busting monies into taking these people and grows off our public land!!!!! Even the biggest private grow is nothing in comparison to these monster grows, in one area a few years back they pulled up 4miles worth of black plastic water pipes. The feds can sue these idiots a multi thousand dollar fine per animal under threatened/endangered animal regs.
    Lets all take a few moments to call our rep’s and demand more be done on public land to get rid of these grows!

  • These poisons should only be available to licensed pest control applicators.

  • We’ve learned that the rats and mice only want the water, not the plant. So we put out water for them in shallow bowls throughout the Season, and their needs are satisfied. Chewed water pipes: same deal with the added factor that irrigation pipe has a “salty” flavor. (Nibble a little to prove it to yourself.) The pipe sweats, the critter comes, licks the pipe, and goes for more. Same solution. Thrift stores carry bowls up the wazoo, cheap.
    Those “sticky traps” get everything from the initial “take” to everything (like owls) that feeds on it. Small snakes, lizards, other bug-eaters, butterflies; everything is caught, even small birds.
    Think about it, please. Roasting immobile in the sun is a horrible death. It’s every bit as cruel and mindless as poison. Water+Bowls. Easy. No harm, no fault, no blame. af

    • Excellent info, Anon, let’s hope the media spreads it far & wide.
      Also, Kym, The SHTF media always promote surviving on rats. it’s dutiful to alert them of possible dangers, without stirring hate or panic.

      • SHTF ? What is that? (Thanks for the kudo, and remember: It is the responsibility of each and everyone of us to teach each other WTF… We are ALL teachers.)

  • Lost Croat Outburst

    This is ghastly. This is being done by wretched people for whom pounds and pounds of rodenticides are one of their cheapest expenses, so who cares? Just dump it everywhere. This is stupid and evil on several levels. Fishers DON’T EAT POT! They are hunters. They EAT RODENTS. You can target woodrats, if they really are a problem, with the big treadle rat traps for $2.00 each. Rubber band whole peanuts on the treadle and place in a sideways gallon flower pot. Peanut butter smells too much and pulls critters in from far away. This is just as bad as the old days when sheep ranchers would use 1080 or other broad-range poison and just kill everything. You don’t need to do this; you should be in jail.

  • No more poison people!!!!
    I use micro ponds in and around my gardens…..if you provide water for the critters……you will see MUCH less damage to your plants. Tanglefoot on the stalks helps to. Product called Fresh cab,active ingredient balsamic fir oil, does a great job repelling rodents. And finally….,accept a little damage….its not all about you……get organic or go home. Tired of paper chasers ruining our home.

    And get you some killers on the payroll…..plenty of homeless kitty’s out there…..would love to live in your garden and take care of your rodent problems. BALANCE PEOPLE.

  • Attention Kim. It would be awesome to see some sort of forum to discuss these things. There is a mite called the Broad Mite, or Cyclamen Mite, that with the help of climate change is heading our way from the south. There is no organic product that works on these guys…..we need to find one….cuzz they are heading our way. Right now it’s all about cultural control and quarantine of imported clones, but we need to find effective control before this problem really gets established. Thanks for your contribution to our community….Black belt is the best.

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