Potent rat poisons used on large-scale illegal marijuana farms sprinkled through forest lands throughout the state may be killing off a rare forest carnivore, according to a groundbreaking study released Friday.

”This could be a game changer,” said Arcata City Councilman Mark Wheetley of the study produced by biologists from University of California Davis documenting the deaths of fishers, reclusive members of the Mustelid family that are candidates for protection under the Endangered Species Act.

”I think this whole study should serve as a wake up call for the public to understand the magnitude of the impact of what’s being done to what we consider sacred, protected public lands,” continued Wheetley, who holds a day job as a senior biologist for the California Department of Fish and Game.

Law enforcement and environmental officials have long complained of the environmental degradation associated with large-scale marijuana cultivation on forest lands. But the evidence has been almost exclusively anecdotal, limited to stories of diverted streams, networks of irrigation piping, piles of trash and large amounts of commercial fertilizers, insecticides and rodenticides.

The study released Friday documents the scientific data behind the stories for the first time, quantifying the environmental impacts of illicit grows.

Mourad Gabriel, lead author of the study and president of Blue Lake’s Integral Ecology Research Center, said the study sprang from efforts to identify and study threats to California’s fisher populations. Because the reclusive forest predators live in coniferous and hardwood forests — mostly forest, park and tribal lands — far away from urban population centers or agricultural fields, Gabriel said researchers were shocked to find they were being poisoned by toxicants at an alarming rate.

The study found that almost 80 percent of fishers found dead by researchers between 2006 and 2011 had been exposed to high levels of anticoagulant rodenticide — commonly referred to as rat poison. Because these fishers were being monitored and lived in remote areas, Gabriel said researchers were initially stumped as to what could be the potential exposure points for them.

Then, Gabriel said, it clicked: Researchers realized that all these fishers’ habitats overlapped with illegal marijuana farms that often used high levels of commercial pesticides and rodenticides to protect their crop. Further, the study notes, all the deaths of exposed fishers occurred between mid-April and mid-May, the optimal time period for planting marijuana outdoors, when growers are most likely to use large amounts of poison to protect their seedlings.

The study describes a grow site discovered by law enforcement less than 7.5 miles from one of the fisher study areas, where large amounts of rodenticide were found sprinkled around plants and lining plastic irrigation lines, presumably to keep rats from chewing them.

The anticoagulant rodenticides inhibit mammals’ ability to recycle vitamin K, making their blood incapable of clotting, leading to uncontrollable internal bleeding and, ultimately, death. The second-generation poisons can be lethal with a single dose, the study notes, but can take up to a week from ingestion to be lethal.

Gabriel said some of the rodenticides are treated with “flavorizers” to make the poisons taste like bacon, cheese or peanut butter, which could also cause fishers and other animals to eat the poison directly. The most likely — and troubling — conclusion, however, is that the fishers were exposed through their prey: small rodents.

This is a troubling notion for biologists and conservationists for several reasons. First, because fishers have the same prey groups as federally protected, threatened or endangered species like condors, spotted owls and martens, those groups may be just as likely to be impacted. Second, these poisons could wipe out a whole prey group — wood rats, deer mice and other small scavenging rodents — in the region, leading to the collapse or partial collapse of a food chain.

Rodenticides, however, are far from the only troubling items found at illicit marijuana growing sites. In a separate paper, Gabriel and others outline what they found during a brief visit to an abandoned marijuana garden in one of their fisher project areas. In addition to pounds of rodenticide, they reported finding 575 pounds of fertilizer, including 200 pounds of fertilizers with 46 percent nitrogen levels, 24 pounds of slug bait and 32 ounces of Malathion, a potent pesticide.

Such findings come as no shock to law enforcement.

Humboldt County Sheriff’s Office Sgt. Wayne Hansen, who currently heads the county drug task force and has spent years heading marijuana eradication efforts for the county, said the large-scale grows believed to be tied to drug trafficking organizations — the ones most likely to be on remote public lands — often utilize huge amounts of poisons and fertilizers, in addition to diverting streams and clear-cutting swaths of forest.

Gabriel said his study simply brushes the tip of the proverbial iceberg. The next step for him and fellow researchers, Gabriel said, is to look at whether the use of rodenticides at grow sites on public lands is depleting the prey pool for fishers and other carnivores. But, Gabriel said, there are a tremendous amount of questions associated with these growing operations that warrant scientific attention, including the impacts of pesticides, fertilizers and stream diversions. The hope, Gabriel said, is that his study and the ones that follow help inform the discussion.

One thing for sure is that the study is already getting loads of attention, having circulated through some professional circles before its public release Friday.

Tommy Lanier, director of the White House-funded National Marijuana Initiative, said Friday he’s very familiar with the fisher study and hopes it will serve to educate the public about some of the ancillary impacts of the marijuana market. To that end, Lanier said, he’s trying to get Sen. Barbara Boxer, who heads the U.S. Senate Committee on the Environment and Public Works, to hold a congressional hearing on illegal marijuana cultivation on public lands. He said he plans on asking Gabriel to come back and address Congress.

”The environmental impacts are huge and have to be a huge part of the discussion,” Lanier said. “(This study) is a great example of some of the effects.”

On the Web:

To read the complete study, or view a video about it, visit www.news.ucdavis.edu/search/news_detail.lasso?id=10287

Thadeus Greenson can be reached at 441-0509 or tgreenson@times-standard.com.