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  • Manny Crisostomo /

    A federal task force special agent examines marijuana at an illegal grow site late last month near the Twin Cities exit off Interstate 5. A recent study finds the use of rodenticides at such sites poses risks to fishers, a struggling weasel species.

  • Manny Crisostomo /

    State and federal agents survey a marijuana grow site last month near Galt. The fisher, a cat-sized member of the weasel family, has been found to be put at risk by such illegal sites' use of poisons.

  • Manny Crisostomo /

    One of the agents holds a starter plant.

Pot grow sites' poisons cited in fishers' survival struggles

Published: Sunday, Sep. 8, 2013 - 12:00 am | Page 1B
Last Modified: Sunday, Sep. 8, 2013 - 11:24 am

It was midday on Aug. 30, and the sun blazed over two undercover law enforcement officers as they entered an illegal pot farm. Like so many in the Central Valley, this farm was hidden in plain sight, a stone's throw from Interstate 5, near Galt.

The sweep revealed no humans, but enough d-CON strewn about to kill several rats.

It was a classic example of the environmental degradation caused by widespread, illegal pot farming on public land. Rat poison threatens whatever species shares habitat with such grow sites, and no animal is more imperiled than the fisher, a cat-sized member of the weasel family who lives in the Sierra Nevada and its foothills.

A recent study has established a link between rodenticide use on illegal pot farms and the failure of the fisher population to expand beyond a meager 300 animals in the Sierra Nevada.

The study, a joint effort among scientists at UC Davis, UC Berkeley and two other entities, used transmitters to track 46 adult female fishers in the Sierra National Forest. Researchers also made an inventory of illegal pot farms in the same area. Wherever a fisher's territory overlapped with an illegal pot farm, it turned out, the species failed to expand its range – an indicator that its population wasn't growing.

In the Sierra, fishers live at elevations between 2,500 and 7,000 feet. The rugged terrain of the fisher's habitat is also an ideal place to grow marijuana undetected.

"This is where you have a constant water source and where you can avoid detection by law enforcement," said Mourad Gabriel, one of the authors of the research and co-founder of the Integral Ecology Research Center.

"You have a band of cultivation there and that's where the fisher is holding on. They're not expanding … and we suspect it's the use of toxicants causing that."

The fisher was once found throughout the state and in the Northwest. Today it is reduced to living in isolated pockets. Besides the group in the Sierra, additional populations live near Lake Shasta and in Humboldt County.

The fisher's habitat has shrunk consistently over the past 100 years. The species almost went extinct in the 1940s because of extensive fur trapping. In the 21st century the state's fisher populations have come under pressure from a new development: the increase and intensity of forest fires.

Fishers are now found in such low numbers that the California Department of Fish and Wildlife is considering listing the animal as endangered.

Released in May, the UC Davis study found that 85 percent of the dead fishers it collected had anti-coagulant rodenticide in their livers, Gabriel said.

Growers, mostly migrants from Mexico, spread rodenticide to keep animals away from marijuana plants and to stop rats from chewing on the black plastic tubing used for crop irrigation. In many cases, the growers dam creeks and streams and then mix pesticides and herbicides in the pooled water for eventual irrigation.

At the empty grow site in Galt, which law enforcement had raided in June, water lines had already been relaid when agents returned two months later. Growers had begun to spread rodenticide, with opened boxes of d-CON rat poison sitting a few steps from a creek.

Many of the chemicals used in illegal pot grow sites are banned in the United States, and are brought in from Mexico. These include Carbofuran – a rodenticide so powerful that a quarter teaspoon can kill a human.

For the fisher, the use of rodenticide is a major concern since it is keen on feeding on carrion – including rodents. In some cases, the fisher eats bait meant for the killing of rats.

That much became clear at an illegal-cultivation-site raid a month ago in the Six Rivers National Forest, where 7,500 marijuana plants and 14 pounds of rodenticide were found. It was the first direct evidence of a fisher death on a grow site.

At that site, a dead fisher was found under a series of hot dogs hanging from treble hooks. The hot dogs had been laced with so much rodenticide that the dead fisher was found with a piece of hot dog lodged in its throat. "That means the fisher died acutely … as he was eating it," Gabriel said.

"We've been looking for that needle in the haystack – a direct poisoning attributable to a grow site," he said. "And now we have one."

Many more fishers die from rodenticide exposure that can be quantified, said Gabriel.

His study contends that exposure to the chemicals also leads to secondary reasons for death, because rodenticide exposure predisposes animals to slower reflexes, a reduced ability to heal from injuries, and neurological impairment.

And with female fishers, it is likely that rodenticide is passed on to offspring.

Presently, an effort is under way to clean illegal grow sites and return them to as close to their original condition as possible. That job falls to individuals such as Shane Krogan, executive director and founder of the nonprofit High Sierra Volunteer Trail Crew.

The nonprofit has been reclaiming sites in partnership with the U.S. Forestry Service and the state's department of Fish And Wildlife. Krogen and his team of volunteers have reclaimed more than 400 sites since 2004. He said it does not take long to find evidence of environmental degradation upon entering a grow site

"We'd go into these sites and we wouldn't find lizards. We wouldn't find mice," he said.

Krogen said establishing rodenticide use was sometimes as easy as counting the toothbrushes found on the site.

"Generally, wherever a grower sleeps is where they will put a lot of rodenticide to keep mice and rats from coming up to them in the middle of the night."

Call The Bee's Edward Ortiz, (916) 321-1071. Follow him on Twitter @edwardortiz.

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