Pot growers have gashed thousands of illegal farms into the remote backcountry of national forests from the Klamath to the Plumas. They have diverted entire streams, bulldozed trees and punched roads onto erosive hillsides.
Fishers were already doing poorly when Gabriel began monitoring them in 2007. Weasel cousins with hatchet-shaped heads, fishers in California total about 2,000 in two populations, one of them in the northwest corner known as the Emerald Triangle for its near-perfect pot-production conditions.
Gabriel found 79 percent of the fishers he had studied by 2012 had been exposed to rodenticides; 5.9 percent of them died. Today 85 percent of all California fishers have been exposed to at least one rodenticide. Poisoning has claimed 10 percent of them.
The area contaminated by pot farms has also grown and now includes almost every county in far Northern California. More disturbing for wildlife, the poisons on grow sites have escalated from anticoagulant rodenticides to include carbofuran, a pesticide so toxic it is prohibited in Canada and under a de facto ban in the United States.
One-eighth of a teaspoon of carbofuran can kill a bear. Researchers found it recently at a grow site mixed in a tuna can deliberately placed for wildlife consumption, said Stella McMillin, senior environmental scientist with the California Department of Fish and Wildlife.
Even the less toxic substances have troubling long-term effects. Over-the-counter anticoagulant rodenticides are more lethal to embryos than adults. They might not kill a bear or a mountain lion, but they may destroy their unborn litters. Scientists do not know how they are affecting the long-term viability of species, McMillin said.
California has taken important steps toward limiting the use of rodenticides. Since 2014 sale of all second-generation anticoagulant rodenticides has been restricted to licensed pesticide operators. Obviously this has not deterred illegal pot growers.
Neither has marijuana legalization. Despite the hopes of wishful thinkers, production is booming and the growing season, which used to begin in May, is becoming year-round. U.S. Forest Service law enforcement has never had the resources to deal with these trespassers. With the agency burning half its budget to fight fires and further cuts proposed, going after pot growers is little more than whack-a-mole.
Gabriel continues to collect fisher and other wildlife mortality data despite threats and the suspicious death of his dog to poisoning. Anything less would be giving in to scientific intimidation, he said.
His research may be our best hope for reclaiming our national forests from an illegal industry. The data deliver a clear message for agencies and policymakers: Marijuana is killing wildlife and poisoning public lands.
And the science has a pointed message for users: The pot you smoke may be grown on the carcass of a dead fisher.