The federal government is considering whether to list fishers as a threatened species in California because of the harm being done by rat poison and other toxic chemicals used on illegal pot farms on public land.
A cousin of the weasel, California fishers now exist in just two isolated populations – one in the southern Sierra just south of Yosemite and the other on tribal lands in the northern part of the state near the Trinity Alps Wilderness area. The two populations are separated by a 270-mile gap.
“The exposure rate for fishers has neither subsided or stabilized – it has gone up,” said Mourad Gabriel, executive director and senior ecologist with Integral Ecology Research Center, a nonprofit research organization.
In October, the U.S. Fish and Wildlife Service proposed listing the fisher as a threatened species under the Endangered Species Act. It recently extended the public comment period on the listing from Jan. 5 to Feb. 5.
Matt Baun, spokesman for the U.S. Fish and Wild Service, said rat poison being used on illegal pot grows can harm other animals as well. “We’re concerned about rodenticide impacts on the ecosystem, and are very much interested in learning more about the impacts on Northern spotted owl, since owls prey on the same types of animals,” Baun said.
“Toward this end, the USFWS has funded studies and (is) awaiting initial data,” he added.
In the Sierra, fishers live at elevations between 2,500 and 7,000 feet. The rugged terrain in the mountain range also makes it an ideal place to grow marijuana undetected.
Gabriel said he ran tests on dead fishers at illegal grow sites this fall. All of the sites were on U.S. Forest Service or National Park Service land. He found that 91percent of dead fishers in the southern Sierra tested positive for at least one rodenticide. Two years ago, 81 percent tested positive.
“These fishers were in areas where they should have never been exposed to rodenticides in the first place,” Gabriel said.
In the north, in the coastal range near the Trinity Wilderness area, the Hoopa tribe has been monitoring roughly 30 fishers. Within the last two years, six in the group have died from rat poisoning.
Gabriel contends that there are exponentially more fishers dying from rodenticide poisoning than anyone knows.
“If you extrapolate, you can make the argument that a large number of fishers across California are mostly likely succumbing to poisoning,” Gabriel said. “They’re not being found because finding a dead fisher in the middle of a national forest is a very rare occurrence.”
Gabriel estimated there are 300 to 1,000 fishers left in Northern California. About a third of those are live in the Sierra, he said.
Historically, the secretive fisher species has faced other man-made threats. It almost went extinct in the 1940s due to widespread fur trapping.
Logging has also taken its toll, as fishers prefer to live in old-growth forest habitats. The old trees and snags provide structure for nesting and den construction, as well as protection from predators.
While logging is still an issue for the species, illegal marijuana cultivation threatens fishers most, said Gabriel.
Illegal pot growing on public land is thought to have started in national forests during the mid- to late 1960s. Today it is a pandemic nationwide. From 2005 through 2010, law enforcement eradicated 3,900 illegal grow sites on national forest land, according to U.S. Department of Agriculture testimony presented to the U.S. Senate in 2011.
In California, illegal pot grows are found in every county in the state – among tree-shaded creeks in the Central Valley off of Interstate 5 as well as in hard-to-reach areas of the Sierra.
Typically, the growers are migrants from Mexico working for drug trafficking organizations. They often spread rodenticide liberally at grow sites to keep rats and other animals away from marijuana plants, and to stop rats from chewing on the black plastic tubing used to irrigate the crop.
In many cases, growers also dam creeks and streams and then mix pesticides and herbicides in the pooled water for eventual irrigation.
“When you have a massive amount of rodenticide out there, it has a potential to kill hundreds, if not thousands, of other prey species,” Mourad said.
The extension of the comment period for listing the fisher as a threatened species is welcome news to Noah Greenwald, director of endangered species at the Center for Biologic Diversity.
“It’s definitely a species that requires protection under the native species act if it’s to survive,” said Greenwald.
It was Greenwald who first filed a petition to list the species as endangered, back in 2000. “Here we are 12 years later,” he said.
Greenwald said he would like to see the species protected not only in California but along its historic range, which runs from the southern Sierra all the way to Canada.
He sees the fisher as a vital part of the food chain. It is one of the few animals that preys on the porcupine, Greenwald said. “Keeping porcupine populations under check is critical since they like to eat small trees,” he said.
Call The Bee’s Edward Ortiz, (916) 321-1071. Follow him on Twitter @edwardortiz.
FISHER, Martes pennanti
* Habitat: Conifer and mixed forests. Likely favors old-growth forests and often makes its home in tree cavities
* Status: Temporarily listed as a threatened species. Permanent listing proposed.
* Size: 2.5 to 4 feet long
* Weight: Males 7 to 13 pounds, females 3 to 5.5 pounds
* Life cycle: Lives up to 10 years; breeding season February through April; young are raised by the mother
* Food: Opportunistic feeder, eating anything it can catch, including mice, rabbits, squirrels and birds
* Unique features: Feet have five toes with retractable claws; rear paws can rotate nearly 180 degrees, allowing the fisher to climb down trees headfirst like a squirrel