Photo Credit: Morgan Heim
June 24, 2020

Fisher Conservation in the Sierra Nevada

CBI's 10+ year history of fisher conservation in the southern Sierra Nevada

Back in the late 1970s, Dr. Reg Barrett at the University of California Berkeley told the US Forest Service that their biggest looming conservation problem in the Sierra Nevada was going to be a large weasel called the fisher. Dr. Barrett saw the fisher's dependence on large, old trees and dense canopy forest as a source of conflict with timber and fire management. It took almost 30 years for Dr. Barrett’s prediction to come true, but by the early 2000’s the conflict between fisher habitat conservation and fire and fuel management that was playing out in federal courts reached the point where a whole new approach, based firmly in field research and an open, transparent analytical process was needed to restore trust and reconcile conflicts. In 2007, CBI was brought into the fray as an independent, non-profit research organization -- an unprecedented arrangement by the Forest Service -- to (1) establish a baseline understanding of fisher status and the relationships between fishers, fires, fuel, and forestry; and (2) develop a new scientific system for determining how to reconcile the conflicts and benefit fishers. In the words of William Zielinski, a highly regarded and now-retired forest researcher, the resulting Sierra Nevada Fisher Baseline Evaluation and the scientific platform CBI developed for testing alternative solutions sets was “much more than about fishers, forestry, and fire—it is an example of how an open process in a contentious environment got the job done.” CBI has continued in the role of synthesizing the copious research information on fishers, fire, and forest ecology into a comprehensive conservation strategy for fishers ever since.

Beginning in 2007 and running through 2020, Forest Service researchers have generated vast amounts of information about the fisher, ranging from what they eat to how far they can travel. 

Some of the most vital information researchers have collected has come from the use of ‘detector dogs’, dogs trained to detect the presence of a wildlife species without actually disturbing the animal itself. Unlike hunting dogs, detector dogs are trained to find the poop (or ‘scat’) of the animal they’re searching for, not the animal itself. These high-energy dogs, rescued from shelters where they ended up after destroying one couch too many, can scan large areas of the forest quickly and can find evidence of a fishers’ presence almost 100% of the time. All for the reward of 10 minutes play with the of the one thing they love above all else, the tennis ball. And from that scat, researchers can use genetic techniques to determine whether that was a male or female, what it was eating, and sometimes even exactly which animal it was. A wealth of information, without ever having to bother the fisher at all. For more information on these amazing dogs and the people they train, check out the Rogue Detection Dog website here
In April 2009, the research took a new twist when a young male fisher was found dead on the forest floor. What made this particular animal special was that researchers could find no evidence of what killed it. It looked healthy, no sign of injury or predation. To help determine what killed it, the carcass was sent to the UC Davis veterinary pathology lab for analysis and the results were clear - rodenticide poisoning. But this only made the puzzle deeper; where did an animal that spent its life in a remote part of the Sierra Nevada, near the border of Yosemite National Park, get into rodenticide? Only after several months of searching were the researchers able to find the source, illegal trespass marijuana grow sites on public land. Like the proverbial canary in the coal mine, this one fisher exposed the tip of what turned out to be a huge problem: thousands of these sites across public lands in the western United States, each with a slew of hazards to both wildlife and people. Since that day, cooperative efforts between law enforcement, researchers and volunteers have begun to try to clean up these sites, but a vast amount of work is left to be done and the poisoning of wildlife continues. Read more about the destructive effects of rodenticide on fishers and the environment here.
Poisoning is not the only emerging threat to fishers. In 2014, a wave of climate-change induced tree mortality swept through the Sierra Nevada. Millions of trees died, including many of the large pines that fishers rely on for denning and rest sites. Used to moving through dense forest, Sierra fishers instead found themselves facing large, open areas where their risk of being spotted and killed by larger predators is much greater. Over just a few years, what was once large areas of dense forest became a fragmented patchwork of open areas, some remnant dense forest, and shrub-dominated hillsides. One student’s research revealed that the changes in habitat had literally increased the level of stress hormones in female fishers’ systems, which is linked to lower reproduction and survival. 
But the future for Sierra Nevada fisher may not be as bleak as all that sounds. In June of 2020, the US Fish and Wildlife Service officially listed the southern Sierra Nevada fisher population as Endangered. And this followed numerous efforts by agencies such as the US Forest Service and National Park Service, along with private organizations such as timber and utility companies, to adopt fisher-friendly management practices. CBI will continue to actively engage in fisher conservation, updating the 2016 Southern Sierra Nevada Fisher Conservation Strategy as new information becomes available, crafting innovative solutions such as how to design fuelbreaks to allow fishers to cross open areas they normally avoid, and ensuring that science remains a driving force behind conservation efforts.
**Wayne Spencer contributed significantly to the writing of this story.
**The banner photo was taken by Morgan Heim; all other photos are courtesy of USFS Pacific Southwest Research Station.


Southern SN Fisher Conservation Strategy

The Southern Sierra Nevada Fisher Conservation Assessment and Strategy is a multi-agency effort to conserve and recover an isolated and imperiled population of Pacific fisher (Pekania pennanti) in the southern Sierra Nevada, California. CBI is ...

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About the author:
Craig Thompson, Ph.D.
Landscape Wildlife Ecologist
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