Preliminary results from Yosemite NP study show more threatened fishers in park than previously known

Yosemite National Park has launched a $45,000, two-year study to determine the population size and status of fishers in the park.


In partnership with the Yosemite Fund, California Department of Fish Game, and University of California at Berkeley researchers, 56 motion-activated camera stations have been strategically located throughout the park to document fisher presence. The first winter’s efforts were focused on the southern portion of the park, and the second season’s efforts will focus on areas north of the Merced River. This study has documented more fishers than any previous research in the park, and provided valuable information on habitat requirements that may give this small population its best chance at survival. 


The first year of the study revealed fisher detections at 20 of the 56 camera stations. Preliminary results suggest that fisher activity in Yosemite is concentrated at the southern areas of the park, in and around the Mariposa Grove of giant sequoias, and along the Wawona Road (Highway 41). Assessments of images obtained from the camera stations suggest that the number of detections range from five to eight individual animals.


The Pacific fisher (Martes pennanti), a candidate species for the endangered species list, is a rare and elusive animal that once ranged from British Columbia through northern California and the Sierra Nevada. The fisher has declined to roughly 50% of its historical range in California and only two native populations remain today – one around the western California/Oregon border, and one in the southern Sierra Nevada Mountains.  Yosemite National Park represents the northern boundary of the small and isolated southern Sierra population which is estimated at between 260 to 320 individuals.  The Yosemite population is threatened by low reproductive capacity, reduced genetic diversity, and ongoing habitat loss. 


A smaller cousin of the wolverine, the fisher inhabits lower elevation forests associated with large mature trees, and eats everything from birds to small mammals to fruit; it is regarded as the one animal tough and clever enough to prey regularly on porcupine.  Not all females produce young each year. In fact, reproductive rates fluctuate widely; successful birthing ranges from 14 to 73%, with typical litter sizes varying from one to four kits.

— USNPS Daily Digest