Pacific Fisher Mammal Research

Rangers tracking Pacific fishers some of Yosemite’s rarest mammals

The Pacific fisher, a member of the weasel family, is a medium-size forest mammal that lives in mature and old growth forests. Its diet ranges from birds to small mammals to fruit and fungi, and it is one of the only animals clever enough to prey on porcupines.

Endangered in California

Due to habitat degradation and other threatening factors including a low reproductive rate, reduced genetic diversity, predators, disease, and more recently, negative interactions with road traffic and exposure to rodenticide, the Pacific fisher has disappeared from more than half its former range in California. As of 2015, the fisher is a candidate for listing under the California and federal Endangered Species Acts.

Studying the Species

To help save this key forest dweller, Yosemite Conservancy in partnership with the National Park Service, the California Department of Fish and Game, UC Berkeley and the Central Sierra Environmental Resource Center, funded a multiyear study (2009-11) designed to collect data to document the fisher’s distribution, abundance, and range in Yosemite in order to better understand the factors limiting the fisher’s comeback.

Highly advanced remote motion-sensing camera stations were placed in suitable habitat throughout the park to determine fisher presence. These sites included areas both north and south of the Merced River.

Unprecedented Findings

The first survey year documented more fisher detections in Yosemite National Park than any previous study, with fisher activity concentrated in the southern portion of the park. The second survey year brought the unprecedented finding of the first documented den tree of a female Pacific fisher with kits (young) in the park. Thanks to Conservancy funding, this study has shed light on the Pacific fisher’s population distribution within Yosemite and played a major role in regional fisher recovery efforts.

Protecting Pacific Fishers

Building on the success of the initial surveys, Conservancy donors continued supporting the protection of this rare mammal in Yosemite by funding additional fisher management and research work. In 2013, a Conservancy-funded project created innovative road-crossing structures by modifying culverts with shelf-style features that allow fishers and other animals to cross roads safely. Fishers often travel through culverts, but are forced onto roads when snowmelt or rain fills the pipes. The new elevated shelf structures ensure that the animals safely navigate roads and avoid vehicle traffic year-round, giving the park’s fisher population a better chance at survival and recovery. Additional funding in 2015 supported further field surveys to study two of Yosemite’s rarest carnivores: the Pacific fisher and the Sierra Nevada red fox.

Photo courtesy of UC Berkeley.

More Wildlife Protected Projects

Project Notes

We are pleased to provide funding to Yosemite Conservancy for the Pacific fisher, given the importance of protecting Yosemite’s wild heritage.

Jamie Williams
President, The Wilderness Society
corporate sponsor of Pacific Fisher Mammal Research in Yosemite National Park

Map of Your Impact

From the reintroduction of bighorn sheep to restoration of Yosemite’s legendary trails, your support has made an impact in every corner of the park.