Pacific Fishers

Pacific Fisher in forest near tree
 

Pacific Fishers

History and Overview
Biology and Description >

Fishers are tree-dwelling carnivores that were once abundant throughout Washington, Oregon, and northern California. Fishers have been extirpated from more than 50% of their previous range and only two native populations survive in California, one near the California-Oregon border and one in the southern Sierra Nevada. Although fishers have faced many threats in the past, biologists are trying to ensure that these fierce little creatures will survive the big challenges ahead.

The decline of fisher populations began in the 1800s when there was an increase in the market for luxurious pelts. Many members of the mustelid family including fisher, mink, and otter were hunted nearly to extinction. California banned trapping of fishers in the 1940s but their numbers have continued to decline because of habitat loss from logging, development, and severe forest fires. More recently, prolonged drought conditions and bark beetle infestations have led to increased loss of mature forest stands that are critical habitat for the small population of fishers that live in the southern Sierra Nevada. Other factors contributing to the decline of fisher populations are predation, vehicular strikes, disease, and poisoning from eating rodenticides remaining in the forest at illegal marijuana grow sites.

The southern Sierra Nevada fisher population has been isolated from their northern relatives for thousands of years. This small population of 150 to 300 fishers stretch from the Merced River in Yosemite to the southern parts of the Sequoia National Forest. Geographical isolation has made this fisher population genetically unique and vulnerable to decline.

  • In August 2015 the California Fish and Game Commission determined that the southern Sierra Nevada fisher population should be listed as a threatened species in California.
  • In April of 2016 the U.S. Fish and Wildlife Service determined that the West Coast Distinct Population Segment, which includes fishers from California, Oregon, and Washington, were collectively not threatened under the U.S. Endangered Species Act.
  • Although the southern Sierra Nevada fisher population does not currently have any federal protection it is considered a sensitive species by the U.S. Forest Service and the Bureau of Land Management and is listed as a species of special concern in Yosemite National Park.
 
Face of a fisher up close

Research and Management

Concerns over the health of fisher populations throughout the U.S. has spurred various research studies and have even led to the reintroduction of fishers in Olympic National Park, North Cascades National Park, Mount Rainier National Park in Washington , and the Stirling Management Area in the northern Sierra Nevada. In the southern Sierra Nevada, two studies have been gathering data on fishers since 2007: the Sierra Nevada Adaptive Management Project, later called the Sugar Pine Fisher Project and the Kings River Fisher Project. These surveys led to the discovery of the first known female fisher den in Yosemite in the spring of 2011.

Researchers from the University of California, Berkeley, in collaboration with various federal and state agencies, initiated the Sierra Nevada Adaptive Management Project, which studied fishers from December 2007 through 2013. Between 2014 and 2016 the project shifted management from U.C. Berkeley to the U.S. Forest Service and was renamed the Sugar Pine Fisher Project. Yosemite biologists collaborated on fisher research in Yosemite from 2009-2015, with significant assistance from the Central Sierra Environmental Resource Center. The goal of these projects was to study the biology and monitor the movements of fishers within Yosemite and the Sierra National Forest. Methods included conducting camera surveys, monitoring female fisher dens, collecting data on den locations, documenting causes of mortality, and trapping and collaring fishers. Because of steep and sometimes inaccessible terrain, biologists tracked fisher locations using radio-telemetry from a fixed wing airplane that was flown over the study area four to five times a week.

It was during one of these tracking missions in 2011, when biologists detected a female fisher within the boundary of Yosemite and later confirmed the first documented fisher den inside the park using motion-activated cameras. Between 2011 and 2016, five female fishers were documented denning in Yosemite and pictures of their kits have helped to confirm that protected lands within the park provide important habitat for the reproduction of this sensitive species.
 
Yosemite and U.S. Forest Service biologists were also interested in identifying methods to reduce vehicle strikes and specifically placed motion-activated cameras on existing road culverts. We learned that fishers and other wildlife use existing culverts to cross safely under the roadway. Researchers are currently determining the characteristics of culverts used by wildlife. For example, we noticed animals did not use existing culverts during high spring run-off.
 
Fishers in culvert when dry and photo of culvert full of water during high runoff
Left and middle: Fishers near and inside culvert, August, 2015. Right: Same culvert as seen in May 2017.
 
Based on these observations, Yosemite biologists initiated the installation of wildlife-friendly culverts by adding safe crossing structures to existing culverts and installing new dry culverts along wildlife travel corridors. The Yosemite Conservancy and Federal Highways contributed funding to make this innovative work possible.
 

Last updated: August 7, 2017

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