Pacific Fisher Assisted Migration

Yosemite National Park » Pacific Fisher Assisted Migration » Document List

The park proposes to release four Pacific fisher kits that are currently in a rehabilitation center into the park during September 2015, to the area just north of the Merced River. This project will jump start a four-year assisted migration of the federal candidate species. Craig Thompson, a researcher with the USFS Pacific Southwest Research Station, modeled the habitat and developed the release plan. He determined that (1) there is enough habitat north of the Merced River to maintain a viable population, and (2) releasing 4 kits this year and 2-4 kits annually over the next three years has a high chance of establishing a viable population. During years there are no rehabilitated kits, the park will move a minimum of 3 juveniles or sub-adults caught in the nearby Sierra Nevada Adaptive Management Project. This project is a partnership between the the park and the USFS Pacific Southwest Research Station and the California Department and Fish and Wildlife and is supported by the Southern Sierra Nevada Fisher Working Group.

In 2015, two denning females died and both litters were successfully rescued. Both litters consist of one male and one female. Both litters were recoverd from the Sierra National Forest. The kits were initially taken to the Fresno-Chaffee Zoo for care, then moved to an outdoor wildlife rescue/rehabilitation facility near Oakhurst, CA when capable of eating solid food. As of July, all four kits are thriving, being fed a diet of both live and dead natural prey items. Given the expected gradual increase of intra-sibling rivalry and the natural dispersal behavior of fishers, it is expected that they will need to be released in September 2015.

The working group proposes to begin using orphan kits to facilitate expansion of the southern Sierra fisher population north of the Merced River in two phases. First, the four kits currently in captivity would be released in the park immediately north of the Merced River in fall 2015. Exact release dates would depend on the kits' development and ability to pursue and capture live prey. These 4 kits would be tracked via VHF-implant transmitters. Their survival and habitat selection would be evaluated; if they survived at rates comparable to wild-born kits and appeared able to find suitable habitat, the area between the Merced River and the Rim Fire perimeter would become the priority release sites for any additional orphans rescued during research activities. In years when no orphans were available, the population would be augmented by 2-3 juveniles removed from the Sierra Nevada Adaptive Management Project/Sugar Pine or Kings River research areas. Such a release would accomplish the following objectives:

1) facilitate migration across the Yosemite Valley/Merced River corridor, currently believed to be a barrier to fisher expansion in the region.

2) come at limited cost to the source population; these orphans are surplus animals that would have died without intervention. Cost to the population will therefore be limited to augmentation in years when no orphans are acquired.

3) provide a seed population and breeding opportunities for any individuals naturally migrating across that corridor. If the orphans do not thrive, it would inform future management decisions.

4) provide a priority release point and monitoring plan for any orphans recovered in future years.

This effort would not represent a focused, large-scale translocation or assisted migration effort in the classic sense, and could potentially fail to facilitate northward migration, however representatives of the Southern Sierra Fisher Working Group believe it represents the best use of these kits in the interest of promoting fisher population viability region-wide. It provides an empirical test of the habitat north of the Merced River, and it would open significant research opportunities in understanding the utility of juvenile animals for conservation efforts.