Fisher conservation in the Pacific States: field data meet genetics.

Abstract

Overtrapping of fishers in the early 1900s, combined with widespread habitat loss from clearcut logging, has resulted in the extirpation of this forest-dwelling carnivore throughout much of its former range in the Western United States. Poor dispersal abilities, low-density populations, and low reproductive rates all hinder the recovery of this little-known relative of weasels, minks, and otters. In the Pacific Northwest, the fisher occupies dense, lower elevation coniferous forests, and uses large live trees, snags, and logs for denning and resting.

In the last 15 years, three petitions have been submitted to list Pacific coast fishers under the federal Endangered Species Act, yet virtually no empirical information was available on the history, distribution, conservation status, or ecology of fishers in the Pacific Northwest. Due in part to research done by PNW scientists, the fisher’s status as a threatened species in this region has recently been deemed “warranted” by the U.S. Fish and Wildlife Service.

Specifically, standardized surveys, field studies, and DNA analyses have shown that the once-continuous distribution of fishers in all three states along the Pacific coast has been reduced to a series of relatively small and disjunct populations. Remnant populations are found only from southwestern Oregon to the southern tip of the Sierra Nevada in California, each of which has alarmingly low levels of genetic diversity. Large expanses of uninhabited forests and natural and human-made barriers preclude interbreeding between most of these populations. In addition, translocations of fishers from British Columbia and Minnesota into Oregon have confounded the genetic affinities of remaining populations.

Citation

Thompson, Jonathan. 2005. Fisher conservation in the Pacific States: field data meet genetics. Science Findings 70. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p