Extirpation and reintroduction of fishers ( Martes pennanti) in Oregon: implications for their conservation in the Pacific states

Abstract

Prior to extensive European settlement, the fisher ( Martes pennanti) occupied most coniferous forest habitats in Washington, Oregon, and California. Human activities since that time have resulted in the apparent extirpation of fishers throughout much of their historical range in the Pacific states. Fisher extirpations in California and Washington have been documented previously, but no comprehensive assessments of the distribution of fishers in Oregon, the history of their translocation into Oregon, or the conservation of fishers in the Pacific states have been conducted. Our objectives are to (1) review historical information on potential causes for fisher population losses in Oregon, (2) document the history of their translocation into Oregon, (3) describe the distribution of fishers in Oregon relative to those translocations and determine if any were successful, and (4) discuss the implications of our findings for the conservation of fishers in the Pacific states. Our results show that extant populations of fishers in Oregon are restricted to two disjunct and genetically isolated populations in the southwestern portion of the state: one in the southern Cascade Range and one in the northern Siskiyou Mountains. In addition, historical changes in the distribution of fisher occurrence records in Oregon and geographic variation in the genetic composition and size of fishers occurring in southwestern Oregon, show that the population in the southern Cascade Range is reintroduced and is descended from fishers that were translocated to Oregon from British Columbia and Minnesota. The loss of fisher populations from central and northern Oregon and throughout Washington has resulted in the isolation of extant populations in Oregon by >650 km from those occurring in southern British Columbia. Our results demonstrate that the historical continuity in fisher distribution that once provided for genetic interchange among fisher populations in the Pacific states no longer exists.