STATUS OF THE FISHER IN BRITISH COLUMBIA by R.D. Weir, R.P.Bio. B.C. Ministry of Water, Land and Air Protection Biodiversity Branch Victoria BC B.C. Ministry of Sustainable Resource Management Conservation Data Centre Victoria BC Wildlife Bulletin No. B-105 March 2003 Wildlife Bulletins Wildlife Bulletins can contain preliminary data, so conclusions based on these may be subject to change. Bulletins receive some review and may be cited in publications. Copies may be obtained, depending upon supply, from the Ministry of Water, Land and Air Protection, Biodiversity Branch, Victoria, BC. National Library of Canada Cataloguing in Publication Data Weir, R. D. Status of the Fisher in British Columbia. (Wildlife bulletin (British Columbia. Biodiversity Branch) ;no. B-105) Cover title. Co-published by Ministry of Sustainable Resource Management, Conservation Data Centre. Also available on the Internet. Includes bibliographical references: p. ISBN 0-7726-4925-1 1. Fisher (Mammal) - British Columbia. 2. Fisher (Mammal) - Monitoring - British Columbia. I. British Columbia. Biodiversity Branch. II. British Columbia. Conservation Data Centre. III. Title. QL737.C25W44 2003333.95’97665 C2003-960053-X This publication is available at http://wlapwww.gov.bc.ca/wld/documents/statusrpts/b105.pdf © Province of British Columbia 2003 Citation Weir, R.D. 2003. Status of the Fisher in British Columbia. B.C. Minist. Sustainable Resour. Manage., Conservation Data Centre, and Minist. Water, Land and Air Protection, BiodiversityBranch, Victoria, BC. Wildl. Bull. No. B-105. 38pp. ii DISCLAIMER “In cases where a Wildlife Working Report or Bulletin is also a species’ status report, it may contain a status recom- mendation from the author. The Province, in consultation with experts, will determine the official conservation sta- tus and consider official legal designation. The data contained in the status report will be considered during those processes.” iii SUMMARY Fishers (Martes pennanti) are medium-sized terrestrial habitat features that Fishers have been reported to use carnivores of the Mustelidae family that inhabit forest- may be higher in these areas. ed regions of central and northeastern British Fishers appear to have specific requirements for Columbia. Although the extent of occurrence of sites used for resting and rearing young. Fishers in Fishers in the province is widespread, the area of occu- British Columbia have been documented using four pancy within this range is probably limited. distinct types of structures: branch; cavity; coarse Fishers have a low reproductive output relative to woody debris (CWD); and ground sites. The selection their lifespan, with adult females typically giving birth of these rest sites by Fishers may be mediated by ambi- to between one and three kits in late winter. Survival of ent temperature. Female Fishers also appear to have the offspring to the age of dispersal is low and further very stringent requirements for structures in which decreases the effective reproductive output. Natural they rear their kits. In British Columbia, Fishers have mortalities within Fisher populations come from a been recorded whelping exclusively in large-diameter, variety of sources, but Fishers have few natural preda- declining black cottonwood (Populus balsamifera spp. tors, probably because their speed and agility make it trichocarpa) or balsam poplar (P. b. spp. balsamifera ) difficult for other predators to catch and prey upon trees, which are atypical and uncommon across the them. Humans are the major source of mortality in landscape. most studied Fisher populations, primarily from fur Fishers appear to be more flexible in their require- trapping. It is unclear as to whether the rate of recruit- ments for habitats in which they forage. These habitats ment into the Fisher population in British Columbia is appear to require the presence of catchable prey and sufficient to balance the mortality rate, although this adequate security cover to be used by Fishers for for- balance probably varies both spatially and temporally. aging. Fishers are generalist predators and typically eat Fishers have intrasexually exclusive home ranges, any animal they can catch and kill, although they may wherein home ranges of individuals of the same sex specialize on Porcupines (Erethizon dorsatum) and overlap very little. Home ranges of Fishers in British Snowshoe Hares (Lepus americanus) in some areas. Columbia are substantially larger than those reported Regardless of species of prey, foraging by Fishers is elsewhere in North America, particularly for males, believed to involve two components: locating patches which contributes to the low density observed in the of habitat with prey; and searching for prey items with- province. Additionally, the distance over which in these patches. This foraging strategy has implica- Fishers can successfully disperse may be quite limited, tions for the effects of habitat disturbance on their because effective dispersal is dependent upon many foraging efficiency. factors in addition to the ability to move through the The current extent of occurrence of Fishers in landscape. Suitable habitat and prey, avoidance of British Columbia is approximately 400 000 km2, predators and other mortality agents, and the presence although the proportion of this area that is occupied by of conspecifics can all act in concert to affect success- Fishers is unknown. Densities of Fishers in British ful dispersal. Columbia may be considerably lower than in eastern In conifer-dominated forests of western North regions and are estimated to be between 1 Fisher per 65 America, Fishers appear to have close affinities to spe- km2 and 1 Fisher per 100 km2 in the highest quality cific habitat features, many of them found in late-suc- habitats in the province. Using the area of each habitat cessional forests. Fishers do not appear to be limited to capability rank within the extent of occurrence of a fixed array of habitats, although some generalities Fishers in British Columbia, the late-winter population seem to exist. Early structural stages typically lack suf- for the province is estimated to be between 1113 and ficient overhead cover to be used by Fishers, particu- 2759 Fishers. With this method, it is expected that 40 to larly during winter, and Fishers generally avoid these 116 adult Fishers may occur within protected areas in habitats. Fishers in British Columbia also show a British Columbia at the end of March each year. strong affinity for forested riparian zones, probably Very little is known about the population trends of because the density of many of the late-successional Fishers in British Columbia and most of the informa- iv tion that we have is derived from harvest statistics. The effects of alterations in habitat quantity and qual- Unfortunately, harvest information can be quite biased ity on Fisher populations are probably dependent upon and dependent upon many other factors in addition to the scale and intensity at which the changes have population size and trends, such as trapper effort occurred. The threats to Fisher habitat are likely to (which is affected by fur prices, economic alternatives, continue to grow because forest harvest will continue. and access) and vulnerability of animals to trapping. Additionally, forests in considerable portions of the The low juvenile-to-mother ratio in the harvest, in Fisher’s range in British Columbia are currently expe- combination with the relatively low fecundity rate of riencing substantial tree mortality caused by outbreaks Fishers, suggests that the Fisher population in British of the mountain pine beetle (Dendroctonus pon- Columbia may have been declining in the early 1990s, derosae) and other insects. despite a province-wide closure of the trapping season. Fishers are also trapped for their pelts on registered Notwithstanding this possible decline, harvests of traplines throughout the Thompson, Cariboo, Fishers since 1994 have remained relatively stable Omineca/Peace, and Skeena Ministry of Water, Land (about 275 Fishers per year), which may be due to the and Air Protection (MWLAP) regions. A portion of the natural recovery of Fisher populations following years of decline. harvest of juvenile Fishers may be compensatory to The primary threats to Fisher populations in natural mortality; however, trapping mortality within British Columbia are likely anthropogenic, occurring the adult cohort is likely additive. Although it is through changes to habitats from development of unclear what effect trapping pressure has on the popu- forested land and changes in survival rates caused by lation dynamics of Fishers in British Columbia, trap- trapping. ping has likely contributed to their current status. Habitat for Fishers in British Columbia has under- Several potential alternatives for the management gone considerable anthropogenic change during the of Fishers and their habitat are presented. Options for past 100 years. Habitat alterations, primarily through management of Fisher habitat come primarily from forest harvesting activities, hydroelectric develop- changes to forest development plans and silvicultural ments, and land clearing, have changed the composi- prescriptions. Management of Fisher harvests is the tion of many landscapes in which Fishers occur. Given joint responsibility of individual trapline owners and the apparent reliance of Fishers upon forests with late- MWLAP, which has the power to set trapping season successional attributes, disturbance of these ecosys- dates,