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COSEWIC assessment and update status report on the wolverine Gulo gulo in Canada

Limiting Factors and Threats

Biological Factors

Biological factors that limit wolverine populations include the species’ low intrinsic rate of increase and low natural densities which limit population growth rates and the ability to recolonize vacant habitats. Maternal den site availability may also limit successful reproduction. Repopulation may take several decades but is possible where factors favour wolverine survival (Johnson 1990, Vangen et al. 2001). Wolverine population recovery in Manitoba was thought to be due to the cessation of wolf poisoning, which also killed wolverines, the increase in the wolf population following the cessation of poisoning, and a trapping season closing date which offered some protection to females with kits. Habitat factors including an adequate ungulate prey base were also necessary. Recent harvest increases in northeastern Manitoba and northwestern Ontario are attributed to a wolverine population response to increased caribou numbers (Dawson 2000, Berezanski, pers. com., 2002).

Harvest and Predator Control

Wolverine trapping and hunting continue to be a threat in western jurisdictions; however, harvest management, including trapping closures, limited seasons, quotas, limited entry, and registered trapping concessions (Slough et al. 1987), and a reduced interest in trapping, have reduced these threats. High pelt prices and a lucrative market to supply zoos and game farms with live wolverines contributed to trapper effort and the overall wolverine harvest in the Yukon. There may be a certain level of financial return per unit effort below which wolverines are not targeted by trappers, as in areas where they are not common (Figure 3). There has been no legal harvest of wolverines in Labrador since 1950, in Quebec since 1981 (except in the James Bay and Northern Quebec Agreement territories) (Fortin et al. 2002) and in Ontario since 2001 (Dawson, pers. com., 2002).

There are winter trapping seasons for wolverines in the four western provinces and 3 territories. These seasons generally begin in November and terminate in January or February, extending to March or April in the territories. Wolverine harvest is prohibited in southern regions of the western provinces where the species is rare or does not occur. There are also fall (August to October) and/or winter hunting seasons in British Columbia and the territories. Bag limits for hunters are generally 1 wolverine, but may be more for residents of the Northwest Territories and Nunavut. There are no quotas for trappers except in Alberta, where the limit is one wolverine.

There is mandatory reporting of wolverines harvested in the Yukon, British Columbia, Alberta and Saskatchewan, either through pelt sealing or provincial fur royalties. Manitoba rescinded pelt sealing in 2001, although all pelts sold or exported must be reported. Wolverine furs exported from the Northwest Territories and Nunavut require permits, however, since a high proportion of wolverines are not exported to fur auctions (Table 1; Nunavut), the harvest has not been accurately documented. Carcass collection programs and harvest studies are being used to monitor harvest in those jurisdictions.

Gardner et al. (1993) estimated that the wolverine population in southcentral Alaska could sustain an annual harvest of 7-8% of the fall population. In a nearby study area the finite rate of population increase (λ) was 1.19, following an annual harvest rate of about 9% (Golden 2001). Golden noted that the annual harvest rate of 9% did not affect wolverine density. There was likely an immigration component from adjacent refugia, but this was not measured. The population was considered healthy and stable, with annual harvests in some areas being low to moderate with respect to annual sustainable yields. Golden (pers. com., 2002), recalculated his statistics using lower birth rates (mean of 0.375 females per adult female per year (F)) giving a λ of 0.86 and an estimated annual sustainable yield of 0.8% of the population. This estimate was based on the relatively small number of litter observations of Magoun (1985) and Copeland (1996). Using larger sample sizes of Pulliainen (1968) Golden arrived at a λ of 0.94 and an estimated annual sustainable yield of 2.5%. This may be more realistic, but it indicates that some local overharvest and exploitation of population refugia may be occurring. In a summary of mortality rates of radio-collared wolverines from 12 studies, J. Krebs (pers. com., 2002) estimated λ at 0.88 in trapped populations and 1.06 in untrapped populations. Again, immigration from untrapped areas is required to sustain wolverines in trapped areas.

Wolf poisoning was curtailed in most of western Canada in the 1970s. Local illegal wolf poisoning was documented in the Yukon in the 1990s and continues in Alberta under special permit. The elimination of poisoning favours wolverine population recovery.

Developments in arctic tundra frequently attract wolverines which may be killed as nuisance animals (Dumond, pers. com., 2002).

Habitat Threats

Habitat loss, habitat alienation and habitat fragmentation continue to threaten wolverine populations. Losses result from conversion of natural habitats for human land uses including urban and suburban developments, agriculture, forest plantations, and hydroelectric reservoirs. Clearcut logging does not result in permanent or even necessarily negative changes to habitats. Logging which mimics natural processes, such as fire, windthrow and insect outbreaks, and creates a landscape matrix of uneven aged forest stands, may actually diversify the prey base and maintain or improve wolverine habitat.

Habitat alienation may result from human activities, such as backcountry recreation, which impact wolverine behaviour patterns such as denning, travel and foraging.

Habitats are fragmented by major transportation arteries which impede wolverine movements and ultimately, gene flow and population stability.

Indirect effects on the prey base will also impact wolverine populations. Such effects include overhunting of ungulates, and ungulate population declines due to fragmentation of their habitats. Of particular concern are the declining mountain caribou populations of Alberta and British Columbia. The decline of these populations is linked to forestry practices and human disturbance.

The existence of parks which may act as refugia from trapping and resource developments are not the insurance to continued existence as described by both Kelsall (1981) and Dauphiné (1989). Parks in developed regions run the risk of holding isolated populations. Such fragmentation can lead to destabilization of populations and local extirpations. Wolverine populations within the parks are not buffered from trapping activities around their peripheries. Wolverines that reside partly in refugia are susceptible to harvest mortality. Treaty/Aboriginal and licensed wolverine trapping is permitted in many national parks and some provincial parks in British Columbia and Manitoba. Another problem with the quality of our current parks system to act as wolverine population refugia lies with the allowance of activities within parks including traversing roads (such as the Trans-Canada Highway), access roads, and activities such as snowmobiling and skiing. Major roads may act as barriers to movements (Austin 1998) and recreational activities during the late winter denning period may result in disturbance to females and their litters leading to relocation or abandonment (Magoun and Copeland 1998, Heinemeyer et al. 2001).

Hash (1987) concluded that “The future of the wolverine appears bright. The species has survived the pioneer periods of unregulated trapping, hunting, and predator control, accelerated and irresponsible natural resource development, and widespread habitat degradation”. He praised the national parks systems, and our greater environmental awareness and responsibility towards endangered species. This is an optimistic scenario which will require vigilance.