Eric C. Lofroth

SYNTHESIS OF SURVIVAL RATES AND CAUSES OF MORTALITY IN NORTH AMERICAN WOLVERINES

Abstract Understanding population vital rates is fundamental to the evaluation of conservation options for wolverines (Gulo gulo). We estimated survival rates and causes of wolverine mortality in trapped and untrapped populations within montane, boreal, and tundra environments using data from 12 North American radiotelemetry studies conducted between 1972 and 2001. Rates were based on data for 62 mortalities of 239 radiomarked wolverines. Mortalities included 22 wolverines that were trapped or hunted, 3 road or rail killed, 11 that were predated, 18 that starved, and 8 deaths of unknown cause. Annual survivorship rates were estimated for sex and age class using Kaplan-Meier staggered-entry techniques. Survival was substantially lower in trapped (<0.75 for all age–sex classes) than in untrapped (>0.84 for all age–sex classes) populations. Human-caused mortality was mostly additive to natural mortality for wolverines in a management context. Logistic growth rate estimates indicated that trapped populations would decline (λ ≅ 0.88) in the absence of immigration from untrapped populations (λ ≅ 1.06). We recommend a system of spatial harvest controls in northern, continuous populations of wolverines and reduction of harvest along with more spatially explicit conservation measures in southern metapopulations.

Multiscale habitat use by wolverines in British Columbia, Canada.

Abstract Wolverine (Gulo gulo) distribution in British Columbia, Canada, includes multiple-use lands where human use and resource extraction may influence habitat selection. We evaluated seasonal habitat use by resident adult wolverines using radiotelemetry locations from 2 multiple-use landscapes in British Columbia. Food, predation risk, and human disturbance hypotheses were considered in logistic regression analyses of used and random landscapes. Male wolverine habitat associations were most supported by the food hypothesis in both summer and winter. Moose (Alces alces) winter ranges, valley bottom forests, and avalanche terrain were positively associated with winter male wolverine use. Habitat use by male wolverines in winter was also negatively associated with helicopter skiing areas in the Columbia Mountains. Habitat associations of females were more complex; combinations of variables supporting food, predation risk, or human disturbance hypotheses were included in most supported models from both summer and winter in both study areas. Females were associated with alpine and avalanche environments where hoary marmot (Marmota caligata) and Columbia ground squirrel (Spermophilus columbianus) prey are found in summer. Roaded and recently logged areas were negatively associated with female wolverines in summer. In the Columbia Mountains, where winter recreation was widespread, females were negatively associated with helicopter and backcountry skiing. Moose winter ranges within rugged landscapes were positively associated with females during winter. Our analysis suggests wolverines were negatively responding to human disturbance within occupied habitat. The population consequences of these functional habitat relationships will require additional focused research. Our spatially explicit models can be used to support conservation planning for resource extraction and tourism industries operating in landscapes occupied by wolverines.

Food habits of wolverine Gulo gulo in montane ecosystems of British Columbia, Canada

Abstract We examined the seasonal food habits of wolverine Gulo gulo in subboreal and interior wet-belt montane environments in British Columbia by analyzing scats collected during the course of two concurrent wolverine studies. Understanding foraging ecology for a wide-ranging carnivore such as the wolverine is important, particularly because reproduction has been demonstrated to be closely linked to food abundance. Wolverine diet was shown to vary regionally and seasonally. Regional variation was related to differences in prey availability between study areas. Moose Alces alces, caribou Rangifer tarandus, and hoary marmots Marmota caligata were abundant and common prey items within both study areas. Mountain goats Oreamnos americanus and porcupine Erithizon dorsatum were more abundant and more frequent prey items in the Columbia Mountains, while snowshoe hare Lepus americanus and beaver Castor canadensis were more abundant and more frequent prey items in the Omineca Mountains. Within the winter season, diet choices by reproductive females were different than other sex and age classes. Caribou, hoary marmots and porcupines were found in significantly higher frequencies in the diet of reproductive females. Foraging observations concurred with the findings of scat analyses. Dependence of reproductive females on a species of current conservation concern (caribou) and one which could be affected by issues related to climate change (hoary marmot) may present conservation issues for wolverines in the future.

The Abundance and Distribution of Wolverines in British Columbia, Canada

Abstract The abundance and distribution of carnivores and their habitat are key information needed for status assessment, conservation planning, population management, and assessment of the effects of human development on their habitat and populations. We developed a habitat quality rating system, using existing wolverine (Gulo gulo) distribution, wolverine food, ecosystem mapping, and human development data. We used this and empirically derived estimates of wolverine density to predict wolverine distribution and abundance at a provincial scale. Density estimates for wolverines in high-quality habitat averaged 6.2 wolverines/1,000 km2 (95% CI = 4.2–9.5). We predicted mean densities ranging from 0.3/1,000 km2 in rare-quality habitat to 4.1/1,000 km2 in moderate-quality habitat. Our predicted population estimate for wolverines in British Columbia was 3,530 (95% CI = 2,700–4,760). We predicted highest densities of wolverines in interior mountainous regions, moderate densities in interior plateau and boreal forest regions, and low densities in mainland coastal regions and drier interior plateaus. We predicted that wolverines would be rare on Vancouver Island, along the outer mainland coast, and in the dry interior forests, and absent from the Queen Charlotte Islands, interior grassland environments, and areas of intensive urban development.

Assessment of the Sustainability of Wolverine Harvest in British Columbia, Canada

Abstract Wolverines (Gulo gulo) are distributed across much of northern and western Canada and Alaska, USA, and they extend south into the mountainous western United States. Wolverines occur in most regions of British Columbia, Canada, with the highest population densities occurring in the interior mountainous areas. Wolverine populations in British Columbia have been primarily managed to provide a sustainable harvest for trappers and hunters. We used spatially based population estimates, population vital rate data, and spatially based harvest data to evaluate the sustainability of wolverine harvest (trapping and hunting) from 1985 to 2004. The median annual provincial wolverine harvest from 1985 to 2004 was 172 wolverines per year (𝑥̄ = 174.8), which was less than the median simulated estimate of provincial recruitment (195.9 wolverines/yr; 𝑥̄ = 209.7). Harvests in individual population units ranged from 0 to 280 over the 20-year period. Spatially, wolverine harvest was likely to have been unsustainable in 15 of the 71 population units with wolverines, and it was likely to have been sustainable in the remaining population units. Harvest in 5 of the other 56 population units was marginally sustainable and thus of potential management concern. To improve harvest management of wolverines in British Columbia, wildlife managers should focus on improved data collection and monitoring at a provincial scale, and they should work with trappers and hunters at regional scales to address issues specific to individual population units. Further research is required to improve the reliability of wolverine vital rate and population data.

Comments on Brodie and Post: Climate-driven declines in wolverine populations: causal connection or spurious correlation?

The recent paper by Brodie and Post (“Nonlinear responses of wolverine populations to declining winter snowpack”, Popul Ecol 52:279–287, 2010) reports conclusions that are unsupportable, in our opinion, due to both mis-interpretations of current knowledge regarding the wolverine’s (Gulo gulo) association with snow, and the uncritical use of harvest data to index wolverine populations. The authors argue that, because the wolverine is a snow-dependent species, average annual provincial snowfall, based on weather station data, can be expected to correlate strongly and positively with wolverine population numbers, which in turn can be accurately indexed by trapper harvests. Thus, correlations between declines in wolverine harvests and declining average snowpack are interpreted to reflect a climate-driven decrease in wolverine populations. This conclusion overstates the nature of the wolverine’s association with snow, and makes unsupportable assumptions about the reliability of harvest data as a proxy for population size.

Evaluation of Live-Capture Techniques for Free-Ranging Wolverines

Abstract Wolverines (Gulo gulo) are a rare carnivore and live-capture efforts often comprise a significant component of field research projects. Wolverine studies have used aerial, snowmobile, hand-capture, and live-trap capture techniques. We reviewed existing wolverine live-capture data to evaluate sex-related biases associated with capture technique. We modified round log live traps, developed a new portable wooden live trap, and evaluated effects of live trap type, trap-site selection, and seasonal timing of trapping on wolverine capture success. Aerial capture techniques had a positive bias for capture of male wolverines. Live-capture rates were highest for portable wooden traps and lowest for barrel traps. Trapping success was highest during March when snow conditions were amenable to wolverine travel and temperatures improved bait effectiveness. Traps in corridor habitats were more successful than traps in noncorridor habitats. This difference was more pronounced in environments with rugged topography. We provide guidance for live-trap operation, describe animal handling procedures, and provide detailed instructions for construction of modified round log and portable wooden wolverine live traps. These will benefit future wolverine studies by increasing trap effectiveness and reducing risk of injury and mortality to captured wolverines.

Density of Fishers in Boreal Mixed-Wood Forests of Northeastern British Columbia

Fishers (Martes pennanti) are medium-sized carnivores of the family Mustelidae that are found in boreal and temperate coniferous and deciduous-coniferous forests across North America (Proulx and others 2004). Fishers are rare, but important members of the forest ecosystems that they occupy, and as mesocarnivores may play an essential role in regulating populations of many mid-sized mammals in these forests (Roemer and others 2009). In British Columbia, Fishers are harvested for their fur and can be legally trapped on registered traplines in the central and northern portions of the province between 1 November and 15 February. Harvest of Fishers has declined considerably in British Columbia over the past 30 y. Causes for harvest declines are unexplained, but may include both declining populations and declining trapper effort. Fishers currently have a provincial status of S2S3 in British Columbia, designating it as a species of ‘‘special concern’’ (BCCDC 2010). To ensure that Fisher harvests are sustainable, wildlife managers and trappers need basic population information. Population density is a key piece of data upon which harvest levels should be based. Because Fishers are secretive and difficult to inventory (Powell and Zielinski 1994), until recently harvest management of Fishers in British Columbia has been largely based on studies from eastern North America, where density estimates range from 50 to 385 Fishers/1000 km (Powell and Zielinski 1994; Fuller and others 2001). Recent work in northcentral British Columbia, however, has demonstrated that the density of Fishers in coniferousdominated western forests are substantially lower (for example, 8.8 Fishers/1000 km, Weir and Corbould 2006), and more conservative harvest management is required relative to eastern Fisher populations. Habitat quality is not uniform throughout British Columbia and, as a result, Fisher density is believed to vary among regions (Weir 2003; Lofroth 2004). This is reflected in the variability of Fisher harvest across the province. The boreal mixed-wood forests of northeastern British Columbia have consistently high harvests of Fishers and are believed to be among the most productive areas for this species in the province (Lofroth 2004). To improve our knowledge of Fisher density in British Columbia, we estimated the density of Fishers in a representative boreal mixed-wood forest landscape in northeastern British Columbia. This information will provide wildlife managers and trappers with better data to evaluate sustainable harvest levels and help facilitate population persistence. Our work builds upon Weir and Corbould’s (2006) estimation of Fisher density in the subboreal spruce forests of north-central British Columbia by applying their methods to Fishers in boreal mixed-wood forests. Because our data was collected, analyzed, and interpreted following methods identical to that of Weir and Corbould (2006), readers are directed to this article for comprehensive details of the capture methodology, density estimation, its biases, and resultant implications for interpretation of the results. Our study area covered 950 km of boreal mixed-wood forests (that is, the moist-warm subzone of the Boreal White and Black Spruce biogeoclimatic zone; DeLong and others 1990) in the Kiskatinaw Plateau and Peace Lowlands ecosections (Demarchi 1995) to the south and west of Dawson Creek, BC (UTM: Zone 10, 674000 E, 6182000 N, NAD83). The climate of the study area is cold and dry, which is typical of continental boreal forests. Mean annual GENERAL NOTES