State of Knowledge for Alberta’s Wolverine Population 2020: Literature Review, Density Estimate, and Gap Analysis
Andrea Morehouse (Winisk Research and Consulting), Sue Peters (ACA), Robert Anderson (ACA), and Doug Manzer (ACA)
The wolverine is considered Data Deficient in Alberta. Alberta uses criteria developed by the International Union for Conservation of Nature (IUCN) when assessing species’ status. IUCN status designations are determined using a variety of criteria including a declining population size, extent of (and changes to) geographic range (e.g., extent of occurrence, or area of occupancy), a determination that population size is small and/or restricted, or a quantitative analysis on the probability of extinction (IUCN 2012). Alberta’s designation Data Deficient is used when the available data are inadequate to determine the degree of threat faced by the species.
Several wolverine studies have occurred within Alberta since the provincial status assessment in 2000, and much more information is now available that will be useful for an updated status assessment, including abundance estimates for some regions of the province, areas of occupancy and occurrence, habitat ecology, and response to anthropogenic change. However, the data on population size within the province remains limited. Some extrapolation techniques might allow for coarse estimates at the provincial level, but there are limitations to these options. In particular, there are currently no robust population estimates for the Boreal Forest Natural Region even though this makes up the vast majority of the wolverine distribution in Alberta.
We estimated wolverine density for the Birch Mountains area using data originally collected for an occupancy study from 2016–2017. The study area was 1,976 km2 with an estimated density within the range of 0.66–3.00 per 1,000 km2 (95% CI). This estimate should be interpreted cautiously because of low precision and the failure to meet spatially explicit capture-recapture model assumptions regarding trap-specific behavioural response. A density estimate in the Rainbow Lake area of Alberta is currently underway; however, the study area was again relatively small and may not be representative for Alberta’s Boreal Forest Natural Region as a whole. Wolverine density estimates from studies in various locations in the Rocky Mountains and Foothills natural regions between 2004 and 2020 range from 1.3/1,000 km2 to 6.8/1,000 km2; however, differences in field and analysis methods make comparisons across studies difficult and should be interpreted cautiously.
In addition, there are limited available data to provide an estimate of population trend over time. Harvest records can provide an index of harvest and changes in the distribution of harvest, though these records are largely influenced by trapper effort, which has not been accounted for with wolverine harvest to date. In summary, data gaps that continue to exist include a current abundance estimate for the northern portion of the Rocky Mountains and Foothills, a reliable abundance estimate to represent the Boreal Forest Natural Region, and information to account for population trend across the province.