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Active wolverine Gulo gulo dens as a minimum population estimator in Scandinavia

Landa, Arild, Tufto, Jarle, Franzén, Robert, Bø, Terje, Lindén, Mats, Swenson, Jon E.
Wildlife biology 1998 v.4 no.3 pp. 159-168
Gulo gulo, age structure, females, monitoring, plateaus, population size, radio telemetry, reproduction, spring, surveys, North America, Norway, Scandinavia, Sweden
Minimum numbers of wolverines Gulo gulo were estimated for Scandinavia, based on the average number of active dens recorded in 1995–1997. To estimate the proportion of females active at dens, we followed individual females using radio-telemetry in northern Sweden, northern Norway and south-central Norway. The sex and age structure of the population was estimated based on a sample of wolverines harvested before the introduction of protective measures and harvest restrictions. Our results are compared with those found in other published wolverine studies, mostly from North America. The Scandinavian population of one-year-old and older wolverines was estimated at 413 ± 71 (SD) individuals (265 ± 55 in Sweden and 147 ± 25 in Norway). This method gave a lower population estimate than those found in earlier surveys based on summation of local (municipality) estimates (Troms) and on local tracking surveys (Nordland). The differences may be explained by the existence of a large number of undiscovered natal dens in the two counties mentioned above, but the previous estimates were based on methodologies with sources of error that could inflate estimates. The population size in south-central Norway (the Snøhetta plateau, Trollheimen, Reinheimen and Rondane), based on the average number of active natal dens during 1995–1997, was estimated to be 26 ± 7 individuals. This was in concordance with the 23–30 individuals estimated from intensive tracking and radio-telemetry in spring 1995. Monitoring wolverine reproduction as a basis for population estimates could provide an important management tool. Based on our results, we recommend that the management authorities in Norway closely monitor the presently high harvest rate of wolverines in parts of the country, and establish population monitoring methods that allow continuous evaluation of management strategies.