Harvesting strategies for conserving minimum viable populations based on World Conservation Union criteria: brown bears in Norway

The World Conservation Union (IUCN) defines populations as vulnerable if th e probability of extinction is larger than 10% within the next 100 years. W ith the objective of minimizing problems with predation on domestic livesto ck and, at the same time, conserving a viable population, we consider diffe rent threshold harvesting strategies for a small population of brown bear, based on a population dynamics model with growth rate and demographic and e nvironmental variances estimated from the present Swedish population. Takin g into account uncertainties in present estimates of the demographic parame ters and in population size, rye show that the population can be harvested when the population size exceeds 34 female bears aged one year and older, i f the entire population exceeding the threshold is harvested. To minimize t he expected long-term population size, however, we show that it is optimal to harvest only a proportion equal to 35% of the population exceeding a low er threshold of 12 female bears. This strategy gives an expected long-term population size of around 20 female bears. If the growth rate of the popula tion is reduced by ca. 3%, the threshold muse, under some conditions, be do ubled. We argue that the small thresholds are mainly a result of the high i ntrinsic growth rate of the population considered in the present paper. How ever, the analysis also suggests that IUCN's criterion might allow a rate o f extinction that is too high.