Estimating brown bear abundance in the Italian Alps with genetic-based CMR models

Abstract

Brown bear (Ursus Arctos) is a flagship species for the conservation of biodiversity and its reintroduction in the Italian Alps represents a great challenge. Given the global decline of large carnivores, documenting the results of such attempts is crucial for future conservation management. Accurate estimates of abundance are extremely difficult to obtain for small populations of large and elusive carnivores, yet fundamental for their adaptive management. This thesis presents a method to estimate brown bear abundance in the Italian Alps based on the use of genetic capture-mark-recapture (CMR) models. Genetic data, obtained from systematic and opportunistic sampling in three consecutive years (2015, 2016 and 2017) by Trento Province, were used to obtain estimates of population abundance, population structure and growth rate. The analyses were conducted using Huggins models with the software RMark. Different combinations of models were tested, and a hierarchical model selection was operated. Results returned a population size of some 55-57 individuals in 2017, including 9-11 newborns. Adult sex ratio was: 54% females and 46% males. Analyses conducted by means of Jolly Seber models, including all years, showed a rapid growth of the population (10,70%). Lastly, the possibility of providing accurate estimations using opportunistic data only was tested, with positive results for Huggins closed population model. This result may allow for a simplification of future analyses, thus for the opportunity of money saving for institutions involved in monitoring, with positive effects on the conservation management measures of the brown bear Alpine population.