Selective Harvests of Brown Bears Associated With Increasing Skull Size and Older Age Structure

Legal harvests of wildlife occur throughout North America, where some big game hunters preferentially target individuals with larger body parts (e.g., horn, antler, body size), a practice referred to as selective harvest. Selective harvests have the potential to influence the phenotypic and age composition of harvested animals (e.g., body size, age structure), although inference about population-level change from harvest data alone is inherently limited. Moreover, professional guides can play an important role in selective harvests by helping their clients more frequently harvest animals with larger body parts compared to hunters without guides. We used records of 6426 legally harvested brown bears (Ursus arctos) (4625 males; 1801 females) on the Kodiak Archipelago, Alaska, USA, from the 1987-2023 regulatory years to evaluate patterns consistent with two nonexclusive hypotheses regarding selective harvests. Based on the selective harvest hypothesis, we predicted that the selection of bears with larger skulls (i.e., older bears) by hunters would result in a decline in skull size and a younger age structure of harvested individuals through time. Based on the hunter origin effect hypothesis, we predicted that, because guides are generally more experienced and more familiar with hunt areas, guided hunters, on average, would harvest bears with larger skulls more often and in less time than unguided hunters. Contrary to expectations under selective harvests, we observed an increase of almost 2 years in age and 1.7 cm in skull size among harvested bears over the 37-year period. Guided hunters, on average, harvested bears with larger skulls more frequently than unguided hunters but spent more days in the field before a successful harvest, compared to unguided hunters. Our results suggest temporal and hunter-related patterns in characteristics of harvested bears and that current harvest regulations on the Kodiak Archipelago are associated with sustained availability of older, larger individuals in the harvested population.