Space use patterns affect stable isotopes of polar bears (Ursus maritimus) in the Beaufort Sea

Space use patterns vary within a population and can influence diet composition of individuals. Within the Beaufort Sea, polar bears (Ursus maritimus) either use offshore areas and follow sea ice retreat (pelagic) or utilize nearshore areas (coastal), exposing individuals to different food sources. We examine the relationship between coastal and pelagic space use patterns and diet quantified by stable isotopes (delta N-15 and delta C-13) of polar bears in the Beaufort Sea between 2007 and 2011. We examined spatial fidelity using home range overlap and assigned bears to one of two space use patterns (coastal or pelagic) based on proximity of home ranges to the coast. We estimated diet composition using inter- and intratissue variability in stable isotopes from hair and claws to examine seasonal shifts in diet. Sectioning of claws provided additional insights on diet, but guard hair sections did not. Polar bears showed spatial fidelity between years. Nitrogen stable isotopes were related to space use patterns. Coastal bears were N-15-depleted compared to pelagic bears due to coastal bears being enriched in N-15 possibly from either scavenging on bowhead whale carcasses (Balaena mysticetus) killed during subsistence hunts or pelagic bears being nutritionally stressed. Although upper trophic level predators can provide insight into trophic dynamics and changes in ecosystem function, knowledge of space use patterns and foraging behavior is an important aspect of diet interpretation.