An adult male Asiatic black bear (Ursus thibetanus), 105 kg in body weight and 130 cm in total length, was captured at a fish farm in Miyadamura village, Nagano Prefecture, Japan in June 2005, due to its nuisance activity. We analyzed δ13C and δ15N in the hairs and plasma of the bear and in the muscles of rainbow trouts (Oncorhynchus mykiss) at the farm to discern whether the bear was actually involved in the farm damages. Both δ13C and δ15N values in the hairs and plasma were similar to those in rainbow trout muscles, confirming that the bear indeed ate a considerable number of the farm's rainbow trouts. The δ13C and δ15N values of serum were closer to those of the trout muscles than those of the hairs, indicating that the bear depended heavily on trouts in the spring of 2005 in comparison with the previous year. Moreover, stable isotope levels in the tips of the hairs were closer to those of trout muscles than those at the bases of the hairs. This suggests that the bear depended much more heavily on trouts in the previous spring than in the previous fall.
