Ecological networks that interconnect different ecosystems are emphasized to conserve a local biodiversity. In Hokkaido islands, spawning salmon (Oncorhynchus spp.) creates marine-terrestrial network via salmon predation by brown bears. However, major human development from the 20th century may have been restricted salmon-bear interactions and marine-terrestrial networks may have been interrupted. In this study, we reconstructed the diet of modern and ancient brown bears using stable isotope analysis and revealed the temporal change of salmon usage by bears.

We divided Hokkaido into 4 regions (south-west, central, northern and eastern area) and collected bone fragments of modern (1996-2008), early-modern (1931-1943) and ancient (0-1920) bears and potential food items of bears in each region. We measured stable carbon and nitrogen isotope ratios of the bone collagen and food items, and estimated contributions of salmon to bear’s diet using SIAR.

Results from SIAR indicated that proportions of salmon in the modern and early-modern bears were almost 0 % in all regions. In contrast, ancient bears showed over 30 % of salmon usage in northern and eastern area. Major decline of salmon usage by brown bears was demonstrated.