Reconstruction of diachronic changes in human fishing activity and marine ecosystems from carbon and nitrogen stable isotope ratios of archaeological fish remains

Stable isotope analysis is one of the most effective methods of reconstructing human fishing practices and changes in past marine ecosystems. The effectiveness of this method can be further improved when considering diachronic changes in stable isotope ratios of archaeological remains of several different fish species that exhibit different behavioral or ecological traits. In this study, diachronic changes in human fishing practices and marine ecosystems were investigated for Epi-Jomon (299-258 BC) and Okhotsk (489-1200 AD) periods in prehistoric Hokkaido, northern Japan, by utilizing the stable isotope analysis of archaeological fish bone collagen. Carbon and nitrogen stable isotope ratios of 242 fish bone samples, representing 12 taxa, excavated from the site of Hamanaka 2 on Rebun Island revealed significantly lower (p < 0.05) nitrogen isotope ratios in cod from the Okhotsk period than the Epi-Jomon period. This difference could be related to the development of fishing gear and/or to changes in fishing strategies in the Okhotsk period, as well as to changes in the behavior of cod because of the rapid cooling climate event separating the two periods. Our results demonstrate that some aspects of past human fishing practices and marine ecosystem change can be reconstructed by considering diachronic changes in the stable isotope ratios of several fish species together.