Tracing 600 years of long-distance Atlantic cod trade in medieval and post-medieval Oslo using stable isotopes and ancient DNA

Marine resources have been important for the survival and economic development of coastal human communities across northern Europe for centuries. Knowledge of the origin of such historic resources can provide key insights into fishing practices and the spatial extent of trade networks. Here, we combine ancient DNA and stable isotopes (δ 13 C, δ 15 N, non-exchangeable δ 2 H and δ 34 S) to investigate the geographical origin of archaeological cod remains in Oslo from the eleventh to seventeenth centuries CE. Our findings provide genetic evidence that Atlantic cod was obtained from different sources, including a variety of distant-water populations like northern Norway and possibly Iceland. Evidence for such long-distance cod trade is already observed from the eleventh century, contrasting with archaeological and historical evidence from Britain and other areas of Continental Europe around the North and Baltic Seas, where such trade developed in a later period. Diverse biological origins are further supported by significant differences of a range of isotopes, indicating that multiple populations living in different environments were exploited. This research highlights the utility of combining ancient DNA methods and stable isotope analysis to describe the development of marine fisheries during the medieval and post-medieval period.