Developing baseline data to understand environmental change: a geochemical study of archaeological otoliths from the Coorong, South Australia

Otoliths are calcium carbonate structures found in the inner ear of teleost fish. While they are routinely studied by marine scientists, analyses of otoliths recovered from archaeological sites in Australia and the Pacific have generally been restricted to identification of species and sometimes the fish age. Otoliths can also provide information on the season of catch, and, through trace element analysis, allow the reconstruction of environmental conditions experienced by fish. In this study, we use otoliths from mid- to late Holocene aged archaeological shell middens at the Coorong (South Australia) to examine species present, season of catch, age of fish and environmental conditions experienced by fish. Results demonstrate that the majority of the fish (identified as Argyrosomus japonicus and Acanthopagrus butcheri) were caught in freshwater environments during the warm season, and had grown to an age and size indicative of their having reached sexual maturity. This study provides data indicating fluctuating levels of salinity in the estuary, which are significantly lower than the hypersaline conditions experienced today. Ultimately, this project highlights the usefulness of conducting more detailed investigations of otoliths, including geochemical analyses, to address a wide range of research questions in archaeology and palaeoenvironmental research.

► Human predation and habitat destruction have significantly impacted native fish populations.
► Coorong salinity levels fluctuated seasonally, ca 2500 BP - ca 200 BP, but were lower than current.
► Subsistence strategies of local Indigenous people can be implied based on data from otoliths.