Morphological and Chemical Analysis of Archaeological Fish Otoliths from the Lower Murray River, South Australia
Disspain, Morgan C. F., Wilson, Christopher J., Gillanders, Bronwyn M., Archaeology in Oceania
We analysed otoliths from excavations along the Lower Murray River (n=24), dating from the mid- to late-Holocene period. We identified the species, and estimated the size and age of fish. The potential habitat that fish used throughout their life was estimated from chemical information in the otoliths. The majority of the fish (identified as Maccullochella peelii n=22 and Macquaria ambigua n=2) were caught in freshwater environments during the warm season, and had grown to an age and size indicative of sexual maturity. These observations accord with Ngarrindjeri oral tradition concerning sustainable management strategies. Data indicate that M. peelii grew to a significantly larger size than present fish; historical data suggests this size reduction may be the result of European fishing practices, introduced species and habitat degradation. The study demonstrates the unique nature of otoliths and their potential for investigating Indigenous subsistence strategies.
Keywords: Otoliths, palaeoenvironmental conditions, middens, Murray River, trace element analysis
The Study of fish otoliths from Australian archaeological sites is a relatively new research area, which can reveal novel information regarding Indigenous people's subsistence strategies in coastal and riverine environments. The three pairs of otoliths found in the inner ear of teleost fish are termed the sagittae, lapilli and asterisci (Secor et al. 1992). They form prior to hatching, grow continuously throughout the life of the fish, and are composed of alternating layers of calcium carbonate (in the mineral form aragonite) and protein deposited on a daily basis (Campana and Neilson 1985; Gillanders and Kingsford 2003:1049; Jones 1986; Pannella 1971:1124). Previous otolith studies have focused on age and growth; however, analyses have increasingly developed beyond the otoliths' chronological capabilities to explore microstructure and chemistry (Begg et al. 2005; Campana 2005).
As they form, otoliths absorb elements from the ambient water, which vary in relation to environmental conditions, such as salinity and temperature; though rates of accretion of some elements seem to be dependent on physiology (Campana 1999; Elsdon and Gillanders 2004; Kalish 1989). Trace elements incorporated in otoliths reflect the physical and chemical characteristics of the ambient water, which may vary among water bodies. In open oceans and bays, elemental concentrations can be relatively stable over time (Jarvie et al. 2000). In contrast, in estuaries and coastal regions, elemental concentrations can vary greatly with time, with differences varying over the scale of days to seasons and even over tidal cycles on individual days (Elsdon and Gillanders 2006; Hatje et al. 2003). As they are aceUular, once the material in otoliths is deposited, it is generally not reworked or resorbed (Campana and Neilson 1985). This is likely to be their most important property, and is one that is not shared by other calcified structures in fish (or other vertebrates). Their chemical composition affords the possibility of environmental reconstruction that, when matched with otolith biochronologies, can allow an individual fish to be placed retrospectively within time and space throughout its life (Campana and Thorrold 2001:37).
Otoliths incorporate lower concentrations of ambient elements than other organisms, such as corals or bivalves (Campana and Thorrold 2001) but the combination of their other unique characteristics, along with technological advances in beam-based probes, allow many elemental assays to be coupled with daily or annual growth increments, thus providing a detailed chronological record (Campana 1999). Such information is used to develop management strategies to ensure the ecologically sustainable use of the fisheries and aquatic environments from which they are extracted. Thus, otoliths are increasingly being used to address a range of multidisciplinary problems, from fisheries management to environmental histories (Begg et al. …