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Morphological and chemical analysis of archaeological fish otoliths from the Lower Murray River, South Australia.

Abstract

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. 2005:478; Fudani et al. 2007:2; Popper et al. 2005).

Despite being frequently conducted on modern samples (e.g. Elsdon and Gillanders 2005; Gillanders 2002; Gillanders and Kingsford 2003), chemical analyses of fish otoliths are not yet commonly employed by Australian archaeologists. Although otoliths can be vulnerable to soil acidity, some archaeological sites can produce large numbers of specimens. Past projects incorporating archaeological otoliths have focused on identifying the species and sometimes the age and size of the fish (e.g. Balme 1995; Bowler et al. 1970; Colley and Jones 1987), using the data to infer information about diet and resource use. Internationally, otolith analyses within archaeology have increasingly included chemical studies (e.g. Carpenter et al. 2003; Rowell et al. 2010; 2005; Walker and Surge 2006).

For accurate reconstructions of environmental history it is necessary to know the relationships between environmental parameters (e.g. salinity) and otolith chemistry. To successfully reconstruct past environmental conditions and fish movement, the concentration of elements within otoliths must change in a predictable manner with environmental variables (Elsdon et al. 2008). Unfortunately, for archaeological samples it is not possible to determine these relationships and therefore it is necessary to use modern day relationships. Changes in the Sr:Ca ratio within an otolith over the life of the fish have been used to demonstrate migratory patterns by detecting periods of freshwater (low Sr) and marine (high Sr) habitation (Brown and Severin 2009; Gillanders and Kingsford 2003), and to distinguish freshwater and saltwater fish within the same species (e.g. Kalish 1990; Secor 1992). Barium decreases with an increase in salinity, and has therefore been used to indicate freshwater exposure (Bradbury et al. 2008; Dorval et al. 2005; Elsdon and Gillanders 2005). Using these relation-ships of increasing ambient and otolith Ba:Ca with decreasing salinity, Elsdon and Gillanders (2005) distinguished fish from fresh- and saltwater environments: fish caught in freshwater had approximately double the Ba:Ca ratios of those from saltwater estuaries. They highlighted the application of fish otolith Ba:Ca in determining the environmental histories of individuals residing in estuaries where Sr:Ca gradients are minimal. Based on these findings, trace element analysis can be used to trace the life history of different species as they migrate through different environments (Gemperline et al. 2002; Gillanders 2005).

This paper presents a study of archaeological otoliths from mid to late Holocene aged archaeological sites excavated along the Lower Murray River, South Australia. The research was conducted to contribute a better understanding of Ngarrindjeri occupation and subsistence strategies in the Lower Murray, and to our understanding of palaeoenviroamental conditions within the area through the analysis of archaeological otoliths. The specific aims were to identify the species of captured fish, to assess their age and size at death, as well as the season in which they died, in order to examine issues of traditional Indigenous fisheries management, and to determine the changing ambient water conditions throughout the lives of the fish.

Background to the Lower Murray study area

The Lower Murray region is situated at the end of one of the largest freshwater catchments in Australia, the MurrayDarling Basin (Figure 1). With its headwaters in the Snowy Mountains, the Murray takes in water from the Darling, Lachlan and Murrumbidgee Rivers, flowing southwest through the Mallee Trench and Mallee Gorge to the Lakes and Coorong district, and finally, to the Southern Ocean, covering a distance of c.2500km. Lakes Alexandrina and Albert near the mouth of the river encompass a natural geomorphically dynamic area that experienced considerable rapid change during the Quaternary as a result of aeolian processes, river flows, wave action and variations in relative sea level as a consequence of global sea level changes and land subsidence (Bourman et al. 2000). While the region is naturally dynamic, human impact, specifically, the construction of barrages in the 1940s and increased water usage for agricultural irrigation, has led to significantly reduced water flows. Consequently, salinity levels and sedimentary infilling have increased dramatically, severely degrading the entire system (Fluin et al. 2007; Shuttleworth et al. 2005).

Archaeological surveys around the Murray River, Coorong and Lower Lakes have recorded a large number of midden sites (Luebbers 1978, 1981, 1982, 1983, 1984; St George 2009; Tindale 1957; Wilson and Fallon 2012). These sites reflect the high levels of natural resources available in the area and support the idea that the area was among the most densely populated in Australia at the time of European arrival, post 1836 (Jenkin 1979; Taplin 1879). The region comprises the traditional ruwe (lands and waters) of the Ngarrindjeri people, who have occupied the area for thousands of years (Ngarrindjeri Tendi et al. 2007). Recent radiocarbon dating of shells and charcoal recovered from shell middens in the Lower Murray demonstrates human occupation in the region from c.8,500 years ago (prior to the approximate time of sea level stabilisation) through to the recent past (Wilson and Fallon 2012).

Excavations of archaeological otoliths were conducted at three sites including Murrawoug (Glen Lossie), Pomberuk (Hume Reserve Midden and Historic Campsite) and Swanport between December 2007 and November 2008 by Wilson. All three sites were excavated to culturally sterile sediment using arbitrary 5cm spits. The excavated materials from each spit were weighed and passed through 5mm and 3mm nested sieves, and the retained sieve residues examined to recover cultural materials. A total of 24 otoliths were available for analysis (Table 1). Where organic material from the same excavation unit as an otolith had been radiocarbon dated, the date was considered to provide an age estimate for the otolith, based on principles of stratigraphic association, If no radiocarbon determination was available from the same excavation unit as an otolith, an age range was assigned to it based on the nearest available ages. All the otoliths are associated with ages ranging from 4250-6410 cal BP (see Wilson and Fallon 2012).

[FIGURE 1 OMITTED]

Methodology

Morphological analysis

Images of each otolith were acquired to create a comprehensive archival record. The proximal and distal surfaces of each otolith were photographed using a Nikon D60 digital camera equipped with a Nikon AF Micro Nikkor 60mm lens and a flash diffuser. Photomicrographs of the sectioned otoliths were acquired using a Leica MZ16A stereomicroscope with a PLANAPO 1.0x lens. Morphological comparisons with modern reference collections held at South Australian Research Development Institute, Aquatic Sciences (Adelaide) and Southern Seas Ecology Laboratories (University of Adelaide) enabled species identifications. Published images were also used to support these identifications (e.g. Furlani et al. 2007).

Otolith weight was used to determine total fish length (TL), defined as the length from the tip of the snout to the extended longest caudal finray. Some otoliths were broken and incomplete owing to post-depositional processes such as physical weathering and breakage; therefore, weights recorded for these specimens are minimum values only, and thus calculated fish lengths should be considered underestimates. Only those otoliths >50% complete (i.e. large enough to be sectioned) were included in the size determination analysis, though all otoliths were weighed. The relationship between otolith weight and fish length for Maccullochella peelii is: TL (mm)=(Otolith weight (g)+0.204)/0.00069 (from Anderson et al. 1992a: 1003) and that for Macquaria ambigua is: TL(mm)=(log(Otolith weight(g)/0.02354))/0.0026393+23.9293329 (from Anderson et al. 1992b: 1116).

Chemical analysis

Otoliths with a nucleus were rinsed using ultrapure water and left to air dry. Approximately 15mg was cut from each sample using a dremmel drill on the slowest setting (avoiding the nucleus). This was done to provide material for future radiocarbon dating, which was stored in a labelled microcentrifuge tube. Remaining otoliths were embedded in latex moulds in Indium spiked resin (40ppm), and placed in an oven at 54.5[degrees]C to harden overnight. They were then sectioned transversely through the nucleus using a Buehler Isomet Low Speed Saw (speed 2.5) equipped with twin diamond edge blades with spacers (0.35 [+ or -] 0.05mm). The sections were mounted on glass slides using crystal bond and labelled, but were not polished using lapping film because of their fragility.

Continuous profiles were made across each otolith section using an Agilent 7500s Inductively Coupled PlasmaMass Spectrometer (ICP-MS) coupled to a Merchantek UP213 (New Wave Research) laser (see Disspain et al. 2011 for operational details). Each profile was positioned to capture the nucleus, growth axis and edge of the otolith, and was pre-ablated (spot size 80/[micro]m, scan speed 10 [micro]m/sec, depth 5[micro]m, pulse rate 5.0 Hz) to remove contaminants and allow the ablation to penetrate the otolith during operations.

The ablations were conducted at a scan speed of 5[micro]m/sec with a spot size of 30[micro]m, and five isotopes analysed (Ca43, Ca44, Sr88, Inl14 and Ba138). To correct for machine drift, a reference sample (National Institute of Standards and Technology, NIST 612) was analysed at the beginning and end of each laboratory session, and after analysis of every five or six samples. Background gases were measured for 30 seconds before each ablation to determine the detection limits of ICP-MS. All samples were above detection limits and precision, as determined from the percent relative standard deviations (% RSD) of the NIST standards, which were less than 8% for each element. GLITTER software (www.glitter-gemoc.com) was used to determine the positions of the background and otolith element mass count data. Data were further processed using Excel to determine concentrations of elements, and ratioed to calcium. We have used the term profiles to describe the analysis of chemicals along a continuous transect across the otolith surface, in line with Elsdon et al. (2008).

Due to the nature of this study, it was not possible to determine the elemental concentrations within the ambient water, which is necessary for accurately determining fish migrations (Elsdon and Gillanders 2006:653; Elsdon et al. 2008). Therefore, modern day relationships between ambient element concentrations, salinity and otolith elemental concentrations from Elsdon and Gillanders (2005) were used. They determined, through laboratory and field studies, that Ba:Ca concentrations <0.005 mmol.[mol.sup.-1, were considered to indicate freshwater levels of salinity, >0.006 mmol.[mol.sup.-1 to indicate marine levels, and 0.005-0.006 mmol.[mol.sup.-1 to indicate brackish water levels. Previously, Elsdon and Gillanders (2004) had established that Sr:Ca concentrations within otoliths can be influenced by a range of environmental variables, though they are often used to determine salinity. Owing to this, Sr:Ca data were used as comparative data. It is impossible to know if fish migrated or if local water conditions changed around an essentially stationary fish without knowledge of the ambient elemental variability (Elsdon et al. 2008). It can be expected that freshwater flowed further downstream, and salt water further upstream at the time the fish were alive, than occurs today because of the absence of river regulation by barrages and dams. However, salinity levels are unable to be determined beyond generalising between 'freshwater', 'brackish' and 'marine' based on the above findings.

Age estimation

The visible annuli of each sectioned otolith were counted to estimate the individual age of each fish at the time of death. Sections were viewed under a Leica MZ16FA stereomicroscope illuminated by transmitted light. The annuli were counted from the nucleus to the outer edge of each otolith on two separate occasions by the same reader (the second count was made with no information on the initial count in order to avoid prejudice). Minor discrepancies of <10% were recorded between the two separate counts. The edge annulus was also recorded as being translucent or opaque, as this information indicates the season during which the fish was caught. The wide, translucent band is laid down during periods of fast growth during the warmer months, while the narrower, opaque bands are laid down during periods of slow growth during the cooler months.

The stereomicroscope images of each otolith section were then viewed using AnalySIS 5 iTEM software to link the trace element data to the appropriate annuli. Each image was calibrated using a lmm scale bar, and the accumulated distance function was used to trace each profile, defining the annuli along the trace. In the case of HRM10, where no annuli were visible, points were defined along the profile at every identifiable colour change or feature in the section in order to compare the measurements with the trace element data.

Results

Species identification and morphological analysis

Twenty-four otoliths were recovered; seven from Glen Lossie Midden and Burial site (GLMBS), ten from Pomberuk (HRM), and seven from Swanport Midden (SP). Of these, 21 were identified as belonging to Maccullochella peelii (Murray cod) (Table 2). One sample (HRM07) was identified as possibly belonging to this same species; however, its fragmentary nature meant that a definite identification could not be achieved, as it may also be from M. macquariensis (trout cod), a species closely related to M. peelii that no longer inhabits this part of the river. While this is acknowledged, the distribution of this species ca. 4000-6000 years ago may have been more widespread. For the purpose of subsequent analyses, HRM07 was included in the M. peelii species group. A further two otoliths (GLMBS01, GLMBS06) were identified as Macquaria ambigua (golden perch). However, one of these samples (GLMBS01) was broken and poorly preserved and the identification is tentative. Excluding the two samples mentioned above, the remaining otoliths appeared to be in good condition with no evidence of taphonomic or diagenetic alteration.

Within the assemblage of 24 otoliths, only 15 were able to be sectioned (see Table 2). Based on these 15 samples, minimum length estimates for Maccullochella peelii range from 685 to 2200mm (see Figure 2). The Macquaria ambigua otolith (GLMBS06) weighed 0.2032g, resulting in a fish length of 355mm.

Of the 15 sectioned otoliths, two (GLMBS02, HRM10) were unable to be aged because of a lack of visible annuli. The remaining 13 otoliths came from fish aged between 5 and 31 years (Table 2). Owing to deterioration, the edge increments of two otoliths were unable to be determined, (GLMBS06 and HRM10). However, from the data available, the majority of the fish were harvested during the warmer months, with 13 otoliths possessing translucent edge increments (Table 2).

Maccullochella peelii chemistry

Distinct patterns emerge within the trace element data of the Murray cod otoliths. All fish were spawned in freshwater environments, as Ba:Ca levels remained above 0.006 mmol.mol-I in the core of the otoliths. The Ba:Ca levels remain above this limit throughout the entire profile for the majority of otoliths (GLMBS04, SP01, SP03, SP06, SP07, HRM09 and HRM10), which would be expected of a freshwater species (Figure 3a). The Sr:Ca levels within these seven profiles all followed relatively similar trends to those of the Ba:Ca levels. This differs from the positive Sr:Ca relationship with salinity levels, suggesting that Sr:Ca is also influenced by water temperature and ambient water chemistry.

[FIGURE 2 OMITTED]

Data from three profiles, (GLMBS02, HRM02 and HRM03) indicate Ba:Ca decreases to brackish water levels (between 0.005 mmol.[mol.sup.-1 and 0.006 mmol.[mol.sup.-1) at different stages after the nucleus. These levels then fluctuate between brackish and freshwater for the reminder of the profile, with the fish residing in freshwater environments at the time of capture. Sr:Ca levels in GLMBS02 fluctuate in a similar pattern to the Ba:Ca levels, while levels in HRM02 and HRM03 show fluctuations with no apparent relationship to Ba:Ca levels (Figure 3b).

Ba:Ca data from profiles in four fish (HRM01, HRM06, SP02 and SP04) display fluctuations between freshwater, brackish and saline environment levels (Figure 3c). The low Ba:Ca levels at the end of two of the profiles (HRM01 and HRM06) imply that the fish died in environments with relatively high levels of salinity. Ba:Ca levels at the end of the profile of SP02 indicate that the fish died in freshwater, while those of SP04 suggest that the fish died in a brackish environment. As above, the Sr:Ca levels in HRM01 and HRM06 fluctuate with no apparent relationships to Ba:Ca levels; however, those of SP02 and SP04 seemingly fluctuate in a similar pattern to the Ba:Ca levels. The corresponding author can provide trace element data for all 15 otoliths upon request.

Macquaria ambigua chemistry

The very high peak of Ba:Ca levels in the centre of the nucleus indicates that the fish (GLMBS06) was spawned in freshwater (Figure 4). The Ba:Ca levels then remain lower than this initial peak, fluctuating throughout the profile, but remaining above levels indicative of marine salinity (0.006 mmol.[mol.sup.-1]). The Sr:Ca levels decrease in the nucleus and increase throughout the rest of the profile fluctuating regularly in opposition to Ba:Ca data, but in accordance with the positive relationship with salinity levels.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

Discussion

Maccullochella peelii, Murray cod, is a large freshwater fish that constitutes the majority of this Lower Murray otolith assemblage. In the period 1955 to 2001, M. peelii was the third most commercially harvested species in the Lower Murray-Darling catchment (Gilligan 2005:63), however the commercial fishery is now closed and the species has been listed as vulnerable under Australia's Environmental Protection and Biodiversity Act 1999 (Federal threatened species legislation) (Koehn and Harrington 2006:327; Lintermans 2009:5). The species generally prefers slow flowing, turbid water in streams and rivers, favouring deeper water around boulders, undercut banks, overhanging vegetation and logs (Koehn 2009). M. peelii has previously been considered to be a largely sedentary, non-migratory species (Reynolds 1983), though recent studies have shown that some adult Murray cod undertake complex movements that follow a seasonal pattern, with large scale movements (>5km) more commonly observed in the period from August to January (Koehn et al. 2009). The species is a member of the family Percichthyidae, is known to live to a maximum age of c.48 years, and to grow to a maximum length of 1800mm and a weight of c.100kg (Anderson et al. 1992a:983). Average lengths in large waterways are usually 900-1000mm, with weights of 15-20kg (Native Fish Australia 2009). Whitley (1955) recorded a maximum length (TL) of Maccullochella peelii of 1800mm, and a weight of 83kg. However, Anderson et al.'s (1992a) more recent study revealed maximum figures of 1400mm and 47.3kg. Three lengths determined from the archaeological M. peelii samples (GLMBS02-1982.32mm, SP02-2166.67 and SP03-2200mm) exceed both of the previously recorded maximums. Further, as these otoliths were broken, these are minimum estimates and the fish may have been larger. While the sample size is admittedly small, these data support suggestions that there has been a general decrease in the size of individual fish. This decrease is likely a result of a combination of factors including European fishing practices, introduced species within the ecosystem, habitat degradation and altered flow regimes. These inferences provide baseline data for the rehabilitation of the native fish species in the Lower Murray and deeper historical analyses, incorporating archaeological data sets, can help to develop better fisheries management systems (Erlandson and Rick 2008).

Murray cod usually spawns at 4-5 years of age, when water temperatures exceed 15[degree]C between September and December (Humphries 2005; Koehn and Harrington 2006; Lintermans 2009). The age at time of death of 6 of the 12 M. peelii archaeological otoliths was estimated to be over 21 years (Table 2). Recovery programs focusing on rehabilitating M. peelii populations were first initiated in the 1970s. These programs have increased the distribution of M. peelii in some areas of the Murray River, but the population remains at a critical level (Rowland 2004:52-56). The comparison between archaeological and modern age data indicates that although the species may be recovering slowly and living longer owing to recovery strategies, the growth rate of the species may have decreased. Fish are estimated to be living as long as they did c.6000 years ago, but not attaining the same size. Human predation is not the only influencing factor, as predation by, and competition with introduced species, as well as environmental degradation may have all contributed to the species' decline. The MDBC (2003) plans to rehabilitate native fish stocks to 60% or better of the pre-European abundance over the next 50 years. In order to do so, an understanding of not only the pre-European distribution of fish, but also of the age and growth of populations of individual species must be attained. As such, the results of this study provide useful baseline data for native fish rehabilitation programs in the Lower Murray.

Macquaria ambigua (golden perch/callop), represented by only two otoliths in the assemblage, is a freshwater species that is distributed throughout most of the Murray-Darling Basin and the Lower Lakes (Sloan 2005:82). They prefer warm, turbid, slow flowing inland rivers, floodplains and lakes, and favour deep pool habitats with an abundance of refuges in the form of snags, undercut ledges and dead trees (Merrick and Schmida 1984). M. ambigua is well adapted to the dynamic conditions of the Murray River and can withstand significant changes in temperature (4-37[degrees]C) and salinity (Harris and Rowland 1996). This flexibility means that the species is ideally suited as a subject for chemical analysis. Golden perch are known to reach a weight of 23kg, although are commonly <5kg (Anderson et al. 1992b). The maximum recorded length measurements for this species are 760mm TL (Lake 1967), and 604mm TL (Anderson et al. 1992b), while the maximum known age is about 26 years (Ye 2004). The one archaeological M. ambigua otolith studied was considerably smaller and younger than this, at 355mm and five years of age. Unfortunately this age difference combined with the small archaeological sample size, mean that the modern and archaeological total length data for this species cannot be usefully compared. Spawning occurs during spring and summer, in a temperature range between 20[degree]C and 250C. Females sexually mature at 4-5 years, and males at 2-3 years (Harris and Rowland 1996) suggesting that the archaeological specimen was mature.

The trace element data provides information about the life history of individual fish. Those of the Maccullochella peelii fish from the Lower Murray sites show distinct variation within the species, though all were spawned in freshwater. Fluctuations between low and higher salinity levels are possibly the result of fish movement further up or down stream as discussed by Koelm et al. (2009), or seasonal fluctuations within the river environment; however, the occurrence of high salinity Ba:Ca concentrations in the data is problematic in that M. peelii are physiologically inclined to reside in freshwater environments. Salinities above 0.34g/L may result in significant impacts on Murray Cod (Chotipuntu 2003) while elevated salinity levels may also affect food sources such as invertebrates, algae and macrophytes, consequently affecting habitat complexity and quality (Koehn and Clunie 2010:15). These data are likely to have been influenced by other variables such as ambient temperature and water chemistry. Notably, the comparative trace element values indicative of salinity are based on data from Acanthopagrus butcheri, an estuarine/marine fish, and species specific differences can occur. As such, these data should be interpreted with caution and further research needs to be done to explore the influences of environmental variables on trace elemental data of different species. All but three of the M. peelii fish were captured in freshwater environments during the warm season. This is in agreement with the idea that freshwater flowed from upstream during spring as a result of rainfall and runoff. The three fish that were caught in more saline waters during the warm season could have travelled further downstream, or could have died during a season when freshwater inflow was exceeded by a combination of marine inflow and evaporation, contributing to higher salinity levels.

The single Macquaria ambigua otolith indicated a fish that was spawned in, and inhabited, freshwater environments throughout its life. This species is able to withstand significant changes in temperature and salinity, and the profile indicates varying levels of Ba:Ca and Sr:Ca, but the Ba:Ca levels do not decrease past the lower freshwater limit of 0.006 mmol.[mol.sup.-1. Edge increment analysis demonstrates this fish was also caught during the warmer months, possibly in the fiver immediately adjacent to, or nearby, the middens. As only one specimen of this species could be analysed, any claims made using these data are merely speculative.

The trace element data has revealed that prior to human interference, water of the Murray River experienced fluctuating salinity levels (as indicated by the trace element data of Maccullochella peelii); however, as a result of barrage construction and water management 2strategies, the river is now predominantly fresh (Fluin et al. 2007). These observations support Disspain et al. (2011) who suggested that people have significantly altered the waterways of the Coorong. Trace element data of the Coorong otoliths associated with shell and charcoal dates ranging from ca 6500 BP to ca 200 BP revealed fluctuating levels of salinity in the estuary, which were significantly lower than the hypersaline conditions experienced in some areas today. As mentioned above, our results are based on values for freshwater versus marine conditions obtained from experiments and field studies on Acanthopagrus butcheri, an estuarine species. Variation in trace elements among species has been found even for fish inhabiting the same region (e.g. Gillanders and Kingsford 2003); therefore, caution is required in definitively attributing concentrations to brackish and saline conditions.

A number of inferences can be made in relation to Ngarrindjeri subsistence strategies and occupation. All of the fish in the middens were caught during the warm season, consistent with ethnographic observations about Ngarrindjeri fishing activities (Berndt et al. 1993:79; Tindale 1981:1878-80) and traditional Ngarrindjeri knowledge. These results align with those discussed by Disspain et al. (2011) concerning the capture of Argyrosomus japonicus (mulloway) within the Coorong at the mouth of the Murray River. Saltwater fish were difficult to catch during the winter, except in protected areas, while freshwater fish were largely inaccessible due to floodwaters. In accordance with this, no fish from the Lower Murray sites were caught during the cold season.

Dependant on species, different fishing techniques were likely used by the Ngarrindjeri. The large predatory Maccullochella peelii could have been caught using spears or clubs. They could also have been caught with nets, however, based on the small numbers of otoliths recovered; this is unlikely, as the technique would have resulted in a larger number of fish of approximately the same size being captured. Disspain et al. (2011) detailed similar findings in relation to the use of nets in the estuary. Both M. peelii and Macquaria ambigua prefer to inhabit warm deep water around trees and snags, possibly making spearing difficult.

Conclusion

The analysis of fish otoliths endeavoured to be of contemporary environmental relevance by providing information concerning the changing fish populations of the region and contributing to the topical issue surrounding the impacts humans have had on the Murray River system and its resulting condition. The study also demonstrates the unique nature of otoliths and their potential for investigating Indigenous subsistence strategies. Within Australia, previous otolith studies have focused on morphological analyses. This project has successfully expanded the examination of archaeological otoliths to include chemical analyses. By integrating various methodological techniques, further understanding of the subsistence strategies of the Ngarrindjeri, and the fish population dynamics and environmental conditions of the Lower Murray River, from the mid-Holocene to the present, can be developed. Impacts that human predation and environmental degradation have had on the fish populations of the study region have also been explored. By utilising numerous analytical techniques, otoliths from the archaeological record can provide informative data that is unable to be acquired by any other archaeological material.

Acknowledgements

The authors wish to thank the Ngarrindjeri Regional Authority and all members of the Ngarrindjeri community who granted permission to conduct this research. We also thank the Department of Archaeology at Hinders University, Adelaide Microscopy at The University of Adelaide and the Research School of Earth Sciences at the Australian National University for providing access to facilities and funding. Thank you also, Dr Lynley Wallis, for providing feedback on earlier drafts of this paper, Kieron Amphlett for drawing Figure 1, Steve Hemming and Claire Smith. This study was supported by funds from AIATSIS (Grant ID: G2008/7398), Hinders University and an ARC grant to BMG (DPl10100716).

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Table 1. Otolith provenance indicating site name, square etc.

                                       Excavation
Otolith   Site Name           Square     Unit

GLMBSOI   Glen Lossie           A          1
          Midden and
          Burial Site
GLMBS02   Glen Lossie           A          2
          Midden and
          Burial Site
GLMBS03   Glen Lossie           A          3
          Midden and
          Burial Site
GLMBS04   Glen Lossie           A          4
          Midden and
          Burial Site
GLMBSOS   Glen Lossie           A          4
          Midden and
          Burial Site
GLMBS06   Glen Lossie           A          4
          Midden and
          Burial Site
GLMBS07   Glen Lossie           A          4
          Midden and
          Burial Site
HRMOI     Pomberuk              A          3
HRM02     Pomberuk              A          4
H13M03    Pomberuk              A          4
H1uv104   Pomberuk              A          4
H12M05    Pomberuk              A          4
HRM06     Pomberuk              A          5
HItM07    Pomberuk              A          5
HRM08     Pomberuk              A          2
H1ZM09    Pomberuk              A          3
HItM10    Pomberuk              A          3
SPO1      Swanport Midden 1     A          5
SP02      Swanport Midden 1     A          6
SP03      Swanport Midden 1     A          7
SP04      Swanport Midden 1     A          7
SPOS      Swanport Midden 1     A          7
SP06      Swanport Midden 1     A          8
SP07      Swanport Midden 1     A          1

Table 2. Otolith analysis results.

                                                 Common
Otolith              Species name                 name

GLMBS01    Macquaria ambigua?                 Golden perch
GLMBS02    Maccullochella peelii peelii       Murray Cod
GLMBS03    Maccullochella peelii peelii       Murray Cod
GLMBS04    Maccullochella peelii peelii       Murray Cod
GLMBS05    Maccullochella peelii peelii       Murray Cod
GLMBS06    Macquaria ambigua                  Golden perch
GLMBS07    Maccullochella peelii peelii       Murray Cod
HRM01      Maccullochella peelii peelii       Murray Cod
HRM02      Maccullochella peelii peelii       Murray Cod
HRM03      Maccullochella peelii peelii       Murray Cod
HRM04      Maccullochella peelii peelii       Murray Cod
HRM05      Maccullochella peelii peelii       Murray Cod
HRM06      Maccullochella peelii peelii       Murray Cod
HRM07      Maccullochella peelii peelii or    Murray Cod or
           Maccullochella macquariensis       Trout Cod
HRM08      Maccullochella peelii peelii       Murray Cod
HRM09      Maccullochella peelii peelii       Murray Cod
HRM10      Maccullochella peelii peelii       Murray Cod
SP01       Maccullochella peelii peelii       Murray Cod
SP02       Maccullochella peelii peelii       Murray Cod
SP03       Maccullochella peelii peelii       Murray Cod
SP04       Maccullochella peelii peelii       Murray Cod
SP05       Maccullochella peelii peelii       Murray Cod
SP06       Maccullochella peelii peelii       Murray Cod
SP07       Maccullochella veelii neelh        Murray Cod

           Preser-     Otolith        Fish TL
Otolith     vation    weight (g)       (mm)

GLMBS01    Partial        0.4347      479.82
GLMBS02    Partial        1.1638      1982.32
GLMBS03    Partial        0.1037   Not sectioned
GLMBS04    Partial        0.6979      1307.1
GLMBS05    Partial        0.2344   Not sectioned
GLMBS06    Complete       0.2032      354.68
GLMBS07    Partial        0.0784   Not sectioned
HRM01      Partial        1.0176      1770.43
HRM02      Complete       0.4511      949.42
HRM03      Partial        0.3711      833.48
HRM04      Partial        0.3579   Not sectioned
HRM05      Partial        0.1914   Not sectioned
HRM06      Partial        0.4787      989.42
HRM07      Partial         0.217   Not sectioned
HRM08      Partial         0.449   Not sectioned
HRM09      Complete        0.269      685.51
HRM10      Partial          0.29      715.94
SP01       Partial          0.34      788.41
SP02       Partial         1.291      2166.67
SP03       Complete        1.314      2200.00
SP04       Partial         0.356      811.59
SP05       Partial         0.152   Not sectioned
SP06       Complete        0.535      1071.01
SP07       Partial        0.1684      539.71

             Estimated        Edge band
Otolith     age (years)         colour

GLMBS01    Not sectioned    Not sectioned
GLMBS02    Unable to read   Unable to read
GLMBS03    Not sectioned    Not sectioned
GLMBS04          23         Translucent
GLMBS05    Not sectioned    Not sectioned
GLMBS06          5          Translucent
GLMBS07    Not sectioned    Not sectioned
HRM01            26         Translucent
HRM02            13         Translucent
HRM03            11         Translucent
HRM04      Not sectioned    Not sectioned
HRM05      Not sectioned    Not sectioned
HRM06            24         Translucent
HRM07      Not sectioned    Not sectioned
HRM08      Not sectioned    Not sectioned
HRM09            7          Translucent
HRM10      Unable to read   Unable to read
SP01             12         Translucent
SP02             31         Translucent
SP03             25         Translucent
SP04             22         Translucent
SP05       Not sectioned    Not sectioned
SP06             14         Translucent
SP07             12         Translucent
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Author:Disspain, Morgan C.F.; Wilson, Christopher J.; Gillanders, Bronwyn M.
Publication:Archaeology in Oceania
Article Type:Report
Geographic Code:8AUST
Date:Oct 1, 2012
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