Big fish in small ponds: investigating 13C and 15N bone collagen stable isotope ratios of Bronze Age to Early Modern gilthead seabream (Sparus aurata L.) in the Gulf of Cádiz (SW Iberia)

Aquaculture, or fish farming, has had a long and storied history within the Mediterranean, from the medieval Italian vallicoltura to the ancient Roman artificial fish ponds known as piscinae. However, evidence for it is scarce in some periods and regions; some forms of aquaculture, such as lagoonal fish farming, are almost invisible in the archaeological record as a result of numerous factors such as a lack of preservation of relevant material and the shifting nature of coastal environments. Stable isotope analysis is presented here as an alternative method of acquiring information about aquaculture, as its information is preserved within the fish bones themselves. It is hypothesized that extended periods of living in hypersaline lagoons would produce a distinctive carbon and nitrogen isotopic signal in bone collagen. The gilthead seabream (Sparus aurata) is a natural choice for a study such as this, fished throughout all time periods in the Mediterranean and found ubiquitously...Show moreAquaculture, or fish farming, has had a long and storied history within the Mediterranean, from the medieval Italian vallicoltura to the ancient Roman artificial fish ponds known as piscinae. However, evidence for it is scarce in some periods and regions; some forms of aquaculture, such as lagoonal fish farming, are almost invisible in the archaeological record as a result of numerous factors such as a lack of preservation of relevant material and the shifting nature of coastal environments. Stable isotope analysis is presented here as an alternative method of acquiring information about aquaculture, as its information is preserved within the fish bones themselves. It is hypothesized that extended periods of living in hypersaline lagoons would produce a distinctive carbon and nitrogen isotopic signal in bone collagen. The gilthead seabream (Sparus aurata) is a natural choice for a study such as this, fished throughout all time periods in the Mediterranean and found ubiquitously throughout archaeological sites in the area. Moreover, it is one of the most-farmed fishes within the Mediterranean and numerous studies have characterized its behaviour and isotopic information. This study, therefore, aims to use stable isotope analysis of gilthead bone collagen in order to characterize the Gulf of Cádiz, a region known throughout antiquity to have a well-developed fishing and fish processing industry. Over 70 gilthead bone samples were acquired from five sites, dating from the Bronze Age until the Early Modern period (c. 1200 BCE – 1700 CE), from which collagen was extracted and analyzed via isotope ratio mass spectrometry. Statistical testing did not prove any correlation between isotope values and the different sites nor time periods, suggesting that similar habitats were exploited for gilthead throughout the gulf. However, some trends could be visually identified, such as a wide range of isotope values indicating a broad spectrum of marine and brackish-water environments, as well as an abnormally large collection of fish with regards to size, which could be explained by overfishing leading to modern fish being smaller and younger on average. Furthermore, there appeared to be a much narrower range of isotope values in Bronze Age fish remains than Iron Age and later remains in sites along the Algarve Coast, which could correspond to a transition from subsistence fishing in select locations to more intensive fishing practices coinciding with the expansion of the Punic fish processing industry in Cádiz. Regarding fish farming, no evidence for extended habitation in hypersaline lagoons was suggested by the isotope values, although this may have been a result of the studied collection, which contained larger bones mostly corresponding to fish over five years old and so likely not products of aquaculture. The breadth of isotope values also underlines the risk of using isotopic information for human diet reconstruction, and best practices such as larger sample sizes and contextualizing the archaeozoological record are needed in further research to avoid erroneous conclusions.Show less

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Big fish in small ponds: investigating 13C and 15N bone collagen stable isotope ratios of Bronze Age to Early Modern gilthead seabream (Sparus aurata L.) in the Gulf of Cádiz (SW Iberia)