Fatty acid and stable isotope analyses to infer diet of antarctic toothfish caught in the southern ross sea

Abstract

To infer important prey resources for Antarctic toothfish (Dissostichus mawsoni) in the southern Ross Sea, their lipid composition was determined and compared to lipid profiles of fish and invertebrate species taken as by-catch in the fishery or collected from the stomachs of toothfish. Stable carbon and nitrogen isotope ratios were also determined to further identify feeding relationships between these species. The aim of this study was to establish the feasibility of tracking the main dietary items of Antarctic toothfish by comparing results of biomarker analysis and conventional diet analysis. Samples were collected during a longline survey of pre-recruit toothfish in February 2012. Results of fatty acid (FA) and stable isotope analyses from this study provide evidence that a combination of these two techniques can delineate the main prey items of Antarctic toothfish and trophic structure of the toothfish-related fish food web in the southern Ross Sea ecosystem. Similarities in total FA compositions and the FA profiles in muscle tissue of Antarctic toothfish, and Pleuragramma antarcticum, Pogonophryne barsukovi, Dacodraco hunteri and Trematomus loennbergii indicated a trophic connection between toothfish and these fish species. Mean delta N-15 values of Antarctic toothfish were higher than those of P. antarcticum, P. barsukovi and T. loennbergii, indicating a higher trophic position of the toothfish. In contrast, similar delta N-15 values between Antarctic toothfish and icefish (D. hunteri) suggested that they occupy the same trophic position. Overall results of this survey are consistent with the frequency and percentage occurrence of prey in Antarctic toothfish stomachs. Further sample collection and biomarker analyses for more pelagic and benthic biota are needed to better understand the entire food-web structure in the southern Ross Sea.