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    An update on the ageing of Antarctic toothfish, Dissostichus mawsoni, from East Antarctica and the Amundsen Sea

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    Document Number:
    G. Nowara, B. Farmer, T. Barnes, P. Ziegler and D. Welsford
    Submitted By:
    Dr Philippe Ziegler (Australia)
    Approved By:
    Dr Dirk Welsford (Australia)

    This paper presents an update on the ageing of Antarctic toothfish, Dissostichus mawsoni, from East Antarctica (Division 58.4.1) and the Amundsen Sea (Subarea 88.2).  Initially, experienced readers at the Australian Antarctic Division (AAD) read a subset of 40 otoliths from the New Zealand reference collection for Antarctic toothfish, with all pairwise comparisons between readers and against the New Zealand reference ages showing a high level of precision (all IAPE < 5%, CV < 7%). Sister pairs of Antarctic toothfish otoliths were also prepared, one using the ‘bake and embed’ method and the other by thin sectioning, in order to assess the comparability of age estimates derived from each method. The values of IAPE and CV were acceptable between the two methods of preparation for individual readers, and between readers for each of the methods (all IAPE < 5%, CV < 6%). The level of ageing precision between the ‘bake and embed’ and ‘thin section’ methods for each reader was particularly high (all IAPE < 2%, CV < 3%), confirming that a similar level of detail is revealed by each preparation method. Therefore, either method can be used to provide reliable age estimates for Antarctic toothfish. Finally, a total of 730 otoliths from Antarctic toothfish which were collected by an Australian vessel in Subarea 88.2 in the 2014-2015 season and in Division 58.4.1 in the 2015-2016 season, were aged using thin sections (IAPE = 2.88, CV = 4.07).  The age estimates provided by this study will be available for use in the estimation of biological parameters and stock assessments of the respective sampling areas in East Antarctica and the Amundsen Sea.