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    Summary of progress on the recommendations of the Independent Stock Assessment Review for Toothfish (2018) for the Ross Sea

    Request Meeting Document
    Document Number:
    A. Dunn and J.A. Devine
    Submitted By:
    Mr Nathan Walker (New Zealand)
    Approved By:
    Mr Nathan Walker (New Zealand)

    In 2018, CCAMLR undertook an Independent Stock Assessment Review for Toothfish (ISART). The review was considered by the Scientific Committee in 2018, and its recommendations were summarised in the 2018 Report of the Scientific Committee. The Scientific Committee also provided a review of progress of the recommendations summarised across all the stocks that had integrated stock assessments.

    We provide a summary of progress against the review recommendations for the stock assessment of Antarctic Toothfish in the Ross Sea region since 2018, including references to papers and discussions in CCAMLR reports.

    Progress has been made on most of the recommendations from the ISART and have resulted in modifications to the Ross Sea toothfish assessment model over time. However, these changes have not yet significantly changed the assessment outcomes or the management advice arising from the assessment. Work is not complete on a small number of recommendations, including investigating how smoothing the age–length key (ALK) matrix would affect the assessment (and given the number of otoliths used to construct the age-length keys would likely result only in a small effect) or those related to tagging mortality (which would require field experiments to resolve).

    The current work on extending the time at liberty for tag recaptures observations highlighted a pattern in the tag-recapture residuals that, although investigated, using models with additional tag-related mortality, tag-loss, or tagged fish dispersion, could not be fully explained. Hence, Additional investigation of the pattern in residuals for the tag recaptures with increasing time at liberty is required. Further work is also needed on the shape of fishing selectivities as patterns remain in the age composition residuals that are not fully explained by time-block changes in fishing selectivity nor extending the range of year class strengths estimated in the model.