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    Maturity and growth estimates of Patagonian toothfish in Subarea 48.3 between 2009 to 2021

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    Document Number:
    J. Marsh, T. Earl, P. Hollyman and C. Darby
    Submitted By:
    Ms Georgia Robson (United Kingdom)
    Approved By:
    Dr Chris Darby (United Kingdom)

    This paper extends the work of Marsh et al. 2022 presented at WG-SAM-22 to compare the influence of two age datasets in the estimation of maturity at age and expected length at age of Patagonian toothfish (Dissostichus eleginoides) in Subarea 48.3. To provide coverage of the full length-class distribution of the catch in toothfish age data, methods for sampling otoliths for reading were revised from a random to a random stratified approach based on length-bins. During 2021/22, the UK began re-sampling and reading of historic otolith samples for length-classes that were under-represented in the age dataset. Marsh et al. 2022 evaluated the effect of including these additional age samples on estimates of maturity and growth.

    This paper incorporates additional age samples from re-sampled historic otoliths for 2009, 2010, 2011, 2017 and 2018, as well as new age data for 2021. Following recommendations at WG-SAM-22, (CCAMLR, 2022, paragraph 3.42), this paper expands beyond the initial study to include a comparison of estimates of growth parameters derived both with and without accounting for the change in otolith reading sampling strategy, i.e. an adjustment for length-stratified age sampling.

    Consistent with previous findings, the change in otolith sampling regime had no influence on the estimation of maturity at age between 2009 and 2021 but did influence the estimation of growth parameters. The results suggested that, in general, not attempting to account for the effects of fishing selectivity and stratified length sampling would likely lead to an underestimation of Linf and overestimation of K growth parameters.