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    An integrated stock assessment for the Heard Island and McDonald Islands Patagonian toothfish (Dissostichus eleginoides) fishery in Division 58.5.2

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    Document Number:
    P. Ziegler
    Submitted By:
    Dr Philippe Ziegler (Australia)
    Approved By:
    Dr Dirk Welsford (Australia)

    This paper presents an updated assessment for the Patagonian toothfish (Dissostichus eleginoides) fishery at Heard Island and McDonald Islands in CCAMLR Division 58.5.2 with data until end of the season 2015/16. The updated assessment model is based on the best available estimates of model parameters, the use of abundance estimates from a random stratified trawl survey (RSTS), longline tag-release data from 2012-2015 and longline tag-recapture data from 2013-2016, and auxiliary commercial composition data to aid with the estimation of year class strength and selectivity functions of the trawl, longline and trap sub-fisheries.

    Compared to the 2015 assessment that was accepted by WG-FSA-15 to be used for management advice, this assessment takes into account (1) new fishery observations up to the end of 2016 including new ageing data from the RSTS and commercial fishery from 2015-2016, (2) updated growth parameters, (3) updated maturity parameters, (4) updated tag loss estimates (5) a bias correction for fish emigrating out of Division 58.5.2, (6) survey biomass and catch proportions instead of survey abundance numbers, and (7) iterative data weighting using the ‘Francis’ method. All model runs were conducted with the CASAL version 2.30-2012-03-21 rev. 4648 that was agreed on by WG-SAM-14.

    The updated assessment model leads to a smaller estimate of the virgin spawning stock biomass B0 than that obtained in 2015, with an MCMC estimate of 77 286 tonnes (95% CI: 71 492-84 210 tonnes). Estimated SSB status was 0.61 (95% CI: 0.58-0.64). Despite the smaller biomass, changes to the model compared to 2015 in particular its higher productivity with the updated maturity parameters, meant that the catch limit that satisfies the CCAMLR decision rules has increased from 3405 tonnes to 3525 tonnes.