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    Revised proposal for the ongoing research plan on Patagonian toothfish (Dissostichus eleginoides) in Division 58.4.4b (2016/17–2020/21)

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    Document Number:
    WG-SAM-2019/08
    Author(s):
    Delegations of Japan and France
    Submitted By:
    Dr Takehiro Okuda (Japan)
    Approved By:
    Dr Taro Ichii (Japan)
    Abstract

    Division 58.4.4b has been a closed area since 2002 (CM 32-02) and scientific research has been conducted with a research plan submitted under CM 24-01 since 2008 by Japan. France joined this research plan in 2015 and a joint proposal was submitted for the first time in 2016 (WG-SAM-16/06 and WG-FSA-16/33 Rev. 1) for a period of 5 years.

    The proposal submitted here has been substantially revised to address the concerns expressed at WG-FSA 2019 and SC-CAMLR-XXXVII (para. 3.158). We followed and improved the revised research plan presented in SC-CAMLR-XXXVII Annex 12 and redefined slightly the research objectives. The survey design has been amended to avoid sea pen hotspots in the eastern part of 58.4.4b_2 (WG-FSA-18/23) and a new French vessel has joined the research plan to increase research survey capacity.

    Toothfish population structure and bycatch analyses will be presented at WG-FSA-19, while the main concerns regarding objective 2 (“Provide an assessment of the status and productivity of Patagonian toothfish stock”) and 5 (“Contribute to scientific research programs on killer whales (O. orca) ecology and depredation”) are addressed in two documents submitted at WG-SAM-19.

    We updated toothfish biological parameters (growth curve, maturity ogive, ALK) using >2000 age readings and incorporated estimations of depredation rate and IUU into an integrated stock assessment model. We built up the CASAL model developed in WG-FSA-15/23 by Taki et al. (2015). Different scenarios of depredation and IUU were tested to account for uncertainties associated with these processes in the model. In parallel, we standardized toothfish CPUE to explore temporal trends.

    Results on killer whales depredation revealed a lower effect than previously estimated due to the absence of interaction in recent years and the low historical interaction and depredation rates in the research blocks b_1 and b_2. Analyses of killer whales photo-identification provided new insights on movements and population dynamics in the South Indian Ocean.

    We made significant progress on the stock assessment and clarified objectives and milestones to facilitate the reviewing process of this research plan. A list of dates by which specific milestones will be completed and reported to CCAMLR working groups was provided and a final report will be provided at WG-FSA in 2021.

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