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    Revised research plan for the 2015/16 exploratory longline fishery of Dissostichus spp. with special reference to the information on spawning dynamics in Division 58.4.3a

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    Document Number:
    Delegation of Japan
    Submitted By:
    Dr Kenji Taki (Japan)

    The current season (2014/15) is the final one of the first three-season research which began in 2013 in data-poor fisheries. In the present report, the next three-season (2016-18) research plan in Division 58.4.3a was revised using the latest CCAMLR C2 and Observer data.

    The stock sizes for block 58.4.3a_1 was estimated by the Petersen estimator and the CPUE x seabed analogy method.

    The stock size using the Petersen estimator was largely different from that using the CPUE method. Predicted numbers of tag recaptures from the estimated stock sizes using the Petersen method were generally consistent with the observed number during 2013-14 seasons, but those using the CPUE method were inconsistent.

    We also made analysis on spawning dynamics for D. eleginoides in Division 58.4.3a and compared to the results in other regions in the Southern Indian Ocean. The stock seems to be self-sustainable because of the existence of fish with advanced gonadal indices in the slope area and recruitment of small sized fish mainly in the shallow area, although the stock has a possibility of metapopulation throughout the Southern Indian Ocean as previous genetic studies indicated.

    Understanding of the resource structure through clarification of their life history is essential to establish stock assessment and robust stock/ fisheries management of Dissostichus spp. population(s) in data- poor exploratory fisheries. During the second three-season research, we will continue enhanced tagging program, and collection and analysis of biological data including otoliths and gonads to clarify migration route and associated life stages of the fish.

    To this end, we propose to follow the current research style in the current research blocks for the second three-season research with the sample sizes estimated following the procedure recommended at the WG-FSA in 2013 in order to maximize the expectation of tag-recapture to the extent possible under the precautionary exploitation rate.