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    The development of spatially and temporally controlled measures of survival and tag-detection for the CCAMLR tagging program

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    Document Number:
    WG-SAM-12/30
    Author(s):
    S. Mormede and A. Dunn (New Zealand)
    Submitted By:
    Sarah Mackey (CCAMLR Secretariat)
    Abstract

    A reliable commercial tagging program is critical to the successful assessment and management by CCAMLR of a number of toothfish fisheries in Antarctica. The evaluation of the tagging programme relies on two key aspects (i) that the tagged fish have a good chance of survival and (ii) that the tagged fish are reliably detected when recaptured. Previous attempts to evaluate individual vessel tagging performance in relation to these two aspects has been thus far inconclusive because of confounding factors such as time and location of tagging and subsequent fishing effort, as well as size of fish tagged.

    We propose that, by controlling for the spatial and temporal confounding factors using a case-control study design, we can derive meaningful indices of relative tagging performance of groups of fishing effort (e.g. vessel, vessel-trip). We developed indices to compare (i) the tag detection rate of recaptured fish and (ii) the tagging survival of released fish.

    This method was applied to the toothfish tagging data in CCAMLR Subareas 88.1 and 88.2. Initial results show that the indices developed can provide evidence of significant differences in tagging performance between different groups of fishing effort. Preliminary investigation showed these indices are robust to the choice of the control group and the area included in the analysis. Subject to further checks, this method could be used to investigate the relative tagging performance of different components of the CCAMLR tagging program across all fisheries, and more generally the relative performance of spatially and temporally heterogeneous data sets.

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