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    Quantifying vessel performance in the CCAMLR tagging program: spatially and temporally controlled measures of relative mortality and tag-detection rates

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    Numéro du document:
    WG-FSA-12/47 Rev. 1
    S. Mormede and A. Dunn (New Zealand)
    Soumis par:
    Sarah Mackey (Secrétariat de la CCAMLR)

    A reliable commercial tagging program is critical to the successful management by CCAMLR of a number of toothfish fisheries in Antarctica, but the evaluation of tagging performance has been thus far inconclusive because the confounding effect of factors such as time and location of tagging, and size of fish tagged, makes meaningful comparisons between vessels difficult.

    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 performance of groups of fishing effort (e.g. vessel, trip, etc). We developed indices of (i) the mortality (or loss of all tags) of released fish and (ii) the detection rate of recaptured fish.

    This method was applied to the tagging data in CCAMLR Subareas 88.1 and 88.2. Results show that the indices developed can provide evidence of significant differences in performance between the different vessels or groups of fishing effort. Further investigation showed these indices are robust to the choice of the control group and the area included in the analysis, as well as variations to the 'space window' within which control hauls were selected and paired with each case haul. This method is a good candidate to investigate the relative performance of the CCAMLR tagging program across all fisheries, and more generally the relative performance of spatially and temporally heterogeneous data sets.

    In the revision duplicate figures have been removed and Figures 2 to 7 now have ‘vessel number’ on the vertical axis (these numbers were allocated at random and are the same for each figure).