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    Progress on the spatial modelling of by-catch patterns for research fishing operations in Subarea 48.6 using VAST

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    Document Number:
    WG-FSA-2021/48
    Author(s):
    K. Sawada and T. Okuda
    Submitted By:
    Dr Kota Sawada (Japan)
    Approved By:
    Dr Taro Ichii (Japan)
    Abstract

    We report the progress on the development of statistical modeling to estimate abundance trends of bycatch species (grenadiers) caught by longline fisheries in CCAMLR Subarea 48.6 using a spatial delta-GLMM implemented by the R package VAST. In response to the comments from WG-FSA-2020 e-group discussions, separate models were constructed for all research blocks within the subarea, and the residuals diagnostics were examined. Although we successfully estimated indices of abundance and the estimation was robust to the choice of covariates, further examinations and improvements are required, given the result of model diagnostics.