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    Developing robust biomass estimates and advice on catch limits in research blocks

    Request Meeting Document
    Document Number:
    S.J. Parker, S. Mormede, A. Dunn, S.M. Hanchet and C. Marsh
    Submitted By:
    Mr Alistair Dunn (New Zealand)
    Approved By:
    Mr Alistair Dunn (New Zealand)

    In 2016, changes to the methods used by CCAMLR to estimate biomass in research blocks resulted in conflicting estimates of biomass between the CPUE by seabed area and the Chapman estimate. The Scientific Committee requested that the changes to the methods be reviewed, that scientific rational for the different biomass estimates be provided.

    In this paper, we develop a modified CPUE by seabed area method that improves on the original CPUE by seabed area method for toothfish populations in research blocks. This uses local Chapman biomass estimates in the reference area instead of the stock biomass estimated by the stock assessment model as the reference biomass. We demonstrate evidence of a linear relationship between CPUE and fish density in the Ross Sea reference area for the first time. The resulting density estimates from Shelf/Slope and North habitat types from the Ross Sea can be used to estimate a CPUE by seabed area biomass in designated research blocks.

    We also develop a Bayesian approach that combines the information from the CPUE by seabed area biomass analogy and Chapman biomass estimates together in an integrated statistical to provide robust estimates of biomass in research blocks.