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    ADDING CATCH AT AGE AND SURVEY DATA TO THE 48.3 TOOTHFISH CASAL ASSESSMENT

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    Document Number:
    WG-SAM-09/13
    Author(s):
    D.J. Agnew and M. Belchier (United Kingdom)
    Abstract

    The catch-at-age based CASAL model for toothfish in Subarea 48.3, which was presented in 2007, is developed and extended here to include survey data. Additional adjustments to the model suggested by WG-FSA-2007 are implemented. Fits to the survey length frequencies are good for recent surveys but in the past some cohorts have been missed by the survey. Fits to the survey CPUE are generally not very good. There is evidence for a size-based influence on post-tagging mortality, post-tagging growth retardation period and rate of tag loss. When these factors are included in the model the fits to the tag recaptures at size improve. However, there is still some evidence for a sex-based influence on the fits, particularly the poor fits observed from tags released in 2004 where significantly more males than females were recovered. A sex-disaggregated model was created, providing substantially similar fits and results to the sex-aggregated model, and no significant improvement to the tagging data fits. Estimates of cohort strength are made by the new model, but there is uncertainty about the estimates of recent cohorts made using short runs of catch-at-age data and the catchability being estimated by the survey. Estimates of cohort strength should be incorporated in calculations of TACs. A number of different mechanisms for doing this are proposed which maintain SSB above 50% B0 in both the short and long term.

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