Initial results for a further four Candidate Management Procedures for the Toothfish (Dissostichus eleginoides) Resource in the Prince Edward Islands vicinity
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2019
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Abstract
Brandão and Butterworth (2019a) proposed a simple target-based Candidate Management Procedure (CMP) control rule based upon recent average values of CPUE to provide future TAC recommendations for the Prince Edward Islands toothfish resource. Several suggestions made by a Task Team that evaluated the performance of this CMP were addressed by Brandão and Butterworth (2019b). Although the proposed CMP performed satisfactorily under most OMs, it was unable to react appropriately especially under the scenario assumed by OM17, which addresses the concern with the poor fit to the trotline CPUE data for the last two years by assuming an increased tag loss rate. Further CMPs are investigated in this paper to try to achieve better performance. These CMPs include changes to the form of the CMP proposed by Brandão and Butterworth (2019b), as well as the incorporation of the cumulative number of recaptured tags. These CMPs are able to secure an increase in the TAC without adversely affecting the status of the resource under OM01 and OM10. However, their performances under OM17 are still not satisfactory, although CMP(dep t) (which incorporates a time-dependent target) performs better than the other CMPs in so far as the median final spawning biomass remains near the current (2017) abundance level and at about BMSY. However, all CMPs still fall well below the target value of median final depletion under OM17. CMP(slope) (based on the recent trend in CPUE) is the only CMP to perform satisfactorily under OM18. Incorporation of the cumulative numbers of tag returns in the CMP has not been successful in improving its performance for OMs which show problematic resource trends such as OM17 and OM18. However, this might mean that further adjustment of this CMP is needed rather than that the tag information is not useful in discriminating amongst the various scenarios covered by the OMs. Further investigation/adjustment of these CMPs is needed.
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Brandão, A., Butterworth, D. 2019. Initial results for a further four Candidate Management Procedures for the Toothfish (Dissostichus eleginoides) Resource in the Prince Edward Islands vicinity.