Initial exploration of single-stock, two-stock and three-stock population models for humpback breeding stocks D, E1 and Oceania under different Antarctic stock boundaries assumptions

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University of Cape Town

A three-stock model with feeding and breeding ground interchange was proposed at IWC 64 for the assessment of Southern Hemisphere humpback whale breeding stocks D (West Australia), E1 (East Australia) and Oceania, with the aim of addressing some inconsistencies that arose in the single-stock assessments. First a two-stock (D+E1) and then a three-stock model with only mixing of stocks on the feeding grounds were developed, but it was found that neither removed these inconsistencies. It was found, however, that substantial improvements could be obtained by shifting the customary Antarctic stock boundaries to allow for more of the Antarctic catches to be allocated to breeding stock D. This paper presents the results of the single-stock, two-stock and three-stock models for both the original Antarctic boundaries, as well as the proposed new boundaries. The aim of the paper is to illustrate the effect of moving the boundaries and to provide a platform for further discussion and development at IWC 65.