University of Cape Town
RS4895_SC_65b_SH04Rev.pdf (353.21 kB)

Assessment results for humpback breeding stocks D, E1 and Oceania following recommendations from SC 65a

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Following recommendations made at IWC 65a, 2013, a single-stock BSD (Breeding Stock D, West Australia) model has been run for a range of Antarctic catch boundaries, and some two-stock BSE1 (Breeding Stock E1, East Australia)+BSO (Breeding Stock Oceania) models have been explored. The single-stock BSD model excluded the Hedley et al. (2011) absolute abundance estimate from the model fits, and instead utilised an uninformative uniform prior on the log of the target abundance estimate. The minimum value for this prior was based on calculations by Hedley of a minimum absolute abundance indicated by the 2005-2008 survey (Hedley et al. 2011). These changes markedly improve the fit to the BSD relative abundance series. The two-stock models considered consist of one model with fixed Antarctic boundaries that allowed for a proportion of each of the BSE1 and BSO stocks to feed in a common feeding ground between 170°E and 170°W, and a second model in which there was no overlap between the two stocks, but a range of different Antarctic catch boundaries have been explored. Results of these models showed that (a) the BSE1 growth rate remained virtually at 0.106 yr-1 (the demographic boundary imposed by the model), (b) fits to the BSE1 mark-recapture data were relatively poor and (c) the Nmin constraint remained problematic for BSO. Further two-stock runs, as well as a three-stock run, have not been included in this paper, but the authors aim to provide the results as an addendum to this paper at the meeting.



Department of Mathematics and Applied Mathematics, University of Cape Town