Browsing by Subject "breeding stocks"

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    Assessment results for humpback breeding stocks D, E1 and Oceania following recommendations from SC 65a
    (University of Cape Town, 2014) Ross-Gillespie, Andrea; Butterworth, Doug S; Johnston, Susan J
    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.
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    Capture-recapture analyses of humpback population sizes and increase rates: breeding stocks C1-C3
    (2008) Johnston, Susan J; Butterworth, Doug S
    Both maximum likelihood and Bayesian methodologies are developed to analyse the photo-ID and genotypic capture-recapture data available for the C1 and C3 breeding sub-stocks of humpback whales in the western Indian Ocean. A simple exponential growth population model is assumed, and estimates of annual growth rate and abundances determined. Maximum likelihood estimates of r are generally imprecise and often the point estimates are demographically infeasible. The most reliable results are probably those from the Bayesian analyses with a prior for r of U[0; 0.106]. The data update this prior somewhat more for C3 than for C1, with a median posterior estimate of 8.0% for the former. Posterior median estimates of abundance for each sub-stock when analysed in isolation are both a little more than 6500. An interchange model is developed to take account of photo-ID information on exchanges between the C1 and C3 regions (only one such exchange has been recorded thus far). The results show little difference between the combined abundances estimated for the two sub-stocks with such interchange, compared to the sum of results for the two analysed in isolation; the posterior median annual probability of an animal from either sub-stock visiting the other’s region in any one year is a little more than 5%, with an upper 5%-ile of some 19%. It should be understood that the results presented are intended to be illustrative, not definitive, having the purpose of facilitating further runs and refinements of the models during Scientific Committee discussions.
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    Preliminary results for a combined assessment of all seven southern hemisphere humpback whale breeding stocks
    (2010) Müller, Andrea; Butterworth, Doug S; Johnston, Susan J
    This paper reports preliminary results from the development of an assessment process that aims to include all seven Southern Hemisphere humpback whale breeding stocks in a single joint assessment, with the purpose of allowing highlatitude historic catches (i.e. catches taken south of 40˚S, where mixing amongst the populations occurs), to be allocated to breeding stocks in proportion to abundance, rather than on set ratios. The approach can be broadened to allow for uncertainties in the placement of the boundaries assumed to link high latitude catches to breeding stocks. Because of the interaction between populations arising from the procedure to allocate high latitude catches amongst breeding stocks, the conventional SIR-based Bayesian approach proved impractical to expand. Instead uniform priors on the various preexploitation level (K) parameters were assumed with the intent to later iteratively adjust these to account for their being informative about the values of the intrinsic growth rate (r) parameters. Initial results (which will need later refinement) are presented purely for the purposes of illustrating the application of the approach.