Browsing by Subject "humpback whales"
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- ItemOpen AccessAssessment of the west and east Australian breeding populations of Southern Hemisphere humpback whales using a model that allows for mixing on the feeding grounds and taking account of the most recent abundance estimates from JARPA(2005) Johnston, Susan J; Butterworth, Doug SThe most recent JARPA survey estimates of abundance are used to update the dynamic production model analyses of West and East Australian humpback breeding populations (Johnston and Butterworth 2002). These analyses take account of the results of both these surveys on the feeding grounds and of breeding area surveys, by applying a model that incorporates mixing of the two breeding populations on the feeding grounds of Areas IV and V. Results are quite precisely determined, with the available data providing a self-consistent picture of population recoveries well above their minima of the 1960’s. Best estimates are projected under continuing zero harvest, and show approaches to pristine levels in some 10 years for the western and 15-20 years for the more depleted eastern breeding population.
- ItemOpen AccessBayesian assessments of Southern Hemisphere humpback whale breeding Sub-stocks C1 and C3, including allowance for interchange on the breeding grounds(2008) Johnston, Susan J; Butterworth, Doug SBayesian stock assessment results for breeding sub-stocks C1 and C3 using models which allow for interchange on the breeding grounds as well as mixing on the feeding grounds are illustrated for two models – the sabbatical model and the resident model (for which interchange is set to zero.
- ItemOpen AccessCapture-recapture analyses of humpback population sizes and increase rates: breeding stocks C1-C3(2008) Johnston, Susan J; Butterworth, Doug SBoth 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.
- ItemOpen AccessReport on discussions on modelling studies of possible interchange between the C1 and C3 breeding Substocks of Southern Hemisphere humpback whales, Cape Town(2009) Butterworth, Doug S; Johnston, Susan JOver the week of 8-12 December, 2008, an International Stock Assessment Workshop was held under MARAM’s auspices at the University of Cape Town. This Workshop reviewed and discussed further lines of research for assessment analyses of five Southern African marine populations. One of these was Breeding Stock C of the Southern Hemisphere humpback whales, with a focus on modelling of possible interchange between breeding sub-stocks C1 and C3. The specific intent in the humpback case was to identify work usefully carried out prior to the IWC Intersessional Meeting (on Assessment Methodology to take account of Mixing/Interchange between Southern Hemisphere Humpback Populations) scheduled for Seattle in February 2009, so as to facilitate progress at that meeting.
- ItemOpen AccessSummary of the data and information available for the assessment of breeding stock B of the Southern Hemisphere humpback whales(2008) Johnston, Susan JFair amount of evidence to suggest two sub-stocks B1 (Gabon) and B2 (west South Africa, Namibia, Angola) • Would make sense to thus try and assess B1 and B2 separately.