Browsing by Subject "humpback"

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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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    Simulation exercise to ascertain the relative utility of collection of various data types for informing future Southern Hemisphere humpback whale assessments and Breeding Stocks D, E1 and the Oceania stocks
    (2015) Ross-Gillespie, Andrea; Butterworth, Doug S
    The existing three-stock model for Breeding Stock D (West Australia or BSD), Breeding Stock E1 (East Australia or BSE1) and the collection of Oceania breeding sub-stocks (referred to as Breeding Stock O or BSO for convenience) is used to simulate future data which might be collected for these stocks, to ascertain which have the best potential to improve estimates of precision of key quantities associated with the population dynamics. For BSD, a future estimate of absolute abundance in 2017 and a series of relative abundance estimates each year from 2016 to 2020, where all estimates have CVs of 0.25, are considered. For BSE1, a similar further relative abundance series is considered, as well as new mark-recapture data collected over 2016 to 2020 where sighting probabilities are taken to be half the average achieved previously. Sighting probabilities are dealt with in a similar manner for future mark-recapture data considered for BSO. Both the further absolute abundance estimate for BSD and especially more mark-recapture data for BSO show some potential for providing improved precision in parameter estimates. However, there seems to be little increase in precision to be gained from further relative abundance data, bearing in mind that these results presume the current three-stock model to be correct. The three-stock model is further used to estimate the range of future observations that would remain compatible with that model’s assumptions. Actual data collected in future could be compared to such ranges to check on the model’s ability to continue to reflect reality.