Browsing by Subject "Bayesian assessment"

Now showing 1 - 8 of 8
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    The age-structured production modelling approach for assessment of the rock lobster resources at the Tristan da Cunha group of islands
    (2011) Johnston, Susan J; Butterworth, Doug S
    The stock assessment approach for all four islands of the Tristan da Cunha group is to use an age-structured production model (ASPM) to fit to catch, longline standardised CPUE and catchat-length (CAL) data. The models consider only catches from 1990, i.e. models are initiated in 1990. The method for setting up the initial population age structure in 1990 is given below.
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    A Bayesian assessment of breeding stocks B, C and G of Southern Hemisphere humpback whales using a prior for growth rate from analyses for stocks D and E
    (2005) Johnston, Susan J; Butterworth, Doug S
    Bayesian assessment of breeding stocks B, C and G of the Southern Hemisphere humpback whales are presented. These assessments incorporate a prior for the maximum growth rate r derived from similar assessments for breeding stocks D and E. This is the first time an assessment for breeding stock B has been attempted. Results show current abundance estimates for breeding stocks B and G are low (less than 0.15K), whilst the current abundance estimate for breeding stock C much further recovered at 0.79K. Projections under a zero continued harvesting strategy estimate breeding stock C to be fully recovered by 2020, whilst breeding stocks B and G will be fully recovered only by about around 2030.
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    Bayesian assessments using models which allow for interchange on the breeding grounds of Southern Hemisphere humpback whale breeding Sub stocks C1 and C3
    (2009) Johnston, Susan J; Butterworth, Doug S
    Bayesian 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 four models – the sabbatical, tourist and migrant models and the resident model (for which interchange is set to zero.) Results are also presented for a range of sensitivity tests. The availability of photo-id data allows the estimation of interchange rates. The estimates of these interchange rates are generally low with posterior median estimates all below 6% p.a., and estimated trajectories are fairly similar for all models considered. With single exceptions, current (2006) posterior median population sizes relative to pre-exploitation levels are all estimated to exceed 80% for C1 and 90% for C3.
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    Corrected assessment results for Southern Hemisphere humpback whales from breeding stocks D and G
    (2007) Johnston, Susan J; Butterworth, Doug S
    Corrected Bayesian stock assessment results for breeding stocks D and G which take into account trend information from the IDCR/SOWER survey results are presented. At the 2006 IWC scientific meeting, the authors presented various stock assessments for breeding stocks D and G (Johnston and Butterworth 2006, IWC 2006). Some of the assessment scenarios presented involved fitting to trend information from the IDCR/SOWER circumpolar surveys which was reported in Branch (2006). The authors inadvertently used the raw abundance estimates provided which had not been adjusted for comparability with respect to areal coverage. Corrected assessment results are thus presented here, for which the appropriate IDCR/SOWER survey trend infomration for comparable areas are used.
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    Prior incoherence within a Bayesian assessment of the Southern Hemisphere humpback whale breeding stock B population
    (2010) Müller, Andrea; Butterworth, Doug S
    In very simple terms, a Bayesian analysis involves drawing estimatable parameter values from some prior distribution, computing population dynamics and assigning a likelihood value to each combination based on comparisons to data containing information on population size and/or trend. A posterior distribution may then be constructed and conclusions drawn about the parameter estimates. In Model Ia (see Appendix) r B1 , r B2 , ( ) 1 arg ~ ln B Nt , ( ) 2 arg ~ ln B Nt are the parameter values drawn from priors for the intrinsic growth rate and the log of the recent abundance for the two populations under consideration.
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    Updated assessments of Southern Hemisphere humpback whale breeding stock C and its component sub-stocks
    (2008) Johnston, Susan J; Butterworth, Doug S
    Bayesian stock assessment results for a mixed model breeding sub-stocks C1 and C2+3 are presented. The modelling approach allows mixing on the feeding grounds and fits to various data sources, including capturerecapture data from both sub-stocks. A baseline case which inputs all capture-recapture data directly suggests posterior median 2006 abundances for each sub-stock of a little more than 7000, with C1 at about 85% and C2+3 at about 55% of their pristine levels. These results are intended to be illustrative only, and the variety of choices available for the various model inputs require further discussion by the IWC Scientific Committee.
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    Updated assessments of Southern Hemisphere humpback whale breeding sub-stock B1
    (International Whaling Commission, 2008) Johnston, Susan J; Butterworth, Doug S
    Updated Bayesian stock assessment results for humpback breeding sub-stock B1, which take into account recently advised capture-recapture data, are presented. These suggest this population presently to be within the range of 65-90% of its pre-exploitation size in terms of posterior median estimates. However, alternative options for inputs to this assessment are possible, and need to be discussed by the Scientific Committee.
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    Updated assessments of Southern Hemisphere humpback whales from breeding stocks D and G
    (2006) Johnston, Susan J; Butterworth, Doug S
    Bayesian stock assessment methodology is used to update the stock assessments of breeding stocks D and G of the Southern Hemisphere humpback whales. These assessments take into account the recently updated historic catch series, as well as the most recent estimates of current abundance and population trend information as presented at the Southern Hemisphere humpback whale workshop held in Hobart in April 2006. These stock assessments provide estimates of current as well as past abundances. Projections under a zero harvesting strategy are also presented.