Browsing by Author "Muller, A"

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    Simulation testing of the sabbatical model estimator for the assessment of Southern Hemisphere humpback whale breeding Stock C and its component Sub-stocks
    (2009) Johnston, Susan J; Butterworth, Doug S; Muller, A
    Johnston and Butterworth (2009) implement four models (Resident, Sabbatical, Tourist and Migrant) to estimate parameters for the C1 and C3 substocks, including the probability of interchange between them, using a Bayesian approach which takes account of capture-recapture information from photo-id data. This estimator generally captures the underlying parameter values reasonably, though with a tendency to estimate r too low and K too high. Interchange rates are also reasonably estimated, both when the true rates are low and high. In the latter case, abundance estimates in terms are lower. Here a range of Operating Models (OMs) are defined and used to test the Sabbatical estimator
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    Open Access
    Test fishing analyses for Nightingale Island
    (2012) Johnston, Susan J; Butterworth, Doug S; Brandão, Anabela; Muller, A
    Because there was no pre-OLIVA fishing in the month of January 2011, the simpler earlier approach of Johnston (2011) to analyse test fishing data by month to assess the OLIVA impact needs to be refined to be able to include data from January 2012. General Linear Models are used for this purpose; these have the additional advantage that they can take more data into account in adjusting for monthly patterns. These models also reveal a regional pattern in the OLIVA impact, which is least in the north and greatest in the southeast. There is some indication that the impact has decreased slightly over time, but the trend is not statistically significant. The best estimate obtained for the OLIVA impact is a decrease of about 50% (SE=5%) in abundance of lobsters above the size limit.