Browsing by Subject "island closure"

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    Re-analysis of the island closure experiment results to implement the suggestions of the December 2020 International Panel
    (2021) Ross-Gillespie, Andrea; Butterworth, Doug
    The suggestions of the December 2020 International Panel for further analysis of the results from the island closure experiment, in particular to use the same data within a common framework to facilitate comparisons, and to include month as a covariate, are implemented for all response variables except chick survival. Broadly, the results indicate that aggregated and disaggregated approaches give the same results for estimates and variances of the island closure effect (see Figure 2). This is especially a consequence of implementing the disaggregated approach with a nesting structure as advocated by the Panel, which is shown to be statistically justified. Inclusion of the month co-variate does impact results to some extent, the more so for foraging data for the west coast islands (see Figure 3). The sensitivities investigated generally make little difference to results; these checks include extensions to incorporate data prior to 2008. As to be expected, REML based estimates of CIs are somewhat wider than those based on MLE.
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    A summary of results for the island closure experiment
    (2021) Butterworth, Doug; Ross-Gillespie, Andrea
    A simple summary is offered of the results of the island closure experiment reported in Ross-Gillespie and Butterworth (2021), which implemented the suggestions of the December 2020 International Panel. A single result in selected for each island/response variable combination, and reasons are provided for preferring the aggregated data approach for this, with increases made to the CI estimates so as to correspond to the unbiased REML method. Integration across the results is problematic for various reasons, but a coarse summary indicates little evidence for any impact (in either direction) of fishing in the neighbourhood of island colonies on penguin population growth rates. Given that the islands in the experiment have been closed for 50% of the period since 2008, some coarse predictions for the extent of improvement in annual population growth rates (on average over time) were these islands to be closed to fishing every year in the future are: Dassen -0.5% (i.e. no improvement), Robben +0.25%, Bird 0% and St Croix +0.5%.