FISHERIES_2021_JUN_SWG-PEL_39rev Updated analysis of results from ICE data.pdf (1.04 MB)

Updated analysis of results from data arising from the Island Closure Experiment

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The results of analyses of data from the Island Closure Experiment reported in Ross-Gillespie and Butterworth (2021) are extended in three ways. First, a more consistent approach is taken for the conversions of the estimates of the effects of fishing parameters to estimates of the corresponding change in penguin population growth rate, though in implementation this leads to minimal modifications. Next the basis for contrasting the results from the aggregated and disaggregated analyses is changed from MLE to REML (or REML-equivalent) for unbiased and therefore more comparable estimates of CIs. Throughout, estimates and CIs from the two approaches remain similar, though overall a majority of aggregated approach CI’s now become slightly smaller rather than slightly larger than their disaggregated counterparts than was the case previously. Finally, the aggregated approach is applied to the chick survival response variable for Dassen and Robben islands, with the results compared to those from a disaggregated approach developed by OLSPS Marine (2021). As with the other response variables, estimates and CI’s from the two approaches to analyse the chick survival data are similar.

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Department of Mathematics and Applied Mathematics, University of Cape Town