FISHERIES_2021_JUN_SWG-PEL_41 Revised summary of ICE results.pdf (454.72 kB)

A revised summary of results for the island closure experiment

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A simple summary is offered of the results of the island closure experiment reported in Ross-Gillespie and Butterworth (2021a and b), which have implemented the suggestions of the December 2020 International Panel for now all the response variables in as consistent a manner as possible. A single result is selected for each island/response variable combination, with reasons provided for preferring the aggregated data approach for this, and 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 very 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 -0.25% (i.e. no improvement), Robben +0.25%, Bird 0% and St Croix +0.5%.

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Department of Mathematics and Applied Mathematics, University of Cape Town