A summary of results for the island closure experiment

• Main Authors: Butterworth, Doug, Ross-Gillespie, Andrea
• Format: Report
• Language: unknown
• Published: Faculty of Science 2021
• Subjects: penguin; island closure; fishing impact; REML; Butterworth; Penguin Island
• Online Access: http://hdl.handle.net/11427/33664; https://open.uct.ac.za/bitstream/11427/33664/1/FISHERIES_2021_JUN_SWG-PEL_36%20A%20summary%20of%20results%20for%20the%20ICE.pdf

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%.