Island closure feasibility study power analysis results for Dassen and Robben islands

Abstract

The power analysis for penguin responses to fishing around Dassen and Robben islands has been completed. Response variables considered are chick condition, active nest proportion, fledging success, chick growth, foraging path length, and foraging trip duration. Although complete results are given here only for the first two of these variables, overall there are clear indications regarding the residual variances associated with these variables. Those variances are now estimable for Dassen and Robben islands with sufficient reliability to allow a decision on whether an experimental closure programme could yield definitive conclusions regarding the impact of fishing close to island colonies on penguin demographics within a realistic time span. Thus the purpose of the feasibility study has been achieved and the study can be concluded, with the island closure experiment commenced for these two islands. Definitive results from the experiment can be expected for both islands with about 2–4 years’ additional data.