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Assessing seabird displacement at offshore wind farms: power ranges of a monitoring and data handling protocol

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Prior to the construction of an offshore wind farm at the Belgian Thorntonbank, local seabird abundance was studied by means of ship-based surveys. ‘Seabirds at sea’ count data, however, exhibit extreme spatial and temporal variation, impeding the detection of human impacts on seabird abundance and distribution. This paper proposes a transparent impact assessment method, following a before–after control–impact design and accounting for the statistical challenges inherent to ‘seabirds at sea’ data. By simulating a broad range of targeted scenarios based on empirical model coefficients, we tested its efficacy in terms of power and investigated how the chance of statistically detecting a change in numbers is affected by data characteristics, monitoring period and survey intensity. Because of high over-dispersion and/or zero inflation, the power to detect a 50% decrease in numbers was generally low, but did reach 90% within less than 10 years of post-impact monitoring for northern gannet (Morus bassanus) and common guillemot (Uria aalge).

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First of all, we want to thank the wind farm concession holders for financing this research in fulfilment of the monitoring requirements of their environmental permits, and the Royal Belgian Institute of Natural Sciences (RBINS) for assigning it to us. A special word of gratitude goes out to DAB Vloot and the Flanders Marine Institute (VLIZ) for providing monthly ship time on RV’s Zeeleeuw and Simon Stevin, and the same goes out to RBINS and the Belgian Science Policy (BELSPO) for the ship time on RV Belgica. In this respect, we also wish to thank all crew members of aforementioned RV’s for their cooperation. We kindly thank Robin Brabant, Steven Degraer & Lieven Naudts from RBINS and André Cattrijsse from VLIZ for their invaluable logistical support and cooperation throughout the monitoring programme. During the early stages of the statistical processing, my colleagues Dirk Bauwens and Paul Quataert provided helpful advice. We are very grateful to all volunteers (especially Walter Wackenier who joined us every month) who assisted during the seabird count surveys. Finally, we wish to thank the three anonymous reviewers for their highly valuable comments, as under their impulse the manuscript has improved considerably.

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Correspondence to Nicolas Vanermen.

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Guest editors: Steven Degraer, Jennifer Dannheim, Andrew B. Gill, Han Lindeboom & Dan Wilhelmsson / Environmental impacts of offshore wind farms

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Vanermen, N., Onkelinx, T., Verschelde, P. et al. Assessing seabird displacement at offshore wind farms: power ranges of a monitoring and data handling protocol. Hydrobiologia 756, 155–167 (2015).

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