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

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...

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Bibliographic Details
Published in:Hydrobiologia
Main Authors: Vanermen, N., Onkelinx, T., Verschelde, P., Courtens, W., Van de walle, M., Verstraete, H., Stienen, E.W.M.
Format: Article in Journal/Newspaper
Language:English
Published: 2015
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Online Access:http://www.vliz.be/nl/open-marien-archief?module=ref&refid=244115
Description
Summary: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).