This report is an additional note to IMARES report number C166/14.
This report is an additional note to the report of Leopold et al. (2014) that evaluates the cumulative effects of offshore wind farm development in accordance with the roadmap of the Social and Economic Agreement (in Dutch: SER-akkoord) on birds and bats in the southern North Sea. In that report, unacceptably high mortalities were predicted for three large gull species: lesser black-backed gull (Larus fuscus), great black-backed gull (L. marinus) and European herring gull (L. argentatus).
To more accurately assess the impact of the projected offshore wind farms as compared to Leopold et al. (2014, 2015), two options were jointly analysed in this second iteration: 1) the density numbers for the aforementioned three gull species were revised; for the Dutch Continental Shelf (DCS) the calculations were based on aerial survey data from the MWTL monitoring programme only. The idea was, that since gulls tend to a aggregate near (active) fishing vessels, density numbers based on ship-based monitoring data (e.g. ESAS data) may (severely) skew the outcome of calculations (Leopold et al. 2015). Therefore, density numbers based only on MWTL data are regarded as more realistic densities. 2) the options of mitigating collision rates by installing larger wind turbines were analysed with Band (2012) model settings for 4 MW and 5 MW turbines. Per turbine type, two variants (different rotor diameter and - as a result of the chosen method - higher hub height) were considered. Note: in the main study and the first iteration, a 3 MW turbine was assessed.