Evaluation of seabird and harbour porpoise monitoring

© Hollandse Hoogte / Friso Spoelstra
Changes in the location or failure of parts of transects of the survey design may have implications for the reliability of seabird and porpoise trends.
The trend in numbers of seabirds and porpoises in the Dutch part of the North Sea is determined on the basis of aerial surveys and coastal sea migration counts. Commissioned by InformatieHuis Marien (IHM), CBS has investigated the possible consequences for trend calculations based on the aerial surveys of three possible or already realised changes: new wind farms, adjustments in the survey design along the coast and reducing the number of counts offshore.