The swift expansion of offshore wind energy development in European waters has sparked concerns
regarding their potential environmental impacts. We studied harbour porpoise (Phocoena phocoena)
presence during the operational phase of Borssele wind farms located in the southern part of the Dutch
EEZ. The passive acoustic monitoring network consists of cetacean click detectors at 14 locations in and
outside the windfarms, co-located with broadband hydrophones at 4 locations. Preliminary results indicate that ambient sound levels inside the windfarms are dominated by low-frequency sound emitted by
the turbines, while ambient sound levels outside the windfarm are higher and deemed typical for an environment close to a shipping lane. Seasonality in harbour porpoise acoustic activity was observed, with
higher detections with decaying sea surface temperature. This corresponds with previous studies at Dutch
offshore wind farms and patterns in coastal sightings, aerial surveys, and strandings (i.e., higher porpoise
density in winter and early spring). Porpoise acoustic activity increased during the night and around slack
tide, possibly related with enhanced foraging opportunities. The monitoring network enables studying the
soundscape in and around an offshore windfarm within a part of the North Sea with the highest shipping
density, and the impact of an offshore windfarm on the presence and activity of harbour porpoises. This
research is part of the WOZEP ecological programme of Rijkswaterstaat. 

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