Offshore wind farms are refuges for porpoises in the German North Sea
New study shows: Porpoise populations remain stable, offshore wind farms are used as habitat by the marine mammals
May 21, 2025. The latest porpoise study by the German Offshore Wind Energy Association (BWO) shows that operating offshore wind farms appear to be attractive refuges for porpoises. Detection rates of the animals are significantly higher within the wind farms than in their immediate surroundings outside the wind farms. This indicates possible reef and refuge effects. Another finding of the study: Porpoise populations in the German North Sea are largely stable.
Porpoise behavior in the German Bight
According to the study, the development of harbor porpoise populations in the German Bight has been largely stable over the 13-year period studied. Regional differences indicate a moderate shift in harbor porpoise habitat—more pronounced from the northwest to more southeastern areas.
Around ten percent more porpoise sightings were recorded within the wind farms than in the vicinity of offshore wind farms – measured up to 2,5 kilometers outside the farms. The researchers attribute this to a combination of fisheries exclusion and reef effects. Offshore wind turbine foundations form reefs that attract fish. The studies also show that maintenance vessels operating within the wind farms do not deter porpoises.
The evaluation of the study also supports the thesis that offshore wind energy and species conservation can be reconciled with careful planning – an important finding in view of Germany's and Europe's expansion goals.
To the study:
The study "Harbor porpoise trends and offshore wind farm effects in the German Bight, North Sea. Analysis of CPOD data” is an investigation into the operational phase and complements the two previous porpoise studies conducted by the BWO, which analyzed the impacts of the construction phase of offshore wind farms on porpoises.
The study is based on passive acoustic monitoring (CPOD) data from 13 years (2010-2023) at over 60 stations in the German North Sea. It was commissioned by the German Offshore Wind Energy Association (BWE) with funding from member companies. BP AEIL, Iberdrola, Ørsted, OWF Gennaker GmbH, RWE Offshore Wind GmbH, shell, TenneT Offshore GmbH, Vattenfall Vindkraft AB.
With scientific partners: DanTysk Sandbank Offshore Wind GmbH & Co. KG, EnBW Hohe See GmbH & Co. KG, EnBW Albatros GmbH & Co. KG, Infrastructure Wind Power Plant Borkum GmbH & Co. KG (Trianel), Northland German Bay GmbH, Ocean Breeze Energy GmbH & Co. KG, OWP Butendiek GmbH & Co. KG, Trianel Wind power plant Borkum GmbH & Co. KG, Trianel Wind power plant Borkum II GmbH & Co. KG, UMBO GmbH, Veja Mate Offshore Project GmbH, WindMW GmbH.
Further BWO studies on porpoises:
– GESCHA I (2016): “Harbour porpoises keep returning: No long-term impact of offshore pile driving in the German Bight on harbour porpoises”
Online at https://bwo-offshorewind.de/gescha-studie-1/
– GESCHA II (2019): “Follow-up study confirms: No measurable effects of offshore pile driving on the harbor porpoise population in the German North Sea”
Online at: https://bwo-offshorewind.de/gescha-2-studie/
– BWO press release on the study: https://bwo-offshorewind.de/pressemitteilung-offshore-windparks-sind-rueckzugsraeume-fuer-schweinswale-in-der-deutschen-nordsee/