For the first time, a study comprehensively investigated the behavior of harbor porpoises during pile driving for offshore wind farms in the North Sea. The study shows that offshore wind farms have no negative consequences for the harbor porpoise population. Despite constantly increasing foundation work, the porpoise population remained constant, and two subzones even saw an increase in the population throughout the course of the project.
In 2014, the OFW – together with several companies from the offshore wind energy sector and the German Offshore Wind Energy Foundation – commissioned three research companies and institutes (BioConsult SH, IBL Umweltplanung, and IfAÖ) to study the disruptive effects of pile driving noise on harbor porpoises in the German exclusive economic zone of the North Sea. A number of wind farm operators and developers, who built eight offshore wind farms with a total of 400 foundations in the German Bight between 2009 and 2013 and/or are currently planning wind farms, provided details from studies conducted for the construction of the wind farms. The researchers also looked at porpoise counts for seven other projects being planned at the time.
Details of foundation installations, data from underwater noise measurements, and harbor porpoise population numbers determined via C-POD and aerial surveys served as the basis of the analyses. The results show that while pile driving occurs, the animals tend to avoid the area for a short time, with a clear distance-based gradient. This reaction was observed for all pile driving work with and without noise mitigation starting at 143 decibels (SEL) for a distance of up to 17 kilometers. When taking into account only pile driving with noise mitigation measures, the animals avoided only up to 14 kilometers around the area. Even in near areas with noise levels of more than 155 decibels (SEL), not all of the animals went elsewhere. Instances of porpoises becoming more or less sensitive as a result of increased pile driving in the studied time period were not observed or were observed only to a very small extent.