Pile driving at offshore wind farms in the German North Sea has not had a negative impact on porpoises, according to a new report by consultancy BioConsult.

The report, which was commissioned by the German Offshore Wind Energy Forum, said that most animals avoid areas by up to 17km in diameter where pile driving is taking place and noise levels reach 143 decibels (dB).

But, it added, that not all porpoises leave the affected areas, even at noise levels of 155dB or more.

“Compared to a baseline period 25–48 h[ours] before piling, porpoise detections declined by over 90% at noise levels above 170dB, but only by about 25% at noise levels between 145 and 15 dB,” the authors found.

“Below 145dB, this decline was smaller than 20% and may thus not clearly be related to noise emitted by the piling process,” they said.

The report also found that the porpoise population remained constant, despite growing pile driving activities, and was even growing in some areas.

Developers that had built eight wind farms with 400 foundations in the German Bight between 2009 and 2013 contributed porpoise census data for the report, together with further information from seven other projects that are under development.

BioConsult combined data from passive acoustic monitoring that used porpoise detectors and from aerial surveys with data on noise levels and other piling characteristics.

Nine offshore wind farm developers, TSO TenneT and Germany’s Offshore Wind Foundation funded the report.

Image: Wikimedia Commons/Erik Christensen