Underwater noise measured at the Wavestar wave energy device has shown that the device is barely audible to marine mammals during operation.
Concerns have been raised as to the impacts of operating marine renewable devices on marine mammals – with collision risks and noise being the most important topics.
The Wavestar wave energy device was created by Wavestar Energy. It is a point absorber device that works by using large floats that rise and fall with the motion of waves. The movements of the floats is transferred by hydraulics to rotate a generator and produce electricity. The advantage of this device over other wave energy converter devices is that the hydraulics and generator are above water level and so less underwater noise should be produced. This was tested by Jakob Tougaard (Aarhus University) and the results are presented in his new publication “Underwater noise from a wave energy converter is unlikely to affect marine mammals“.
The device tested was a full-scale converter with 2 floats. Underwater noise was measured 25m from the device while it was operating at almost maximum power. The results show that the median broad band SPL did not change between times when the device was operating vs not operating. The highest SLP was a 150Hz signal when the device was stopping or starting. This was the sound of the hydraulic pump that lifts and lowers the floats at the start/end of operations. Overall, the noise produced by the device was barely detectable above ambient noise at the recorded distance of 25m and Tougaard concludes that the device would barely be audible to harbour seals and likely not audible at all to harbour porpoise. It is noted that these results are only from a device using 2 floats, and that a full scale 20 float offshore device may produce higher noise levels, though it is still expected that it would be inaudible to harbour porpoise.