Pile Driving is presently the most common method used to attach wind turbines to the sea bed. To assess the impact of pile driving sounds on harbor porpoises, it is important to know at what distance these sounds can be detected. Using a psychophysical technique, a male porpoise’s hearing thresholds were obtained for series of five pile driving sounds (inter-pulse interval 1.2-1.3 s) recorded at 100 and 800 m from the pile driving site, and played back in a pool. The 50% detection threshold sound exposure levels (SELs) for the first sound of the series (no masking) were 72 (100 m) and 74 (800 m) dB re 1 Pa 2 s. Multiple sounds in succession (series) caused a ~5 dB decrease in hear ing threshold; the mean 50% detection threshold SELs for any sound in the series were 68 (100 m) and 69 (800 m) dB re 1 Pa 2 s. Depending on the actual propagation conditions and background noise levels, the results suggest that pile driving sounds are audible to porpoises at least at tens of kilometers from pile driving sites.
This report was presented at a symposium at Naturalis in Leiden on September 8, 2015. A complete report containing brief abstracts of all studies presented at the symposium can be found here.