Jakob Tougaard. 2021. Thresholds for behavioural responses to noise in marine mammals. Background note to revision of guidelines from the Danish Energy. Aarhus University, DCE – Danish Centre for Environment and Energy, 32 pp. Technical Report No. 225 http://dce2.au.dk/pub/TR225.pdf
The available scientific literature on behavioural reactions to pile driving noise by Danish species of marine mammals was reviewed. The relevant species groups were phocid seals (harbour seal and grey seal), harbour porpoises, dolphins (whitebeaked dolphin) and mysticete whales (minke whale).
Only for harbour porpoises was the empirical evidence sufficient to provide guidance on a generalized threshold for behavioural reactions (avoidance) to noise from pile driving of wind turbine monopile foundations. The reviewed results came both from field studies of reactions of wild porpoises to full-scale pile driving and studies in captivity involving playback of pile driving noise at greatly reduced levels. When received sound pressure levels at the onset of behavioural reactions were weighted with the auditory frequency weighting function appropriate for porpoises, the results were consistent across studies. Based on these results a generalized threshold for onset of behavioural reactions in porpoises for pile driving noise is suggested to be 103 dB re. 1 µPa, VHF-weighted and calculated as a root-mean-squared level over 125 ms.
Only two relevant studies were available for phocid seals, one for grey seals and another for harbour seals. Both were field studies on wild seals tagged with satellite transmitters and conducted during a period where offshore wind farm pile driving was undergoing. The lowest sound pressure levels where reactions to the sound was observed was 120 dB re. 1 µPa and 138 dB re. 1µPa, for grey seals and harbour seals, respectively, and both weighted with the appropriate phocid seal auditory weighting function. The limited data does not allow more precise guidance on a generalized threshold for avoidance in seals.
Insufficient data is available for dolphins and mysticete whales and no specific guidance on thresholds for behavioural reactions to pile driving noise could be provided.
