277 A.N. Popper and A. Hawkins (eds.), The Effects of Noise on Aquatic Life, Advances in Experimental Medicine and Biology 730, DOI 10.1007/978-1-4419-7311-5_61, © Springer Science+Business Media, LLC 2012 J. Tougaard () • L.A. Kyhn National Environmental Research Institute, Aarhus University, DK-4000 Roskilde, Denmark e-mail: jat@dmu.dk M. Amundin • D. Wennerberg • C. Bordin Kolmården Djurpark, SE-618 92 Kolmården, Sweden 1 Introduction Pile driving of large steel monopiles in offshore waters has increased rapidly in recent years due to the expanding development of offshore wind energy. In particular, Phocoena phocoena (harbor porpoise) has been the focus of attention with respect to a possible negative impact. Impact pile driving, where a large steel monopile is driven 20-30 m into the seabed, is capable of generating very loud sound pressures, exceeding 230 dB re 1 mPa peak-peak in source levels and detectable at distances of tens of kilometers (Bailey et al. 2010). Such high sound pressures, coupled with the repetitive emission of sounds (1–2 strokes/s) at a high duty cycle (10%) gives the potential for exposing nearby animals to very high and potentially damaging sound exposure levels (Gordon et al. 2009). Besides the potential to inflict acute injury, the pile-driving noise has the potential to affect behavior of marine mammals over an even larger area. 2 Regulation of Pile Driving and Other Loud Sound Sources Focus on the regulation of pile driving has so far been mainly on acute injury, i.e., measures to reduce the risk that marine mammals are exposed to sound levels that could damage their auditory system. Mitigation is primarily in the form of deterrent devices (pingers and seal scarers) deployed before pile driving and soft start (ramp up) of the piling procedure. Deterrent devises and soft start protocols (ideally) allow animals to vacate the zone of injury before the full-power pile driving commences, but they do not reduce the size of the zone of injury nor the size of the zone of behavioral reaction. Thus, even with a carefully designed protocol to protect against injury, there may still be an impact due to behavioral reactions to the sound. Because the zone of behavioral reactions for pile driving could be very large, the number of individuals affected by behavioral reactions is likely to be considerably larger than the number of individuals potentially exposed to injuring sound levels. Behavioral Reactions of Harbor Porpoise to Pile-Driving Noise Jakob Tougaard, Line A. Kyhn, Mats Amundin, Daniel Wennerberg, and Carolina Bordin