OFFSHORE WIND FARM IMPACTS Hearing thresholds of a harbor porpoise (Phocoena phocoena) for playbacks of seal scarer signals, and effects of the signals on behavior Ronald A. Kastelein • Lean Hoek • Robin Gransier • Christ A. F. de Jong • John M. Terhune • Nancy Jennings Received: 3 March 2014 / Revised: 18 July 2014 / Accepted: 6 September 2014 Ó Springer International Publishing Switzerland 2014 Abstract Acoustic Mitigation Devices (AMDs) are used to deter marine mammals from construction sites, in order to prevent hearing injury by offshore pile driving noise. To estimate the distance at which two AMDs designed as ‘seal scarers’ (Ace Aquatec and Lofitech) are detected by harbor porpoises, the 50% hearing detection thresholds for playbacks of recordings of the AMD sounds were assessed. Both became audible at a received broadband sound pressure level (SPL) of 55 dB re 1 lPa. The effect of the AMDs on porpoise behavior was quantified at three SPLs determined during a pre-test: one which just did not cause a behavioral change, one which caused a small change in surfacing and swimming pattern, and one which caused the harbor porpoise to swim away from the transducers. The corresponding mean received SPLs in the pool were respectively: Ace Aquatec: 77, 117, and 139 dB re 1 lPa; and: Lofitech: 91, 121, and 151 dB re 1 lPa. As the mean received SPL increased, greater displacement occurred, and higher numbers of surfacings and increased swimming speed occurred in test periods than in associated baseline periods. By combining these results with the source level, the current local propagation conditions and the back- ground noise, the deterring distance at sea for the AMDs can be calculated. Keywords Acoustics Á Behavior Á Odontocete Á Pile driving Á Seal scarer Á Offshore wind park Introduction Offshore pile driving produces loud underwater impulsive sounds, which may disturb and cause injury to marine mammals (Southall et al., 2007). Negative effects on the hearing of marine mammals can be reduced or avoided if animals are deterred from Guest editors: Steven Degraer, Jennifer Dannheim, Andrew B. Gill, Han Lindeboom & Dan Wilhelmsson / Environmental impacts of offshore wind farms R. A. Kastelein (&) Á L. Hoek Á R. Gransier Sea Mammal Research Company (SEAMARCO), Julianalaan 46, 3843 CC Harderwijk, The Netherlands e-mail: researchteam@zonnet.nl Present Address: R. Gransier KU Leuven, Department of Neurosciences, ExpORL, Herestraat 49 bus 721, B-3000 Leuven, Belgium C. A. F. de Jong TNO, Acoustics and Sonar, Oude Waalsdorperweg 63, 2597 AK, Den Haag, The Netherlands J. M. Terhune Department of Biology, The University of New Brunswick, P.O. Box 5050, Saint John, NB E2L 4L5, Canada N. Jennings Dotmoth, 1 Mendip Villas, Crabtree Lane, Dundry, Bristol BS41 8LN, UK e-mail: nancy@dotmoth.co.uk 123 Hydrobiologia DOI 10.1007/s10750-014-2035-x