Transmission loss patterns from acoustic harassment and deterrent devices do not always follow geometrical spreading predictions
Shapiro, Ari D.
Jorgensen, Poul Boel
Kyhn, Line A.
Balle, Jeppe Dalgaard
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KeywordAcoustic harassment device (AHD); Acoustic deterrent device (ADD); Non-geometrical acoustic spreading; Sound exposure level; Multi-path interference; Marine mammal-fisheries interactions; By-catch
Acoustic harassment and deterrent devices have become increasingly popular mitigation tools for negotiating the impacts of marine mammals on fisheries. The rationale for their variable effectiveness remains unexplained but high variability in the surrounding acoustic field may be relevant. In the present study, the sound fields of one acoustic harassment device and three acoustic deterrent devices were measured at three study sites along the Scandinavian coast. Superimposed onto an overall trend of decreasing sound exposure levels with increasing range were large local variations in sound level for all sources in each of the environments. This variability was likely caused by source directionality, inter-ping source level variation and multi-path interference. Rapid and unpredictable variations in the sound level as a function of range deviated from expectations derived from spherical and cylindrical spreading models and conflicted with the classic concept of concentric zones of increasing disturbance with decreasing range. Under such conditions, animals may encounter difficulties when trying to determine the direction to and location of a sound source, which may complicate or jeopardize avoidance responses.
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Marine Mammal Science 25 (2009): 53-67, doi:10.1111/j.1748-7692.2008.00243.x.
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