MARMAM, On behalf of my co-authors, I would like to let you know about a new paper on the audibility of high frequency sonar systems to some marine mammals. We investigated the acoustic "leakage" of energy into side lobes from the 200 kHz center frequency of three commercially-available sonar systems. These active sonar systems were being used in efforts to detect and track marine mammals around a tidal power turbine site and they were not expected to be audible to the animals based on their very high frequency. However, behavioral observations of killer whales suggested they were in fact detecting them. Our acoustic analysis of the systems indicates that there is sufficient downward spread of energy in the side bands to expect that these odontocete cetaceans could in fact hear them. We conclude that received levels at animals would very likely be well below those that could be harmful, but that they could be audible and potentially affect behavior over ranges of hundreds of meters. A reference to the paper, weblink to the Open Access manuscript, and the article abstract are given below. The lead author was PNNL engineer Zhiqun (Daniel) Deng and both he and I would appreciate any comments or questions on the paper. Thank you, Brandon Southall Deng ZD, Southall BL, Carlson TJ, Xu J, Martinez JJ, et al. (2014) 200 kHz Commercial Sonar Systems Generate Lower Frequency Side Lobes Audible to Some Marine Mammals. PLoS ONE 9(4): e95315. doi:10.1371/journal.pone.0095315 http://dx.plos.org/10.1371/journal.pone.0095315 <http://dx.plos.org/10.1371/journal.pone.0095315> The spectral properties of pulses transmitted by three commercially available 200 kHz echo sounders were measured to assess the possibility that marine mammals might hear sound energy below the center (carrier) frequency that may be generated by transmitting short rectangular pulses. All three sounders were found to generate sound at frequencies below the center frequency and within the hearing range of some marine mammals, e.g. killer whales, false killer whales, beluga whales, Atlantic bottlenose dolphins, harbor porpoises, and others. The frequencies of these sub-harmonic sounds ranged from 90 to 130 kHz. These sounds were likely detectable by the animals over distances up to several hundred meters but were well below potentially harmful levels. The sounds generated by the sounders could potentially affect the behavior of marine mammals within fairly close proximity to the sources and therefore the exclusion of echo sounders from environmental impact analysis based solely on the center frequency output in relation to the range of marine mammal hearing should be reconsidered. -- Brandon L. Southall, Ph.D. President, Senior Scientist, SEA, Inc. Research Associate, University of California, Santa Cruz 9099 Soquel Drive, Suite 8, Aptos, CA 95003, USA 831.332.8744 (mobile); 831.661.5177 (office); 831.661.5178 (fax) Brandon.Southall@sea-inc.net; www.sea-inc.net http://www.fastpencil.com/publications/4263-Ocean-Journeys-Beginnings