Effective beam pattern of the Blainville's beaked whale (Mesoplodon densirostris) and implications for passive acoustic monitoring
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The presence of beaked whales in mass-strandings coincident with navy maneuvers has prompted the development of methods to detect these cryptic animals. Blainville's beaked whales, Mesoplodon densirostris, produce distinctive echolocation clicks during long foraging dives making passive acoustic detection a possibility. However, performance of passive acoustic monitoring depends upon the source level, beam pattern, and clicking behavior of the whales. In this study, clicks recorded from Digital acoustic Tags (DTags) attached to four M. densirostris were linked to simultaneous recordings from an 82-hydrophone bottom-mounted array to derive the source level and beam pattern of the clicks, as steps towards estimating their detectability. The mean estimated on-axis apparent source level for the four whales was 201 dB(rms97). The mean 3 dB beamwidth and directivity index, estimated from sequences of clicks directed towards the far-field hydrophones, were 13 degrees and 23 dB, respectively. While searching for prey, Blainville's beaked whales scan their heads horizontally at a mean rate of 3.6 degrees/s over an angular range of some +/-10 degrees. Thus, while the DI indicates a narrow beam, the area of ensonification over a complete foraging dive is large given the combined effects of body and head movements associated with foraging. [http://dx.doi.org/10.1121/1.4776177]
Shaffer , J W , Moretti , D , Jarvis , S , Tyack , P & Johnson , M 2013 , ' Effective beam pattern of the Blainville's beaked whale (Mesoplodon densirostris) and implications for passive acoustic monitoring ' Journal of the Acoustical Society of America , vol 133 , no. 3 , pp. 1770-1784 . DOI: 10.1121/1.4776177
Journal of the Acoustical Society of America
Copyright 2013. Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America. The following article appeared as Effective beam pattern of the Blainville's beaked whale (Mesoplodon densirostris) and implications for passive acoustic monitoring Shaffer, J. W., Moretti, D., Jarvis, S., Tyack, P. & Johnson, M. Mar 2013 In : Journal of the Acoustical Society of America. 133, 3, p. 1770-1784 and may be found at http://scitation.aip.org/content/asa/journal/jasa/133/3/10.1121/1.4776177
This work was funded by two partners under the National Oceanographic Partnership Program: the Ocean Acoustics Program of the U.S. National Marine Fisheries Service, Office of Protected Resources, and the International Association of Oil and Gas Producers Joint Industry Programme on Exploration and Production Sound and Marine Life. Research permits were issued to John Boreman (US NMFS 1121-1900), Peter Tyack (US NMFS 981-1578), and Ian Boyd (Bahamas permit #02/07). M.J. and P.T. are supported by the Marine Alliance for Science and Technology Scotland.
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