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)
[email protected]; www.sea-inc.net
http://www.fastpencil.com/publications/4263-Ocean-Journeys-Beginnings
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