PNNL says whales, dolphins may hear sonar sounds

MATT BENOIT MURROW NEWS SERVICEApril 26, 2014 

RICHLAND -- Killer whales and other marine mammals may be hearing sonar signals originally thought to be outside their hearing capacities, according to a newly published report by Pacific Northwest National Laboratory in Richland.

The report was published this month by the Public Library of Science's PLOS-ONE website, a compendium of peer-reviewed scientific papers.

The study, to which marine mammal expert Brandon Southall also contributed, consisted of measuring the frequencies of three commercially available 200 kHz sonar devices to figure out whether marine mammals could still hear sounds at weaker frequencies.

Daniel Deng, a PNNL engineer and one of the study's authors, explained that commercially available sonar equipment operates at a frequency originally thought to be outside the hearing range of marine mammals.

It was thought that sonars operating beyond a frequency of 150 kHz would not affect marine mammals, he said.

The study, however, found otherwise, as all three sonar units generated secondary sounds between 90 and 130 kHz, within the hearing ranges of marine mammals including killer whales, beluga whales, Atlantic bottlenose dolphins, and others.

"Even though they're small (frequencies), some marine mammals can still hear (them)," Deng said.

Deng said the secondary frequencies were not close to a threshold that would injure the mammals, but did have the potential to affect behavioral changes in some of the more sensitive species.

The hope, Deng added, is that the study can help provide scientific evidence for regulatory agencies to use regarding the environmental impact analysis of sonar use.

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