Thursday, May 15, 2014

Whales hear us more than we realize

By Tom Rickey via Pacific Northwest National Laboratory, 1 May 2014


A sperm whale off the coast of southern California. credit A. Friedlaender.

Killer whales and other marine mammals likely hear sonar signals more than we've known.

That's because commercially available sonar systems, which are designed to create signals beyond the range of hearing of such animals, also emit signals known to be within their hearing range, scientists have discovered.

The sound is likely very soft and audible only when the animals are within a few hundred meters of the source, say the authors of a new study. The signals would not cause any actual tissue damage, but it's possible that they affect the behavior of some marine mammals, which rely heavily on sound to communicate, navigate, and find food.

The findings come from a team of researchers at the Department of Energy's Pacific Northwest National Laboratory, working together with marine mammal expert Brandon Southall of Southall Environmental Associates. The findings were published April 15 in the journal PLOS ONE.

A team led by Zhiqun (Daniel) Deng, a chief scientist at PNNL, evaluated the signals from three commercially available sonar systems designed to transmit signals at 200 kilohertz. The impact of such systems on marine mammals is not typically analyzed because signals at 200 kilohertz can't be heard by the animals.

The team found that while most of the energy is transmitted near the intended frequency of 200 kilohertz, some of the sound leaks out to lower frequencies within the hearing range of killer whales and other animals such as harbor porpoises, dolphins and beluga whales. The three systems studied produced signals as low as 90, 105 and 130 kilohertz.

Continue to the full article,
http://www.pnnl.gov/news/release.aspx?id=1053

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