Naval sonar resembles killer whales' call
2 October 2008
Mass strandings of whales and dolphins may be down to the similarity between navy sonar and the sounds killer whales make.
Killer whales use a particular call when hunting. Navy sonar transmits at a similar frequency.
The sounds killer whales use to communicate when they are hunting prey has a similar frequency to the sonar emitted by navy warships. This could be confusing some species of whales making them flee the area in search of safety.
A team of scientists from the Sea Mammal Research Unit and Woods Hole Oceanographic Institution in the United States is on board a research vessel near the Bahamas studying the effects of different marine sounds on deep-diving whales.
'One theory is that these whales confuse the sonars for killer whale calls and have a magnified anti-predator response.'
Professor Ian Boyd
'We have about 30 scientists here carrying out experiments to determine the response to deep-diving cetaceans, including beaked whales, to the sound of naval anti-submarine sonars,' says Professor Ian Boyd, director of the Sea Mammal Research Unit, from the research ship Roger Revelle.
More than 21 dolphins became stranded on the banks of the Percuil river in Cornwall in June 2008.
Mass strandings of whales and dolphins were first reported in the 1960s. The navy was the prime suspect as it had recently started using sonar in its training exercises. And it seems other types of ships that use sonar haven't been linked to whale or dolphin strandings.
Boyd added, 'One theory is that these whales confuse the sonars for killer whale calls and have a magnified anti-predator response that ends up with them becoming stranded.' The navy sonar is very loud.
Scientists are researching the effects of sounds on the deep-diving Blainville whale.
Last year, the research team tagged a shy Blainville's whale to investigate its feeding patterns, movements and sonar pulses. When the researchers played a recording of sounds made by a pod of killer whales, the animal stopped emitting sonar and surfaced immediately, before swiftly leaving the area.
When the researchers repeated the experiment using navy sonar instead of killer whale sounds, the whale behaved in a similar way.
Navy sonar is in a similar frequency range to the range used by killer whales, but civilian ships and fishing vessels use a higher range, which could explain why only navy sonar is linked to strandings.
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