04-07-2009, 11:50 PM
PARIS - VERY loud, repeated blasts of sonar can cause a dolphin to temporarily lose its hearing, according to an investigation into a suspected link between naval operations and cetacean strandings.
Numerous beachings of whales, dolphins and porpoises have occurred over the past decade, prompting a finger of blame to be pointed at warship exercises.
A theory is that the mammals' hearing becomes damaged by the powerful mid-frequency sonar used by submarines and surface vessels, prompting the creatures, which themselves use sound for navigation, to become disoriented.
A paper published in the British journal Biology Letters on Wednesday provides the first lab-scale investigation into this idea, although its authors stress it does not provide proof that warship sonar is to blame.
Marine biologists led by Dr Aran Mooney at the University of Hawaii exposed a captive-born, trained Atlantic bottlenose dolphin to progressively louder pings of mid-frequency sonar.
The experiment took place in open water pens at the Hawaii Institute of Marine Biology and in the presence of the dolphin's trainer. The scientists fitted a harmless suction cup to the dolphin's head, with a sensor attached that monitored the animal's brainwaves.
When the pings reached 203 decibels and were repeated, the neurological data showed the mammal had become deaf, for its brain no longer responded to sound.
The deafness, though, was only temporary and the dolphin was not hurt in the experiment, said Mooney.
The hearing was typically restored after 20 minutes, and its loss only occurred after the dolphin was exposed to five rounds of noise. Each round comprised a block of three pings, with 24 seconds between each block.
Other sensors showed that the dolphin's breathing rose significantly when the sonar was turned on. -- AFP
Further work needed
'We definitely showed that there are physiological and some behavioural effects , but to extrapolate that into the wild, we don't really know,' Dr Mooney said in an interview with AFP.
'The sound levels that we used were essentially the equivalent of if an animal is about 40 metres (yards) from the sonar source.'
... more
http://www.straitstimes.com/Breaking%2BN...60937.html
Numerous beachings of whales, dolphins and porpoises have occurred over the past decade, prompting a finger of blame to be pointed at warship exercises.
A theory is that the mammals' hearing becomes damaged by the powerful mid-frequency sonar used by submarines and surface vessels, prompting the creatures, which themselves use sound for navigation, to become disoriented.
A paper published in the British journal Biology Letters on Wednesday provides the first lab-scale investigation into this idea, although its authors stress it does not provide proof that warship sonar is to blame.
Marine biologists led by Dr Aran Mooney at the University of Hawaii exposed a captive-born, trained Atlantic bottlenose dolphin to progressively louder pings of mid-frequency sonar.
The experiment took place in open water pens at the Hawaii Institute of Marine Biology and in the presence of the dolphin's trainer. The scientists fitted a harmless suction cup to the dolphin's head, with a sensor attached that monitored the animal's brainwaves.
When the pings reached 203 decibels and were repeated, the neurological data showed the mammal had become deaf, for its brain no longer responded to sound.
The deafness, though, was only temporary and the dolphin was not hurt in the experiment, said Mooney.
The hearing was typically restored after 20 minutes, and its loss only occurred after the dolphin was exposed to five rounds of noise. Each round comprised a block of three pings, with 24 seconds between each block.
Other sensors showed that the dolphin's breathing rose significantly when the sonar was turned on. -- AFP
Further work needed
'We definitely showed that there are physiological and some behavioural effects , but to extrapolate that into the wild, we don't really know,' Dr Mooney said in an interview with AFP.
'The sound levels that we used were essentially the equivalent of if an animal is about 40 metres (yards) from the sonar source.'
... more
http://www.straitstimes.com/Breaking%2BN...60937.html