Shocking. So, it turns out, that directing really loud bursts of sonar at dolphins makes them deaf. Keeping in mind that sonar is how dolphins hear, this is astonishing. That would be the equivalent of loud noises, like explosions or amplified music damaging human hearing. Unthinkable.
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.
What a theory it is! Kudos to these scientists for conceptualizing an experiment in which captive dolphins are subjected to sonar until they become deaf. Don't worry though, it didn't hurt them at all, it just made them freak out and temporarily lose their hearing. I know I would not be concerned if I became deaf for a period.
Marine biologists led by 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.
Fascinating. Again, as I am having a hard time grasping this, directing loud sonar frequency waves at dolphins is detrimental to them. Wow.
On the other hand, a cetacean that sought to escape a persistent loud sonar may not easily find an escape route, said Mooney.
"In the ocean, sound doesn't attenuate in a normal fashion. Sound can sometimes get trapped at the surface, in layers called thermoclines, at the top 325 feet or so.
"Maybe in those conditions it's more difficult to get away from the sound to a quieter area."
Yeah, maybe.
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