A new study has found that loud sonar can cause deafness in dolphins.
The study found that loud, repeated blasts of sonar caused dolphins to temporarily lose their hearing for 20 to 40 minutes.
Published in the British journal Biology Letters on Wednesday, the findings could provide further evidence that human made noises can be attributed to dolphin and whale deaths.
The study, led by Aran Mooney Marine Biologist at the University of Hawaii, exposed an Atlantic bottlenose dolphin to progressively louder pings of mid-frequency sonar. The dolphin was born in captivity and was trained.
A suction cup was fitted to the dolphin’s head, with a sensor attached that monitored the animal’s brainwaves.
“What we found was if you play sound you can cause temporary hearing loss. The sounds have to be surprisingly loud and they have to be repeated over an extended period of time – two to three minutes.” Mooney said. “In that time you would expect them to swim away as fast as possible. They have to be within 40 metres of a ship, but when you have certain oceanographic conditions it’s hard for the animals to get out of the way.”
Many people believe that human made noises, also referred to as acoustic smog, has been the cause of whale and dolphin beachings around the world.
Mooney acknowledges that, given the study was undertaken in a lab with a captive-born dolphin, it does not provide proof that military sonar is to blame for mass strandings.
“We definitely showed that there are physiological and some behavioural effects [from repeated, loud sonar], but to extrapolate that into the wild, we don’t really know,” Mooney told AFP.