Natural Environment Blog

Dolphins can be deafened by loud noises, which can lead to death.

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.

I’ve been reading a little about ‘acoustic smog’ and its affect on marine life within our oceans.

Acoustic smog is basically another way of saying ‘noise pollution’. In particular, it is a term often used to describe the noise in our oceans that come from man-made sources. This typically includes sources such as:

The Impact of Acoustic Smog on Nature

It seems that acoustic smog could be having a devastating affect on the whales, dolpins, and other mammals in our oceans. Sound plays an important part in the survival of the 80 or so cetacean species, which includes whales, dolpins and porpoises.

Because these animals use acoustic signals for orientation, reproduction, and even feeding, the introduction of man-made noises over the last hundred years or so appears to be impacting on the cetaceans’ ability to do these things. There’s also widespread concern that acoustic smog is directly contributing to the death of many cetaceans. 

It is thought that the affects of acoustic smog on cestaceans include:

• displacement
• avoidance reactions
• collisions with ships
• mass stranding
• hearing damage
• death

Furthermore, evidence strongly suggests that man-made noise often causes lesions in acoustic organs of cestaceans, which are severe enough to cause death. 

Further Research

Unfortunately, there isn’t enough scientific knowledge to be able to come to strong conclusions on understanding the relationships of frequencies, intensities, and duration of exposures in producing damage. More research needs to be done in this area, and many research bodies are appealing for assistance in this area.

Sons de Mar, for example, say this about their continued efforts in this area:

Academic research generally depends on external funding through public channels and commercial companies. Since the effects of noise pollution on the marine environment have not yet been completely implemented in national programs, funding through these sources is limited.

And:

Therefore, we appeal to private sources to guarantee the continuity of this research. ‘Sons de Mar’ (Sounds of the Sea) was created as a public interface aimed at involving society through donations that will allow to collaborate with all the aspects of the scientific work.

The impact of dangerous sonor on marine life is not a new concern. The Cetacean Society International (CSI) website provides articles on this subject dating as far back as 1995. 

Also, the Natural Resources Defense Council (NRDC) first wrote a report on this subject in 1999. The report has since been updated and is called Sounding the Depths II: The Rising Toll of Sonar, Shipping and Industrial Ocean Noise on Marine Life. The online report includes an acompanying movie, narrated by Pierce Brosnan.