Powerful Sonar Causes Deafness In Dolphins

Hugh Pickens writes "Mass strandings of dolphins and whales could be caused because the animals are rendered temporarily deaf by military sonar, experiments have shown. Tests on a captive dolphin have demonstrated that hearing can be lost for up to 40 minutes on exposure to sonar and may explain several strandings of dolphins and whales in the past decade. Most strandings are still thought to be natural events, but the tests strengthen fears that exercises by naval vessels equipped with sonar are responsible for at least some of them. For example, in the Bahamas in March, 2000, 16 Cuvier's beaked whales and Blainville's beaked whales and a spotted dolphin beached during a US navy exercise in which sonar was used intensively for 16 hours (PDF). 'The big question is what causes them to strand,' says Dr. Aran Mooney, of the University of Hawaii. 'What we are looking at are animals whose primary sense is hearing, like ours is seeing. Their ears are the most sensitive organ they have.' In the experiment, scientists fitted a harmless suction cup to the dolphin's head, with a sensor attached that monitored the animal's brainwaves, and 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. 'We definitely showed that there are physiological and some behavioral effects [from repeated, loud sonar], but to extrapolate that into the wild, we don't really know,' said Mooney."

Comments

203 decibels?

[TheLink]

Wow. I think if you expose me to a 203 decibel sonar, it's not just my ears that would go poof.

Re:203 decibels?

[Shakrai]

Couldn't the sonar be replaced by something less damaging? I guess water muffles radio waves, so a water radar is not a good idea. Maybe a very low frequency radar?

The problem with that theory is that you'd need such a low frequency that your wavelength would be hundreds to thousands of miles. The antenna requirements alone would make such a system impractical on a mobile basis. Some of the antennas used for ELF submarine communications systems were up to 20 miles long.

Unless you can change the laws of physics I'm afraid we'll be stuck using sonar for the foreseeable feature. If you accept that then you have to accept the fact that the Navy needs to practice with it before they need it in an actual shooting war. Sucks that it apparently harms marine life but what can you do?

Re:203 decibels?

[Macthorpe]

Sucks that it apparently harms marine life but what can you do?

Stop human beings from killing each other over nothing, obviating the need for submarines and therefore sonar?

I like to start small and work up.

Re:203 decibels?

[Shakrai]

Stop human beings from killing each other over nothing, obviating the need for submarines and therefore sonar?

Good luck with that.

Experiments like these...

[fprintf]

Experiments like these are like putting people next to a jet engine to see if their hearing gets damaged. I am no PETA freak, but putting 200+ decibels is bound to do permanent damage. I know they said it is temporary, but that might be like my "temporary" hearing loss from the Boston show a few months back. Yes, I could hear fine afterward* but I wonder what incremental loss I might have had from all that loudness.

*I have higher pitch loss that apparently came from shooting a lot many years ago without hearing protection.

Re:Experiments like these...

[radtea]

I am no PETA freak, but putting 200+ decibels is bound to do permanent damage.

The document linked on the Bahamas stranding says that source levels were 223 - 235 dB and levels were less than 180 dB at 300 m horizontally and 200 m vertically, so unless the dolphins were EXTREMELY close to the ships when the sonar was turned on the odds of even temporary deafness due to the use of sonar in the wild are quite low. Remember: a 40 dB difference in signal is a factor of 10,000 in amplitude of the pressure wave, so unless the dolphins were within a few meters of the source they would be very unlikely to get anything close to 200 dB.

This is a bit like dropping a 10 kg mass on a person and noticing it causes serious damage, and then arguing that you can say something about the effects of dropping 0.001 kg masses on people based on the 10 kg data.

That's not to say that it isn't plausible that dolphin sonar can be screwed up by powerful sonar, but this experiment just doesn't seem relevant to the question.

Re:Experiments like these...

[INeededALogin]

The document linked on the Bahamas stranding says that source levels were 223 - 235 dB and levels were less than 180 dB at 300 m horizontally and 200 m

180 db is still extremely strong. Now, compound that with the fact that the Submarines are moving, pinging and that Dolphins are curious anmials and like to follow ships... and I think you will find that the chances for Dolphins being near one of these ships greatly increased.

Also, I understand the need to defend the human race, military and blowing stuff up, but ask any blind person how much noise pollution hurts and then comment again.

Re:Experiments like these...

[Kamokazi]

I think you're both essentially right.

If the dolphins were further away, the sonar would be far less damaging, but it could still interefere with their navigation.

It's also very possible that the dolphins were following the ships and exposed to deafening decibel ranges.

This study (like most studies) is just a stepping stone to narrow down criteria/goals for other studies...we need to A) Determine the effect of lesser decibel levels and B) Gather real observational data on how often dolphins and other marine life venture very near to naval vessels.

Ultimately results of these studies should just regulate situations on when active sonar is used, where you can train with it, etc, because active sonar is necessary until something better is developed. Despite the very slim chances of nuclear war, as tragic as it is, I'm willing to sacrifice a few hundred sea critters (I wold hope it's a much smaller number though) just to know that we can effectively track and destroy nuclear missile subs (as well as the many other uses for sonar). That's just my opinion and you can call me a barbarian for it if you like.

to the "wellduh" taggers

[dAzED1]

My wife is a wildlife conservation researcher, and specifically works with animals in the Delphinidae family (which include dolphins). There's a lot of stuff she, and others, have to - must - verify, even if it seems to be a "wellduh."

The alternative would be that science just thinks correlation = causation. Is that what we want? "Well, Navy ships used sonar, and these whales stranded themselves...must be related. Case closed." Instead, someone did actual science showing that sonar causes real deafness in these animals. And someone wants to harsh that?

I say instead that there should be a tag, "abouttimetheyverified"

Re:Dolphin stranding in ancient Greece

[raddan]

Or maybe the causes of stranding are a many-to-one relation, i.e., that there is more than one cause, and that use of sonar is only one of them. E.g., you find dead birds with broken necks all the time. It is disingenuous to say that windows are the cause of all broken bird necks, and we can point out that people have found dead birds with broken necks even in antiquity. But it is equally disingenuous to say that windows have nothing to do with it.