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

That sucks for them

[Em Emalb]

Guess dolphins and whales can't go to concerts. Although, I hear The Pingers have quite the underwater following.

In other news, when exposed to brilliant flashes of light, humans are rendered temporarily blind.

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...

[Anonymous Coward]

Unfortunately, neither you nor I can assess what "203 decibels" means. That is because that is a meaningless phrase. Here is the information that the AFP left out:

• Where was the 203 dB measured? Was it measured at a reference range relative to the transducer, as is common practice, or was it measured at the dolphin? This implies to me that they produced a sound equivalent to 203 dB as heard at a 40 m range, but I am just guessing.

  The difference between the reference range measurement and the receiver measurement, assuming spherical spreading (which we're likely to see at a 40m range), is 20 log r, where R is the ratio of the reference range and the receiver range. If the dolphin is 100 m away from a source emitting 203 dB at a 1 yard reference range, it will be hit with acoustic energy at 163 dB (203 - 20 log 100).

• In what units are they working? Contrary to popular belief, decibels are not a unit, but rather a scale. Saying the dolphins were exposed to 203 dB is equivalent to saying they were exposed to 2 x 10^8. 2 x 10^8 whats? Watts? Micropascals? 20 Micropascals?

  By the way, the sound pressure levels you're accustomed to reading about as an land-lubber are probably dB//20 uPa -- i.e., measured in multiples of 20 micropascals. In underwater acoustics we almost always use dB//1 uPa -- i.e., measured in multiples of 1 micropascal. To convert from the in-air numbers to under-water numbers, add 26 dB. A 203 dB sound to an underwater physicist would be a 179 dB to an atmospheric physicist.

Unfortunately I cannot find this article on the Biology Letters web site to check the facts.

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:Disarmament

[initdeep]

you do realize that 99%+ of the time, these terrible nuclear submarines don't even use ANY form of sonar other than underwater microphones don't you?
To a similar (though not as high degree) neither do surface ships.

I didnt think so.

yet another example of a slashtard talking out of their ass with absolutely NO idea what they are talking about.

And yes, I did happen to serve on one of these terrible nuclear submarines.

and in the case of missle subs, it's probably closer to three nines or more.

ssbn subs are holes in the water that strive to make absolutely no noise.

you can hear the original sound wave a lot further off than you can hear the return echo which is always weaker.

and that's before you even throw in the effect of temperature gradients and convergence zones.

another thing to ponder is what was the frequency used?
and does this matter.

the reason i say this is that MOST sonar is low frequency or extremely low frequency, with the exception being high frequency sonar used to search for underwater mines and to penetrate ice fields.

of course, why mention these type things as they will just muddy the waters and potentially invalidate the test.........

(I said potentially, not that they do, i have no idea and based on the report, neither does anyone else)

Not all decibels are the same!

[Reverberant]

WRT to all of the "203 decibels, OMG!" comments: water decibels aren't the same as SPL decibels.

A decibel is the logarithmic relationship between one quantity and a reference quantity. For sound pressure level, we use the RMS pressure of the sound wave compared to a reference pressure that represents the threshold of human hearing (20 microPa): 20*Log10(P/20e-6)

Other types of decibels use different reference quantities. For example, vibration velocity in the USA uses a reference quantify of 10^-6 in/sec. Sound intensity (sound power through a unit area) uses a reference quantity of 10^-12 W/m2. So comparing sad sound intensity decibels to vibration velocity decibels is meaningless without normalizing the units.

In the case of water decibels, we use pressure as we do for SPL in air, but the reference quantity is different: for water, the reference quantity is typically 1 microPa. Therefore the 203 dB in water is approximately equivalent to about 170 dB SPL in air. Of course you still can't directly compare water dB to SPL because the wavelengths of sound in water are so much longer than wavelengths of sound in air.

In any event, 203 dB in water is very loud (and obviously harmful to aquatic life as demonstrated in the articles), but not necessarily in the same way that 173 dB SPL is loud/harmful to us.

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?

[cthulu_mt]

Now that we possess the ultimate weapon dolphins won't dare to challenge our control of the planet.

Re:203 decibels?

[oldspewey]

Exactly. It's generally about confusion over things like how our oil got under their sand.