Naked Science Forum
General Science => Question of the Week => Topic started by: thedoc on 17/05/2011 15:56:14
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I have a question that I was hoping that you might be able to address.
It occured to me during a recent visit to Sea World in San Diego California. I was sitting there enjoying the whale show with its whale tricks and loud music and thought that the music was very loud. I wasn't sitting too close to the speakers as to avoid ingesting any more sea water for the day but was still bothered by the volume and can only imagine how unbearable it would have been closer to the speakers, such as in the water where the whales were. My understanding is that noise travels even better in water than air and whales have ears too, so are we tormenting these poor whales subjecting them to all this loud music at these shows?
Thanks, Rob
Asked by Robert Stevens
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We put this question to Mariana Melcon from the Scripps Institution of Oceanography at the University of California in San Diego...
Mariana - As far as I know it hasn’t been studied whether whales are bothered by loud music in Sea World. It’s true actually that the sound propagates better in the water than in the air. However, when the airborne [img float=right]/forum/copies/RTEmagicC_SeaWorldBelieve.JPG.jpg[/img]sounds reach the water, lots of energy is lost. This means that the loud music would not be as loud in the water as it is in the air. Since whales spend much more time underwater than performing aerial displays, I wouldn’t expect them to be as bothered as humans could be. I guess though that people hitting the glass walls and shouting could be somewhat disturbing.
Now their own sounds could also be affecting them because toothed whales produce high intensity sounds. They are reflected from objects and return as echoes. So, the animals analyse these echoes to, for instance, find their prey. Now imagine how loud it can be for them, emitting these sounds which can be approximately as loud as ships, reflecting in the surrounding walls. So summarising, animals may be annoyed by the loud music, but in terms of acoustics, I think that there are other factors that could be affecting them more.
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We received this email from Andrew Crane:
"Hi I'm Andrew and I am a sailor in the royal australian navy where I use sonar to find submarines. We have restrictions on when we can use sonar around whales. Now an important point to make is that humans have a frequency range in their ears of 20Hz to 20kHz. Whales however, depending on the species, have a lower frequency range in their "ears". Now sound being played outside of the water will be mostly be reflected, scattered by the surface and absorbed by the air. There is a small amount that will be refracted into the water. This sound in the water will be attenuated by the water by either spherical absorbsion or cylindrical absorbsion which reduce the power of the sound. If there are speakers under the water this would of course change the equation.
In summary whales will not be deafened because the sound is at too high a frequency and the absobsion (transferring sound energy into heat). I hope this answers the question.
Also sound travels about 1500m/s in sea water (at 20degrees C and 35 parts per thousand salinity)
600m/s in air
5000m/s in metal"