Sound in water

Prof John Montgomery, the head of Auckland University Leigh Marine Laboratory, explains how sound travels in water and how this is different to how sound travels in air. He explains why sound can travel so much further in the ocean compared to on land.

Point of interest: In this clip. you’ll hear the ‘song’ of the humpback whale. The humpback whale song is known to travel large distances through the ocean.

Transcript

PROF JOHN MONTGOMERY
Sound in the marine environment hasn’t been that well studied, but we know, I guess, from our original work where the question was, we know that fish can detect reefs, but how do they detect it? And our hypothesis was that it was based on sound. So we went and tested that, and found that larval fish do orient towards reef sounds, so we could record reef sound on a reef, take it out into a place where there wasn’t a reef and it would show up thinking there was a reef there. So that gives a really good indication of the likely importance of the soundscape, that it may be an important cue for animals in terms of migrations to reefs.

One of the real advantages of sound from a biological point of view is that there is a lot of it there and that it travels really well. So it can give you information about things that are happening from long distances away, and clearly that’s important for all sorts of biological activity.

The main difference between sound in air and sound in water is that air is a far less dense medium, so it doesn’t take much to move air, but sound attenuates reasonably quickly with distance and air, whereas under water, you need a sound that’s intense enough to move the water, which is quite dense and heavy, but it’s not very compressible so the sound then will propagate long distances.

In water, marine creatures can hear sound from vast distances and the extreme is probably the song of the humpback whale. and that sound can travel across whole oceans. so you could get, potentially, humpbacks at one end of the Pacific listening to humpbacks at the other.

Acknowledgement:
Canadian Broadcasting Corporation
Andrew Stevenson http://www.youtube.com/watch?v=eOS20plm7UM