Subject: Do sounds vary with depth?

Lindsay J Porter (h9390327@hkucc.hku.hk)
Sun, 7 Dec 1997 23:16:45 +0800

>do sounds vary with depth?  are whales affected?

Underwater noise levels are determined by both their acoustic ower output
and the sound transmission conditions at the noise source.  That is, a
moderate sound level could have further reaching effects than a very loud
level IF the conditions at source allowed for the effective propogation of
sound.  Many factors, including depth, density, temperature and topography
all effect sound propogation.  Shallow water truncates noise quickly due to
surface and bottom effects - and effectiveness of propogation in deep water
is dependant on the wavelength  of the sound source,i.e., relatively short
wavelengths can generally travel for great distances in deep water.  There
is concern that teh increasing 'noise' within the underwater habitat is
effecting  whales - particularly low frequency noises which can have a far
reaching effect.  The discussions and  theories within this particular field
are diverse.  SOme good texts to read for indepth  discussion on both teh
theory of underwater noise and implications for marine mammals are

Marine Mammals and Noise. 
Richardson, W.J., Greene, C.R., Malme, C.I. and Thomsom, D.H. 1995
London: Academic Press
ISBN 0-12-588440-0

Underwater Noise Pollution and its Significance for Whales and Dolphins
Jonathan Gordon and Anna Moscrop 
pages 281-320 in 
"The Conservation of Whales and Dolphins.  Science and Practice" 
eds Simmonds, M.P.  and Hutchinson, J.D. 
New York: Wiley and Sons
ISBN 0-471-96561-8

Hope this is of help
best wishes

Lindsay
email h9390327@hkucc.hku.hk
Dolphin Research Group
The Swire Institute of Marine Science
The University of Hong Kong
Cape d'Aguilar
Hong Kong
website: http://www.webdivers.co.uk/dolphin/index.html