This feature has been investigated by some manufacturers, but the triggering system has encountered problems (Iwama et al, l998). Sound transmission along the acoustic axis of the transducer will be spherical until the bottom or water surface cause reflections. As a result, there ... M. (l996) Effects of underwater sounds on escape behaviour of Stellar sea lion. ... Canada, http://www.eao.gov. bc.ca/ PROJECT/AQUACULT/SALMON/Report/final/vol3/ vol3 e.htm Last updated l998/07/20.