Sound Cannons at Sea

http://www.nytimes.com/2009/11/19/world/africa/19pirates.html?hp

What are these “long-range acoustical devices?” Wonder what it does to the sea animals who hear it too. If ship’s propellors are thought to have screwed with whales and seal’s senses, what would a sound cannon do? ‘Course it’s better to rebuff pirates sonically than with bullets. Or cutlasses.