This speed can be altered depending on the salinity, temperature and depth of the water. Early marine scientists were not aware of this property of water and originally the ocean was considered a vast and silent realm. However, when the first hydrophone was dropped in the water, they realized the level of ambient noise underwater was incredible. As water is such an efficient transmitter of sound, many marine animals have adapted to use sound as a tool. Humans create underwater sound mostly through boat traffic, especially the large shipping freighters.
Humans create sounds by expelling lots of air over our vocal cords.
Aquatic animals do not have the luxury of wasting so much oxygen. Therefore, animals in the marine environment have developed a way to create amazing repertoires of sounds with minimal use of air. Shrimp and other crustaceans create sound through cavitation. There are thought to be over 280 species of fish that make sounds. They do so by vibrating the air in their swim bladders.