As the previous pages have shown, underwater sound allows marine animals to gather information and communicate at great distances and from all directions. The speed of sound determines the delay between when a sound is made and when it is heard. The speed of underwater sound is five times faster than sounds traveling in air. Sound travels much further underwater than in air. Thus marine animals can perceive sound coming from much further distances than terrestrial animals. Because the sound travels faster, they also receive the sounds after much shorter delays (for the same distance). It is no surprise that marine mammals have evolved many different uses for sounds.

Marine animals rely on sound to acoustically sense their surroundings, communicate, locate food, and protect themselves underwater. Marine mammals, such as whales, use sound to identify objects such as food, obstacles, and other whales. By emitting clicks, or short pulses of sound, marine mammals can listen for echoes and detect prey items, or navigate around objects. This animal sense functions just like the sonar systems on navy ships. It is clear that producing and hearing sound is vital to marine mammal survival.

Sound is very important to marine mammals, such as this bottlenose dolphin. Dolphins use sound to detect and identify objects the size of a golf ball at a distance of 100 meters (more that the length of a football field). Photo ©Tom Kieckhefer

Sound is also important to fishes. They produce various sounds, including grunts, croaks, clicks, and snaps, that are used to attract mates as well as ward off predators. For the toadfish, sound production is very important in courtship rituals. Sound is produced by the male toadfish to attract the female for mating and is especially important in the murky waters that toadfish inhabit where sight is limited. Marine invertebrates also rely on sound for mating and protection. Little research has been done on marine invertebrates that produce sounds, but for those that do, like shrimp and lobsters, sound is very important for survival against predators.

Sound is important to fish, such as this rock hind, for mating, feeding and survival. Photo courtesy of ©Peter Wirtz, biomar@dragoeiro.uma.pt, http://www.medslugs.de/E/Photographers/Peter_Wirtz.htm#photos

As you can see, sound is very important to its underwater inhabitants. Most marine animals rely on sound for survival and depend on their unique adaptations that enable them to communicate, locate food, and protect themselves underwater.