Many marine mammals rely on their hearing almost as much as humans rely on vision to navigate through their environment and to find food. In a manner similar to bats, some whales and dolphins use what scientists call echolocation to learn about the size, shape, and distance of objects around them that they are unable to see. They do this by emitting high-frequency clicks and whistles and then listening for those sounds to echo, or bounce off the objects. To a whale or dolphin, vocalizations bouncing off of structures on the ocean floor sound much different from those bouncing off of a school of fish or squid. Many species possess such highly attuned echolocation abilities that they are able to find and catch prey in complete darkness.

Unfortunately, as tranquil as our oceans may appear in underwater documentaries, they are becoming increasingly polluted with human-made noise -- from freighters in crowded shipping lanes, underwater drilling and explosions, and sonar devices used by the military -- and this noise may be negatively impacting many species of whales and dolphins. Some believe that whale strandings, or beachings, may be related to ear damage or confusion caused by underwater noise. Many scientists are working to better understand both how and what whales hear in an effort to minimize the impact of human activity on these important creatures.