Echolocation is a sensory system that dolphins and other creatures use for understanding their environment.
Although dolphins have acute vision, their ability to echolocate in the water is essential to their survival.
Prof Joseph Mobley, University of Hawaii – "The great majority of our sensory world is determined by vision, and that's because light enjoys certain advantages when travelling in air, but light does not travel in water very well at all. Sound in fact travels about five times faster in water than it does in air, so marine species and marine mammals in particular have adapted to take advantage of the tremendous range of travel that sound has in water, in the ocean. So I think it's a safe statement to say that they literally do see with sound."
Dolphins create sound by moving air in and out of three pairs of sacs located under their blowholes.
These sounds are focused and emitted through their melon – the fatty rounded section of their forehead.
Dr Adam Pack, Marine Mammal Laboratory, Hawaii – "Dolphins in general make two different types of sounds. The whistles, which can span up to about 20 or 30kHz are continuous frequency or frequency modulated, meaning that they change, in pitch and they are used as social sounds by the dolphins. The other type of sound is used by the dolphins for echolocation, and these are short burst-like pulse sounds, they span in frequencies from a couple of kilohertz all the way up to 120 or 130kHz."
Communication = up to 30 kHz
Echolocation = 2 to 130 kHz
The sound waves travel through the water and are reflected back when they hit an object.
Dolphins receive these echoes in their jaws, where specialised fatty tissues act to transfer the vibrations to their middle and inner ears.
They are then passed to the brain to be interpreted.
The amount of time that different echo frequencies take to return, allows them to interpret their physical surroundings – even giving them the ability to find fish hiding under the sand.
Echolocation can reveal:
Size and shape of objects
Distance, speed and direction
Dolphins' use of sound is complex and a critical part of their lives, allowing them to navigate, hunt and communicate in their ever-changing marine environment.