In the darkest depths of the ocean or in murky water, dolphins are unable to see their prey. By creating click sounds they are able to accurately locate objects. They use what is called sonar, or echolocation.
Echolocation is quite simple. A dolphin sends out rapid clicks that bounce off an object and return to the dolphin. It is rather similar to an echo in a cave. Water, however, allows the sound waves to travel 4.5 times faster in water than in the air.
These clicks are such a high frequency that humans are unable to detect or produce them. Dolphins’ hearing is extremely sharp and they are able to distinguish the slightest change in frequencies. When trying to find out more about an object, a dolphin will use a lower frequency click since it is able to travel further. Lower frequencies, however, do not provide as much detail as the higher frequency clicks. As a dolphin gets closer to the object, it increases the frequency of the clicks to learn more.
Dolphins have become experts at the process of echolocation. The nasal passages in dolphins produce clicks which are then sent through the forehead (melon). The dolphin directs these focused beams in the direction of an object such as a human diver. Once the sound waves reach an object, the sound waves are reflected back to the dolphin. The echo is absorbed in a passage of fat in the jaw, which sends the sound to the inner ear, at which point nerve impulses are exchanged with the brain. The dolphin’s brain is then able to create an “image” of the fish. It is able to distinguish certain characteristics, such as the size, shape and inner structure of the fish.
Dolphins are then able to determine how far away a fish is by evaluating the time lapse between when the clicks were sent out and when the echo returns. Once dolphins locate a squid or fish, they continue to send out rapid clicks to track and hone in on their prey.
Usually dolphins hunt in groups and cooperate together to attack their prey. They employ a range of tactics. Dolphins will typically encircle a school of fish and then condense them to form a smaller mass. Then it is much easier for the dolphins to take turns attacking the fish.
Another method used by dolphins is to herd the fish to a sandbar, shoreline or mud bank. In shallow water it is much easier to prevent the prey from escaping and surely they will be able to make a kill.