Never seen a shark with ears? Well, sharks only have an inner ear. Two holes on either side of a shark's head might be the only clue you'd have to the presence of shark ears. Yet sound is often the shark's first tip-off that prey is nearby. The prey doesn't even have to be that close. Because sound travels farther and faster underwater, sharks are easily able to detect their prey from distances of more than 800 feet (243 meters) [source: SeaWorld]. That's more than two football fields.
The shark's ear is made up of three semicircular canals, which primarily provide the shark with balance. However, inside each canal are four sensory maculae, some of which are tasked with auditory function [source: Carrier]. The three sensory areas responsible for both balance and sound perception are called the sacculus, the lagena and the utriculus. These parts are lined with tiny hairs that help the shark detect vibrations in the water. The vibrations that the shark is trying to pick up include splashing and the sounds of an injured prey, which create different sound frequencies.
Sharks hear deep low-pitched sounds the best. According to the Shark Trust conservation organization, sharks hear sounds with frequencies ranging from 10 hertz to 800 hertz, and they are particularly responsive to sounds lower than 375 hertz. For comparison, 10 hertz is 1.5 octaves below the lowest note on a piano [source: PBS]. Humans, on the other hand, hear sounds ranging from 25 hertz to 16,000 hertz [source: Shark Trust]. Sharks can hear sounds much lower than we can, while we hear sounds much higher than sharks.
On the next page, we'll look into shark sight.