Fish aren’t the only creatures that can hear underwater. Many other aquatic animals have unique hearing capabilities in order to communicate with each other, catch prey or avoid danger. Let’s take a look at some examples of how aquatic animals hear underwater.
Have you ever seen a shark’s ears? Probably not. This is because sharks only have an inner ear. This inner ear is composed of three semicircular canals, which are used for balance. Inside each canal are four sensory membranes. Three of these are used for both balance and registering sound. These sensory membranes are called the sacculus, the lagena, and the utriculus, and they are lined with tiny hairs to aid sharks in detecting vibrations in the water.
Sharks have extremely sensitive hearing. They can hear sound frequencies from 90 – 250 metres away, ranging from 10 Hz to 800 Hz, and they hear low-pitched sounds (below 375 Hz) best. Comparably, human’s audible frequency in the air is roughly 20 Hz to 20 kHz. Underwater humans are unable to hear low frequency sounds but can detect higher frequencies, up to 100 kHz. While sharks hear a smaller range of sounds than humans, they can hear low frequency sounds that are inaudible than humans.
Similar to fish, sharks also use their lateral line to assist with hearing. The network of neuromasts along the length of the shark, detect vibrations in water that help them locate potential predators and prey.
Until recently, it was thought that octopuses were deaf because they don’t have a gas-filled chamber like the swim bladder that many fish use to hear. However, sensory physiologist, Hong Young Yan concluded that octopus and other cephalopods like squid use another organ called the statocyst to hear and balance. It was then discovered that octopus can register sounds at a range of 400 – 1000 Hz, and sounds at 600 Hz are heard best. Octopus’s hearing is limited however, due to the fact they can’t amplify sounds.
Dolphin’s have much better hearing than humans, 7 times better in fact. They can hear a wider range of frequencies and ultrasounds (high frequency) exceptionally well. A dolphin’s hearing range is from about 20 Hz to 150 kHz.
Dolphins do have ear openings behind their eyes but they use other body parts to assist their hearing. Dolphin’s use their foreheads or melon, as it is called, for sound recognition.
Their teeth also assist in hearing. Dolphin’s teeth are arranged to function similarly to an antenna, and help receive incoming sound. They also feel sound vibrations in their jaw. A dolphin’s jawbone is filled with a type of fat that has sound conducting abilities which it then uses to conduct sounds to the middle ear. Dolphins use echolocation to locate objects and identify their shape, size, orientation, direction, and speed.
Dolphins also use sound to communicate underwater. They produce two kinds of sounds, a high-pitch whistling and a clicking sound. The whistling is used to communicate with other dolphins, as each dolphin has its own unique sound. The clicking acts as a sonar function, which dolphins use for echolocation.
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