Scientists discover how well sharks hear: They react to sounds from 74 metres away

Scientists discover how well sharks can really hear

Scientists have long struggled to determine exactly how well sharks hear. A new study carried out off the coast of Florida now shows that blacktip sharks can detect underwater sounds from as far as 74 metres away.

Hearing is an essential sense for marine animals. Sound can help them locate prey, avoid danger, navigate their surroundings and interact with other animals. Measuring shark hearing, however, is difficult because controlled laboratory environments can significantly alter the way sound travels through water.

Studying sharks in their natural habitat

Researchers from Florida Atlantic University therefore studied blacktip sharks (Carcharhinus limbatus) directly in the ocean.

Low-frequency pulsing sounds were played from a boat while underwater microphones measured how the signals travelled through the water. At the same time, a drone flying approximately 40 to 50 metres above the surface recorded the sharks' movements and reactions.

Three test sounds with different frequencies were used, together with a control signal outside the sharks' expected hearing range.

Blacktip sharks were particularly suitable for the experiment because large numbers of them gather off southeastern Florida during winter. The relatively shallow and clear water also allows researchers to monitor their natural behaviour from the air.

Sharks responded from dozens of metres away

The results showed a clear difference between the test signals and the control sound.

The sharks largely ignored the control signal but reacted to the test sounds in approximately 71 to 87 percent of cases, depending on frequency.

The most distant recorded response by an individual shark occurred at 74 metres, while responses to all three tested frequencies were observed at distances of up to 62 metres.

Their movements were particularly revealing. When sharks detected the sound, they made sharp directional turns, suggesting that they were able not only to hear the signal but also to determine where it was coming from.

How do sharks hear?

Unlike many bony fish, sharks do not have a gas-filled swim bladder that can help convert changes in sound pressure into vibrations.

Researchers therefore believe that blacktip sharks may directly detect the movement of water particles caused by sound waves.

The latest findings are important because they demonstrate this ability in free-swimming sharks at considerable distances from the sound source.

An ocean full of sound

The study highlights just how important the acoustic environment is for animals living beneath the surface.

Being able to detect distant sounds could give sharks valuable information about prey, potential threats, other animals and their surroundings.

The next challenge for researchers is to understand more precisely how the shark sensory system detects and processes these distant signals.

Field experiments are particularly valuable because testing sharks in tanks can produce reflections from walls, creating complicated acoustic signals that do not accurately represent conditions in the open ocean.

Sources: ScienceAlert and Integrative Organismal Biology Znanstvenici otkrili koliko dobro morski psi čuju. Reagiraju na zvuk s 74 metra - Index.hr