Wild blacktip sharks may have a more sophisticated sense of hearing than scientists previously realised. A study by researchers at Florida Atlantic University found that free-swimming sharks can detect low-frequency sounds from as far as 74 metres, or roughly 243 feet, away and respond by turning sharply away from the source. The findings were reported by ScienceDaily and Florida Atlantic University, with the research published in Integrative Organismal Biology. Scroll down to read more…
Sharks hear more than scientists could previously measure
Sound is particularly important underwater, where visibility can quickly become limited. For a predator such as the blacktip shark (Carcharhinus limbatus), noises and vibrations travelling through the water could provide information about prey, predators or other animals long before they become visible. Scientists already knew that sharks respond to low-frequency sounds. What had remained unclear was how far a wild shark could detect such a signal and whether it could determine its direction.The new research provides one of the clearest field measurements yet. Researchers studied wild blacktip sharks in the clear, shallow waters off southeastern Florida. Rather than testing captive animals, the team observed sharks swimming freely in their natural environment, allowing them to examine hearing behaviour under more realistic conditions.
An underwater speaker became the test
To investigate the sharks’ response, scientists placed an underwater speaker in the water and played controlled, low-frequency sounds. At the same time, an aerial drone recorded the movements of sharks from above. The sounds were tested across several frequency ranges, including 100–200 Hz, 200–400 Hz and 400–800 Hz. The researchers also used a much higher-frequency sound as a control.The sharks responded to the tested low-frequency signals from distances of at least 62 metres. Some responses occurred at approximately 74 metres, demonstrating that the animals could react to sounds well beyond the acoustic near field, where scientists had previously expected their ability to detect sound to be strongest.
The sharks did more than simply react
One of the most interesting observations was the direction of the sharks’ movements. When they detected the sound, the animals made sudden turns ranging from about 20 to 160 degrees and then rapidly moved away from the speaker. That consistent directional response gave researchers evidence that the sharks were not merely detecting that a sound existed. They could determine where it was coming from.Across 209 recorded responses, 71.6% occurred in the acoustic far field. The sharks also failed to respond to the high-frequency control sound, despite it being played at a comparable volume. That distinction matters because it challenges the idea that sharks’ ability to orient toward underwater sounds is restricted to the immediate vicinity of a sound source.
Why directional hearing matters underwater
The ability to detect a distant sound and determine its direction could be valuable in an environment where vision is often unreliable. A sound travelling through the ocean can carry information well beyond the distance at which a shark could visually identify another animal. Detecting such signals could therefore give a shark additional time to investigate a potential food source or move away from a possible threat.The study does not show that blacktip sharks use sound alone to hunt or navigate. Instead, it demonstrates that acoustic information can trigger a strong directional response at surprisingly long distances. For researchers, that opens a wider question about how sharks combine hearing with their other highly developed senses.
A new look at the shark’s acoustic world
The findings are particularly significant because they come from sharks behaving freely in the ocean rather than animals tested in laboratory tanks. Observing the animals from above with a drone allowed researchers to measure changes in swimming direction without interfering with their movement.The work also adds to a growing understanding of how marine predators perceive an environment in which sound can travel farther and more reliably than many visual signals. For blacktip sharks, a faint underwater sound may therefore be much more informative than it appears to humans standing above the surface. What sounds like distant background noise to us could provide a shark with a directional clue from hundreds of feet away.
