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Sharks can detect low-frequency sounds from nearly 250 feet away and rapidly turn away from their source, according to a new study by researchers at Florida Atlantic University.
The findings provide the first quantified evidence that freely swimming sharks can detect and orient away from sounds in the acoustic far field, offering new insight into a sensory ability that remains poorly understood.
Published in Integrative Organismal Biology, the study focused on blacktip sharks (Carcharhinus limbatus) in the coastal waters of Southeast Florida. Researchers used an underwater speaker, calibrated hydrophones and a drone to monitor how wild sharks responded to controlled sounds.
Blacktip sharks were selected because they gather in large numbers along the Palm Beach County coast during winter and can be found there throughout much of the year. The shallow, clear waters also allowed researchers to observe the animals from above without significantly disturbing their natural behaviour.
“Their abundance and accessibility made it possible for us to observe them from above without disturbing their natural behavior, while also presenting controlled underwater sounds,” said Stephen Kajiura, senior author of the study and a professor of biological sciences at FAU.
For the experiments, researchers anchored a boat and placed an underwater speaker in the water, allowing it to drift with the current. They played three ranges of low-frequency sounds — 100–200, 200–400 and 400–800 hertz — at levels designed to trigger a startle response.
A 10-kilohertz sound, which is beyond the known hearing range of sharks, was used as a control.
Hydrophones measured the sound reaching different points in the water, while a drone flying 40 to 50 metres above the surface recorded the movements of the sharks. Researchers later analysed the footage frame by frame to determine each shark’s distance from the speaker and changes in its swimming direction.
The sharks responded to all three low-frequency sound ranges but showed no reaction to the 10-kilohertz control signal.
They were able to detect the sounds from distances of up to 74 metres (243 feet), considerably farther than previously demonstrated in freely swimming sharks.
The sharks also frequently made abrupt turns away from the speaker, suggesting that they were not merely detecting the presence of sound but could also determine its direction.
The findings indicate that sound may provide sharks with important information about events occurring well beyond their immediate visual range. Sounds produced by prey, predators and other marine animals could help them interpret their surroundings and respond to potential threats or opportunities.
The researchers say the study provides a rare field-based measurement of shark hearing and helps clarify how sharks use underwater sound while moving through their natural environment.