Sharks Can Detect Underwater Sounds From Nearly 250 Feet Away, Study Finds

Sharks possess a remarkable ability to detect underwater sounds from nearly 250 feet away and can determine the exact origin of these noises, according to a recent study.

The research, conducted off the coast of southeast Florida, utilized underwater speakers and drone cameras to observe the behavior of blacktip sharks in response to various sounds. Scientists found that the predators consistently reacted to low-frequency noises, often altering their course even when the sound source was hundreds of feet distant.

"The ocean is an acoustic environment, and sharks are clearly tuned into it in ways we are only beginning to understand," said Professor Stephen Kajiura, a senior author of the study from Florida Atlantic University. "Being able to detect and respond to sounds from hundreds of feet away gives these predators an important source of information about their surroundings."

The study took advantage of a natural aggregation of blacktip sharks that gather in southeast Florida each winter. This seasonal presence in clear, shallow waters allowed researchers to observe the animals without disturbing their natural behavior.

Researchers anchored a boat and deployed an underwater speaker, allowing it to drift up to 19 meters (62 feet) away to minimize the boat's influence. They tested three ranges of low-frequency sounds—100 to 200 Hertz, 200 to 400 Hertz, and 400 to 800 Hertz—along with a 10-kilohertz control sound outside the known hearing range of sharks. The sounds were played at a high intensity to startle the sharks rather than attract them.

Published in the journal Integrative Organismal Biology, the findings indicated that the sharks reacted to all three low-frequency sound ranges but ignored the high-frequency control sound. The predators demonstrated an ability to detect noises from as far as 74 meters (243 feet), a greater distance than previously documented in free-swimming sharks. Many sharks swiftly changed direction upon hearing the sounds, suggesting they could accurately pinpoint the noise's source.

The researchers noted that sharks were particularly sensitive to lower-pitched noises, detecting them from greater distances and at quieter volumes. This sensitivity is significant because sharks lack the gas-filled swim bladder that many fish use to detect sound. Instead, scientists believe sharks rely on highly sensitive inner-ear structures to pick up vibrations and movement as sound waves travel through the water.

Lead author Caroline Sullivan highlighted the importance of conducting these experiments in the natural ocean environment. "Trying to do hearing experiments in a tank results in the sound bouncing off the walls which causes complex and confusing signals – it is like being in a house of mirrors," Sullivan said. "This is why it is so important to do these types of experiments in the ocean with wild sharks to get a natural response."

The study's authors are keen to further explore how sharks' sensory systems enable them to interpret these distant sounds.