Blacktip Sharks Detect Low-Frequency Sounds From 243 Feet Away
Wild blacktip sharks can detect low-frequency sounds from as far as 74 metres, or about 243 feet, away, according to a study from Florida Atlantic University. Researchers studying the coastal predators observed that the animals could not only hear distant sounds but also determine their origin and quickly turn away from the source. The findings offer new insight into how sharks use their hearing as an early warning system in the ocean.
While laboratory experiments have previously identified what frequencies sharks can detect, they have struggled to capture how freely swimming animals respond to sound in their natural environment. According to Science Daily, blacktip sharks gather in the shallow, clear waters of Southeast Florida, providing researchers with an unusual opportunity to observe individual sharks from above without disrupting their behaviour.
Underwater Speakers and Drone Tracking Reveal Shark Eavesdropping
To test the sharks’ hearing range in the open ocean, the research team anchored a boat offshore and placed an underwater speaker in the water. To separate the experimental sound from boat noise, the speaker was allowed to drift with the current as far as 19 metres from the vessel, as reported by Science Daily. Researchers played low-frequency sounds across three distinct ranges: 100 to 200 hertz, 200 to 400 hertz, and 400 to 800 hertz. A 10-kilohertz sound, which lies outside the known hearing range of sharks, served as a control.
During the trials, a drone flying roughly 40 to 50 metres above the surface captured the sharks’ movements on video. The research team later analysed this footage frame by frame, tracking each animal’s position and changes in swimming direction. Calibrated hydrophones measured sound levels at various points in the water, allowing scientists to determine what sound each shark was hearing when it reacted.
Far-Field Acoustic Sensitivity Without a Swim Bladder
The results showed that blacktip sharks responded to all three low-frequency ranges while showing no comparable reaction to the 10-kilohertz control. More than 70 percent of the recorded responses occurred in the acoustic far field, where sound behaves differently than it does close to its source. The sharks frequently made abrupt turns away from the speaker, indicating they could pinpoint the direction of the signal rather than simply noticing its presence.
This sensitivity is particularly notable because sharks lack the gas-filled swim bladder found in many bony fish, an organ that typically assists with sound pressure detection. Instead, researchers believe a specialised sensory structure called the macula neglecta plays an important role. This sensory system enables them to detect the vibrations and particle movement associated with sound travelling through water over considerable distances.
Natural Environment Testing Versus Tank Experiments
The FAU study highlights the limitations of testing aquatic animals inside artificial tanks. Sound does not behave the same way in enclosed spaces, where wall reflections create complicated acoustic patterns that distort an animal’s response. By conducting behavioural experiments in open coastal waters, the research team avoided artificial echoes and captured a more accurate picture of how sharks process everyday acoustic information.
While the study establishes a clear hearing range of up to 74 metres (243 feet) for blacktip sharks, scientists note that questions remain about how their sensory system allows them to pick up and interpret such distant signals. As human-generated noise from boats and oil rigs increasingly alters the ocean soundscape, understanding these auditory capabilities provides critical context for protecting sensitive marine predators.
Frequently Asked Questions About Shark Hearing
Do sharks have external ears?
Sharks have ears, though they are not as externally visible as humans’.
How do sharks detect sound without a swim bladder?
Sharks rely on a specialised sensory structure called the macula neglecta, which detects the particle motion and vibrations of underwater sound.
What frequencies were tested in the Florida Atlantic University study?
Researchers tested three low-frequency ranges—100 to 200 hertz, 200 to 400 hertz, and 400 to 800 hertz—alongside a 10-kilohertz control sound.