The farthest turn came at 74 meters, or 243 feet. A blacktip shark off the coast of Palm Beach County, Florida, abruptly changed course and swam away from an underwater speaker that distance off, a response that Florida Atlantic University researchers filmed from a drone and measured frame by frame.
That figure is a ceiling, not an average. Across all the sound frequencies tested, the sharks’ responses ranged from 11.1 to 74.0 meters from the speaker, and the typical response sat much closer.
A speaker on a drifting line, a drone overhead
The team, led by senior author Stephen Kajiura with lead author Caroline Sullivan and co-author Edmund Gerstein, worked in coastal water off Southeast Florida. According to the university’s release, an underwater speaker drifted up to 19 meters from an anchored boat while calibrated hydrophones mapped how loud the sound was at different distances. A drone flying 40 to 50 meters above the water recorded the sharks’ movements, and the footage was analyzed frame by frame for the distance and direction of any reaction.
Sullivan did the work for her master’s degree in biological sciences. The research was supported by the Colgan Foundation and the National Save the Sea Turtle Foundation, ScienceDaily noted.
The drone supplies the measurement. Filming from 40 to 50 meters up let the team mark the frame in which the speaker came on and then read each shark’s distance from it and its heading before and after, so that a reaction could be tied to the onset of the sound rather than judged by eye from a boat. Each presentation became a short, scored video clip: turned or did not turn, and at what range. Altogether the record holds 165 positive responses, 45 trials that drew none and 209 control presentations, an uneven but substantial ledger for animals filmed in open water rather than in a tank.
Response criteria and frequency bands
The measured behavior was specific. In the paper in Integrative Organismal Biology, a response was “a sudden change in trajectory immediately following the onset of the stimulus,” and the abstract record reports 165 positive responses against 45 trials with no reaction. Sharks turned an average of 72.7 degrees away from the speaker; a summary of the paper gives the range as a sudden 20 to 160 degree turn, followed by rapid swimming away.
Three bands of low-frequency sound were played: 100 to 200 hertz, 200 to 400 hertz and 400 to 800 hertz. Mean response distances were 40.7 meters, 41.0 meters and 30.0 meters respectively, and higher-pitched bands had to be louder to provoke a turn: thresholds rose from 16.0 decibels at 100 to 200 hertz to 44.6 decibels at 400 to 800 hertz. A 10 kilohertz control tone, presented 209 times at an equivalent volume, produced no response at all.
Sharks reacted from at least 62 meters at every tested frequency, and 71.5% of the 165 responses came from beyond the acoustic near field. ScienceDaily adds that the silence to the 10 kilohertz control shows the animals were not simply reacting to the boat or to any loud noise, only to the low frequencies.
Particle motion and the far field
The near-field distinction carries the scientific weight. Close to a source, water itself sloshes back and forth, a motion a fish can feel on its body; farther away that motion fades and what remains is a pressure wave. Sharks have no gas-filled swim bladder, the organ that helps bony fish register pressure, and they rely instead on inner-ear structures including the macula neglecta, as ScienceDaily describes.
“This suggests they are detecting the particle motion associated with sound even at considerable distances from the source,” Kajiura said in the FAU release. Because 71.5% of responses occurred beyond the near field, the data point to a hearing range in free-swimming sharks that extends well past what had been documented before.
Blacktips are a sensible species for the test. The Florida Museum describes them as common in shallow Florida bays and estuaries, reaching about 4.9 feet on average and up to roughly 8 feet, and as hunters of small schooling fish that tend to be timid. They are listed as Near Threatened by the IUCN.
The experiment did not test every question it raises. It recorded sharks fleeing a speaker, which says they detected and located the sound; it does not say what natural sounds would draw them in, and it leaves open how the 74-meter ceiling compares with other species and sound types. The 45 trials with no reaction are also part of the record: a response was the usual outcome in these trials, not a guaranteed one, and no single shark’s behavior at 243 feet should be read as a rule for every individual in the water.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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