Wild blacktip sharks off Florida turn away from low-pitched sounds up to 74 meters away

The best piece of design here is the control. The 10-kilohertz tone came from the same speaker, beside the same anchored boat, filmed by the same drone ^[5][8]. It sits 12.5 times above the top of the highest test band ^[1]. The sharks ignored it ^[9]. That rules out the rig itself as the trigger, because the boat, the speaker in the water and the drone were all present for the control too. The speaker was also allowed to drift as far as 19 meters from the boat to reduce the chance that the vessel affected the sharks ^[4].

Florida Atlantic University describes the paper, published in Integrative Organismal Biology, as the first quantified evidence that free-swimming sharks detect and orient away from sounds in the acoustic far field ^[3]. The release does not give the number of sharks filmed, the number of responses scored, or the share of responses that were turns away from the speaker. So "more than 70 percent" of responses in the far field ^[10] is a fraction of an unstated total. "Often" is the release's only word on how consistently the sharks turned away ^[2]. Seventy-four meters is the farthest response recorded ^[1].

That distance also depends on the loudspeaker. The team did not try to lure sharks toward the speaker; it played sounds loud enough to provoke a startle ^[6]. Sound fades with distance, so a louder source would cross a shark's detection limit farther out and a quieter one closer in. The measurement that transfers is the one the calibrated hydrophones took: the sound level at each shark's position when it reacted ^[7]. The frequency result comes from those levels too. Lower frequencies were detected from greater distances and at lower sound levels ^[11].

Detecting a sound and knowing where it came from are separate abilities. The rapid turns away from the speaker are the evidence for the second ^[2]. Stephen Kajiura, the senior author and a professor of biological sciences at FAU ^[17], singled out where the responses happened. "What makes this finding particularly interesting is that the sharks were responding to sounds beyond the acoustic near field, where the sound behaves differently than it does close to the source," he said ^[12]. That, he said, "suggests that they are detecting the particle motion associated with sound" ^[13].

Blacktips were chosen because they gather predictably off Palm Beach County, in water clear and shallow enough to watch from the air ^[14]. The result covers one species in one habitat. The release sets up the open question in terms of sounds from prey, predators and other animals ^[16]. For people assessing human noise in the ocean, the study establishes that a free-swimming shark can hear a loud low-frequency source at tens of meters, work out where it is and swim away from it ^[1][2]. Finding out whether quieter or continuous noise produces the same turn, and whether sharks stop turning after repeated exposure, needs trials built to find thresholds instead of startles.