A shark can circle a camera, vanish from view and return later—but the pattern on its fins may reveal whether it is the same animal. Off Cat Island in The Bahamas, researchers used that clue to identify more than 50 endangered oceanic whitetip sharks in underwater video.
Knowing how many sharks are in an area, and whether their numbers are changing, is vital to protecting a species. But counting animals in the open ocean is far harder than surveying wildlife on land. FIU marine biologist Yannis Papastamatiou said researchers cannot simply take an airplane survey and count sharks from above. Cameras offer a way to watch them, but the deep water around Cat Island made it impossible to anchor cameras to the seabed.
The team instead used pelagic baited remote underwater video stations, known as pBRUVS. These cameras are not attached to the seafloor or a reef. FIU alumna Candace Fields, who earned her Ph.D. in marine biology in 2025, tested two ways to deploy them: letting them drift freely and tethering them to a boat. The boat-tethered cameras helped the researchers collect more video. They also let the team test whether boat noise changed shark behavior. In this study, it did not.
To tell sharks apart, the researchers looked at distinctive pigmentation on their fins and the shape of the fin tips. Identifying sharks from video was not guaranteed: animals could circle the camera, show up more than once or approach from an angle that hid their markings. Still, the researchers estimated they could recognize an individual about 80% of the time.
That made a major difference to the count. Traditional video surveys often record the largest number of sharks visible at one time. But sharks may arrive one after another, so that method can miss visitors. Matching fin patterns allowed the team to distinguish animals even when only one shark appeared in the frame at a time. The number of sharks visiting a camera could be as much as three times the traditional count suggested.
For Papastamatiou, the study’s key finding is that a relatively cheap, straightforward camera method can help researchers track changes in oceanic whitetip numbers in The Bahamas. The species is critically endangered, and repeated surveys could help show whether its local population is declining, stable or recovering. The method does not count every shark in the ocean, but it offers a practical way to compare sightings over time.
The research also helped build local expertise. Fields now works at the Cape Eleuthera Institute in Rock Sound, Eleuthera. She said she was encouraged to return home and contribute to shark research in The Bahamas, where she hopes to become a Bahamian shark expert. With fin patterns serving as natural identifiers, researchers have a new way to learn who is passing through these deep waters—and to keep watch on how the population changes.