In June 2025, scientists released extraordinary footage of Pacific sleeper sharks in the South China Sea. It was the first time the species had been caught on camera in this part of the world, offering vital new clues about the behaviour and distribution of these elusive deep-sea giants.
The video was recorded as part of a study, published in the journal Ocean-Land-Atmosphere Research, exploring how large animals feed in deep-sea environments.
To investigate the subject, researchers lowered a cow carcass to a depth of 1,629m, south-east of Hainan Island. They placed a camera at the site and waited. It was then that they filmed the Pacific sleeper sharks.
These slow-moving predators are normally found in the colder waters of the North Pacific Ocean – places such as the Bering Sea, the Gulf of Alaska and Baja California. The unexpected sightings in the South China Sea pushes the known range of the species significantly further south, says the study.
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Pacific sleeper sharks in the South China Sea
The team, led by researchers from Sun Yat-sen University and the Southern Marine Science and Engineering Guangdong Laboratory, observed multiple Pacific sleeper sharks feeding at the study site.
Larger sharks (those over 2.7m long) were seen aggressively tearing at the carcass, while smaller individuals circled more cautiously.
One of the most intriguing observations was the sharks’ apparent queuing behaviour. Individuals approaching from behind appeared to take priority over those already feeding.
“This behaviour suggests that feeding priority is determined by individual competitive intensity, even in deep-water environments, reflecting a survival strategy suitable for non-solitary foraging among Pacific sleeper sharks,” said Han Tian from Sun Yat-sen University.
Tian also noted that “the highly aggressive behaviour of sharks observed in the South China Sea suggests that this region still harbours abundant food sources in the deep sea. But what exactly are they? This question is intriguing for both animal distribution and behavioural research.”
What else did the scientists discover?
The study also reveals that the sharks display a unique eye retraction motion while feeding. Unlike many predators, Pacific sleeper sharks lack a protective eye membrane. Researchers believe this motion may serve as a defensive reflex, protecting their eyes while they feed.
The team noticed something else interesting: every shark observed in the footage was female. The study notes that other deep-sea species such as the megamouth shark also show female bias in the South China Sea, raising the possibility that this area may serve as a nursery ground for some large shark species.
Find out more about the study: Predating Behavior of the Pacific Sleeper Shark in the Deep Waters of South China Sea
Image and video credit: Han Tian, Ocean-Land-Atmosphere Research
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