[Article déjà publié le 18 juillet
2025]
In the deep ocean, each camera movement can reveal a still unknown part of marine life. By submerging a cow carcass more than 1,600 meters deep, researchers triggered much more than an experiment on decomposition. They witnessed the appearance of species previously absent from this map of life. Among them, Pacific sleeper sharks, whose presence in the South China Sea is shaking up established knowledge on the distribution of large marine predators.
What a carcass dropped at a depth of 1,629 meters reveals
It all started with a scientific operation with well-defined objectives. To understand what happens to cetacean carcasses when they sink into the abyss, Chinese researchers decided to simulate the phenomenon by placing a dead cow on the ocean floor, more than 1,600 meters deep, off the island of Hainan. But it wasn’t the decomposition that caught their attention. A few hours after the deposit, cameras fixed on the site captured the arrival of eight large predators previously unknown in this area.
The images clearly showed Pacific sleeper sharks, a species that can dive beyond 1,000 meters but whose habits remain largely mysterious. The event marks the first-ever documented sighting of this species in the South China Sea, according to work published in Ocean-Land-Atmosphere Research on June 26, 2025. The discovery took scientists by surprise, who did not expect to see these placid giants at such a latitude.
Among Pacific sleeper sharks, order reigns even at the table
Beyond the geographical surprise, the images collected have opened a rare window on the feeding behaviors of this species. Far from the stereotype of brutal predators, the sharks observed seemed to display astonishing discipline. Individuals followed one another in front of the carcass in an almost orderly file, some giving way to those who arrived behind them. This attitude, described as a food queue, evokes a form of social hierarchy based on the competitive intensity of each animal.
The researchers also noted a marked difference depending on the size of the specimens. The taller ones, over 2.70 meters tall, took a more direct and aggressive approach. The smaller ones preferred to circle slowly around the carcass, visibly assessing the situation before approaching. Other details, such as a characteristic eye retraction movement during feeding, were also observed. This gesture, highlighted in the Eurekalert press release, is similar to a protective mechanism in this species which does not have a nictitating membrane, unlike other sharks.
Finally, the cameras revealed the presence of parasites, including copepods housed on the heads of some individuals, as well as other opportunistic species, such as deep-sea amphipods and a snail fish. This unexpected procession highlights the richness of an ecosystem that science is only just beginning to explore.
A presence that reshuffles the cards for the distribution of large predators
The discovery of Pacific sleeper sharks in the South China Sea raises a major question. Is this a simple coincidence linked to the fleshy bait on the carcass, or an indication of a more profound change in the distribution of this species? Until now, their presence was mainly documented in the North Pacific, from the cold waters of Japan to Alaska and Baja California. An isolated sighting had been made off the coast of the Solomon Islands, representing until now the southernmost point known.
In their publication, researchers from Sun Yat-sen University question this possible extension of the distribution area. Warming deep waters could make some areas more hospitable to once temperature-limited species. The fact that all the specimens observed are females also suggests a phenomenon of spatial segregation according to sex, already identified in other species of large sharks, such as the megachasma. Some researchers even hypothesize that this region could function as a nursery area.
This unexpected foray into a little-known territory therefore invites us to reassess the balances of deep ecosystems. It shows that despite the depth, marine life remains dynamic, structured and potentially changing.
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
