The ocean is full of surprises. Sometimes, as happened several years ago in Canada, enigmas appear floating in a of human feet adrift. However, in others, the majority, you have to go down to the depths to try to solve the mysteries. That was precisely what a group of researchers proposed. It all started by throwing the carcass of a cow.
A cow at 1,600 meters. In one of the most unusual marine experiments in recent years, a group of scientists threw a dead cow 1,629 meters deep on a continental slope of the South China Sea, off the Chinese island of Hainan, with the aim of simulating the sinking of a whale and studying the scavenger behavior of deep waters.
What they found surprised even the most experienced researchers: eight sleeper sharks of the Pacific (Somniosus pacificus) appeared at the site, marking the first documented observation of this species in the region. The discovery not only unexpectedly expands the distribution map of this elusive shark, but also provides valuable information about its behavioral patterns, feeding hierarchies, physiological adaptations and its possible geographical expansion.
An unexpected visitor. Although the Pacific sleeper shark is a species with a wide distribution in the northern Pacific Ocean (from Japan to Alaska and south to Baja California), its detection in waters off southern China was not only unexpected, but raises questions about the actual extent of its habitatits possible displacement due to the effect of climate change or even the existence of a stable and not yet registered population in that region.
Food label. The recorded images The underwater cameras not only confirmed its presence, but also revealed unusual behavior for large predators: a kind of shift systemin which the sharks lined up to feed on the corpse, giving way to other individuals that approached from behind.
This type of “food label”rarely observed in predatory species, suggests that feeding order could be determined by the competitive intensity of each individual, rather than a chaotic struggle for resources, which would indicate a more complex level of social organization than previously suspected in these animals.
New clues. He study also documented variations in behavior depending on body size. The specimens that exceeded 2.7 meters in length were very more aggressive and direct in attacking the carrion, while the smaller sharks opted for cautious movements, circling the carcass before approaching.
The pattern suggests that even in an environment where food is scarce and opportunities are random, sleeper sharks could have developed a coexistence strategy with hierarchical ranks that minimize direct conflict.
One more thing. Another notable finding was a behavior of eye retraction observed during feeding. Since this species lacks nictitating membrane (the protective “third eyelash” that other vertebrates such as cats or certain reptiles have), researchers believe that this retraction reflects a evolutionary adaptation to protect the eyes during bites or struggles, which provides new information about the defensive physiology of these sharks in their natural environment.
The unknown. And more, since the recordings also showed other revealing aspects. To wit: several sharks carried visible parasites in his eyes, identified like copepodsalthough it was not possible to accurately classify the species. This detail reinforces the biological parallel between Pacific sleeper sharks and their better-known relatives, the Greenland sharkswhich also tend to harbor parasites in their visual organs.
Aside from sharks, the experiment attracted a surprising variety of deep-sea fauna, such as snail fish and numerous amphipodsall attracted to the source of decaying organic matter. These records confirm that the deep areas of the South China Sea not only host a biodiversity that is still poorly documented, but could be more productive than previously believed, contrary to the idea that the tropical depths are biologically poorer than their polar counterparts.
The great unknown. Ultimately, the presence of these sharks raises a crucial question: is this a recent expansion of their range due to global warming, or has it always been part of their habitat and simply never been observed? The species is known to have occasionally appeared in such remote regions like Palau or the Solomon Islandssuggesting that there could be more southern populations than the scientific literature indicates.
However, the “frequent occurrence” in the southwest China Sea, according to the team itself researcher led by Han Tian, suggests rather a structural lack of data in an underexplored region rather than a recent change in the distribution pattern. In that sense, the experiment with the cow corpse has not only provided a specific observation, but has also opened a way to review key concepts about the marine biogeography of abyssal species.
The new discovery. In February 2026, it was documented, for first time in historya shark (of the sleeper family, possibly a southern sleeper shark, a very close relative of the Pacific sleeper shark) off the South Shetland Islands, in Antarctic waters, 490 meters deep.
This is the first time that an elasmobranch has been filmed in the Southern Ocean, and several experts suggest that warming waters could be facilitating the movement of this family of sharks to areas where they were not previously expected, although they also warn that they could have been there for a long time without having been detected.
Know the depths. All these findings They highlight the usefulness of simple but carefully designed experiments to obtain data about remote, inaccessible and often poorly understood environments. The idea of simulating a whale sinking with a cow not only proved effective, it proved to be a powerful ecological magnet capable of revealing complex biological interactions.
In a context where the climate change and human activity are altering ecosystems even at great depth, this type of research is crucial to understanding the invisible functioning of the deep ocean. The appearance of eight sleeper sharks where no one expected them, behaving with order, measured aggression and sophisticated adaptive mechanisms, is further proof that the deep sea they keep secrets that we are only beginning to understand.
A version of this article was published in July 2025
Image | Ocean-Land-Atmosphere Research (2025)
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