Sharks never seen before? In an unprecedented expedition, a team of scientists dropped a cow carcass at a depth of over 1,600 meters in the South China Sea. Their goal was to simulate a whale fall and study how abyssal fauna reacts. What they didn’t expect was the arrival of eight Pacific sleeper sharks, a species never before recorded in that area.

The Unexpected Appearance of Sharks in Asian Waters

The experiment took place off China’s Hainan Island, where researchers from Sun Yat-sen University sought to understand the effects of decomposing large organic bodies on the seafloor. To do so, they launched the cow carcass to a depth of 1,629 meters, expecting to observe amphipods and other deep-sea scavengers. However, cameras captured something entirely unexpected: eight Pacific sleeper sharks (Somniosus pacificus), whose presence in that region had never been documented.

These sharks, known for preferring cold, deep waters, typically inhabit the North Pacific, from Japan to Alaska. Their presence as far south as the South China Sea puzzled researchers, who suspect they may be witnessing a habitat expansion driven by climate change—or simply revealing a lack of prior data.

The discovery not only expands the species’ known distribution map, but also allowed observation of unique behaviors. Videos showed the sharks waiting their turn to feed in a queue—an underwater “etiquette” revealing complex dominance hierarchies. The larger specimens, over 2.7 meters long, were more aggressive and charged at the carcass without hesitation, while smaller ones approached more cautiously.

This coordinated behavior among solitary sharks raises fascinating questions about their intelligence and survival strategies in the deep ocean.

Behaviors, Parasites, and Biological Mysteries in the Abyssal Depths

Beyond the surprise of their presence in an unusual region, the team led by Han Tian also recorded various observations about their biology and behavior, offering new insights into this species.

One notable behavior was the sharks’ ocular retraction while feeding—a protective mechanism, as Pacific sleeper sharks lack a nictitating membrane (a “third eyelid” found in other species), making them more vulnerable during feeding frenzies .

Additionally, some sharks had parasites attached to their eyes, possibly copepods, though precise identification wasn’t possible. These findings align with previous observations in Greenland sharks, close relatives of Pacific sleepers, which also host ocular parasites .

Sharks weren’t the only visitors to the feast. Cameras captured snailfish and various amphipod species, showcasing the biodiversity that emerges around a large carcass on the seafloor. Such “whale fall” events supply nutrients to deep ecosystems for years, and using a cow allowed real-time observation of these dynamics.

Regular presence of these sharks in the southwestern South China Sea could imply more abundant food sources in the region than previously assumed. Tian noted that this aggressive behavior suggests active competition for resources, opening new research avenues into deep-sea food chains.

Reference:

• Ocean-Land-Atmosphere Research/Predating Behavior of the Pacific Sleeper Shark in the Deep Waters of South China Sea. Link

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