In the mysterious depths of the South China Sea, a remarkable discovery has illuminated the hidden lives of one of the ocean’s most enigmatic predators—the Pacific sleeper shark (Somniosus pacificus). This elusive deep-water shark has long evaded scientific observation due to its extraordinary habitat, residing at depths that often exceed 1,000 meters. Now, thanks to pioneering research deploying stationary cameras in these abyssal realms, scientists have captured groundbreaking footage revealing the predatory behaviors and social dynamics of Pacific sleeper sharks for the first time in this region. The findings, recently published in Ocean-Land-Atmosphere Research, not only expand the known distribution of these sharks but provide unparalleled insight into their complex feeding strategies beneath the waves.
The innovative study took place on the continental slope southeast of Hainan Island, where researchers strategically deployed a cow carcass to simulate a natural whale fall environment at an impressive depth of 1,629 meters. This method effectively mimics one of the ocean’s most critical deep-sea ecological phenomena—where the carcasses of large marine animals create nutrient hotspots that sustain diverse scavenger communities. Unexpectedly, the recorded footage unveiled multiple Pacific sleeper sharks congregating around the carrion, documenting for the first time their presence in the South China Sea’s deep waters. Prior to this research, these sharks had only been documented in the colder North Pacific regions, making this sighting the southernmost known occurrence and prompting new inquiries into their environmental adaptations.
Analyzing the video in detail showed a fascinating tableau of predatory behavior. The sharks exhibited discernable feeding hierarchies along with a striking queuing behavior, with individuals feeding sequentially and showing social awareness by yielding their position to oncoming sharks. Such a pattern suggests a complex social structure that may minimize conflict while optimizing feeding efficiency in the resource-scarce deep ocean. This behavioral trait stands in contrast to the traditionally assumed solitary nature of many deep-sea predators and offers new perspectives on how Pacific sleeper sharks negotiate space and food in extreme environments.
A critical observation stemming from the footage was the marked difference in feeding strategies between larger and smaller sharks. Those measuring over 2.7 meters demonstrated highly aggressive, direct attacks on the carcass, rapidly consuming large portions of flesh. Meanwhile, the smaller sharks, defined by researchers solely by size for analytical purposes, adopted a more cautious approach, circling at the periphery. This disparity illustrates potential age or size-related roles in the scavenging community, perhaps linked to dominance hierarchies or physiological constraints influencing risk-taking behavior and feeding priority.
An intriguing physiological adaptation underscored in the study was the distinct eye retraction movements exhibited by these sharks during feeding. Unlike many elasmobranchs equipped with protective nictitating membranes, members of the genus Somniosus lack such a feature. Consequently, Pacific sleeper sharks appear to compensate with dynamic eyeball withdrawal, likely serving as an evolutionary mechanism to safeguard their vision from damage incurred during aggressive feeding on hard or sharp bones of carcasses. This subtle yet vital behavior highlights the specialized adaptations these sharks have evolved to survive in their demanding environment.
Of particular interest was the polite ‘queueing’ behavior noted when individual sharks yielded their position to others approaching from behind. The ecological drivers behind this behavior remain speculative; however, researchers hypothesize it mirrors the hierarchical interactions observed in shallow-water shark species feeding on whale carcasses at the surface. Alternatively, it may represent a strategy to avoid unnecessary physical confrontation, which could be detrimental in such energy-limited ecosystems. This behavior underscores the complex social dynamics that can arise even in the remote, deep-sea habitats traditionally perceived as solitary realms.
The presence of Pacific sleeper sharks in the South China Sea is ecologically significant, not only because it extends their known geographical range but also because it suggests potential shifts or expansions linked to changing oceanographic conditions. Historically, their range was limited to colder temperate waters stretching from Japan, through the Bering Sea, to Alaska and Baja California. The recent discovery in tropical waters raises questions regarding the biological and environmental factors driving their distribution, such as ocean currents, temperature gradients, prey availability, or competition pressures, making this a compelling subject for further oceanographic and ecological investigations.
Importantly, all individuals captured on video were identified as female, which, coupled with the known presence of female megamouth sharks in the area, suggests that the South China Sea may serve as a crucial nursery or reproductive ground for large deep-sea sharks. This insight challenges previous assumptions about the life history strategies of these species and opens new avenues for research into gender-specific habitat use, breeding behaviors, and juvenile survival strategies at great depths within this biodiverse marine corridor.
The researchers involved in this study emphasize that the observed aggressive feeding behavior indicates abundant food resources in deep waters of the South China Sea, a region previously understudied in terms of its capacity to sustain large-bodied predatory fish. Identifying the exact nature of these resources remains an open question, vital for understanding the energy flow and trophic interactions that underpin the deep-sea ecosystem. Such knowledge is paramount for anticipating how these ecosystems may respond to environmental changes driven by climate dynamics and human impacts.
This research represents a significant interdisciplinary collaboration between the Deep-Sea Life and Ecology Team at the Southern Marine Science and Engineering Guangdong Laboratory in Zhuhai, Sun Yat-sen University’s School of Marine Sciences, and the Institute of Acoustics of the Chinese Academy of Sciences. By integrating cutting-edge imaging technology with ecological analysis, the team has set a new standard for studying remote and challenging environments, paving the way for future explorations into the mysteries of deep-sea marine life.
Looking forward, the study’s authors advocate for coordinated comparative research across different marine regions to enrich understanding of deep-sea biodiversity, population connectivity, and energy dynamics. Collaborative efforts will provide comprehensive biological evidence necessary for conserving these fragile and poorly understood ecosystems, especially in the face of rapid environmental shifts and increasing anthropogenic pressures on ocean health.
The profound insights gleaned from this study underscore the undeniable complexity and resilience of deep-sea predators like the Pacific sleeper shark. As scientists continue to unveil the hidden behaviors and ecological roles of these remarkable creatures, the deep ocean increasingly reveals itself as a dynamic, interconnected world vital to global marine biodiversity and ecosystem function. The revelations from the South China Sea provide both inspiration and imperative for continued exploration, driven by the hope of unraveling further secrets from the ocean’s depths and safeguarding its future.
Subject of Research: Not applicable
Article Title: Predating Behavior of the Pacific Sleeper Shark in the Deep Waters of South China Sea
News Publication Date: 1-Jun-2025
Web References: http://dx.doi.org/10.34133/olar.0095
Image Credits: Ocean-Land-Atmosphere Research
Keywords: Marine life, Oceanography, Marine ecology
