Pacific Sleeper Sharks Documented for First Time in South China Sea

 

A team of marine researchers from Sun Yat-sen University has captured important footage that expands our understanding of Pacific sleeper shark distribution and behavior. For the first time, these elusive deep-sea giants have been documented in the South China Sea, extending their known range southward and providing new insights about their feeding behavior.

Established Research Method Yields New Species Record

The discovery emerged from research designed to study natural whale fall processes in deep-sea environments. Led by researchers from Sun Yat-sen University and the Southern Marine Science and Engineering Guangdong Laboratory, the team deployed a cow carcass as bait at a depth of 1,629 meters, southeast of Hainan Island.

This methodology, while unconventional, provided unprecedented access to observe natural feeding behaviors in one of Earth's most inaccessible environments. The placement of cameras at the bait site allowed researchers to document behaviors that had never been observed in Pacific sleeper sharks before.

Expanding the Known Range of Pacific Sleeper Sharks

Pacific sleeper sharks (Somniosus pacificus) were previously documented in the colder waters of the North Pacific Ocean, including the Bering Sea, Gulf of Alaska, and waters off Baja California. This South China Sea documentation represents a southwestern extension of their known range, marking the first recorded instance of the species in this region.

This range extension indicates that Pacific sleeper sharks may be more widely distributed than previously documented. As Han Tian from Sun Yat-sen University notes, "Although Pacific sleeper sharks have also been found in the deep waters of their typical distribution range in the North Pacific, their frequent occurrence in the southwestern region of the South China Sea suggests that our understanding of this population remains significantly limited."

Notable Feeding Behaviors Observed

Size-Based Feeding Patterns

The footage revealed different feeding approaches based on shark size. Larger sharks (those exceeding 2.7 meters in length) directly and aggressively attacked the carcass, while smaller individuals (under 2.7 meters) exhibited cautious and deliberate circling behavior before approaching.

This size-based difference in feeding strategy suggests behavioral adaptations that may reduce competition and potential injury risk among individuals of different sizes.

Previously Undocumented "Queuing" Behavior

One of the most interesting observations was apparent queuing behavior where sharks yielded their feeding positions to individuals approaching from behind. The research team documented external scars on the pectoral fin of one shark, possibly indicating previous competitive encounters.

According to Han Tian from Sun Yat-sen University, "This behavior 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."

The researchers note this behavior resembles hierarchical feeding patterns observed when sharks scavenge from large floating whale carcasses at the surface, though they acknowledge the possibility that departing sharks may simply be avoiding competitive risk.

Eye Retraction During Feeding

The research team documented distinct eye retraction movements during feeding. Unlike many predator species that possess protective eye membranes, Pacific sleeper sharks lack this anatomical feature. Researchers believe this retraction behavior serves as a defensive reflex, protecting their eyes during feeding activities.

This behavioral adaptation demonstrates one way these sharks have evolved to protect vulnerable anatomical features while feeding on tough carcasses in their deep-sea environment.

Parasites and Ecosystem Interactions

The footage also documented several white organisms, presumed to be female copepods with two long posterior extensions interpreted as egg sacs, in the dorsal head region of larger sharks. While the parasites could not be precisely identified due to limited comparative ecological imagery, the documentation provides direct evidence that Pacific sleeper sharks can be parasitized by large and uncommon copepods.

The research team noted questions about whether these represent obligate parasites specializing in Pacific sleeper sharks, or if the parasites were transported from surface waters to the deep sea. Additional deep-sea organisms appeared in the footage, including snailfish (Liparidae family), Bathynomus species, and various colored deep-sea amphipods (Hirondelleidae family).

Female-Only Observation Raises Questions

All eight sharks documented in the footage were identified as female. This finding aligns with observations of other deep-sea species, including megamouth sharks, which also show female bias in South China Sea waters.

The consistent presence of only females raises questions about whether this region may serve as important habitat for female Pacific sleeper sharks, though more research would be needed to confirm any nursery function or determine if this represents seasonal aggregation patterns.

Implications for Deep-Sea Ecosystems

The feeding behavior observed by the research team suggests that the deep waters of the South China Sea contain food resources sufficient to support these large predators. As Han Tian notes, "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."

The presence of Pacific sleeper sharks feeding at depth indicates that deep-sea food webs in this region may be more complex than previously documented. The research suggests that large chunks of organic material falling to the deep sea floor may be more frequent than previously thought in the South China Sea.

Conservation Considerations

The documentation of Pacific sleeper sharks in the South China Sea provides important baseline information for understanding their distribution. These slow-growing, late-maturing sharks can be vulnerable to fishing pressure and environmental changes. Accurate distribution data is valuable for developing appropriate management strategies.

The potential aggregation of female sharks adds another consideration for conservation planning, as protecting areas where females may concentrate could be important for population maintenance.

Scientific Methodology and Future Research

This research, published in Ocean-Land-Atmosphere Research, demonstrates the value of innovative research methods in studying deep-sea ecosystems. The use of organic bait to attract and observe natural behaviors provides insights that would be impossible to obtain through traditional sampling methods.

The success of this approach opens possibilities for similar studies in other unexplored deep-sea regions. Future research may reveal additional range extensions and behavioral insights for Pacific sleeper sharks and other deep-sea species.

Understanding Sleeper Sharks in the Fossil Record

From a paleontological perspective, this discovery enhances our understanding of how shark distributions have changed over time. Pacific sleeper sharks belong to a lineage with an extensive fossil record, and understanding their current distribution patterns helps interpret historical biogeographic data.

While sleeper shark teeth are rarely encountered in fossil collections due to their deep-water habitat and preservation challenges, specimens that do exist provide valuable insights into the evolutionary history of this remarkable lineage.

The Broader Context of Shark Research

This groundbreaking research exemplifies the importance of continued deep-sea exploration and study. Despite covering over 95% of Earth's living space, deep-sea environments remain largely unexplored. Each new discovery, like these Pacific sleeper sharks in the South China Sea, fundamentally changes our understanding of marine ecosystems.

For naturalists and collectors interested in shark biology and evolution, this research highlights the dynamic nature of our understanding. Scientific discoveries continue to reveal new aspects of shark behavior, distribution, and ecology, reminding us that there is still much to learn about these remarkable predators.

Conclusion

The first documentation of Pacific sleeper sharks in the South China Sea provides valuable new information about their distribution and feeding behavior. This research reveals interesting behavioral patterns, including queuing behavior and size-based feeding strategies, while documenting the species' presence in previously unrecorded habitat.

The observed behaviors—from queuing patterns to eye retraction—demonstrate adaptations that allow these sharks to feed effectively in deep-sea environments. For the scientific community and those interested in shark biology, this research contributes to our understanding of how these predators utilize deep-sea resources and interact with their environment.

The study raises new questions about Pacific sleeper shark ecology and distribution that warrant further investigation. As deep-sea exploration continues, research like this helps build our knowledge of these poorly understood ecosystems and the animals that inhabit them.

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This research was published in Ocean-Land-Atmosphere Research and conducted by the team at Sun Yat-sen University and the Southern Marine Science and Engineering Guangdong Laboratory. The study, titled "Predating Behavior of the Pacific Sleeper Shark in the Deep Waters of South China Sea," represents a significant contribution to our understanding of deep-sea shark ecology.