Deep-Sea Mining and the Survival Crisis of Sharks and Chimaeras

（圖片來源：Judah AB et al. (2025)，採用 CC BY 4.0 授權）

The deep ocean has long remained one of the least explored regions on Earth. Yet today it faces growing pressure from human resource extraction. As attention turns toward the vast mineral reserves lying on the seabed—such as polymetallic nodules, polymetallic sulfide deposits, and cobalt-rich ferromanganese crusts that formed over millions of years—there is increasing concern that exploiting these resources could unintentionally destabilize deep-sea ecosystems. A study conducted by scientists from the University of Hawai'i and several international institutions indicates that deep-sea mining may pose greater threats to sharks, rays, and chimaeras than previously recognized.

The research analyzed 1,223 species of marine cartilaginous fishes worldwide and found that 30 species have habitats that strongly overlap with areas designated by the International Seabed Authority as potential mining zones. These overlaps occur mainly in international waters of the Pacific, Indian, and Atlantic Oceans. Alarmingly, nearly two-thirds of these species are already categorized as threatened or vulnerable, meaning that the additional pressure from mining activities could further increase their risk of extinction.

These animals are closely tied to deep-sea environments. Some species occasionally dive to great depths, such as the whale shark (Rhincodon typus), while others spend their entire lives in the dark depths thousands of meters below the surface, including members of the order Chimaeriformes. Disturbances in deep-sea environments can therefore alter their habitats, behavior, and ecological interactions.

The study identifies two primary pathways through which deep-sea mining could threaten these animals. The first pathway involves direct disturbance of the seabed. Mining vehicles moving across the ocean floor scrape sediments and mineral layers while generating large sediment plumes and intense noise. Such disturbances can destroy habitats that some species rely on for reproduction. For example, certain catsharks attach their egg cases to deep-water corals, while some skates deposit eggs within coral gardens on seamounts. If mining disrupts these environments, long-established reproductive grounds may disappear.

Some deep-sea skates have even been observed laying eggs near hydrothermal vents, where warm water currents may help incubate embryos. If mining activities target mineral deposits around these vent systems, these natural nurseries could be eliminated.

The second pathway of impact arises from discharge plumes released into the water column. After mineral-rich sediments are pumped up to mining vessels, excess water and fine particles are discharged back into the ocean. These plumes can spread horizontally for many kilometers and vertically across large portions of the water column. Fine particles may remain suspended for days to months, and the smallest particles may persist even longer, drifting across wide areas with ocean currents.

For predators that rely on vision to locate prey, increased turbidity can severely reduce hunting efficiency. Suspended sediments may also cause respiratory stress and expose animals to toxic metals. Large filter-feeding species such as the whale shark and the giant manta ray (Mobula birostris) are particularly vulnerable because they filter enormous volumes of water while feeding. When plumes pass through their habitats, they may ingest fine sediments and heavy-metal particles.

These effects are unlikely to remain confined to the immediate mining site. Ocean currents can carry sediment plumes more than a hundred kilometers away, potentially triggering cascading ecological consequences. Plankton populations may decline or shift distribution, affecting the entire food web. Reduced light penetration may also disrupt the bioluminescent signaling used by many deep-sea organisms to communicate, hunt, or evade predators.

The study also examined how the depth ranges of different species overlap with mining activities. More than eighty percent of the identified species occur at depths that intersect with proposed mining zones. For instance, the chocolate skate (Rajella bigelowi) has approximately 75 percent of its depth range overlapping with polymetallic sulfide mining depths. Because this species lays eggs directly on the seafloor, mining operations could directly damage its reproductive habitat.

Other species also show substantial overlap with mining depths, including the Portuguese dogfish (Centroscymnus coelolepis), the great lanternshark (Etmopterus princeps), and the small-eyed rabbitfish (Hydrolagus affinis), each with more than seventy percent depth overlap with some mining scenarios. Once large-scale extraction begins, these species may have little ability to avoid the disturbances.

Minimum and maximum habitat depths of multiple chondrichthyan species and the calculated proportion of overlap with different mining activities and discharge plume depths; (A) polymetallic nodules (PMN); (B) polymetallic sulfides (PMS); (C) cobalt-rich ferromanganese crusts (CFC)（圖片來源：Judah AB et al. (2025)，採用 CC BY 4.0 授權）

The researchers also modeled how different depths of discharge plume release could influence ecological risk. Their analysis suggests that if discharge plumes are released at depths shallower than about 1,000 meters, almost all of the affected species could experience exposure. However, if plume discharge occurs deeper than roughly 2,000 meters, the overlap with many species decreases dramatically. For this reason, the depth of approximately 2,000 meters is considered a critical ecological threshold that could reduce potential impacts.

Nevertheless, deeper plume release does not completely eliminate risk. Mining machinery itself produces strong vibrations and noise that may interfere with sharks' highly sensitive sensory systems. Artificial light from vessels and equipment could also alter the behavior of deep-sea animals. In addition, mining vessels may act like floating fish aggregation devices, unintentionally attracting marine animals. Over longer timescales, metal particles released into the environment could accumulate through food webs and ultimately reach commercial fisheries and human consumers.

To mitigate these risks, the researchers propose several recommendations. First, international organizations such as the International Union for Conservation of Nature and the Convention on the Conservation of Migratory Species should incorporate deep-sea mining into conservation risk assessments for cartilaginous fishes.

Second, comprehensive baseline monitoring programs should be established before mining begins. These programs should track the abundance, behavior, and movement patterns of sharks, rays, and chimaeras over time. Instead of relying solely on occasional sightings, scientists should deploy baited cameras, tagging technologies, and other long-term monitoring tools to obtain accurate ecological data.

Third, protected zones similar to Areas of Particular Environmental Interest should be created around mining regions to safeguard biodiversity. Conservation initiatives such as Important Shark and Ray Areas could also help identify critical habitats that require protection.

Finally, discharge plumes should ideally be released at depths deeper than 2,000 meters—or as close to the seabed as possible—to minimize interactions with midwater species.

Sharks, rays, and chimaeras are already among the most threatened vertebrates on Earth. The expansion of deep-sea mining introduces yet another pressure on species that are often slow-growing, long-lived, and vulnerable to environmental disruption. As humanity pursues the metals needed for emerging technologies and renewable energy systems, an essential question remains: if even the deepest parts of the ocean lose their role as ecological refuges, what does “sustainable development” truly mean?

Author: Shui-Ye You

Reference:

Judah AB et al. (2025). Deep-sea mining risks for sharks, rays, and chimaeras. Current Biology.