It's a Shark Eruption! 🦈🌋 | Sharkcano Full Special

Key Concepts

Shark-Volcano Synergy: The powerful, multifaceted attraction and ecological relationship between sharks and volcanic environments.
Turbid Water Hunting: The ability of certain shark species, particularly bull sharks, to hunt effectively in murky, low-visibility waters.
Bull Sharks: An aggressive shark species known for its stout body, small eyes, and reliance on senses other than vision, thriving in turbid conditions.
Gray Reef Sharks: A common reef-dwelling shark species found around coastal areas and reefs of volcanic islands.
Great White Sharks: Large pelagic predators that utilize remote volcanic islands as predictable hunting grounds for concentrated prey.
Ampullae of Lorenzini (Electroreception): A specialized sensory organ in sharks that detects weak electric fields, potentially also used for magnetic field detection.
Magnetic Navigation: The theory that sharks use their electroreceptors to detect Earth's magnetic field and magnetic anomalies in volcanic rock for navigation.
Submarine Volcanoes (Kavachi): Underwater volcanoes, some of which are active and can host unique shark populations.
Dormant vs. Active Volcanoes: The distinction between volcanoes that are no longer erupting (dormant) and those that are currently active, each presenting different ecological conditions.
Volcanic Islands as Oases: The concept that remote volcanic islands create thriving ecosystems in otherwise barren open ocean, attracting diverse marine life.
Erosion and Sedimentation: Natural processes on volcanic islands where heavy rainfall causes soil and rock to flow into the ocean, creating turbid waters.

The Mysterious Attraction: Sharks and Volcanoes

The video explores the intriguing and powerful connection between sharks and volcanoes, a phenomenon investigated by world-renowned shark scientist Dr. Michael Heighthouse. This isn't science fiction; it's a real-world synergy observed globally. The French island of La Reunion in the Indian Ocean serves as a prime example, being home to one of Earth's most active volcanoes and some of the ocean's deadliest sharks. Since 2011, La Reunion has experienced 24 shark attacks (11 fatal, 13 resulting in limb loss), leading to a ban on swimming since 2013. While local experts attribute these incidents to a "perfect storm of human and natural causes," Dr. Heighthouse posits an additional factor: a direct synergy between Reunion's active volcano and its shark population. He states, "When you look at Reunion Island, it's not an island with a volcano. It is a volcano that has built an island."

Turbid Waters: A Bull Shark's Advantage

Active volcanic islands, particularly in tropical climates with heavy rainfall, undergo significant erosion. The absence of stabilizing vegetation leads to sediment flowing downstream and into the ocean, creating "turbid waters" – murky, low-visibility conditions often described as "chocolate milk." In Reunion, most attacks are attributed to bull sharks, a species distinguished by their stout bodies, broad rounded snouts, and small eyes, growing up to 7 feet long. Bull sharks are known for their aggressive nature and ability to attack prey almost their own size, unlike most sharks that target prey around 10% of their size.

Crucially, bull sharks possess a unique sensory advantage. Their smaller eyes suggest less reliance on vision, but they have an "amazing sense of smell." This allows them to find and catch prey easily in murky water, potentially giving them an advantage over prey with less developed sensory systems. Other shark species, like white sharks, prefer clear water. To observe these conditions safely, Dr. Heighthouse used an "underwater camera" (a periscope-like device) near river mouths in Reunion, confirming visibility of only "greenish blue gunk" extending merely three to four feet. This observation aligns with the statistic that "about 2/3 of the shark attacks here on Reunion have occurred in turbid water conditions like these."

Experiment: Bull Shark Hunting in Zero Visibility

To understand how effectively bull sharks hunt in murky conditions, Dr. Heighthouse conducted an experiment at Bimini Island in the Bahamas, known for its bull shark population. He teamed up with veteran underwater cameraman Duncan Break.

Methodology:

Clear Water Test: Sharks were first observed feeding in clear water. They attacked bait "the instant it hits the water," demonstrating rapid prey acquisition in high visibility.
Simulated Turbid Water Test: A blower was used to churn up the sandy bottom, creating "near zero visibility" or "near blackout volcanic conditions," simulating the turbid waters of Reunion.
Safety Measures: Dr. Heighthouse observed from inside a steel shark cage, while Duncan Break, needing clear footage of shark behavior, worked outside the cage with a safety diver. Duncan expressed significant wariness, noting bull sharks' unpredictability and temperament shifts.
Observation in Zero Visibility: Duncan was effectively "swimming blindfolded." Dr. Heighthouse utilized an "imaging sonar" to track the sharks' movements.

Results: The bull sharks "feed in volcanic zero viz conditions with absolutely no problem." The sonar revealed that these animals moved "gracefully and pretty much in the same way they do when the visibility is good." Dr. Heighthouse concluded that "turbid water, it doesn't make too much of a difference to cold search." This experiment convinced him that bull sharks not only tolerate but "thrive in" turbid volcanic areas, which serve as "perfect hunting grounds" by "turning the lights out for a lot of their prey."

Dormant Volcanoes: Reef Oases for Sharks

The investigation extended to dormant volcanic islands, which also attract sharks by fostering rich marine ecosystems. Dr. Heighthouse visited Mauritius, an 8-million-year-old volcanic island 100 miles east of La Reunion, covered in thick vegetation. This provided a "window into what Reunion might look like several million years in the future."

Observations in Mauritius: Unlike Reunion, Mauritius featured "crystal clear water" and "lush reefs" with "jagged volcanic terrain" offering abundant "nooks and crannies for corals to take hold and for fish to hide from predators." Despite strong currents, Dr. Heighthouse and Duncan Break found shelter in a large volcanic cavern known as "the cathedral," where they observed a "healthy congregation" of gray reef sharks. These sharks, common in the region, "love being close to these drop offs" and "rule" these reef areas, sometimes displaying aggressive "pectoral fins down and arch their back" behavior if provoked.

Conclusion: Volcanic islands, whether active or dormant, act as "oases in the desert where you've got food chains that are just thriving." These remote islands are "critical food source for sharks," attracting not only coastal species like reef sharks but also large pelagic predators.

Volcanic Outposts: Hunting Grounds for Great Whites

Remote volcanic islands also serve as crucial hunting grounds for large pelagic sharks. Guadalupe Island, a volcanic palisade 150 miles west of Baja Mexico, is a prime example. It's an annual birthing ground for seals and sea lions, including the enormous elephant seal. These intelligent seals, capable of diving to 8,000 feet and holding their breath for two hours, are "not easy for a white shark to take down, but very lucrative if they do."

The unique topography of volcanic islands plays a key role: "Volcanic islands have steep underwater flanks, allowing white sharks to come right up to the beach." This creates a "narrow zone" where seals are highly vulnerable when entering or exiting the water. Cinematographer Andy Cassagrandi captured a chilling encounter at Guadalupe, filming a great white shark devouring an elephant seal. This demonstrated that "big pelagic sharks like the great white seem to understand that big juicy meals like elephant seals can be scored around these remote volcanic outposts."

Magnetic Navigation: The Shark's Sixth Sense

A fundamental question arises: how do sharks find these tiny, isolated volcanic islands in the vast open ocean? Dr. Heighthouse believes the answer lies in the shark's mysterious "sixth sense." Sharks possess all five human senses plus an additional one: the ability to detect electric fields. This is facilitated by the Ampullae of Lorenzini, an array of pores across their snout that pick up "tiny changes in electric energy." This "superpower" is primarily used for hunting prey.

Dr. Heighthouse, collaborating with Dr. Steven Kajura (Florida Atlantic University), hypothesized that if sharks can detect electric fields, they might also detect magnetic fields, given the close intertwining of electricity and magnetism. This could enable sharks to use Earth's magnetic field as a compass and detect "anomalies in the lava" of volcanic islands as navigational "way points."

Experiment on Magnetic Detection:

Target Species: Hammerhead sharks (chosen for their numerous Ampullae of Lorenzini) and nurse sharks (which also appeared).
Setup: An open-water laboratory in Bimini. Three powerful 50-pound magnets were arranged in an arc to the right, and three identical-looking non-magnetic aluminum control blocks were placed to the left. Bait lured sharks into the test field.
Observations:
- Hammerheads: Ignored the aluminum controls but "clustered around the magnets," with one observed to "jerk its head a bit when it got close."
- Nurse Sharks: Showed an even "stronger response," becoming "agitated" and "biting at the magnets," swarming the area.
Conclusion: Both hammerheads and nurse sharks "did respond to the magnets." This suggests that "those weak magnetic fields that are locked in volcanic rock are something that the sharks could detect and may be able to use in navigation." Sharks likely use Earth's magnetic field for broad navigation and volcanic lava anomalies as specific waypoints.

Active Volcanoes as Shark Habitats

The most astonishing discovery came from Dr. Brennan Phillips (National Geographic grantee), who found sharks inhabiting the caldera of an active submarine volcano "almost by accident." His expedition focused on Kavachi, an active underwater volcano in the South Pacific, whose caldera is only 60 feet beneath the surface and can erupt at any time.

Methodology:

Surface Robot: A remote-controlled robot with a camera and sensors was deployed close to the volcano, capturing an eruption.
National Geographic Drop Camera: An autonomous, self-powered camera was "chucked off the side of a boat" directly into Kavachi's crater.

Findings: The drop camera recorded "live images of sharks swimming inside the caldera of an active volcano." Despite the extreme conditions – "heat and the caustic nature of all the water that's coming out of the volcano" – these sharks "seem to be fine and thriving in there." Dr. Phillips hypothesized that they might leave during eruptions, sensing them and getting "right out of the way," suggesting a "community that is used to this activity." Possible reasons for their presence include food sources or "nice warm water" for energy, digestion, or reproduction. Dr. Phillips famously stated, "Did we discover a sharko? Yeah, we did. We found sharks living in a volcano."

Synthesis and Conclusion

The evidence overwhelmingly demonstrates a profound and multifaceted connection between sharks and volcanoes. Volcanoes are "critical to ocean ecosystems," serving as "oases out in the middle of nowhere." This attraction manifests in several ways:

Active volcanoes create turbid waters that provide ideal hunting grounds for specialized predators like bull sharks.
Dormant volcanic islands foster rich, biodiverse reef ecosystems, offering abundant food and shelter for various shark species.
Remote volcanic outposts act as predictable hunting grounds for large pelagic sharks, concentrating prey due to unique topography.
The magnetic properties of volcanic rock may serve as crucial navigational waypoints for sharks utilizing their electroreception.
Remarkably, some sharks can even directly inhabit the calderas of active submarine volcanoes, possibly for food or warm water.

This research highlights that "the incredible fact that sharks are inside a volcano shows these two fearsome forces of nature share a powerful connection." The video concludes by emphasizing that "we're really only scratching the surface of what we need to know about how volcanoes affect sharks and all the other species that call these waters home."

It's a Shark Eruption! 🦈🌋 | Sharkcano Full Special | @natgeokids