Sharks Filmed Inside Underwater Volcano Just After Eruption

Sharks have been filmed inside an underwater volcano not long after an eruption. The footage is part of a documentary investigating the link between sharks and volcanoes, with species of the group found living near geological hotspots around the world.

Shark scientist Michael Heithaus, from the Department of Biological Sciences at Florida International University, became interested in the connection after reading about sharks that lived in Kavachi—one of the most active underwater volcanoes in the south-west Pacific Ocean. The sharks were first found inside the volcano caldera by Brennan Phillips in 2015.

"Seeing that got me thinking about just how important volcanoes are to life in the ocean," Heithaus told Newsweek in an email interview. "And it isn't just about active volcanoes. It's about the habitat they create out in the middle of the ocean."

The documentary, Sharkcano, will premiere on National Geographic on July 21. It is part of Nat Geo's Sharkfest. This includes three weeks of programming dedicated to the science of sharks and their behavior on Nat Geo, and two weeks on Nat Geo WILD.

In the program, Heithaus travels to locations across the globe looking at how different species of shark have taken advantage of the conditions submarine volcanoes provide. Off the coast of Réunion, in the Indian Ocean, he finds bull sharks taking advantage of the turbulent water, using it as a way of ambushing prey. In Guadalupe Island, west of Baja in Mexico, the team finds an abundance of baby seals that provide easy meals for sharks.

Heithaus says volcanic islands are attractive spots for sharks as they tend to have nutrients flowing into the water, providing the basis of food chains. "And where you have lots of food you tend to have lots of sharks, if there isn't too much fishing to reduce their populations," he said.

"Most of the open ocean is a place without a ton of food...In the open ocean it's volcanoes that have created most of the land out there. So, at the base level many sharks depend on volcanoes in ways most people wouldn't think about. If there hadn't been volcanoes in certain areas there would be no reefs or no land. That would mean that the species of sharks that need those habitats couldn't live in those areas without the presence of a volcano."

He said there may also be other benefits of living near volcanoes. If the volcano is still active, it can provide warm water they use for nurseries.

In the case of Kavachi, Phillips and the team arrive at the site in time for an eruption. The volcano sends ash up above the sea level. The caldera lies just 60 feet beneath the surface of the ocean and, while the volcano is known to erupt on a regular basis, Phillips said it caught them "off guard."

Shark photographed from below. A new National Geographic documentary looks at the relationship between sharks and volcanoes. National Geographic

They then sent an autonomous, robotic camera into the volcano to get a closer look at the life inside. The camera sunk into the volcano and filmed what was happening as it descended. Images showed cloudy water until, "out of nowhere," they saw numerous sharks moving quickly around. Phillips said there are many reasons for the sharks to not go into the volcano, yet they appeared to be "thriving" in there. He said they do leave when there is an eruption and appear to sense it before it happens. "This seems to be a community that is used to this activity," he says in the program.

Heithaus believes the sharks are inside the volcano because they like the warm water or are looking for food. In terms of their being able to sense an eruption, he said: "Sharks have incredible sensory systems. Like many other species they have the ability to detect changes in the environment before we do. They head for deeper waters before hurricanes hit—probably because they can detect changes in the atmospheric pressure. For eruptions, we don't know but they might sense vibrations in the water or detect some of the sounds that come before an eruption."

Scientists are now working to understand this behavior, he said. Heithaus will now continue to study shark behavior to, ultimately, learn how we can better protect them. "A big part of that work is understanding what determines where sharks naturally occur. The types of islands they associate with—including volcanoes—is part of that puzzle. Ultimately, what I really want to know is when, where and why are sharks important to the health and function of ecosystems so we can start to restore their populations and functions in the many places their populations have crashed."

Sharkcano will premiere on National Geographic on Tuesday, July 21.

This article has been updated to include more information on Sharkfest.

Schedule for National Geographic's Sharkfest National Geographic