Sharks found living in active volcanoes, scientists puzzled on why

There are many theories why sharks would willingly seek out such extreme conditions, but one theory is that they are simply safer there.

Dusky shark (Carcharhinus obscurus) at SeaWorld, Queensland (photo credit: SEAWORLD SHARK / WIKIMEDIA COMMONS)
Dusky shark (Carcharhinus obscurus) at SeaWorld, Queensland
Several species of sharks continue to baffle scientists due to their presence in what should be one of the most dangerous environments on the planet: Active volcanoes.
The ability of sharks to not only inhabit volcanoes, but to thrive in them and actively seek them out, is a mystery that has confused many scientists, but it is something one researcher, Florida International University marine ecologist Prof. Michael Heithaus, is determined to answer, the Daily Express reported.
The discovery of sharks inhabiting a volcano first occurred in 2015 during a National Geographic documentary, where they – alongside close relatives, stingrays – were seen inhabiting the undersea Kavachi volcano in the Solomon Islands.
”I thought it sounded like a sci-fi movie. It's an amazing find," Heithaus said, according to the Daily Express.
"It just demonstrates how adaptable sharks are.
"Extreme environments are something they can clearly handle; whether it's a volcano or surviving thousands of meters underwater.
"It's really not yet known why they are there. It could be something to do with reproduction, or who knows what else is living in there... maybe they're just sniffing out a meal."
Now informally known as "Sharkcano," Kavachi is one of the most active marine volcanoes on the planet, which makes studying the sharks very difficult. However, the conditions there are very extreme to begin with. The sharks are, essentially, residing in an active crater 18 meters below the surface of the ocean. Temperatures in the waters at this depth are incredibly dangerous, approaching boiling point.
Heithaus, however, hypothesizes that the key may be the ampullae of Lorenzini, a cluster of pores found on their snouts, which he suspects provides sharks with a sixth sense of sorts that can detect changes in the planet's magnetic field. This, in turn, would allow sharks to detect volcanic eruptions ahead of time and swim to safety, as well as helping them find other volcanoes, the Daily Express reported.
This theory is far from unprecedented.
"You would think it's dangerous but studies have shown us they can detect approaching hurricanes and cyclones, so they may be able to detect when something bad is about to happen and move out of the way," Heithaus explained.
But why are sharks so drawn to volcanoes? Kavachi is, after all, far from the only example. Another such example can be found in Piton de la Fournaise, an active volcano – in fact, one of the most active in the world – on Réunion Island in the Indian Ocean. The volcano is on land, but that has not stopped sharks from being so prevalent that swimming in the ocean was actually made illegal in recent years, the Daily Express reported.
Despite being on land, sediment still washes into the ocean from the volcano's slope, causing the water to appear cloudy. It is these waters that Heithaus believes draws the shark to the island, as they make an idea hunting ground.
There are other theories put forward as for why sharks swarm volcanos.
"It's really not yet known why they are there. It could be something to do with reproduction, or who knows what else is living in there... maybe they're just sniffing out a meal," Heithaus explained.
However, there is another, simpler possibility: these habitats are simply safer for them.
This is due to the fact that such extreme conditions serve as protection against the greatest danger facing sharks: overfishing.
”The biggest threat to sharks by far is overfishing," Heithaus explained, according to the Daily Express.
“There are just too many being caught and that is being driven by the demand for fins and shark meat.
"You're not going to go fishing around a volcano and probably some of the bigger sharks, who are predators, will be less inclined to go in there.
"We may not know exactly why they are there but the fact we saw so many in a fairly short window of time, suggests it is an important place to those sharks.
"If it wasn't a great place to live they probably wouldn't be there… who doesn't like a hot tub?"
This theory has further precedence in Israel, where sharks gather in large numbers unlike almost anywhere else in the Mediterranean. For several years, sharks have been seen gathering in large numbers to the shores of Hadera, specifically near the warm waters found near the Rabin Lights power plant. Just like Heithaus, researchers from the Morris Kahn Marine Research Station of Haifa University have theorized that sharks somehow sense the heat and go there, but this was just a theory.
The large grouping of sharks is an especially rare phenomenon, particularly in the Mediterranean, where shark numbers are dwindling. In addition, sharks also have been seen gathering near some of Israel's other beaches, with dozens of sandbar sharks seen gathering near Ashdod back in May. Combined with the groupings seen in Hadera, the massive gatherings off the coast of Ashdod lend further credence to Israel becoming a "desert oasis" of sorts for sharks.
The reason for this? According to Dr. Avad Sheinin, head of apex predator research at the Morris Kahn Marine Research Station, it's because Israel is safer for them.
As Sheinin explained, it is illegal to fish for sharks and stingrays in Israel, where they are registered as protected natural assets.
"It's important to remember not to harm the [sharks and stingrays] or their environment," Sheinin explained.
"Sharks are the predators of the marine ecosystem and understanding their patterns and behavior is essential to understanding our entire system."
He added that "It seems that while in most Mediterranean areas the sharks are endangered, while here, our beaches are exceptionally welcoming for them."
As sandbar sharks are so rare, being endangered in the Mediterranean, efforts to tag and track them were underway. However, the Morris Khan Marine Research Station was forced to shut down the research earlier in 2020 due to the coronavirus pandemic. It is hoped that when research is able to resume, it could answer many questions about one of the ocean's most famous apex predators.
Celia Jean contributed to this report.