A shocking video showing a shark almost bitten in half by another shark has emerged, as experts ask whether cannibalistic attacks among the creatures are more common than we might realize.

A clip from Nat Geo WILD documentary Cannibal Sharks shows an enormous predator attempting to bite a smaller shark. Cannibal Sharks is running as part of Nat Geo WILD's SHARKFEST, which features user generated content shot around the globe.

There is "mounting evidence that shark-on-shark attacks happen a lot more than we ever realized," according to Nat Geo WILD.

The video was shot by divers off Neptune Island, South Australia, near the city of Adelaide, a spot known for being home to Great White Sharks.

In the video, a diver is heard yelling profanities as he watches the shark rising out of the water towards another shark, whose tail can be seen flapping in apparent distress.

Adam Malski from Sydney, Australia, who shot the footage in 2014, told News.com.au at the time: "I had literally just come up from my 25 [meter] dive and dried off and grabbed my camera. I said to the dive master 'what would happen if a smaller shark got in the way of a bigger one?' They said they had never seen it before and literally within about six seconds—it happened. I was filming the whole thing trying to keep still and calm because it was so incredible. They're such an elusive creature so I was so fortunate to be there."

The snippet from the documentary also showcases a jaw-dropping image taken off North Stradbroke Island in Queensland, near Brisbane, where a shark's fleshy pink insides are exposed after almost being bitten in half by another, bigger shark.

According to a Sky News report from 2009 when the image was taken, the shark was believed to have measured more than 5 meters long, while the smaller shark was 3.7 meters long. The smaller great white was being towed after being caught on a drumline when it was attacked.

Dr Mark Meekan, a fish biologist at the Australian Institute of Marine Science who has studied the effects of fishing on sharks in northern Australia, commented on the photo in the documentary.

"What an amazing photo," he said. "I mean, this is an enormous shark, it's 12 feet long but look at the size of that bite. It's absolutely massive. That's an immense amount of power you need to take a bite out of another shark like that. You have to be pretty big yourself."

Michael Heithaus, professor in the Department of Biological Sciences at Florida International University who also appeared on the documentary, told Newsweek: "Sharks eat other sharks more often than most people might think. For some species of large sharks, like bull sharks, great hammerheads, and tiger sharks, smaller sharks are a favorite prey item.

In some cases, sharks will cannibalize smaller individuals of the same species, he explained. "The reason that a lot of species have nursery areas in shallow protected waters is to stay safe from larger sharks that would eat them until they grow big enough to be safe." 

In fact, experts think sharks devouring one another dates back hundreds of millions of years. 

One study published in 2016 concluded sharks living 300 million years ago likely ate their offspring in times of need. Scientists who published their findings in the journal Palaeontology analyzed the feces of Orthacanthus sharks, and found the teeth of juvenile animals indicative of an act known as "fillial cannibalism".

Howard Falcon-Lang of Royal Holloway University of London, who co-authored the study, commented at the time: "We don't know why Orthacanthus resorted to eating its own young.

"However, the Carboniferous Period was a time when marine fishes were starting to colonise freshwater swamps in large numbers. It's possible that Orthacanthus used inland waterways as protected nurseries to rear its babies, but then consumed them as food when other resources became scarce."

And despite their cannibalistic ways, Heithaus said sharks are unfairly given a hard time. He told Newsweek: "One of the biggest misconceptions is that they are mindless killing machines that are eating all the time. Sharks spend the vast majority of their time not eating and are not attacking everything that they see."

Pointing out another misconception, he stressed sharks aren't all the same size.

"There are more than 500 species and they vary in size from the palm of your hand to almost the size of a school bus," said Heithaus.

This article has been updated with comment from Michael Heithaus.

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