WHEN an electronic tag from a huge shark washed up, the data revealed the predator had been eaten – but no one knows what by.

SMITHSONIAN CHANNEL KING OF THE DEEP: But this mighty creature was overthrown by something

Filmmaker Dave Riggs was given the job of tagging sharks along Australia's coast, and was blown away by the fearlessness of one in particular. The enormous creature – dubbed Shark Alpha – barged Riggs' boat as the crew placed a tag on its side, before disappearing into the depths of the ocean. Four months later the tag was found on a beach two-and-a-half miles away – and what it's data revealed would spark a mystery that continues today.

“What's going to eat a shark that big? What could kill a three-metre great white?” Dave Riggs On Christmas Eve, 2003, the great white plunged at high speed 1900ft down into the vanishing blackness where something very strange happened. Its temperature rocketed from 46 to 78 degrees fahrenheit – a heat the shark could only reach in the belly of another animal. For eight days the tag stayed at that temperature, moving between the surface and a depth of 300ft before being belched up. "When I was first told about the data that came back on the tag that was on the shark I was absolutely blown away," said Riggs.

SMITHSONIAN CHANNEL STUMPED: Dave said he doesn't know what killed the shark

* * MONSTER OF THE DEEP: VIDEO CLAIMS TO SHOW 60ft SHARK * * The question that not only came to my mind but everyone's mind who was involved was, 'what did that?' It was obviously eaten. He asked: "What's going to eat a shark that big? What could kill a three-metre great white?" Well nobody knows for sure, but there are some theories.

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Riggs told a 2014 documentary that the likeliest answer was an even bigger shark. "The internal temperature of the animal that ate the shark is a weird one," he told the Smithsonian Channel. "It appears to be too low for a killer whale and too high for another shark, unless it was massive."

SMITHSONIAN CHANNEL LUNCH: The shark was in the vanishing depths of the ocean when it was eaten by something

It's the same theory reached by YouTube channel Animalist, which gave an idea of its size. "According to researchers the supposed colossal cannibal great white shark would have been 16ft long and over two tons," said one video. "No one is quite sure why this happened but experts suspect that it may have been the result of a territorial dispute or extreme hunger."