When we think of super-predators in the ocean, we usually think of the great white shark, or the killer whale. But the disappearance of Alpha Shark calls into question the place of great white sharks in the food chain.

In 2003, off the coast of Australia, filmmaker Dave Riggs placed a tag on a great white shark he nicknamed Alpha Shark. His aim: to track its movements with a team of researchers. Four months later, the tag is found washed up on a beach, and the data it reveals is disturbing to say the least.

After several weeks of "normal" shark activity along the south-west coast of Australia, 43.5 miles (70 km) off Bremer Bay, the shark dived very suddenly and at full speed, reaching a depth of 1,900 feet (580 meters). It's a behavior that biologists had difficulty explaining, until they discovered the information from the beacon's thermal sensors.

At a depth of 1,900 feet (580 meters), the water temperature rose from 47.8°F (8.8°C) to 78.8°F (26°C) in just a few seconds. The only scenario that could explain this sudden change is that Alpha Shark dived in an attempt to escape from a bigger fish, but was eaten anyway.

However, these data are of concern to biologists for a number of reasons.

Firstly, great white sharks are considered to be super-predators, meaning that they are at the top of the food chain in their habitat. It is therefore extremely rare for an adult individual to be devoured in this way.

Above all, the body temperature of 78°F (26°C) of the animal that devoured Alpha Shark does not correspond to any of the marine predators capable of killing a great white shark.

It's important to understand that in the ocean, the only predators capable of such a feat are killer whales and other great white sharks. And although cases of so-called 'killer' killer whales have already been observed, such as the two males nicknamed Port and Starboard that killed and devoured at least five white sharks off the coast of South Africa in 2017. It's hard to believe that a killer whale is responsible for Alpha Shark's fate, because the temperature doesn't match up.

The body heat of a killer whale varies between 97.5°F (36.4°C) and 100°F (38°C), so it's pretty close to our own body temperature, but more importantly 19.5°F (10°C) higher than the temperature recorded by the tag.

So the killer of Alpha Shark is not a killer whale.

But just when you think the culprit is obvious, since the only other killer of a great white shark is one of its own kind... the temperature doesn't match either.

The body heat of great white sharks varies enormously, as they can adapt their body temperature from 9 to 21.5°F (5 to 12°C) higher than the water around them. But when Alpha Shark was eaten, the temperature rose from 47.8°F (8.8°C) to 78.8°F (26°C), which is 9.5°F (5°C) higher than the maximum temperature that another great white shark could have produced.

So it wasn't eaten by one of its own kind, but by another predator that remains a real mystery to this day.

Moreover, the existence of such a predator to the great white shark would dethrone the shark from its position as super-predator. Not to mention that to swallow a ten-foot-long (three-metre) beast, this sea monster would have had to be at least twice as big. 

No wonder Alpha Shark tried to flee in the face of such a threat.