What mystery super-predator devoured a 3-m long Great White Shark? It could be an even bigger shark!

Tuesday, June 10, 2014, 6:31 PM - What's more frightening than a 3-metre-long Great White Shark roaming around your coastline? The 4.5-metre-long 'super-predator' shark that ate it!

A team of researchers who were tagging sharks along Australia's coast, in order to track their movements, faced a real mystery recently. A beachcomber returned one of their tracking devices, which he'd found washed up along a stretch of beach. Examining the data from it, they discovered that it was one they'd deployed only four months earlier, to tag a 3-metre-long female Great White Shark, only a few kilometres down the coast from where the device was found. 

Even more surprising was the actual tracking data it held. The tag, which was attached to the shark's skin, logged a temperature of around 8 degrees C (46 F) as the shark very quickly dove deep along the continental shelf, and then the temperature suddenly spiked up to 25.5 degrees C (78 F) in just a few seconds. It measured that steady temperature for more than a week, while continuing to move around in the water - even between the depths and the surface where temperatures can vary by about 10 degrees C - before it again started reading temperatures consistent with the water around it.

The explanation that matches this? This 3-metre-long Great White was eaten by another, bigger shark! A "colossal cannibal Great White Shark," the researchers said, according to Gizmodo, that's likely up to 4.5 metres long and tipping the scales at over 2 tons.

This may seem like something the SyFy Channel would offer up as its latest 'mega-shark' movie, but it's actually quite possible. Most sharks are cold blooded (thus their body temperature matches the water temperature), but Great Whites are different. They (along with other members of the Lamnidae family) have a strip of red muscle in their core that keeps their internal body temperature roughly 14 degrees Celsius higher than the water around them. Also, whatever it was would have to be fast enough to not only overtake a Great White, but also big enough to scare this 3-metre shark into making a run for it. Something like a giant squid could certainly kill a shark, but they're cold-blooded, so it wouldn't match the temperatures measured by the tracker. A killer whale is another possibility, but since they're mammals, their core temperature is much higher, around 37-38 degrees C. However, a Great White's core temperature in water that's around 8-9 degrees C would roughly match the 25.5 C temperature the tracker recorded. So, a bigger, meaner shark could certainly fit the bill.

The Smithsonian Channel produced a documentary about the efforts to solve this mystery. The clip below gives a taste of what they'd found.