Seals are just full of surprises. Not only have these big-eyed, innocent looking pinnipeds been the prime suspects for a decade-long murder mystery case involving hundreds of harbor porpoises, but the pesky mammals have also been caught trying to have sex with penguins. Now, adding to this list of startling behaviors, scientists have caught the animals killing and then partially gobbling up mid-sized predatory sharks.

Although this is the first documentation of such an event, if it turns out to be commonplace, then the discovery could have implications in our understanding of the role that seals play in the marine food web. The observations have been published in the African Journal of Marine Science.

Back in 2004, photographer and shark expert Chris Fallows noticed something rather bizarre whilst on a boat trip near Cape Point, South Africa: a young male seal chasing after a blue shark. When the pursuer caught up with the shark, it hurled the victim into the air and then devoured its innards, or viscera, leaving the flesh. Despite the fact that Fallows often spends as much as 200 days of the year at sea studying sharks, he had never seen this before and did not witness a repeat incident for almost a decade. Then, in December 2012, he watched something even more extraordinary unravel.

During a baited dive for a bunch of tourists in the same area, Fallows witnessed a male Cape fur seal rudely gatecrash the blue shark gathering before proceeding to viciously attack them, killing and feeding on the guts of five of the ten sharks present.

“In more than 2,000 expeditions working with sharks over the last 21 years,” Fallows said at the time, “this is the only time I have ever seen a seal kill several sharks and I can find no record of such an event happening elsewhere.”

Cape fur seals and blue sharks ordinarily share a similar diet, feasting on smaller fish, crustaceans and squid. Both are also known to dine on small shark species, and blue sharks have been seen chasing after fur seals before, although they never managed to catch up. But never before had anyone witnessed fur seals preying on sharks this size, some of which were almost a meter and a half in length (4.5 feet).

Understandably, marine biologists are surprised that the animals would go for such a risky lunch. “You don’t want your meal to come bite you in the ass, and the shark has some potential to cause serious harm,” marine predator expert Dominic Tollit told New Scientist.

Something else which also piqued the scientists’ interests was the observation that the seal only went for the sharks’ viscera. Although this is the richest part of the shark in terms of energy, as pointed out by Smithsonian, the fact that the seal didn’t bother to eat the rest demonstrates that it could afford to be choosey and probably wasn’t lacking in food sources. This could have important implications for the marine food chain since, if seals are only eating the guts of larger prey, then they will need to kill a lot more than if they were eating the whole animal. But right now it’s difficult to determine whether seals could be affecting blue shark populations given the fact that this feeding behavior has only been observed twice.

[Via Smithsonian and New Scientist]