What goes on off the coast of the Western Cape in South Africa? Since the beginning of May 2017, great white sharks (Carcharodon carcharias) began to wash up on the beaches of the Gansbaai Harbour. These specimens all had one thing in common: they were found partially eaten and most notably without their liver.
The latest shark to have washed up was just this summer. According to the team from the Dyer Island Conservation Trust who examined the animal, it was a male measuring 4.1 meters long. The autopsy revealed that its liver, as well as its testicles and stomach, were missing.
“The carcass may be a few days old but it seems relatively fresh and bled out massively,” explained DICT biologist Alison Towner on the Marine Dynamics Blog, a society that provides a shark cage diving experience. The Gansbaai harbour is a reputable destination for this due to its large shark population.
No one was around during the last moments of the four sharks that were discovered dead, but the wounds on their bodies suggest that the culprit was orcas (Orcinus orca). These animals are known for being dangerous predators and although great whites are not their usual prey, it’s not unprecedented.
Like great white sharks, orcas live just of the west coast of South Africa where the Atlantic and Indian Oceans meet. Although Andrew Nosal, a specialist at Saint Katherine College in San Marcos (California), interviewed by LiveScience, has never heard of a shark being attacked by Orcas in this area, he does know that it happens in other regions.
In 2014 for example, a group of Orcas was filmed violently attacking a tiger shark. These marine animals are also known for hunting smaller sharks like the broad nose seven-gill shark, whose livers they often eat which isn’t just a random organ.
Big and fatty
Sharks have a relatively large liver. As Andrew Nosal explains “Bony fishes have a swim bladder that they can fill with gases and those gases provide buoyancy for the fish. Sharks do not have a swim bladder. Instead, they have a very large liver.” Meaning this, therefore, is organ that allows the sharks to float.
In addition to being rich in fats, a shark’s liver is “very energy- and nutrient-rich.” So it’s not surprising that killer whales attack them. “They have a high metabolism, and they have a lot of nutrient needs, and so those fats might really help them out,” added Nosal.
According to the Marine Dynamics Blog, a pair of orcas was effectively spotted off the coast of Danger Point during the morning of the day where the fourth shark washed up in the harbour. Similarly, there were no great white sharks spotted underwater during all the dives that were done that same day. The question now is whether the killer whales are really behind the shark's death.
Killed or just eaten?
With no witnesses or video proof, it is difficult to know if the orcas had actually killed the sharks before eating them or if they had just attacked sharks that were already injured or even dead. However, Andrew Nosal dismisses the theory that great whites may have been involved in a boat collision.
“These sharks are certainly common at the surface, and so a boat strike is possible,” he told LiveScience. “However, because three sharks washed up around the same time, three boat strikes are unlikely.”