How do orcas really hunt sharks

Video: Orcas eat great white sharks

When Alisa Schulman-Janiger heard a few years ago that the carcasses of great white sharks without liver had been washed up on South African beaches, she was shocked.

"I thought it was going to start again," says the biologist.

The first documented case

In October 1997, tourists on a whale watch boat near San Francisco witnessed two killer whales attacking a great white shark and devouring its liver.

It was the first documented sighting of killer whales to eat great white sharks at the time. The incident sparked some fascinating questions:

How could any ocean predator, even a killer whale, control the almighty great white shark?

As it turns out, it wasn't a coincidence. In 2017, five great white sharks were found stranded in the Western Cape of South Africa. Although no one saw the South African killer whales - also known as orcas - kill the sharks, the parallels with the other attacks made the orcas the likely culprit.

Significant impact on the food chain

Overall, the incidents show that interactions between these two predators can have a significant impact on the food chain.

For example, a recent study shows that the presence of orcas scares off sharks from colonies of elephant seals, which in turn benefits the seals, the great prey of the great white sharks.

Tasty livers

Alison Kock, marine biologist at the Cape Research Center in Cape Town, South Africa, had already examined two orcas that attack and eat the liver of seven-gill broad-nosed sharks.

When the great white shark carcasses washed ashore in 2017, Kock and colleagues suspected that the orca duo was to blame. They performed CSI-style necropsies on the bodies, which were intact except for an impressively clean tear between the two pectoral fins.

Apparently the orcas knew exactly where the liver was and sucked the organ out of the open wound.

"It's fascinating that these two whales seemed to have somehow refined this to perfection," says Schulman-Janiger

Orcas are likely to target shark liver because they are high in fat and delicious. "People do the same thing - that's why we love fatty foods".