Swimming up the Food Chain; Marine Biology

Port and Starboard are two orcas that are suspected to have been hunting great white sharks off the coast of South Africa. (Alison Knock/South African National Parks)

"Great whites and sevengills are the most important top predators in their ecosystems, with a key role in keeping their environments clean and diverse."

"The abrupt loss of such a large number of sharks will inevitably change how the food web works and the behaviour of the hunted sharks, whose numbers are already low."

"They likely initially learn by experience when first predating a new species. Once they know where the liver is, or any other body part they are specifically interested in, they will remember it forever and become more efficient."

Alison Kock, marine biologist

An orca jumps out of the water in the sea near Rausu, Hokkaido, Japan. New footage out of South Africa shows killer whales hunting and eating a great white shark. (Kim Kyung-Hoon/Reuters)

"When I saw the footage, of course, it just confirmed everything. And as haunting it is to see the behaviour, one can't help but be awed by it as well. It's really quite a novel piece of natural history to observe."

"We had carcasses that were washed up, ripped open, livers missing. We had sightings of orcas in the area, [followed by] disappearances of the white shark."

"I always refer to the orcas as being like the wolves of the ocean. They've kind of got the edge on this because, you know, they're co-ordinated and they've got teamwork, whereas the white sharks are on their own. They're caught by surprise and they're basically just panicking."

"What does everybody associate an orca with, typically? We all think of Free Willy, right? Or Sea World? And we think cute and cuddly, and obviously very charismatic."

"They are prolific hunters. They're extremely efficient. They're rather savage actually, because they're so good at what they do."

"White sharks have this very apex predator role, and they're quite feared. But now they've definitely been knocked off the top pedestal here."

Shark biologist Alison Towner, South Africa's Rhodes University

Alison Towner, a shark biologist, studies a mangled great white shark carcass that washed ashore in South Africa. She has long suspected orcas are behind these shark killings, and now she has video proof. (Hennie Otto/Dyr Island Conservation Trust/Marine Dynamics)

They've become infamous in marine circles, a pair of adult male killer whales in South Africa. They're broadnose sevengill sharks (named for the number of gill slits they have). They've been under observation by marine biologists for quite a few years. One is named Port for a dorsal fin that leans to the left, while the other has been named Starboard, with a fin leaning to the right. And they've gained notoriety as elite predators.

As it happened, last week they launched a killing spree when they attacked 17 sharks, targeting them solely for their livers. The two orcas ate the livers of the sharks and left the carcasses to wash up on shore. This is their modus operandi, it's what they do, working together, a well-coordinated killing machine, the killer-whale duo of renown. First observed in 2014, five years later the duo was credited with upsetting marine life in False Bay, South Africa.

In response to the two whales' actions, great white sharks in their hundreds, normally found in the area and which have become a tourist attraction, have left the area. The two killers put on a show last week at Pearly Beach. Marine biologists are in general agreement that their activities are overturning the marine hierarchy.

In the absence of the great whites, the broadnose sevengill appears to have moved up the marine food chain. They have become more populous and as such have become easier prey for the orcas. Alison Kock has been studying Port and Starboard for years. Photographs taken of the surgically predated sharks indicate the capability of identifying the precise location of the liver, by the orcas. 

 

A shark liver is rich in oils, fats and high in calories, accounting for up to a third of the animal's body weight.The Orcas target their bite precisely between the pectoral fins of the sharks, in the process removing the livers, and leaving the other organs uneaten. 

 

What's more it has been observed that the orcas have transmitted their learned skills in shark-hunting to other orcas. Simultaneously, the great whites have made themselves scarce in the area, fleeing for their lives, as it were. "How many more times can it happen before the entire population is displaced? It's really hard to predict what will happen", noted Dr.Towner.

A great white shark swims in Shark Alley near Dyer Island in Gansbaai, South Africa. The deadly sea creatures, it appears, are no longer the top predator in this part of the ocean. (Ryan Pierse/Getty Images)