Hundreds of years ago, sailors saw the orcas gather in hunting groups to attack other large whales. They named them ‘whale killers’, which morphed into ‘killer whales’. As one of the most widely distributed mammals on earth, they roam all the oceans, including the South African coastline. Orcas hunt a variety of prey, including other mammals such as seals, fish, seabirds and sea turtles.

In 2017, great white sharks started washing up on beaches near Gansbaai, 120km south of Cape Town. Seven out of eight had their livers removed, while the hearts of some were missing. Sharks have a large liver to give them buoyancy as they don’t have a swim bladder. According to researchers, orcas target the liver because it is packed with oils, fats and nutrients.

The shark carcasses initially mystified everyone, including marine biologists. But through observation and research, as well as the distinctive wounds, it was clear they were made by the same male orcas. Known as Port and Starboard because of the direction of their dorsal fins, the pair was first spotted around Cape Point in 2012, disappeared, and then started appearing frequently from late 2015 onwards, in the region of False Bay and Gansbaai. The first great white shark mortalities corresponded with these first sightings of Port and Starboard.

On August 21, a great white shark washed up on the beach at Hartenbos near Mossel Bay on the Garden Route. It was the first in this location, but the ninth of these marine predators to end up on a South African beach after an orca attack since 2017. Five great whites had washed up near Gansbaai between February and June 2017.

The first footage ever of orcas hunting and killing a great white was released as part of ‘Shark Week’ on the Discovery Channel in July. It was taken by Christiaan Stopforth of Drone Fanatics and showed a highly co-ordinated attack by a pod of orcas in Mossel Bay in May.

Stopforth remained tight-lipped about the footage until it aired, when he had this to say: “It all started when they were just playing around in the shallows when, all of a sudden, they dove down and came up 50m from where they were. They did not come up on their own, but with a great white shark in their mouths. It was definitely one of the most exciting days of my life. Filming these animals and observing them is a feeling you will not be able to describe to people.”

The shark carcass at Hartenbos and the world-first footage of the orca attack coincided with the publication of a new study in the African Journal of Marine Science, showing how great white sharks have been avoiding certain regions of the South African coast, especially around Gansbaai, presumably because of a fear of being hunted by orcas. Over a period of five and a half years, 14 sharks were tracked and observed fleeing the area when the orcas were present. Visual sightings of great whites also considerably dropped at the same time.

Shark biologist at the Dyer Island Conservation Trust Alison Towner, who has studied great whites for the past 15 years, was the lead author of the paper. She says what they have witnessed during their studies seems to be a large-scale avoidance strategy by great whites.

“This is mirroring what we see used by wild dogs in the Serengeti in Tanzania, in response to increased lion presence. The more the orcas frequent these sites, the longer the great white sharks stay away.”

Dwindling numbers of great whites

Great whites are classified as a vulnerable species on the Red List of the International Union for Conservation of Nature, with a worldwide population of fewer than 3 500. It is estimated that between 350 and 520 of these apex predators exist along the South African coastline.

The increase of orca predation on great whites is therefore of great concern for an already vulnerable species. Towner says we need to look at the bigger picture as the ripple effects on local marine life and the ocean’s ecosystem could be catastrophic.

“There is no doubt that orcas can impact the presence of the sharks, but once the sharks are in deep water, they are safe from orcas.

“Balance is crucial in marine ecosystems – with no great white sharks restricting Cape fur seal behaviour, the seals can predate on critically endangered African penguins, or compete for the small pelagic fish they eat. That’s a top-down impact.

“To put it simply, although this is a hypothesis, there is only so much pressure an ecosystem can take, and the impacts of orcas removing sharks are likely far wider reaching.”

In 1991, South Africa became the first country in the world to declare great whites a protected species. This means they may not be caught and if one is unintentionally killed, its whole carcass must be handed over to a fisheries officer.

However, Towner cautions that orcas are but one additional pressure on great whites in South African waters, saying that the decline in shark numbers was detected long before the orcas came along.

“We know that great white sharks face their highest targeted mortality in the anti-shark bather protection nets in KwaZulu-Natal, with 1 318 captured between 1978 and 2018, which is 32 a year.

“South Africa also has scattered regulations and no quotas set on shark fisheries, which threatens the future sustainability of our smaller shark populations. These smaller sharks are the staple diet of the great white shark. The smooth-hound shark has declined by 95% in our area over three years.

“It’s no wonder the great white sharks are suffering. Not at the hands of orca whales, but actually at the hands of humans. The question is, how can we protect an animal if we do not protect its food and environment?” asks Towner