Two killer whales are hunting down great white sharks, Hannibal Lecter style

While other killer whales have been documented preying on sharks in the area, Port and Starboard are believed to be the primary offenders. They usually work together, but scientists believe they are part of a larger group from which they often break off to hunt.

The killings have had far-reaching implications. To steer clear of the roving killer whales, researchers say, great white sharks have fled their former favourite haunts, causing cascading effects up and down the food chain.

Populations of the great whites’ food, including Cape fur seals, have spiked – and these animals, in turn, have grown bolder while feasting more heavily on their prey. There are tourism impacts, too: TV crews that once routinely made an annual pilgrimage to South Africa to capture great white footage now go elsewhere.

“I can’t believe we still, in less than a decade, have seen such profound impacts,” Towner said.

A shocking discovery

A decade ago, great white and sevengill sharks ruled False Bay next to Cape Town on the south-western edge of South Africa. They preyed on bony fish, rays, small cetaceans and other sharks.

They were also some of the bay’s marquee stars, fuelling an ecotourism industry that includes scuba diving, cage diving and boat tours. Divers could routinely observe dozens of them during an hour-long dive on the west side of the bay at Miller’s Point, which one website hailed as “the epitome of shark diving worldwide”.

But starting in 2009, tourism boats started documenting the arrival of another predator: killer whales. Over the ensuing years, although the number of orcas in False Bay increased, the apex predators coexisted, with the orcas feeding on marine mammals, especially common dolphins and whales such as the humpback.

“Their presence was very rare in that area,” said Alison Kock, a marine scientist with South African National Parks who has been studying False Bay’s sevengills.

Then came November 9, 2015. Cage divers at Miller’s Point hoped to be dazzled by the bustling sevengill population – only to find that the sharks had vanished overnight. Instead, divers soon found several sevengill carcasses, each with a gaping wound on its underbelly near the pectoral fins.

Researchers assumed humans must have been responsible. Fishers had long favoured using oily shark liver as bait for other sharks, Kock said. And marine biologists didn’t think any animal could so precisely target a particular organ.

Then, in April 2016, several more carcasses were found littered on the seabed and at Miller’s Point. This time, divers recovered them, allowing Kock and other marine biologists to perform necropsies.

She found that, like the sharks killed the previous November, they had a gaping wound across their pectoral girdle with little other damage. Their hearts, stomachs and other major organs were still intact – with one exception.

“In each case, the liver had been removed,” wrote Tamlyn Engelbrecht, who co-authored a 2019 paper with Kock titled Running Scared: When Predators Become Prey.

Engelbrecht also noted that shark livers, which can account for up to a third of a shark’s body weight, are high in fatty, energy-rich lipids.

Marine biologists found bite marks on the sharks’ pectoral fins and bruising of the underlying tissue. Armed with these observations, they re-examined photographs of the sharks that had been killed five months earlier and found the same kinds of bite wounds on their pectoral fins, which had also been marred by rake marks – scratchlike injuries caused by orcas when they scrape victims with their teeth.

The scientists had cracked the case: Their killers were killer whales.

It was a shocking discovery. Orcas eat a wide range of food as a species, from fish to squid to marine mammals such as seals. But different groups often have specialised diets based on culture. While orcas had been documented eating sharks, instances of them targeting bigger ones at the top of the food chain were rarer.

What happened in South Africa was rarer still. It was the first time anyone had recorded killer whales using force to extract a shark’s liver.

Up to that point, Kock had focused her research on sharks, while many of her impressions of killer whales grew out of Free Willy. Her discovery upended the 1993 movie’s heartwarming depiction of the animals, which can grow to more than nine metres long and weigh up to 10 tonnes.

“Seeing their immense impact on white sharks and how they prey on them, and how Hannibal Lecter it is, I think that Free Willy really was a bit of a lie, and The Silence of the Lambs was a little bit more accurate,” she said.

Researchers quickly homed in on two suspects.

Port and Starboard

A pair of killer whales were first spotted in 2012 at the south end of False Bay near the Cape of Good Hope. The two males, eventually nicknamed Port and Starboard because their dorsal fins had collapsed in opposite directions, then disappeared for three years.

They showed up in the bay again in January 2015 and were spotted multiple times over the next 10 months, including just days after the sevengill attacks in November of that year. As Kock and her team performed two dives after the second sevengill massacre in April 2016, they approached their boat. Kock compared sighting records of Port and Starboard from dive boat operators to the places where carcasses had been found – they matched up.

She had found the shark killers.

But the carcasses kept coming. Dave Hurwitz, the owner of ecotourism business Simon’s Town Boat Company – who nicknamed the killer whales – said about 20 sevengill sharks were killed that year.

And those are just the ones that washed ashore or were found by divers. Undoubtedly, experts said, many more had sunk to the ocean floor.

The following year, Port and Starboard turned their attention to bigger game. The first great white shark carcass washed ashore in February 2017, in Gansbaai, about 50 kilometres south-east of False Bay. Over the next several months, four more were found, all with tears to their underbelly near their pectoral fins and missing livers.

Marine biologists also found rake marks on their bodies, leading Towner and others to conclude that the creatures that had been hyped into monsters by Jaws had become prey.

“All of a sudden, they’re the victims,” she said. “So it really did turn everything on its head.”

Marine biologists don’t know why they started hunting off the coast in the first place. Killer whales usually rove farther offshore. Experts haven’t figured out why, although they have theories that include overfishing.

An enduring threat to sharks

The effects of Port and Starboard’s decade-long hunting campaign have been pronounced and enduring, for the sharks most of all, especially because they’re the most threatened fish in the ocean, Towner said.

Humans are their biggest danger. About 70 per cent of sharks face serious pressure from overfishing, which is rampant and off the radar in southern Africa, Towner said. Climate change has altered ocean conditions, which is modifying the travel patterns of their prey and for sharks themselves. And underwater shark nets, designed to protect swimmers, trap and kill sharks. Orca predation only adds to their woes, Towner said.

Port and Starboard are still terrorising the South African coast. One marine biologist described them as “roving bandits” looting the coasts of southern Africa, as far north as Walvis Bay in Namibia and as far east as Algoa Bay in South Africa. Most recently, in October, Port and Starboard killed more sevengills in nearby bays.

No one knows where they are now, but biologists say it’s only a matter of time before they show up again – and leave a watery graveyard in their wake.

The Washington Post