A shocking discovery

A decade ago, great white and sevengill sharks ruled False Bay. They preyed on bony fish, rays, small cetaceans and other sharks.

They were also some of the bay’s marquee stars, fueling 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 Nov. 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, even though the population usually peaks in the Southern Hemisphere’s late spring. 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 favored 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.

“We really didn’t know what had caused this,” Kock said.

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, the ones being examined 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 reexamined 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. Killer whales eat a wide range of food as a species, from fish to squid to marine mammals such as seals. But different groups often have specialized 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 was rarer still. It was the first time - anywhere - that 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,” a 1993 movie in which a 12-year-old boy befriends and helps free an orca whose owners plan to kill him for insurance money. Kock’s discovery upended the movie’s heartwarming depiction of the animals, which can grow up to 32 feet and weigh as much as 11 tons.

“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 ‘Silence of the Lambs’ was a little bit more accurate,” she said.

Researchers quickly homed in on two suspects.