Orca pair savage 17 sharks in a day

The killing efficiency of the Orcas, known as Port and Starboard, has overturned the marine hierarchy in their hunting grounds.

A shark swims in Walker Bay, Cape Town.

A notorious pair of orcas killed 17 sharks in one day and ate only their livers during their deadliest hunt yet off the coast of South Africa.

The killing efficiency of the adult males, known as Port and Starboard, has overturned the marine hierarchy in their hunting grounds. Their arrival in False Bay, in the Western Cape province, in 2015 caused sightings of the world’s most famous great white sharks to crash and their remains to wash up on Cape beaches.

Sevengill “dinosaur” sharks, which were killed in the most recent attack, have moved up the food chain in the absence of the great whites and become easier pickings for the orcas, also known as killer whales.

Sevengills are named after their number of gill slits – great whites and most other sharks have five – which are a throwback to the species’ ancestors in the early Jurassic period.

Killer whales typically work in pairs or groups.

Port and Starboard are easily identified by their distinct collapsed fins. Researchers from the Marine Dynamics Academy, who regularly observe them, said last week’s hunt off Pearly Beach, 185km along the coast from Cape Town, was their most deadly.

Killer whales typically work in pairs or groups to grip their prey’s pectoral fins in their jaws before flipping the shark and ripping it open.

Seventeen shark carcasses, all females and two that were pregnant, have been found with a clean tear between their pectoral fins and their livers absent but all other organs intact.

A shark liver is rich in oils and high in calories and accounts for 25 per cent of its body weight, which can be two tonnes. The discovery of more carcasses was likely, researchers said.

The “flying” great whites of False Bay are infamous for churning water red with seal blood as they breach and stun their prey before killing them. The phenomenon, which is not seen anywhere else in the world, has been featured in wildlife films and draws tens of thousands of visitors a year to dive with the sharks in cages.

In addition to the negative impact of dwindling great whites on the tourism industry, there is concern about the impact that the killer whales may have on the environment.

“Great whites and sevengills are the most important top predators in their ecosystems, with a key role in keeping their environments clean and diverse,” said Alison Kock, a marine biologist who has been studying Port and Starboard for years.

“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.”

The Times