After a pair of orcas went on a shark-killing spree in South Africa in late February, the internet was curious and shaken by how these killer whales killed their prey.
Each of the 17 sharks massacred had been ripped open and lacked a liver. news week spoke to a marine biologist to find out why.
“Different populations of killer whales have specialized diets, so few populations [ecotypes] Killer whales specialize in eating sharks,” said Andrew Trites, professor and director of the Marine Mammal Research Unit at the Institute for the Oceans and Fisheries at the University of British Columbia news week.
“For example, in British Columbia we have one ecotype that specializes in eating sharks, while two other local populations specialize in eating either fish or marine mammals.”
Although orcas are called killer whales, they are actually large dolphins. They can grow up to 32 feet and weigh up to 6 tons National Geographic. While they primarily eat fish and small marine mammals, some orca populations have developed a predilection for sharks.
During February’s attack, the port and starboard orcas appear to have removed their victims’ organs with surgical precision in a heated shark-foie-gras frenzy.
In a study published in the African Journal of Marine Sciences In 2022, marine researchers reported that since 2017, eight great white shark carcasses had washed up on nearby beaches in the Western Cape near Gansbaai. Their bodies bore the telltale marks of orca bites, and seven of the eight sharks also had their livers ripped out.
“The reason killer whales target shark livers is because it’s full of oil and therefore full of calories, in addition to being large and rich in vitamins,” Trites said. “It is therefore a great food for killer whales, which have a high cost of living and need high-calorie food to sustain their energetically expensive lifestyle.”
“Sharks have large livers with lots of oil, which helps maintain buoyancy because sharks don’t have a swim bladder like most fish. The liver makes up 5 to 10 percent of a shark’s weight, which is extremely high compared to humans and other animals.”
Of course, there are downsides to eating sharks too – they are apex predators and have evolved tooth-like scales to reduce friction from the water.
“One of the challenges of eating sharks is that their skin is like sandpaper, which means it wears down the teeth of killer whales biting sharks,” Trites said.
But eating sharks doesn’t just affect an orca’s teeth. It can affect entire ecosystems. Alison Towner, a great white shark biologist who has studied port and starboard, previously said news week that great white sharks seem to keep their distance from the area, perhaps to avoid suffering the same fate.
“Balance is crucial in marine ecosystems,” she said. “For example, if great white sharks do not restrict the behavior of Cape fur seals, the seals may eat critically endangered African penguins or compete for the small pelagic fish they eat.
“To put it simply, while this is a hypothesis for now, there are limited pressures that an ecosystem can withstand, and the impact of orcas removing sharks is likely more far-reaching.”