Orcas have a taste for shark liver and prey on great white sharks in Australian waters, researchers have confirmed by using DNA analysis.
In October 2023, the maimed carcass of a 4.7m great white shark washed ashore near Portland, in southwest Victoria, missing its liver, digestive and reproductive organs.
Two days earlier, citizen scientists witnessed several killer whales, including locally catalogued animals known as Bent Tip and Ripple, catch large prey in the area.
Suspecting a killer whale was the behind the shark’s death, researchers swabbed and analysed DNA samples taken from the distinctive bite wounds.
The results, published this week in Ecology and Evolution, confirmed the presence of killer whale DNA in the area around the largest bite, a wound measuring 50cm in diameter near the shark’s pectoral fin. Tests also found the presence of genetic material from scavenging broadnose sevengill sharks in three smaller bite wounds.
This was the first confirmed evidence – using DNA and citizen science data – of orca predation on great white sharks – also known as white sharks – in Australia, and their likely selective eating of shark liver in Australian waters.
Isabella Reeves, a Flinders University researcher and the lead author of the findings, said “killer whales and white sharks are both top predators”. The carcass found in Victoria had “four distinctive bite wounds”, she said – one showed killer whales had deliberately torn out its liver.
The phenomenon was previously observed off South Africa, where in one published case, an individual orca incapacitated a great white and ate its liver in under two minutes.
“It shows we’re probably really underestimating how often and where this behaviour is actually occurring,” Reeves said.
She said understanding what orcas eat and their nutritional needs could help with preserving them, their prey and the rest of the ecosystem.
According to the paper, killer whales, the largest member of the dolphin family, feed on a wide range of species: other cetaceans, seals, squid and octopus, fish and sharks. They have previously been recorded specifically choosing certain organs, such as whale tongue, as well as shark liver.
Dr Rebecca Wellard, a marine scientist based at Project ORCA and Curtin University who was not involved with the study, said killer whales were “remarkable predators at the very top of the marine food chain”.
She said orcas, often referred to as the “wolves of the sea”, get their hunting advantage from “their exceptional intelligence, strong family and social bonds, and their ability to work together in highly synchronised pods” – able to work in packs to bring down prey as large as great white sharks and blue whales.
Griffith University marine ecologist Dr Olaf Meynecke, also not involved in the study, confirmed that killer whales were known to eat particular body parts. “Why the liver is eaten is not fully clear, but could suggest a nutritional deficiency that the orcas try to compensate for,” he said.
“In South Africa, sharks have disappeared in areas when orcas are around,” he said. “So this behaviour can have a strong impact on white shark distribution.”
Dr Adam Miller, an associate professor in marine science and ecological genomics at Flinders University and co-lead author, said while scientists did not know how often killer whales preyed on white sharks, the interactions could contribute to already declining white shark populations.
“We know that white sharks are key regulators of ecosystem structure and functions, so it’s very important we preserve these top predators. Therefore it is important that we keep a tab on these types of interactions in Australian waters where possible,” he said.
