Study Confirms Killer Whale Predation on Great White Shark in Australia

Scientists say the find raises questions about the frequency and impact of interactions between the species.

Research has confirmed a great white shark that washed up on a beach in south-west Victoria was the victim of killer whale predation.

In October 2023, the 4.7-metre shark's mauled body was found by residents near Cape Bridgewater, west of Portland.

In the days after the carcass was found, researchers took swabs of the bite wounds on the shark to test for killer whale DNA.

The results of that testing, published in the journal Ecology and Evolution on Monday, confirmed killer whale DNA was present in the major bite wound where the shark's liver had been extracted.

The study's lead author, Flinders University and Cetacean Research Centre PhD candidate Isabella Reeves, said the attack was the first confirmed instance of killer whale predation on a white shark in Australia.

"That a white shark washed up relatively soon after being predated upon with enough remnant DNA to confirm killer whales were responsible for this event is spectacular."

Evidence of picky eating

The research found bite wounds on the shark were consistent with liver extractions of white sharks by killer whales near South Africa.

Predation on other shark species has been observed, and a killer whale pod reportedly attacked a white shark at Neptune Islands, off South Australia's Eyre Peninsula, in 2015.

Ms Reeves said the study was a step towards understanding tissue selectivity by killer whales, as feeding with other killer whales observed eating whale tongues and skin.

"It also suggests that killer whales' selective feeding on specific prey tissues creates opportunities for scavenging species, highlighting how their picky eating has the potential to affect the ecosystem."

Cascading impacts on ecosystem

Marine scientist and investigation co-lead Adam Miller said while it was unclear how frequently these events occurred in Australian waters, in South Africa they had impacted on already declining white shark numbers.

"When the white sharks were displaced or directly killed as a result of the killer whale predation, it led to cascading shifts in the wider marine ecosystem," Dr Miller said.

"[White sharks] are key regulators of ecosystem structure and functions, so it's very important we preserve these top predators.

Citizen scientists reported seeing the killer whales "corralling and tossing a large prey item" in Bridgewater Bay before the shark carcass was found.

"It raises really interesting questions around predator-prey interactions and the behaviour and intelligence of killer whales," Dr Miller said.

Public key to rare find

Two days before the body washed up, citizen scientists observed at least three killer whales at Bridgewater Bay with anecdotal reports they were engaged in hunting behaviour.

Two of the killer whales are so well known to citizen scientists, they have been given nicknames: Bent Tip and Ripple.

"Without an established citizen science group within that area, we wouldn't even be able to comprehend who they are or if they're ecologically important to Australia," Ms Reeves said.

David Donelly is the curator of the Killer Whales Australia citizen scientist program, which collates data on sightings and collaborates with researchers.

Photos taken during the predation were used to identify the individuals through a catalogue kept by Killer Whales Australia.

"They're very rarely in one place for more than a few hours at a time, so citizen science really is the only way to study killer whales in the eastern half of Australia," he said.

Mr Donnelly said while it was not surprising to see the group in that area, the predation was "very insightful".

"We always expected they were hunting seals because there's a seal colony there," he said.

"Now it turns out they're not just hunting seals. They're probably hunting a range of species and one of those happens to be white sharks."