Why Sharks Are Feasting on Their Own: The Story Behind Cannibalistic Predators

Australia's killer whales hunted a white shark for its liver, according to DNA evidence. The study determined that killer whales were in charge of eating the middle region that contained the nutrient-dense liver based on DNA analysis from the bite wounds on the carcass of a large white shark that washed up on the coast in Victoria in 2023 close to Portland.

For the first time, killer whales in Australia have been proven to have hunted a white shark for its liver based on DNA evidence.

The Flinders University-led study found that killer whales were in charge of eating the mid-section that contained the nutrient-rich liver, based on DNA analysis from the bite wounds on the body of a large white shark that washed up on the coast in Victoria in 2023 close to Portland.

As previously reported in California and South Africa, killer whales (Orcinus orca) have been seen feeding on a variety of shark species, including white sharks (Carcharodon carcharias), all over the world.

A unique chance to identify the predator by analyzing characteristic bite wounds was presented by the finding of a 4.7-meter white shark missing its liver on a beach in southeast Australia.

Lead author Isabella Reeves, a PhD candidate with the Southern Shark Ecology Group at Flinders University and the West Australian Cetacean Research Centre (CETREC), says, "The liver, digestive, and reproductive organs were missing, and there were four distinctive bite wounds, one of which was characteristic of liver extraction by killer whale, similar to what has been observed in South Africa."

"Swabs from the white shark's bite wounds were sequenced to look for any remaining genetic information from the shark's predator. While DNA from scavenging broadnose sevengill sharks was found in the other three wounds, we were able to corroborate the presence of killer whale DNA in the primary bite area.

"These findings provide compelling evidence of killer whale predation on white sharks in Australian waters, with a strong indication of selective liver consumption. This suggests that such predation events may be more widespread and prevalent across the globe than previously believed."

The study, published in Ecology and Evolution, used wildlife forensic techniques to confirm killer whales were responsible for excising and consuming the liver from the white shark. Civilian bystanders had witnessed several killer whales, including locally known individuals called 'Bent Tip' and 'Ripple, catching a large prey in Bridgewater Bay two days before the white shark carcass washed ashore.

State government fisheries officers gathered the beached huge white shark carcass for examination.

In Australia, killer whales have been known to hunt on a variety of shark species, such as tiger sharks (Galeocerdo cuvier), shortfin mako (Isurus oxyrinchus), porbeagles (Lamna nasus), blue sharks (Prionace glauca), and ground sharks (perhaps school sharks, Galeorhinus galeus). However, despite multiple instances of such behavior in California and by the famed duo "Port" and "Starboard" in South Africa, white shark liver consumption had not yet been reported in Australia.

There have been numerous reports of killer whale-white shark encounters in Australia, including at least one probable kill in February 2015 at the Neptune Islands Group Marine Park in South Australia.

In that case, no carcass was found to verify the kill, but after the encounter, an oil slick suggestive of a successful predation was seen.

Similar killer whale predation on white sharks has disrupted local shark populations in both South Africa and California, according to Dr. Alison Towner, a marine biologist at Rhodes University (South Africa) and one of the study's authors. "However direct observations of these interactions remain rare and their frequency is poorly understood," she states.

"We don't know how frequently these events occurred in Australian waters and therefore how significant these findings are," says Adam Miller, a senior author and adjunct associate professor at Flinders University. Miller is also a senior ecologist at Cesar Australia.

Evidence points to a cascade of changes in the broader marine ecology as a result of the white sharks being driven out of South Africa or killed outright due to killer whale predation.

It's critical that we protect these top predators because we know that white sharks play a crucial role in regulating the structure and functioning of ecosystems. As a result, wherever feasible, we should monitor these kinds of interactions in Australian seas.

Dr. Lauren Meyer, a research fellow at Flinders University, says, "This study also provides DNA evidence that scavenging is facilitated by killer whales' tissue selection, whereby the liver and internal organs are consumed, but much of the carcass remains as a nutrient source benefiting local ecosystems."