In October 2023, a 4.7-meter great white shark washed ashore near Portland in southwest Victoria, Australia, missing its liver, digestive organs, and reproductive organs, and bearing distinctive bite wounds consistent with killer whale predation, according to The Guardian. This rare discovery provided scientists with the first DNA-confirmed case of orcas preying on great white sharks for their livers in Australian waters.
Two days before the shark's appearance on the beach, residents spotted several orcas, including two individuals nicknamed Bent Tip and Ripple, capturing a large prey in Bridgewater Bay, reported ABC News Australia. These sightings heightened interest in the unusual shark death and prompted further investigation.
Scientists from Flinders University, including PhD candidate with the Southern Shark Ecology Group, Isabella Reeves, undertook an analysis of the shark carcass. "Samples were taken from the bite marks on the white shark carcass and the remaining genetic material from the predator was sequenced. We were able to confirm the presence of orca DNA in the main bite area, while three other wounds revealed DNA from the seven-gill shark Notorynchus cepedianus scavenging the carcass. The results provide compelling evidence that orcas are hunting white sharks in Australian waters and seem to be targeting their livers. This demonstrates that such predatory behavior may be more widespread globally than previously thought," Reeves said, according to ABC News Australia.
The study, published on January 27 in the journal Ecology and Evolution, used wildlife forensic techniques to confirm that killer whales were responsible for excising and consuming the liver from the large white shark.
The shark carcass had four distinctive bite wounds, including a characteristic bite to remove the liver, similar to what was observed in South Africa, and a 50-centimeter wound near the pectoral fin consistent with those from killer whales, according to The Guardian. Genetic analysis confirmed the presence of killer whale DNA around this large wound.
"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," Reeves said.
Associate Professor Adam Miller, a co-author of the study, noted the ecological significance of these interactions. "Evidence suggests that the white sharks being displaced or directly killed as a result of the killer whale predation in South Africa has led to cascading shifts in the wider marine ecosystem," Miller said, according to Phys.org. "Therefore, it is important that we keep a tab on these types of interactions in Australian waters where possible."
Prior to this confirmation, orcas had been observed preying on shark species in Australian waters, including blue sharks, porbeagle sharks, shortfin mako sharks, school sharks, and tiger sharks, noted IFLScience. However, intentional liver removal from white sharks in these waters had not been confirmed until now.
In South Africa, orcas have frequently attacked great white sharks, tearing them apart and consuming their livers while leaving the rest of the body untouched. This phenomenon has impacted local shark populations, according to GEO France. Dr. Olaf Meynecke, a marine ecologist at Griffith University who was not involved in the study, commented on this behavior. "Why the liver is consumed is not entirely clear, but it could suggest a nutritional deficiency that the orcas are trying to compensate for," he said, as reported by The Guardian.
The study suggests that orca predation on great white sharks could have consequences on the balance of the marine ecosystem, as evidenced by cascading shifts observed when white sharks are displaced or killed. White sharks are considered a keystone species, affecting the structure and function of marine ecosystems.
Miller emphasized the importance of protecting this apex predator species. "[White sharks] are key regulators of ecosystem structure and functions, so it's very important we preserve these top predators," he stated.
This article was written in collaboration with generative AI company Alchemiq