Orcas have a style for shark liver and prey on nice white sharks in Australian waters, researchers have confirmed by utilizing DNA evaluation.
In October 2023, the maimed carcass of a 4.7m nice white shark washed ashore close to Portland, in southwest Victoria, lacking its liver, digestive and reproductive organs.
Two days earlier, citizen scientists witnessed a number of killer whales, together with domestically catalogued animals often known as Bent Tip and Ripple, catch giant prey within the space.
Suspecting a killer whale was the behind the shark’s demise, researchers swabbed and analysed DNA samples taken from the distinctive chew wounds.
The outcomes, revealed this week in Ecology and Evolution, confirmed the presence of killer whale DNA within the space across the largest chew, a wound measuring 50cm in diameter close to the shark’s pectoral fin. Assessments additionally discovered the presence of genetic materials from scavenging broadnose sevengill sharks in three smaller chew wounds.
This was the primary confirmed proof – utilizing DNA and citizen science information – of orca predation on nice white sharks – also referred to as white sharks – in Australia, and their probably selective consuming of shark liver in Australian waters.
Isabella Reeves, a Flinders College researcher and the lead writer of the findings, mentioned “killer whales and white sharks are both top predators”. The carcass present in Victoria had “four distinctive bite wounds”, she mentioned – one confirmed killer whales had intentionally torn out its liver.
The phenomenon was beforehand noticed off South Africa, the place in one revealed case, a person orca incapacitated an ideal white and ate its liver in beneath two minutes.
“It shows we’re probably really underestimating how often and where this behaviour is actually occurring,” Reeves mentioned.
She mentioned understanding what orcas eat and their dietary wants might assist with preserving them, their prey and the remainder of the ecosystem.
In response to the paper, killer whales, the most important member of the dolphin household, feed on a variety of species: different cetaceans, seals, squid and octopus, fish and sharks. They’ve beforehand been recorded particularly selecting sure organs, corresponding to whale tongue, in addition to shark liver.
Dr Rebecca Wellard, a marine scientist based mostly at Challenge ORCA and Curtin College who was not concerned with the research, mentioned killer whales have been “remarkable predators at the very top of the marine food chain”.
She mentioned orcas, sometimes called the “wolves of the sea”, get their searching benefit from “their exceptional intelligence, strong family and social bonds, and their ability to work together in highly synchronised pods” – in a position to work in packs to carry down prey as giant as nice white sharks and blue whales.
Griffith College marine ecologist Dr Olaf Meynecke, additionally not concerned within the research, confirmed that killer whales have been identified to eat specific physique elements. “Why the liver is eaten is not fully clear, but could suggest a nutritional deficiency that the orcas try to compensate for,” he mentioned.
“In South Africa, sharks have disappeared in areas when orcas are around,” he mentioned. “So this behaviour can have a strong impact on white shark distribution.”
Dr Adam Miller, an affiliate professor in marine science and ecological genomics at Flinders College and co-lead writer, mentioned whereas scientists didn’t know the way usually killer whales preyed on white sharks, the interactions might 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 mentioned.
