Fri, Jan 31, 2025 page3

• Orcas hunt white sharks to eat their livers: study

  • The Guardian
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  Orcas have a taste for shark liver and prey on great white sharks in Australian waters, researchers have confirmed 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.

  

  An orca known as J35, foreground, swims with others near San Juan Island in US’ Washington state on Aug. 11, 2018.

  Photo: Ken Balcomb, Center for Whale Research via AP

  Suspecting a killer whale was the behind the shark’s death, researchers swabbed and analyzed 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.

  That was the first confirmed evidence — using DNA and citizen science data — of orca predation on great 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 of which 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 less than two minutes.

  “It shows we’re probably really underestimating how often and where this behavior 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.

  The paper said that killer whales have previously been recorded specifically choosing certain organs, such as whale tongue, as well as shark liver.

  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 synchronized pods” — able to work in packs to bring down prey as large as great white sharks and blue whales, said Rebecca Wellard, a marine scientist based at Project ORCA and Curtin University who was not involved with the study.

  Griffith University marine ecologist 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 behavior can have a strong impact on white shark distribution.”
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