(CN) — One day last summer, two observational vessels encountered a gruesome scene off the coast of Mossel Bay, South Africa.
The scene turned out to be a treat for both marine biologists and for a killer whale named Starboard.
Researchers spotted two killer whales in the water. One boat came upon a bloody slick churning on the ocean surface. The distinctive scent of shark liver lingered in the air.
Researchers and tourists onboard the vessels watched as the two whales, named Port and Starboard for the opposing bends in their dorsal fins, prowled the area within 100 meters of the boats. Then the observers spotted a juvenile white shark. Starboard appeared in close pursuit.
The killer whale grabbed the shark’s left pectoral fin with its strong jaws and began to thrust repeatedly, according to the authors of a new research article published Friday in the African Journal of Marine Science.
Seconds later, the whale tore into the shark’s flesh. Observers got a glimpse of the shark’s peach-colored liver as the whale devoured the organ.
Killer whales are known to gather in groups to hunt a single shark. This process can take hours as the whales block the shark in prior to attack.
It’s also common for killer whales to eat a shark’s liver and leave the carcass behind — but detailed observations of a whale hunting and killing a shark alone are unusual. The other whale, Port, remained at a distance during the entire predation event, which lasted less than two minutes.
“Witnessing a white shark’s fin break the surface initially sparked excitement, but that turned to a somber realization as Starboard swiftly approached," said Esther Jacobs, an author of the study who witnessed the event firsthand. "The moment Starboard rapidly preyed on my favorite shark species was both devastating and intensely powerful."
Evidence of individual whales learning to kill sharks solo instead of in groups may shed light on how predatory mammals evolve and specialize in certain prey species, the authors of the article believe.
They say this information could aid in conservation efforts, as biologists work to understand how species adapt to ecosystem alteration driven by climate change and other human activity.
Juvenile white sharks generally range from eight to 12 feet long. An 8-foot shark weighs about 220 lbs., and its liver could weigh from 11 to 52 lbs. The organ is rich in lipids, providing a concentrated energy source for the whales.
The day after researchers observed Starboard making quick work of the juvenile white shark, another shark carcass washed ashore. This carcass also had its liver removed.
The authors suspect that this kill may have been part of the previous day’s events — either from the bloody scene that the boats first encountered or from a separate kill, most likely by either Port or Starboard. The washed-up carcass revealed stretch marks on the shark’s skin along its midsection, indicating some form of violent torsion leading up to removal of the liver.
The observation of Starboard’s kill did not capture exactly how the whale had removed the shark’s liver with such precision. In a previous study, authors speculated that the liver’s buoyancy may allow it to float out of the body cavity once the shark is eviscerated.
For those interested in marine biology, the study also brought some troubling news: Sharks have fled the area after predation events, it noted, leading to a reduced presence of sharks in Mossel Bay.
This is concerning to conservationists because sharks help regulate other predatory species. A decline in shark populations can have ripple effects further down the food chain, lead author Dr. Alison Towner noted.
“The study raises critical questions about the impact of killer whale predation on shark populations in South Africa,” Towner said. “The displacement of various shark species due to killer whale presence may have implications for mesopredator release and potential trophic changes in the marine ecosystem.”
The predation of sharks by Port and Starboard has also affected tourism in the area, which is a destination for shark lovers eager to observe the predators on cage dives hosted by local businesses.
Killer whales have long engaged in hunting sharks for the fatty livers, but studies have noted that the behavior may be spreading.
Starboard’s quick dispatch of the white shark in this observation indicates a considerable level of skill — although stress due to the presence of nearby human activity may also lead to a more rapid predation event, according to the study authors.
Going forward, scientists and conservationists want to learn more about how these skills are transmitted among whale populations and how changes in whale consumption patterns can impact regional ecology.
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