Long considered the kings of the oceans, great white sharks are seeing their supremacy challenged by an unexpected adversary: orcas. These cetaceans, known for their intelligence and cooperation, specifically target the livers of sharks, a nutrient-rich organ. A recent discovery in Australia confirms this behavior, already observed in South Africa, and raises questions about the balance of marine ecosystems.
In October 2023, a 15.4-foot (4.7-meter) great white shark washed up near Portland, Australia, missing its liver and several internal organs. DNA analysis has just revealed that the injuries matched orca bites. This discovery marks the first genetic evidence of orca predation on great white sharks in Australia. Researchers also noted the presence of scavenger sharks attracted to the carcass.
Why the sharks' liver?
The liver of sharks is particularly rich in lipids, providing a concentrated energy source for orcas. The latter seem to have developed a precise technique to extract this organ, as evidenced by the injuries observed on the carcasses. This behavior, already documented in South Africa, suggests a specific dietary adaptation.
Orcas do not just hunt sharks: they carefully select the most nutritious parts. This strategy could indicate a deep understanding of nutritional needs, reinforcing their reputation as intelligent and opportunistic predators.
Impact on marine ecosystems
Orca predation on great white sharks could have significant consequences on the populations of the latter. In South Africa, the presence of orcas has already led to a decrease in shark sightings in certain areas. These changes could disrupt the balance of ecosystems, as white sharks play a key role in regulating marine populations.
A) Orcas Ripple (EA_0005) and Bent Tip (EA_0007) observed together in Port Phillip Bay, Australia, in 2015.
B) Great white shark carcass found in Bridgewater Bay, Australia, on October 17, 2023.
C) Bite wound at the pectoral girdle with orca DNA detection.
D) Bite wounds 2, 3, and 4 with DNA detection of a sevengill shark (Notorynchus cepedianus).
Scientists are questioning the long-term repercussions of these interactions. A decline in great white shark populations could lead to an increase in the species they hunt, such as pinnipeds, with cascading effects on the food chain.
The intelligence of orcas in question
Orcas are known for their ability to develop complex hunting strategies. Their targeted attack on great white sharks, specifically aiming for the liver, demonstrates remarkable behavioral adaptation. This precision suggests an in-depth knowledge of their prey's anatomy, acquired over generations.
Their collective intelligence, combined with sophisticated communication, makes them formidable predators. These traits could explain their success in hunting great white sharks, despite the latter's reputation as apex predators.
Interactions to monitor
Recent observations in Australia and South Africa highlight the importance of better understanding the dynamics between orcas and great white sharks. These interactions could influence species distribution and the health of marine ecosystems. Researchers call for increased monitoring to assess the impact of these predations on great white shark populations, already weakened by other factors.
By studying these behaviors, scientists hope to better preserve these iconic species and maintain the balance of the oceans.
Article author: Cédric DEPOND