Orcas, also known as killer whales, are apex ocean predators known for their intelligence and diverse hunting strategies. A striking behavior involves their targeted consumption of shark livers. This specific dietary preference highlights the complex marine ecosystem dynamics. Understanding why orcas focus on this organ reveals insights into their nutritional needs and sophisticated hunting adaptations.
Targeting Shark Livers
Observations worldwide confirm orcas selectively target and consume shark livers, often leaving the rest of the shark’s body intact. In South Africa, orcas Port and Starboard have been linked to numerous incidents where great white sharks washed ashore with precisely removed livers. DNA evidence from a great white shark carcass in Australia also confirmed killer whales consumed its liver-containing mid-section. These cases demonstrate a deliberate, specialized feeding behavior.
The Nutritional Advantage
The primary reason orcas target shark livers is their exceptional nutritional density. A shark’s liver is disproportionately large, often 5% to 25% of its total body weight, and up to 90% of its body cavity in some species. This organ is packed with fat and oils, making it a highly concentrated source of calories and essential nutrients.
A significant component is squalene, a lipid comprising 15% to 69% of liver weight in some deep-sea sharks, and up to 90% of the oil in certain species. Squalene is highly caloric, providing over twice the calories per gram compared to protein. This rich fat content is valuable for orcas, contributing to blubber reserves, sustained energy, buoyancy, and reproductive success. A single shark liver can sustain an orca for several days, making it an efficient and desirable food source.
Sophisticated Hunting Techniques
Orcas employ intelligence and cooperative strategies for precise liver extractions. When hunting sharks, especially large ones like great whites, orcas often work together to isolate their prey. A common technique involves ramming the shark and flipping it upside down. This induces tonic immobility, a temporary paralysis occurring when certain shark species are inverted.
Once immobilized, orcas make precise incisions, often near the pectoral fins, to access and remove the liver. Their advanced echolocation allows them to “see” internal organs, guiding them to the nutrient-rich liver while avoiding less digestible parts. This specialized hunting method demonstrates skill and coordination, learned and passed down through generations within orca pods.
Ecological Ripple Effects
The specialized predation of sharks by orcas has broader implications for marine ecosystems. Where orca predation is frequent, shark populations, particularly great white sharks, may decline or abandon traditional habitats. For instance, specific orcas in South Africa have led great white sharks to largely avoid certain aggregation sites.
This shift in shark distribution and abundance can initiate trophic cascades, ripple effects through the food web. Sharks, as apex predators, regulate the populations of their prey. Their reduced presence can increase species sharks typically consume, potentially affecting ecosystem balance and impacting other marine life, such as seals, abalone, and penguins.