Sharks are commonly viewed as the undisputed rulers of the ocean, occupying the top tier of the marine food web. This perception of the shark as the ultimate apex predator, however, is a simplification that overlooks the complex reality of ocean ecology. While large, mature sharks face few natural threats, they are not immune to predation or mortality. The life of a shark, particularly its early stages, is fraught with dangers from specialized marine hunters and, increasingly, from human activity. The oceanic world includes predators that have evolved highly effective strategies to challenge even the largest sharks.
The Specialized Attack of the Orca
The most significant natural predator of large sharks, including the Great White, is the Orca, or Killer Whale. Orcas often work in coordinated pods to isolate and incapacitate their prey. Their primary method involves ramming the shark to flip it upside down, which induces a state known as tonic immobility.
Tonic immobility is a temporary, trance-like paralysis that occurs in many shark and ray species when they are inverted. This state renders the shark completely defenseless. The Orcas then target the shark’s liver, which is exceptionally large and rich in oils and lipids, sometimes accounting for up to 25% of the shark’s body mass.
The consumption of the liver provides a massive, high-caloric energy boost, demonstrating a specialized feeding behavior. Documented attacks off South Africa and the Gulf of California have resulted in Great White Sharks evacuating entire seasonal hunting grounds for months. This sophisticated hunting strategy confirms the Orca’s position as a hyper-predator in the marine environment.
Predation by Other Sharks
Within the shark community itself, predation is a common occurrence, taking the form of both intraguild predation and cannibalism. Intraguild predation involves larger, more robust shark species preying on smaller or weaker species that are also potential competitors. For example, mature Tiger Sharks and Bull Sharks are known to consume various smaller reef sharks and conspecifics, especially when food resources are scarce.
Cannibalism can also begin before a shark is even born, in a dramatic process known as intrauterine cannibalism. The Sand Tiger Shark is the most famous example, where the developing embryos in the mother’s two uteri engage in a battle for survival. The first, largest embryo to hatch begins consuming its siblings and the mother’s unfertilized eggs, a practice called adelphophagy.
This intense competition ensures that only the two strongest pups, one from each uterus, are born, often at a substantial size of approximately one meter long. This pre-birth elimination results in one of the lowest reproductive rates among sharks.
Threats to Juvenile and Smaller Species
While large sharks have few enemies, the vast majority of shark mortality targets the young and smaller species. Shark pups and juveniles, which spend their initial years in shallow nursery areas, are particularly vulnerable to a wide array of predators.
Large bony fish, such as Groupers and Barracudas, consume young sharks before they reach a size that affords them protection. Other marine mammals, including seals and sea lions, also prey on young sharks opportunistically in coastal waters. The eggs of smaller shark species, such as those laid in fixed egg cases, are even vulnerable to invertebrates like predatory marine snails.
Human Interaction and Mortality
The most significant factor in shark mortality worldwide is the impact of human activity, dwarfing all natural predation combined. An estimated 80 to 100 million sharks are killed annually due to commercial fishing and associated practices.
A major component of this mortality is bycatch, where sharks are unintentionally caught in nets and lines targeting other fish species. Targeted fishing, often driven by the demand for shark fins, also contributes substantially to population declines. Even where finning is regulated, overall shark mortality has shown an increase. Beyond direct harvest, habitat destruction, pollution, and climate change further compromise shark populations globally.