The Great White Shark (GWS) is widely recognized as an apex predator at the top of the marine food web. Despite this formidable status, the species is not invulnerable and faces various threats that lead to mortality across its life stages. These threats range from specialized natural predators to pervasive dangers introduced by human activity and environmental factors. Understanding the agents that kill the Great White Shark provides a clearer picture of its complex position in the ocean ecosystem.
Predation by Killer Whales
The Killer Whale, or Orca, represents the most significant natural threat to a healthy, adult Great White Shark. These marine mammals are intelligent and often hunt sharks using coordinated strategies in locations like South Africa and the Gulf of California. Their specialized technique involves working together to push the shark to the surface and maneuvering it onto its back.
This inversion induces tonic immobility, a temporary, trance-like state that paralyzes the shark and renders it defenseless. Once immobilized, Orcas selectively target and extract the shark’s liver. The liver is prized for its large size—sometimes making up nearly 25% of the shark’s body weight—and its high energy density, being packed with oils and lipids.
The presence of Orcas causes a dramatic behavioral shift in Great White Sharks, leading to a fear-driven evacuation of the area that can last for months. This avoidance strategy prevents Orcas from repeatedly killing adult sharks in the same area, though it also changes the ecosystem dynamic. Documented cases, such as those involving the Orcas named Port and Starboard in South Africa, demonstrate the effectiveness of this specialized predation.
Mortality Caused by Human Activity
Statistically, human activity is the greatest cause of death for Great White Sharks, particularly through commercial fishing operations. The primary driver of this mortality is bycatch, the unintentional capture of sharks in gear set for other species like tuna or swordfish. Sharks become fatally entangled in gillnets and longlines, which are indiscriminate fishing methods contributing to the species’ overall population decline.
This incidental capture is detrimental because Great White Sharks have a slow reproductive rate; females take up to 33 years to reach sexual maturity. High mortality rates from bycatch make it difficult for populations to recover, as it can take decades for a single lost individual to be replaced. Historically, targeted hunting and shark finning also contributed to deaths, though many regions now protect the species from intentional capture.
Habitat degradation and pollution introduce indirect but widespread threats. Chemical runoff and plastics lead to microplastics entering the food chain, which accumulate in the sharks’ bodies. As apex predators, Great White Sharks are susceptible to biomagnification, accumulating toxins like mercury, polychlorinated biphenyls (PCBs), and DDT in their tissues. These toxins can impair reproductive health and increase mortality rates.
Vulnerabilities in Juvenile Sharks
The dangers faced by Great White Sharks change drastically during their early life stages, where mortality rates are highest. Juvenile sharks, typically under 9.8 feet (3 meters) in length, inhabit shallow coastal nursery grounds for protection and access to smaller prey. These young sharks primarily feed on fish, skates, and rays, as they are not large enough to hunt marine mammals.
Despite the safety of nurseries, juvenile sharks are vulnerable to predation from larger bony fish, other shark species such as Bull Sharks, and even adult Great White Sharks. Data from tracking studies in the Northeastern Pacific suggest that the greatest cause of death for young white sharks is unintentional capture in fishing gear. The estimated annual survival rate for these young sharks is around 63%.
Non-Predatory Biological Stressors
Beyond direct predation and human interaction, Great White Sharks can succumb to death from internal or ecological failures. Disease and parasitic loads represent natural stressors that can weaken or kill a shark. For instance, a recent spike in deaths has been linked to meningoencephalitis, an inflammation of the brain tissue, though the infectious agent remains under investigation.
Severe injuries sustained from territorial disputes, failed hunts, or scavenging on large carcasses can lead to death through infection or inability to hunt. Long-term starvation, often caused by a decline in local prey populations, poses a slow threat compounded by environmental instability. Shifts in the ocean environment, such as changes in water temperature or oxygen levels, place physiological stress on the sharks, leading to illness or death.