The great white shark, an apex predator, plays a significant role in maintaining marine ecosystem balance. The International Union for Conservation of Nature (IUCN) classifies it as a vulnerable species, indicating a declining global population and extinction risk. This decline is attributed to human activities and the shark’s inherent biological characteristics.
Overfishing and Bycatch
Human fishing activities are a primary threat to great white shark populations. Historically, they were hunted for fins, teeth, meat, and sport. While targeted fishing is now illegal or protected in many regions, including Australia, South Africa, and the United States, black markets still contribute to their removal.
Accidental capture, known as bycatch, poses an even more significant threat. Great white sharks are frequently caught unintentionally in commercial fishing gear. Gillnets and longlines are particularly problematic; gillnets alone account for over 80 percent of reported young great white shark bycatch in some Southern California nursery grounds. Entanglement or hooking often results in high mortality, especially for sharks that must keep moving to breathe, as they can suffocate.
Reported bycatch of young great white sharks in fisheries, such as those targeting California halibut and swordfish, has averaged over 10 sharks annually since the 1980s, with increasing numbers. The actual extent is likely higher due to low observer coverage. This unrecorded removal directly impacts population numbers and hinders recovery, even in legally protected areas.
Habitat Degradation and Pollution
Marine habitat degradation significantly contributes to challenges faced by great white sharks. Coastal development destroys critical nursery grounds like estuaries, mangroves, and coral reefs that young sharks rely on for safety and sustenance. Loss and fragmentation of these vital areas reduce space for sharks to breed, hunt, and grow, impacting survival rates.
Ocean pollution further compounds these issues, directly harming sharks and compromising their health. Plastic pollution, including large debris and microplastics, can be ingested, leading to internal injuries, blockages, or starvation. Chemical contaminants like polychlorinated biphenyls (PCBs), DDT, and heavy metals such as mercury accumulate in shark tissues. Young sharks off Southern California, for instance, have shown some of the highest recorded mercury levels globally for any shark, and elevated PCB and DDT concentrations.
These pollutants can weaken immune systems, impair reproduction, and reduce their ability to find food, indirectly affecting populations. The combined effects of habitat destruction and chemical contamination create a hostile environment, reducing prey availability and overall health, making sharks more susceptible to other threats.
Climate Change Impacts
Broader environmental shifts caused by climate change also impact great white shark populations. Ocean warming leads to changes in water temperature, which can cause prey species to shift distributions. As food sources move to cooler waters, great white sharks may follow, disrupting traditional hunting grounds and potentially leading to new ecological imbalances. This has been observed off California, where young great white sharks moved northward into previously cooler waters, affecting local ecosystems.
Ocean acidification, a consequence of increased carbon dioxide absorption, threatens the marine food web. Research indicates increased acidity can impair sharks’ ability to detect prey through smell (olfaction), reducing hunting success and potentially impacting growth rates. These environmental changes indirectly stress populations by altering habitats and food availability, adding to existing pressures.
Inherent Biological Vulnerabilities
Great white sharks possess inherent biological traits that make them susceptible to population declines. They exhibit a slow growth rate, taking many years to reach full size. They also reach sexual maturity late; males typically around 26 years old, and females around 33 years old. This extended immaturity means they must survive numerous threats for decades before reproducing.
Once mature, great white sharks have long gestation periods, estimated up to 18 months. They produce relatively few offspring per litter, typically 2 to 10 pups. Females are also suspected to have a reproductive cycle of two to three years, not reproducing annually. These combined factors—slow growth, delayed maturity, long pregnancies, and low reproductive output—mean populations recover very slowly from declines, making them highly vulnerable to sustained pressures from human activities and environmental changes.