The blue shark (Prionace glauca) is a highly migratory predator that inhabits the world’s temperate and tropical oceans. This species is one of the most widely distributed sharks. Averaging about 10 feet in length, the blue shark is a top-level carnivore, feeding primarily on squid and small pelagic fish. Its slender body and deep blue coloration allow it to blend seamlessly into the water column, aiding its hunting success.
Apex Predators Targeting Adult Blue Sharks
Despite the blue shark’s position as a large oceanic predator, a few species prey on healthy, fully grown adults. The most formidable natural threat comes from the Orca (Orcinus orca), which hunts large sharks in coordinated family groups. Orcas possess the intelligence and size to incapacitate marine animals, sometimes working together to target the shark’s vulnerable liver. Observational evidence confirms that adult blue sharks actively flee from orcas, highlighting the dominance of the marine mammal.
Large Great White Sharks (Carcharodon carcharias) also pose a significant threat through opportunistic encounters. While both species are apex predators, a larger Great White Shark may successfully prey on a blue shark. The Shortfin Mako (Isurus oxyrinchus) is another shark capable of taking adult blue sharks. It shares the same open-ocean habitat and can reach impressive size and speed.
Vulnerability of Juvenile Sharks
The greatest natural mortality occurs among the youngest individuals, pups and juveniles. Blue shark pups are born in offshore nursery areas, typically measuring 16 to 20 inches at birth, which makes them susceptible to a wider range of predators. Larger species of oceanic sharks, such as the Tiger Shark (Galeocerdo cuvier) and larger conspecifics, frequently prey on these smaller individuals.
Predation on juveniles is highly dependent on their size, with larger pelagic sharks consuming them before they reach maturity. California sea lions (Zalophus californianus) have also been documented to prey on juvenile blue sharks, especially in coastal areas where their ranges overlap. Young sharks must survive this gauntlet of predators until they grow large enough to be primarily threatened only by orcas and the largest sharks.
Human Interaction and Mortality
While natural predators consume blue sharks, human activity represents the primary source of mortality for the global population. The blue shark is the most heavily fished shark species, with millions caught annually, mostly as unintentional bycatch. Commercial fishing operations, particularly those using longlines and driftnets for tuna and swordfish, inadvertently catch enormous numbers.
This high rate of incidental capture results in significant discard mortality. Blue sharks are also targeted for their fins, which are highly valued in the global shark fin trade. Due to these sustained pressures, the species is listed as “Near Threatened” globally by the IUCN, with some regional populations, such as those in the Mediterranean, designated as “Critically Endangered”.