The blue shark (Prionace glauca) is a pelagic shark found across the world’s oceans. A member of the Carcharhinidae family (requiem sharks), it inhabits both temperate and tropical waters.
Distinctive Features and Ocean Home
The blue shark has a sleek, slender body with long pectoral fins and a pointed snout. Its distinctive iridescent deep blue dorsal side fades to bright blue flanks and a pure white underside. This countershading provides effective camouflage in the open ocean. Males typically measure 1.8 to 2.8 meters (6 to 9.3 feet) long, while larger females commonly reach 2.2 to 3.3 meters (7.2 to 10.8 feet). Some specimens can exceed 3.8 meters (12.5 feet) and weigh over 200 kilograms (440 pounds).
Blue sharks are primarily oceanic and epipelagic, inhabiting the open ocean from the surface down to about 350 meters (1,150 feet). They prefer cooler waters but tolerate a wide temperature range. In tropical regions, they reside in deeper, cooler waters. This species is found in all major oceans except the Arctic, and while generally offshore, they may approach coastlines or oceanic islands.
Life in the Deep: Diet and Habits
Blue sharks primarily eat squid, a primary prey item. They also consume various bony fish, such as mackerel, herring, sardines, and anchovies. Their opportunistic feeding habits occasionally lead them to prey on crustaceans, small sharks, or even seabirds. Blue sharks are active hunters, primarily at night, but can feed throughout a 24-hour period.
Blue sharks undertake extensive seasonal migrations across ocean basins. These movements are influenced by prey availability and reproductive cycles, with some individuals covering thousands of kilometers annually. They exhibit social behavior, often forming schools segregated by size or sex, particularly as juveniles. While typically in the upper 350 meters, blue sharks can dive to 1,000 meters or more, often displaying diel vertical migration by staying deeper during the day and moving shallower at night.
Blue Shark Conservation and Human Encounters
The blue shark is listed as “Near Threatened” globally by the IUCN Red List, though some regional populations, such as those in the Mediterranean Sea, are “Critically Endangered.” Commercial fishing poses the primary threat, as they are frequently caught as bycatch in tuna and swordfish longline fisheries. Despite being one of the most abundant pelagic sharks, millions are estimated to be caught annually, and their fins are highly sought after in international trade.
Blue sharks are generally not considered aggressive towards humans. Attacks are rare, with only a small number of unprovoked incidents recorded worldwide. These encounters are often described as exploratory bites rather than predatory attacks. Blue sharks play an important role as top predators in marine ecosystems, helping to regulate prey populations and contributing to the overall health and stability of ocean environments.