Blue shark (Prionace glauca)

Physical characteristics

Blue sharks have a slim, streamlined body with large eyes and a long, pointed snout. Their pectoral fins are relatively long and help with efficient cruising in open water. Adults commonly reach lengths of up to around 3.8 metres and can weigh on the order of a few hundred kilograms, though most individuals are smaller. The upper surfaces are typically dark blue to blue-grey while the belly is white, producing the familiar two-tone appearance.

Distribution and habitat

This species is highly migratory and occurs worldwide in temperate and tropical seas. Blue sharks occupy surface waters down to several hundred metres and are often associated with oceanic fronts, seamounts and continental slopes where prey concentrates. They tolerate a range of temperatures but are most common in cooler temperate waters and subtropical zones.

Diet and behaviour

Blue sharks are active predators that feed mainly on small bony fish, squid and other cephalopods, and occasionally crustaceans. They are capable of long-distance movements and often travel in loose aggregations, particularly where food is abundant. Their cruising lifestyle, paired with good swimming efficiency, makes them frequent visitors to longline and recreational fishing areas.

Reproduction and lifecycle

Like many requiem sharks, the blue shark is viviparous: embryos develop inside the mother and are nourished via a placental connection. Litters may include multiple pups, and the young are relatively well developed at birth, adaptable to the open-ocean environment. Growth rates and maturity ages vary by region and size; females typically mature later than males.

Importance and conservation

Blue sharks play an important role as mid-level predators in pelagic ecosystems, helping to regulate prey populations. They are also among the most commonly caught sharks in pelagic longline fisheries, both as targeted catch and as bycatch; parts such as fins enter international trade. Because of their life history and heavy fishing pressure in some regions, populations have shown local declines and the species is subject to conservation assessments and management measures in various jurisdictions. International attention focuses on bycatch reduction, trade controls and improved monitoring to ensure sustainable populations.

Notable distinctions

• Distinctive blue coloration and slender profile compared with other requiem sharks.
• Highly migratory; capable of long transoceanic movements.
• Often encountered in pelagic fisheries, making it both ecologically significant and frequently subject to human impacts.