Prionace glauca, Lineu, 1758

Identification

The common name comes from the blue color of the skin, unique among the sharks. A slim torpedo shaped shark with metallic blue colouration on top and white underneath. They have distinctively long pectoral (front) fins, conical snout, large eyes, and curved triangular upper teeth with saw edges. 

Biology

Blue sharks are curious, predators that live throughout the global ocean, from the tropics to cold temperate waters. They spend most of their lives far from the coast and are truly a pelagic species. Though they may reach lengths of up to 3m, blue sharks specialize in relatively small prey, including small pelagic fishes and small squids, and they undertake regular feeding dives to deeper pelagic waters, likely to hunt. Blue sharks are known to be highly migratory, with individuals making several trips across entire ocean basins throughout their lifetimes. Experts believe that blue sharks use their large pectoral fins to ride long currents, conserving energy as they migrate. Blue sharks go on these long migrations to reach areas of dense food resources and to find potential mates. For most of the year, males and females of this species live in different places. Only during the mating season do they come together, briefly, and reproduce via internal fertilization. Males may aggressively bite females during mating, so females have thick protective skin, to prevent injury when they come in contact with males. Sexually mature at 250 cm long and 4-5 years old. The female gives live birth up to 80 young measuring 40 cm long, gestation lasts almost a year.

Behaviour

In some places, the blue shark is an important species to marine tourism. They are often seen swimming slowly at the surface with the tips of their dorsal and caudal fins out of the water. Although blue sharks are not usually aggressive, they are curious animals, known to approach divers, especially spearfishers when food is involved. In rare instances, individuals have bitten people, but this happens only very infrequently. The blue shark has one of the largest geographic distributions among the sharks. Its wide distribution and dense population structure makes the blue shark a target of fisheries in some areas and a common accidentally caught species in gillnet and longline fisheries targeting other species. Furthermore, its fins are considered highly valuable, and blue sharks may be the target of illegal ‘shark finning’ operations, where the fins are cut off and kept, while the rest of the shark is wasted.