The blue shark, Prionace glauca, is a carcharhinid shark which is found in the deep waters of the world’s temperate and tropical oceans. They prefer cooler waters and are not found, for example, in the Yellow Sea or in the Red Sea. Blue sharks are known to migrate long distances, from New England to South America for example. Although generally lethargic, they can move very quickly. Blue sharks are viviparous and are noted for large litters of 25 to over 100 pups. They feed primarily on small fish and squid, although they can take larger prey. Blue sharks often school segregated by sex and size, and this behavior has led to their nickname “wolves of the sea”.
The blue shark is the most wide ranging geographically of all fish. Being pelagic, it is to be found in every sea and ocean the world over. They can reach 15 ft in length, and frequently travel in schools that consist of similarly sized sharks, that are either all female or all male. They are not considered dangerous although they have caused 4 fatalities, usually after being caught. Up to 20 million of them are fished from global waters annually, and their numbers are now classed as ‘vulnerable’ on the IUCN list of threatened species.
Blue sharks like swimming in cooler waters. While in the North Atlantic they are to be found swimming near the surface, in the tropical Indian or Pacific Oceans, they may be found at depths of 350 metres (over 1,000 feet).
Blue sharks are shy and nervous around people. Should you ever come face to face with a blue shark, any sudden movement on your behalf with see it shoot off into the darkness of the surrounding ocean.
Blue sharks can grow to 12 feet long, and sometimes even bigger, but are generally around 4’ to 6’ in length. It is said they can live for 30 years, but we will know better in future thanks to studies being carried out now.
Squid are important prey for blue sharks, but their diet includes other invertebrates such as cuttlefish and pelagic octopuses, as well as lobster, shrimp, crab, a large number of bony fishes, small sharks, mammalian carrion and occasional sea birds. Whale and porpoise blubber and meat have been retrieved from the stomachs of captured specimens and they are known to take cod from trawl nets. The sharks have been observed and documented working together as a “pack” to herd prey into a concentrated group from which they can easily feed. Blue sharks rarely eat tuna, which have been observed taking advantage of the herding behavior to opportunistically feed on escaping prey. It is interesting to note that the observed herding behavior was undisturbed by different species of shark in the vicinity that normally would pursue the common prey. The blue shark can swim at fast speeds, allowing it to catch up to prey easily. Triangular teeth allows the Blue shark to easily catch slippery prey.