The pelagic zone’s elegant hunter
The Blue shark (Prionace glauca) is a species of requiem shark, in the family Carcharhinidae. They inhabit deep waters in the world’s temperate and tropical oceans. Blue sharks prefer cooler waters and migrate long distances from New England to South America. They move gracefully and can move quickly but are often lethargic in movement. The Blue shark is known for having very large litters from 25 to 100 pups. Blue sharks are considered dangerous to humans.
Photo: © 2018, Harry Stone, Planet Shark Divers, all rights reserved.
Family: Carcharhinidae – Requiem sharks
Status: IUCN Red List Near Threatened
Average Size and Length: Up to 13 feet
Average Weight: Usually between 300 and 400 pounds.
Teeth and Jaw: The Blue shark has curved, saw-edged, triangular upper teeth, 14 on either side. Teeth on the lower jaw number 13 to 15 on either side and have fine serrated edges, nearly erect cusps and are triangular, nearly symmetrical, shape.
Head: The Blue shark has large, circular eyes (no spiracles) on the sides of its narrow head. Its snout is long and conical.
Demographic, Distribution, Habitat, Environment and Range: The Blue shark prefers deep temperate and tropical waters. It will sometimes swim to the surface, but usually remains within ranges as deep as 1,100 feet. The Blue shark can be found off the coasts of every continent except Antarctica. It can be found as North as the northern tip of Norway to the southern most tip of Chile. The Blue shark is possibly the most wide-ranging shark. The Blue shark is oceanic and pelagic, and usually off the continental shelf (0-1150 feet, but deeper in warmer waters. The Blue shark endures major trans-oceanic migrations, and also make frequent vertical excursions to thermoclines, then return to the surface (to prevent body cooling). They may venture inshore at night. They prefer cooler water ranging from 44.6-60.8°F (7-16°C) but are known to have tolerances for water 69.8°F (21°C ) or greater.
Diet: The Blue shark has a varied diet of fishes like cod, mackerel, haddock, and other aquatic animals such as cuttlefish, squid, shrimp and octopus. The Blue shark will eat small or large animals and are capable of attacking larger animals. Some Blue sharks have had contents in their stomachs including seal and whale. Blue sharks can go sometimes 2 months in between feedings.
Predators of the blue shark include California sea lions (Zalophus californianus) and larger sharks including the Shortfin Mako (Isurus oxyrinchus) and the white shark (Carcharodon carcharias).
Ram-Suction Index: Ram
Aesthetic Identification: The Blue shark is deep blue to indigo from above in color, vibrant blue on its sides and flanks, and a white, counter-shaded underbelly. The Blue shark is very slim, long and slender and is streamlined in shape.
Due to the violent mating rituals, female Blue sharks can usually be identified by heavy scarring all over their bodies.
Biology and Reproduction: The Blue shark is prone to parasites such as tapeworms. Unfortunately, a variety of copepods are known to use the blue shark as a host, with some carrying over five different species at one time. Species of these copepods include Pandarus satyrus, which attaches itself to the pectoral fins, Kroeyerina elongata, which lives in the nose, Echthrogaleus coleoptratus, a body surface dweller, and Kroyeria carchariaeglauci and Phyllothyreus cornutus, both species that inhabit the gills. Parasite loads can exceed 3,000 individuals and can lead to sight impairments and changes in gill structure.
The female Blue shark’s skin has evolved to be much thicker than the male’s skin because the male Blue shark tends to violently bite the females back and fins during mating.
The dermal denticles are closely arranged, typically overlapping and small. The blades are broad with usually 3, but up to 4 or 5 ridges. The skin is smooth to the touch.
The male Blue shark reaches sexual maturity at 6 feet, and the female at 7 feet. They mate during summer, and females breed annually. Blue sharks are viviparous, and their gestation period is between 9 and 12 months. Blue sharks have anywhere from 4-135 pups (average 20-50), and their young average 15 to 17 inches in length. One interesting fact is that a female Blue shark has the ability to hold and nourish male Blue shark sperm for several months or years while she waits for ovulation. Blue shark nurseries are offshore.
Blue sharks have a life span of about 20 years.
Behavioral Traits, Sensing and Intelligence: Like all sharks, Blue sharks rely heavily on sensing electrical currents through their Ampullae of lorenzini and their lateral lines.
They cruise slowly at the surface, but are capable of graceful, quick swimming. They are most active in early evening and at night, where they may move more inshore.
Blue sharks do form large aggregations.
Blue sharks are known to harass spear-fisherman, and tend to be aggressive and curious, and never back down. They have been seen biting floating objects at the surface. They will circle swimmers, divers and boats for long periods of time before biting.
Blue sharks segregate by age, sex and reproductive phases, only coming together to mate.
Speed: The Blue shark’s streamlined slender body, and long pectoral fins allows it to swim and move very quickly, but ever so gracefully. Interesting enough, they tend to be quite lethargic.
Blue Sharks Future and Conservation: Blue sharks are the most heavily fished sharks in the world, millions a year taken mostly in bycatch. The fins are valued, and carcasses are thrown back into the sea.
Blue Shark Recorded Attacks on Humans: Having been known to attack humans and boats, blue sharks are considered to be a dangerous species. Twelve unprovoked attacks and four boat attacks have been documented by the International Shark Attack File. Three documented attacks resulted from air or sea disasters and there are several accounts linking blue sharks to attacks on shipwrecked sailors floating in the open ocean.