Most sharks are known to use body language to signal aggression, but there is little data available on whether sharks utilize other forms of communication between individuals. Like all sharks, blue sharks have highly developed senses of smell, sight, and touch. The lateral line is a sensory organ running down the length of their body that detects pressure waves from movements in the water, allowing the sharks to perceive movements of prey. They also possess electroreceptors called Ampullae of Lorenzini on the underside of the snout, which detect electrical fields generated by the muscle contractions of prey items.
Communication Channels: visual
Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical ; electric
Although not usually a targeted species, blue sharks are caught as bycatch by longline and dragnet fishing fleets, and to a lesser extent by sport fishermen. International conservation projects have been implemented to decrease the harvest of pelagic sharks, including this species. In 1991, the Australian Government implemented legislation that banned Japanese longline fishing fleets from taking shark fins without their attendant carcasses. Canada issued a fishery management plan for shark species in 1995 that established catch limits of 250,000 kg for blue sharks, and implemented limitations on finning and gear use, licenses, areas and seasons, and bycatch limits. Management plans have been in place in the US since 1993. Proper licensing and commercial quota limits have been introduced, and finning has also been banned within the US Exclusive Economic Zone. However, exploitation by the shark finning industry has still decreased populations globally, and the IUCN lists this species as "Near Threatened".
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: near threatened
After fertilization, embryos develop inside the female's uterus, nourished by a placenta-like yolk sac. Females give birth to fully-developed, live young. Blue sharks have one of the fastest growth rates of all sharks, growing up to 30 cm annually until maturity. Blue sharks are 35to 50 cm in length at birth, and will grow up to 400 cm (although the average length is 335 cm). Both sexes reach adulthood at about 220 cm in length. Juveniles usually stay in pupping areas of the sub-Arctic boundary (42°N North Pacific Ocean) until they reach maturity at 5 years of age.
Development - Life Cycle: indeterminate growth
Blue sharks are considered by commercial fishermen (particularly those of mackerel, pilchard, and salmon) to be a nuisance species, as they prey on target species and ruin nets by becoming entangled in them.
Due to their pelagic lifestyle, blue sharks are not often encountered by divers and swimmers. They are considered to be a dangerous species, however, with the International Shark Attack File recording a dozen confirmed, unprovoked attacks (4 fatal), and nearly two dozen additional, provoked attacks.
Negative Impacts: injures humans (bites or stings)
Although mainly caught indirectly as bycatch on long lines and in gill nets, blue sharks, like many shark species, are valued commercially for their fins, squalene (liver oil), skin, cartilage, and their teeth and jaws. Their meat is less valued because of its high ammonia content.
Positive Impacts: food ; body parts are source of valuable material
Blue sharks are top-level predators that help to regulate prey populations in the marine pelagic environment.
Pilotfish (Naucrates ductor) have a mutualistic symbiosis with blue sharks. They clean the shark's teeth and gills and removes any parasitic species that have attached themselves to the shark's skin. In return, pilotfish gain protection from predators and a ready source of food.
Many species of copepods are found on the gills and outer skin of blue sharks. Several tapeworm and one nematode species have been found in the stomach and spiral valve of blue sharks, resulting from consumption of infected fish that are the intermediate hosts of these parasites.
Mutualist Species:
Commensal/Parasitic Species:
Blue sharks prey on up to 24 species of cephalopods and 16 species of fish. They primarily feed upon non-active, gelatinous, mesopelagic/bathypelagic cephalopods such as blanket octopus (genus Tremoctopus), bathyscaphoid squids (family Cranchiidae), and pelagic octopus (Ocythoe tuberculata). Prey also includes small schooling fishes, such as long-snouted lancetfish (Alepisaurus feroxe), snake mackerel (Gempylus serpens), and castor oil fish (Ruvettus pretiosus). During their reproductive migration cycles off of the coast of Brazil, blue sharks were found to have consumed seabirds, including great shearwaters (Puffinus gravis).
Animal Foods: birds; fish; mollusks
Primary Diet: carnivore (Piscivore , Molluscivore )
Blue sharks are one of the most wide ranging shark species and can be found in all major oceans (except the Arctic), as well as the Mediterranean Sea and in temperate and tropical pelagic waters.
Biogeographic Regions: indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )
Other Geographic Terms: cosmopolitan
Blue sharks inhabit the epipelagic and mesopelagic zones (from the surface to about 350 m in depth), in water temperatures ranging between 12 and 20°C. While they are mainly found in pelagic, open-ocean waters, they may sometimes be found closer to shore in the neritic zone, near the edge of continental shelves.
Range depth: 0 to 350 m.
Habitat Regions: temperate ; tropical ; saltwater or marine
Aquatic Biomes: pelagic
Blue sharks in the wild have an average lifespan of 15 to 16 years. Blue shark life expectancy decreases to an average of 8 years when held in captivity, likely due to their inability to engage in their pelagic and migratory lifestyle.
Range lifespan
Status: wild: 20 (high) years.
Range lifespan
Status: captivity: 8 (high) years.
Average lifespan
Status: wild: 15 years.
Typical lifespan
Status: captivity: 8 (high) years.
The striking coloration of blue sharks makes them one of the most distinctive species in the family Carcharhinidae (requiem or whaler sharks). The dorsum is a deep shade of indigo, while the flanks are a vibrant blue. The ventral surface fades to a light grey, exhibiting the typical pelagic countershaded coloration that deceives the eyes of bottom-dwelling prey or predators by blending in with light coming from the sun. The body is streamlined and thin, with an elongated heterocercal caudal (tail) fin, making it one of the fastest sharks in the ocean. The second dorsal fin is approximately half the size of the first, and the pectoral fins are proportionately longer than in most other shark species. The eyes are large, and the mouth is lined with several rows of triangular, serrated teeth; each tooth is usually replaced every 8 to 15 days. Blue sharks can reach 4 m in total length and weigh up to 240 kg.
Range mass: 240 (high) kg.
Range length: 4 (high) m.
Average length: 3.35 m.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger
Aside from predation by humans for the lucrative shark fin trade, blue sharks are not frequently preyed upon. Occasional predators can include larger sharks such as shortfin makos Isurus paucus and great whites (Carcharodon carcharias), as well as killer whales Orcinus orca, while juveniles can also be taken by California sea lions (Zalophus californianus).
Due to their pelagic lifestyle, blue sharks exhibit countershading. The lighter coloration on the ventral surface helps to camouflage the sharks against the background of lighter-colored water when viewed from below. In contrast, the darker shades of blue and silver on the dorsal side allows them to blend in with the depths below when viewed from above. This countershading, along with a streamlined body shape, allows blue sharks to maneuver both swiftly and unnoticed as both predator and prey.
Known Predators:
Anti-predator Adaptations: cryptic
Blue sharks congregate together on continental shelves during the summer. Mating begins when a male bites a female between her first and second dorsal fins. For this reason, the skin over most of a female's dorsum may be up to three times as thick as in males. Insemination occurs via insertion of one of the claspers into the female's urogenital opening. Pair bonding does not occur, and after mating, individuals separate.
Mating System: polygynandrous (promiscuous)
Males reach sexual maturity at 187 cm in length, while females become mature at 220 cm. It is not definitively known if females breed every year and deposited sperm may be stored within the female's oviductal gland for several months after mating. Once pregnant, females migrate north to birthing and pupping grounds in the sub-Arctic boundary. Gestation lasts from 9 to 12 months, and up to 130 pups in a litter have been documented, but 25 to 50 pups are born on average. Pups average 39 cm at birth. Unlike bony fish, sharks utilize internal fertilization. The male bites down and insert a clasper inside the female to transfer sperm. Females have thick skin to protect them from injury when the males bite them during mating. Blue sharks are viviparous.
Breeding interval: It is unknown whether female blue sharks breed annually, or less frequently.
Breeding season: In the northern Pacific, most births occur from December to April.
Range number of offspring: 25 to 130.
Range gestation period: 9 to 12 months.
Range age at sexual or reproductive maturity (female): 5 to 6 years.
Range age at sexual or reproductive maturity (male): 5 to 6 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous ; sperm-storing ; delayed fertilization
As in other viviparous species, female blue sharks provide nourishment and protection to their young as they develop. After birth, shark pups separate from their mother and have no further contact.
Parental Investment: female parental care ; pre-hatching/birth (Provisioning: Female, Protecting: Female)
