#blue shark

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BLUE SHARK

Azores

Mike Harterink

Blue Shark

Colin Garrett

Blue shark

Prionace glauca

Family: Carcharhinidae

The blue shark is a sleek, graceful species of requiem shark, instantly recognizable by its striking deep blue coloration. It is one of the most wide-ranging and abundant pelagic sharks in the world, found across tropical and temperate oceans.

Physical Description and Size

The blue shark has an elegant, slender, and streamlined body designed for efficient swimming in the open ocean. Its most distinctive feature is its coloration: the dorsal side is a striking deep indigo blue, the flanks are bright blue, and the ventral side is white — a countershading pattern that provides camouflage in the open ocean.

Other distinctive features include a long, conical, pointed snout; large, round eyes adapted for hunting in low light; extremely long, slender, and pointed pectoral fins; and a moderately sized first dorsal fin positioned closer to the pelvic fins than to the pectoral fins. This species also lacks an interdorsal ridge.

Size and Weight: ◦ Length: Most adults measure 1.7 to 2.2 meters. ◦ Weight: Maximum recorded weight is approximately 206 kg.

Distribution and Habitat

The blue shark has a circumglobal distribution and is likely the most wide-ranging shark species in the world.

It is found in temperate and tropical waters of the Atlantic, Pacific, and Indian Oceans, from 60°N to 50°S latitude, occurring off the coasts of every continent except Antarctica

◦ Western Atlantic: From Newfoundland, Canada, to Argentina. ◦ Eastern Atlantic: From Norway to South Africa, including the Mediterranean Sea. ◦ Indo-Pacific: From East Africa to Indonesia, Japan, Australia, New Zealand, and New Caledonia. ◦ Eastern Pacific: From the Gulf of Alaska to Chile

It is rarely found close to shore, except in areas where the continental shelf is narrow or around oceanic islands.

Behavior and Diet

The blue shark is a highly migratory, opportunistic predator known for its speed and nocturnal activity.

In terms of migration, blue sharks are among the most highly migratory shark species, traveling vast distances across ocean basins, moving to higher latitudes in summer and returning to lower latitudes in winter.

Regarding activity patterns, they are most active at night, particularly in the early evening. During the day, they tend to remain at shallower depths (around 30 meters), while at night they venture slightly deeper (around 40 meters) and exhibit more vertical movement.

They also display social behavior: the species may form hierarchical groups segregated by sex and size, and individuals have been observed hunting cooperatively in coordinated groups to herd prey into concentrated schools.

Diet: ◦ Primary: Squid is the most important prey item; they also feed on small bony fishes such as herring, mackerel, cod, haddock, anchovies, and hake. ◦ Secondary: Crustaceans (crabs, shrimp, lobsters), small sharks, cetacean carrion (whale and porpoise blubber), occasional seabirds, and opportunistic scavenging of discarded material.

Reproduction and Life Cycle

Blue sharks are viviparous and have a relatively high reproductive capacity compared to many other shark species. Females give birth to litters of 4 to 135 pups, typically 25 to 50, after a gestation period of 9 to 12 months. The wide range in litter size may reflect regional differences.

Females use specific nursery areas, separate from adult ranges, to give birth. These areas provide a safer environment for newborns during their early months. Research suggests females may exhibit natal and reproductive philopatry, returning to specific sites to give birth.

The maximum lifespan is estimated at 15 to 20 years in the wild. In captivity, blue sharks tend to fare poorly and rarely survive for extended periods.

Relationship with Humans

The blue shark is not considered aggressive toward humans and is generally curious but timid. However, as wild predators, they can be attracted by bait and may become bold during feeding frenzies, and should always be treated with respect.

⚠️Conservation Status

The International Union for Conservation of Nature (IUCN) classifies the blue shark as Near Threatened globally. However, regional assessments vary significantly:

◦ North Atlantic: Listed as Endangered (EN). ◦ South Atlantic: Listed as Vulnerable (VU). ◦ Mediterranean: Listed as Critically Endangered (CR).

Primary threats include targeted and bycatch fishing, the fin trade, and commercial exploitation of meat, hides, and liver oil.

Conservation Efforts: The blue shark has been listed on Appendix II of the Convention on the Conservation of Migratory Species (CMS) since 2017, encouraging range states to cooperate on conservation measures. Regional fisheries management organizations (RFMOs) such as ICCAT (International Commission for the Conservation of Atlantic Tunas) have also implemented catch limits and retention bans in certain areas.

🦈Fascinating Facts

Blue sharks are remarkable long-distance swimmers. In one long-term electronic tagging study, a tracked individual covered an estimated 28,139 km — among the greatest distances ever recorded for any shark. Another tagged individual traveled over 11,000 km in 8–9 months, averaging approximately 43 km per day.

Female blue sharks have evolved skin three times thicker than that of males, an adaptation that allows them to withstand the repeated biting from males during courtship and mating. This is a direct product of sexual conflict.

The upper teeth of the blue shark are triangular and serrated, making them highly effective for grasping and tearing the slippery bodies of squid and fish.