Blue SharkPrionace glauca
Named for their distinct blue color that fades to a crisp white underside, blue sharks have the requiem's long, sleek body and an elongated conical snout. They eat mostly squid and other invertebrates and small fish, but have been found with many other marine animal (and even sea birds) remains in their stomachs, proving to be opportunistic eaters. Although blue sharks are not overly aggressive, these slow-movers are not shy and have been know to attack or pursue humans if there is food involved. A female can have a litter of anywhere from 4 to over 100 pups at a time.
Order - Carcharhiniformes
Family - Carcharhinidae
Genus - Prionace
Species - glauca
English language common names include blue shark, blue dog and blue whaler. Other common names are tiburon azul (Spanish), tintorera (Spanish), verdemar (Spanish), blauwe haai (Dutch), blauhai (German), blauer hai (German), peau bleue (French), sinihai (Finnish), blåhaj (Swedish, Danish), zarlacz blekitny (Polish), pas modrulj (Serbo-Croat), guelha azul (Portuguese), pas modrulj (Portuguese), verdesca (Italian), Squalo azzurro (Italian), glucose (Greek), karcharias (Greek), glafkcarcharias (Greek), canavar balik (Turkish), pamuk baligi (Turkish), peshkagen (Albanian), karish kakhol (Hebrew), kalb al bhar (Arabic), mouch labhar (Arabic), blouhaai (Afrikaans), and yoshikirizame (Japanese).
Importance to HumansRecreationally blue sharks are considered a sport fish and larger individuals provide a challenge for fishermen using light tackle. Most commercially caught blue sharks are considered bycatch and it is estimated that 10 to 20 million are killed each year, possibly having a negative impact on world populations. The salmon, mackerel and pilchard fisheries are affected by blue shark predation on catch and entanglement in nets. Keeping blue shark meat is difficult since it ammoniates quickly so most blue sharks that are not released are fined. The fins are then sold to Asian markets and are used to make shark-fin soup.
Danger to 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. The blue shark will sometimes circle swimmers or divers it encounters for up to fifteen minutes or more. While not overly aggressive it is not a timid shark and needs to be approached with caution, especially if it has been circling since it may attempt an exploratory bite in test feeding.
ConservationCurrently blue sharks are regulated in the commercial longline shark fishery on the east coast of the United States by the National Marine Fisheries Service. The entire fishery is limited to landing 136.5 metric tons (150.5 short tons) dry weight during the summer of 2003 season. On the west coast the blue shark is not considered overfished so there is currently no specific regulations on its harvest. Conservation issues that need to be addressed regard minimizing mortality rates of blue sharks caught as bycatch.
The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species.
Geographical DistributionBlue sharks are found world wide in temperate and tropical waters. They are a pelagic species that rarely comes near shore but have been known to frequent inshore areas around oceanic islands and locations where the continental shelf is narrow. In the Atlantic they can be found from New Foundland, Canada to Argentina and from Norway to South Africa, including the Mediterranean. They range from South Africa to Indonesia and from Japan to New Zealand in the Indian and western Pacific Oceans. In the eastern Pacific, blue sharks range from the Gulf of Alaska to Chile.
Being a pelagic species the blue shark's habitat consists of open ocean areas from the surface to 1,148 ft (350 meters) in depth. 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. When in the tropics the blue shark tends to seek deeper waters with cooler temperatures. This is evident in the tropical Indian Ocean where the majority of blue sharks are found at depths of 262-722 ft (80-220m) where water temperatures range from 53.6-77°F (12-25°C). In the Pacific, at latitudes between 20°N and 50°N, they are known to migrate to higher latitudes during the summer and lower latitudes during the winter but their populations remain constant throughout the year between 20°N and 20°S latitude.
1. Body is slender
2. Snout is long and rounded
3. Caudal fin is nonlunate
4. Pectoral fins are very long and pointed
5. First dorsal fin is closer to pelvic fins than pectoral fins
The blue shark has a slender, sleek-looking body with a large eye and a long conical snout that is longer than the width of its mouth. It has extremely long, pointed pectoral fins, which generally are as long as the distance from its snout to posterior gill slit. The dorsal fin is moderate in size and set back where it is actually closer to the pelvic fin insertion than the pectoral insertion point. There is a slight keel on the caudal peduncle and the tail is narrowly lobed with a long ventral lobe.
The blue shark's name comes from its distinct dark blue dorsal surface and bright blue sides. Its ventral surface is a well-defined, crisp white color. This contrast in colors is known as counter-shading and provides camouflage for the shark in the open ocean.
The upper teeth of the blue shark are triangular with curved cusps, serrated edges and bases that overlap each other. The upper jaw generally has one symmetrical median tooth and has 14 teeth 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.
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.
Size, Age, and Growth
The largest blue shark on record measured 12.6 feet (383 cm) but they are rumored to get as large as 20 feet (609.6 cm). Males are believed to be mature at four to five years of age and at lengths between 6 feet (182 cm) and 9.2 feet (281 cm). Females mature slightly older ages ranging from five to six years and longer lengths from 7.3-10.6 feet (221-323cm). They are believed to live for more than 20 years.
Gestation periods of the blue shark range from 9 to 12 months and result in litters averaging 25 to 50 individuals. Pups are approximately 16-20 inches (41-50 cm) in length at birth. Blue sharks are viviparous, which means they give birth to live young that have hatched from eggs internally. After hatching the young are nourished by a placental yolk sack until they are fully developed. Litter sizes are believed to be related to the size of the female and have been known to range from 4 to 134 pups. Sex ratios of litters are generally one to one but it is not uncommon for one sex to have slightly more individuals.
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.
TaxonomyThe blue shark was originally named Prionace glauca by Linnaeus in 1758. Prionace is derived from Greek, "prion" meaning saw and "akis" meaning point, while the species name glauca is derived from the Latin term "glaucas" meaning bluish gray or green in English, referring to the blue coloration of this shark. Since then they have also been referred in the literature as Squalus glaucus Linnaeus 1758, Squalus caeruleus Blainville 1826, Thalassinius rondelettii Moreau 1881, Carcharias pugae Perez Canto 1886, Carcharias gracilis Philippi 1887 and Prionace mackiei Phillips 1934.
Prepared by: Pete Cooper