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THE BLUE SHARK

Prionace glauca

 

Common names: Blue Shark, Blue Dog, Blue Whaler, Peau Bleue (Fr), Tiburón Azul (Es).

 

SYNONYMS

Squalus glaucus (Linnaeus, 1758), Squalus adscentionis (Osbeck, 1765), Squalus rondeletii (Risso, 1810), Squalus caeruleus (Blainville, 1825), Galeus thalassinus (Valenciennes, 1835), Thalassorhinus vulpecula, (Valenciennes, 1838), Carcharias hirundinaceus (Valenciennes, 1839),  Thalassinus rondelettii (Moreau, 1881), Carcharias pugae (Perez Canto,  1886), Carcharias gracilis (Philippi, 1887), Hypoprion/Hemigaleus isodus , (Philippi, 1887), Carcharias aethiops (Philippi, 1896), Prionace macki (Phillipps, 1935).

 

 

APPEARANCE

Slender body

Long, rounded snout.

Very long pointed pectoral fins.

First dorsal fin closer to pelvic than pectoral fins

Second dorsal fin equal in size to and directly above anal fin

Caudral fin non lunate with a large terminal lobe.

The Blue Shark is a large, slender-bodied requiem shark with a long  narrow snout. The first dorsal fin originates well behind the pectoral fin free tips in individuals over 100cm. The pectoral fins are long and curved. The second dorsal fin is roughly equal in size to the anal fin., over which it is positioned. The dorsal lobe of the caudral fin is larger than the ventral lobe and has a terminal lobe which covers less that a third of its length (Compagno, 1984).

it is distinct metallic blue on the back and flanks, ventrally it is pure white. The counter-shading provides some camouflage in the open ocean. It reaches a maximum size of 383cm (Cooper, unknown)

 

DISTRIBUTION

Possibly the widest ranging of all chondrichthyans the Blue Shark is found in temperate and tropical waters worldwide. In the east Atlantic it is found from Norway to South Africa, Including the Mediterranean. It is also found in the west Atlantic Ocean, the whole Pacific Ocean and the whole Indian Ocean (Kohler et al., 2002; Cooper, Unknown).

 

Text & Illustrations © Shark Trust 2009

 

 

SIMILAR SPECIES

Prionace glauca, Blue Shark

Carcharhinus falciformis, Silky Shark

Isurus oxyrinchus, Shortfin Mako Shark

Isurus paucus, Longfin Mako Shark

Lamna nasus, Porbeagle Shark

Galeorhinus galeus, Tope

 

 

 

 

 

 

 

Prionace glauca, Blue Shark

 

 

Carcharhinus falciformis, Silky Shark

 

 

Isurus oxyrinchus, Shortfin Mako Shark

 

 

Isurus paucus, Longfin Mako Shark

 

 

Lamna nasus, Porbeagle Shark

 

 

Galeorhinus galeus, Tope

 

 

Not to scale

 

 

ECOLOGY AND BIOLOGY

HABITAT

A pelagic species, the Blue Shark can be found from the surface to at least 600m. It has a preference for temperate and subtropical waters from 12–20 *C but can tolerate temperatures from 8–29.5 *C . The Blue Shark is found in the tropics but tens to seek cooler water at depth (Kohler et al,, 2002) In the tropical Indian Ocean the temperature can fall from 25*C at 80 m to 12*C at 220 m (Cooper, Unknown)

In the North Atlantic, tag and recapture studies have shown that a regular clockwise trans-Atlantic migration occurs following the major currents. It appears that sharks tagged off the east coast of the USA follow the Gulf Stream to Europe, ride various currents south along the coasts of Europe and Africa and then follow the Atlantic North Equatorial Current to the Caribbean. Because of this, the entire North Atlantic population is considered a single stock. There have been reports of tagged sharks crosssing the equator into the South Atlantic. While this appears to be a rare occurence, it shows that there is some genetic exchange bewteen the two areas. There is considerable sexual segregation in populations with females more abundant at higher lattitudes than males (Kohler et al,. 2002)

 

REPRODUCTION

The Blue Shark reproduces through placental, or yolk-sac, viviparity. At the start of the gestation period, the embryos are nourished by a yolk supply in a very similar way to the 60% of elasmobranchs which reproduce vivipariously. However once this yolk supply is used up, the yolk-sac changes, becoming more folded and wrinkled. It can now interlock with the lining of the mothers uterus. The blood supply to both the yolk-sac and the uterus wall increases allowing nutrientsand oxygen to pass from the mother to the embryo and vise versa for waste, very much like a mammalian placenta (Martin, 1994).

Males are believed to reach sexual maturity between four and five years of age at a length of 182-291cm. Females mature later between five and six years at a length of 221-323cm (Cooper,Unknown). In temperate waters, mating occurs from late spring to early winter. Gestation varies from 9-12 months and young are born in spring to early summer. In tropical seas, mating is thought to occur all year round (Compagno,1984). The number of young born is highly variable with litters from 4-135 pups recorded. although the average is around 35. These pups measure 35-50cm in length and remain in nursery areas for the first few years of life, during which they grow rapidly. It appears that for Atlantic sharks, the Mediterranean is an important nursery area (Kohler et al, 2002)

 

DIET

The diet of the Blue Shark consists mainly of small pelagic fish and cephalopods, particularly squid. However, invertebrates (mainly pelagic crustaceans), small sharks, seabirdsand cetaceans (possibly carrion) are also taken. Most of the prey is pelagic although botton fishes are also found in stomach contents. It appears to feed 24 hours a day with increased activity in the early evening and at night. (Stevens, 2000).

 

COMMERCIAL IMPORTANCE

Thought to be the most heavily fished shark, the Blue Shark is mainly taken as bycatch in pelagic longlines but also in pelagic trawls, hook and line and bottom trawls inshore (Compagno,1984). Keeping the meat is difficult as it ammoniates quickly, therefore the vast majority are discarded at the sea after their fins are removed for sale in the Asian fin trade (Cooper, Unknown). When it is landed whole its flesh an be used for human consumption, its liver for oil, its carcass can be processed for fishmeal and its hide can be used for leather. (Compagno. 1984).

 

 

IUCN RED LIST ASSESSMENT

Near Threatened (2000).

 

THREATS, CONSERVATION, LEGISLATION

Thought to be one of the most abundant and widespread large animals on the planet, the Blue Shark is heavily fished throughout its range by pelagic longlines and hook-and-lines. Its flesh is not highly valued but its fins are, meaning many Blue Sharks are finned at sea and subsequently discarded. It is also considered a game fish and large numbers are taken by recreational anglers every year, although may now return the sharks they catch aive. (Stevens, 2000).

In the northeast Atlantic, the Blue Shark is covered by EC Regulation No. 1185/2003 which prevents the removal of fins at sea and the subequent discard of the body. This applies to all vessels operating in EC waters, as well as to EC vessels operating anywhere (CPOA Sharks, 2009). However, loopholes in this legislation allow many fishing boats to continue this practise. In addition, as it is a highly migratory species, localised legislation may have little effect on wider populations.

While the Blue Shark is relatively highly fecund and has a wide range which buffers it from the effects of heavy fishing pressure, population declines are still being observed across its range. Catches need to be monitored and legislation needs to be created, changed or enforced if population declines are to be halted. (Stevens, 2005).

 

 

HANDLING AND THORN ARRANGEMENT

Handle with care

Large shark with powerful jaws and sharp teeth

Abrasive skin

 

 

REFERENCES

COMPAGNO, L . J V.1984. FAO Species Catalogue, Vol4, Part 2, Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known top Date. FAO. Rome, Italy.

COOPER, P. Unknown. Blue Shark. Florida Museum of Natural History. http/:www.flmnh.ufl.edu/fisk/.

KOHLER,N. E, TURNER, P.A, HOEY, J. J. ,NATANSON, L.J., BRIGGS, J. 2002 Tag and Recapture Data for Three Pelagic Shark species: Blue Shark (Prionae glauca), Shortin Mako (Isurus oxyrinchus), and Porbeagle (Lamna nasus) in the North Atlantic Ocean. Col Vol. Sci. Pap. ICCAT, 54 (4) :1231-1260.

MARTIN, R. A. 1994. From Here to Maternity. Reefquest Centre for Shark Research. www.elasmo-research.org

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sue Daly

 

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