Blue shark

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A blue Christmas can't be complete without Prionace glauca, the blue shark. Prionace is Greek, prion meaning ‘saw’ and akis meaning ‘point;’ the species name glauca is Latin from glaucas or ‘bluish gray’ or ‘green’ in English, referring to their color. As its name implies, this shark has a dark blue dorsal surface, and bright blue flanks before blending into a white ventral underbelly. A sleek, long animal, with large pectoral fins, it has big eyes... the better to watch you with, my dear.

Blue sharks are a cosmopolitan, pelagic shark that rarely is seen near the shore (though known to be seen around islands and continental shelves). They prefer cooler water ranging from 7-16°C (44.6 - 60.8 °F) but tolerate 21°C (69.8 °F) or greater. When in the tropics, this shark sticks to deeper waters with cooler temperatures.

The dentition of this shark differs from the upper/lower teeth. The upper teeth are triangular and have curved cusps with serrated edges. The bases overlap. The lower jaw has erect cusps, finely serrated edges and are almost symmetrical in shape. These teeth are perfect for catching their prey: small teleost fish, squid, cuttlefish, and octopi, all of which can be super slippery. They can be seen perusing large breeding aggregations of squid, gulping up easy meals. They are opportunistic feeders, too, and have been observed feeding from gill nets and scavenging dead animals.

This critter has predators that include California sea lions (Zalophus californianus) and larger sharks, like the shortfin mako (Isurus oxyrinchus) and the great white shark (Carcharodon carcharias). Smaller, more unsuspecting animals also use the blue shark as a host: copepods. There have been documentations of sharks swimming around with up to five different species! These include Pandarus satyrus (on the pectoral fins), Kroeyerina elongata (in the nose), Echthrogaleus coleoptratus (on the body), and Kroyeria carchariaeglauci and Phyllothyreus cornutus (found on/in the gills). These different animals can cause sight impairment and even change the structure of the gills!

Gestation period in the blue shark is anywhere from 9-12 months, with litters having 25-50 pups. Litter sizes may be related to the size of the mommy shark and have observed to vary from 4 - 134 pups. This still needs to be researched more before anything definitive is stated. Pups are born through viviparity.
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Recreationally these sharks are targeted by sport fishermen, as the largest of the blues prove to be hard to catch. Commercially, they are regulated on the east coast of the United States by the National Marine Fisheries Service. They are caught as bycatch though, something conservation efforts will need to address (as with many sharks). The blue shark is currently listed as Near Threatened (NT) by IUCN.

ever heard of this shark?

glossary

• Bycatch: The part of a fishery’s catch that is made up of non-target species.
• Commercial fishery: The activity of catching fish and other seafood for profit.
• Continental shelf: Extends from a continent underwater, resulting in a shallow-water area.
• Cosmopolitan: Worldwide distribution.
• Dorsal fin: Fin located on the back.
• Dorsal side: The top of an animal.
• Flank: Sides of the animal.
• Gestation: The period in which a fetus develops, beginning with fertilization and ends at birth.
• IUCN: International Union for Conservation of Nature.
• Pectoral fins: Fins located behind the gills on either side.
• Pelagic shark: Live in the open waters of the seas and oceans.
• Pelvic fins: Fins located behind the gills on either side.
• Pup: Give birth to baby sharks (pups).
• Pups: Baby sharks.
• Recreational fishery: Also called sport fishing, it is fishing for pleasure or competition.
• Teleost fish: Bony fish.
• Viviparous: Eggs hatch inside the female's body and the babies are fed by a placenta which transfers nourishment from the mother to the babies (via an umbilical cord which is connected to the baby shark between the pectoral fins).​

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