Blue Shark, Prionace glauca
The Blue Shark, Prionace glauca, whose common Spanish name is tiburón azul, is a member of the Requiem Shark or Carcharhinidae Family, known collectively as tiburónes gambuso in Mexico. Their common name is derived from their overall blue color. Globally, there is only one species in the genus Prionace, the species described here, which is found in Mexican waters of the Atlantic and the Pacific.
The Blue Sharks have elongated, slender, and fusiform bodies. They are dark blue dorsally and have intense blue flanks and a white belly. The tips of their anal and pectoral fins are dark. Their caudal fin is strongly asymmetrical; the long lower lobe is well-developed and the upper lobe has an undulating ridge along its top edge, a notch under the tip, and pits at the base, which has a small keel. Their first dorsal fin is low with its origin well behind the pectoral fins and the center of the base closer to the pelvic fins than the pectoral fins. They have very long, narrow, and slightly curved pectorals with pointed tips. Their head has an elongated conical snout that is longer than the width of the mouth. They have large rounded eyes. Their mouth is equipped with one median tooth, 14 triangular teeth that are curved cusps with serrated edges and overlapping bases on the top jaw, and 13 to 15 finely serrated, erect triangular cusps on both sides of the lower jaw. They have five gill slits, the last two being over the pectoral fins.
The Blue Sharks are abundant pelagic oceanic sharks that are widespread in temperate and tropical waters from the surface to depths of 1,150 feet. They rarely frequent inshore waters. They reach a maximum length of 3.8 meters (12 feet 6 inches) and weight of 205 kg (450 pounds). They are found in waters ranging from 7oC (44oF) to 16oC (61oF) and on rare occasions in waters up to 21oC (70oF). They are highly migratory and make seasonal migrations to cooler waters during the summer and return in the fall. They are known to make trans-Atlantic and Pacific migrations of up to 9,200 km. They have known mating areas and pupping areas and are relatively fast growing reaching sexual maturity in four to six years. They are opportunistic feeders that consume small pelagic fish and cephalopods, particularly squid as well as pelagic crustaceans, small sharks, cetaceans, and seabirds. They are known to feed 24 hours a day but are more active at night and in the early evening. Juveniles are preyed upon by California sea lions and larger sharks including the Shortfin Mako and the White Shark and rely on counter-shading for camouflage in the open oceans. Reproduction is viviparous with 11 to 12-month gestation periods and litter sizes of 25 to 50 pups. At birth, the pups measure between 41 cm (16 inches) and 50 cm (20 inches) in length and are immediately capable of caring for themselves. Their skin is smooth to the touch. Females have skin three times thicker than males allowing them to withstand the extensive courtship bites of males. They have a lifespan of up to 20 years.
In Mexican waters the Blue Sharks are found in all waters of the Atlantic and the Pacific.
The Blue Sharks can be confused with the Shortfin Mako, Isurus oxyrinchus (white under snout; head bigger than pectorals; first dorsal fin over pectoral border) and the Longfin Mako, Isurus paucus (dark under snout; bluntly pointed snout; very small anal and second dorsal fins).
The Blue Sharks are not fished commercially but are a major by-catch of longline, purse seines and driftnet fisheries. They are also a focused target of recreational sportsfishermen. Their meat is not deemed to be of value since it has a very short shelf-life. It is used on a very limited basis to produce jerky. Blue Sharks were a food source of Native Americans. Most are finned and their bodies discarded. Their fins are exported to Asia and resold for use in shark fin soup. They are a major component of the curio trade including in art, carvings, jaws, leather goods, photos, stamps, and teeth. Although abundant, fast growing, maturing rapidly, highly fecund, and widely distributed globally, they are considered Near Threatened from a conservation perspective. The removal of so many apex predators from the ocean has most definitely had a major impact on the oceans ecosystem. They are caught at a level of 20 million individuals annually. No valid population assessments are presently available. License limitations, bans on finning, restrictions on gear, by-catch limits, and recreational catch regulations are currently in place in a handful of countries. They are known to attack humans and boats and are considered a dangerous fish.
Blue Shark, Prionace glauca, fetus. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, June, 2010. Length: 34 cm (13 inches).
Blue Shark, Prionace glauca. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, June, 2010. Length: 1.04 meters (3 feet 5 inches).