The blue shark (Prionace glauca) is an oceanic shark found in temperate and tropical waters worldwide. Its distinctive physical characteristics allow it to navigate and hunt efficiently in its open-ocean habitat.
Defining Physical Traits
The blue shark has a slender, elongated, fusiform (spindle-like) body, highly streamlined for movement through water. Adult blue sharks typically measure between 1.7 to 2.2 meters (5.6 to 7.2 feet) in length, though some individuals can reach up to 4 meters (13.1 feet).
A defining characteristic is its namesake coloration, featuring a deep indigo to brilliant blue on its dorsal surface. This vibrant blue fades to a lighter blue on its flanks and transitions sharply to a stark white on its ventral side. This distinct pattern, known as countershading, serves as camouflage, helping the shark blend with the ocean’s surface when viewed from above and the lighter sky when viewed from below. Recent research suggests that the blue shark’s skin, containing nanostructures called dermal denticles with guanine crystals, may allow it to subtly alter its coloration in response to environmental cues such as depth and water pressure.
Adult male blue sharks typically weigh between 27 to 55 kilograms (60 to 121 pounds), while larger females range from 93 to 182 kilograms (205 to 401 pounds). The heaviest recorded blue shark weighed 391 kilograms (862 pounds). These sizes reflect the species’ adaptation to a pelagic predatory lifestyle.
Detailed Anatomical Characteristics
The head of the blue shark features a long, pointed, and conical snout. Its eyes are relatively large and round, adapted to detect prey in the low light conditions of its deep-water habitat. Unlike some other shark species, the blue shark does not possess spiracles, which are small openings behind the eyes that aid in respiration.
A prominent feature is its unusually long, slender, and somewhat scythe-shaped pectoral fins, which can be as long as the distance from the tip of its snout to its last gill slit. The dorsal fin is moderate in size and set further back on the body, positioned closer to the pelvic fins than to the pectoral fins. The caudal (tail) fin is asymmetrical, with a longer upper lobe, and the shark also has a weak keel on its caudal peduncle.
The blue shark’s teeth are suited for its diet of slippery prey like squid and small fish. Upper teeth are triangular, curved, and serrated for gripping and cutting. Lower teeth are straighter, more slender, and have finer serrations. These teeth are continuously replaced throughout the shark’s life. Blue sharks possess five long gill slits on each side of their head, along with unique papillose gill rakers that prevent small prey from escaping. While appearing smooth, the blue shark’s skin is covered in tiny, tooth-like scales called dermal denticles, giving it a feel similar to fine sandpaper.