Many marine animals use camouflage to survive in the ocean, blending into their surroundings to evade predators or ambush prey. Blue coloration is a common adaptation, helping species disappear within the vast blue waters.
The Iconic Blue Shark
The Blue Shark, Prionace glauca, is widely recognized for its striking coloration, a deep indigo to bright blue on its back that transitions to a crisp white on its underside. This sleek, slender shark has a long, conical snout and noticeably long, scythe-shaped pectoral fins, which extend nearly to its first dorsal fin. Males typically mature at lengths between 1.8 to 2.8 meters (6 to 9.3 feet), while females are larger, commonly reaching 2.2 to 3.3 meters (7.2 to 10.8 feet) at maturity.
This highly migratory species inhabits temperate and tropical waters across the world’s oceans, ranging from the surface down to depths of about 350 meters (1,150 feet). Blue sharks primarily feed on small fish and squid, though their diet can also include other invertebrates, small sharks, and even seabirds.
Other Sharks with Blue Tones
Beyond the iconic Blue Shark, several other shark species display blue or bluish coloration, though it may not be as prominent or defining a feature. The Shortfin Mako Shark (Isurus oxyrinchus) is renowned for its speed and possesses a brilliant metallic blue on its dorsal surface, sharply contrasting with its white belly. These powerful sharks can reach lengths of up to 4 meters (13 feet) and weigh over 570 kilograms (1,260 pounds), inhabiting offshore temperate and tropical seas globally.
The Great White Shark (Carcharodon carcharias), while often described as gray, can exhibit a dark bluish-gray hue on its back, which blends into a white underside. Great Whites are among the largest predatory fish, with females reaching over 6 meters (20 feet) in length, and are found in coastal surface waters of all major oceans.
The Salmon Shark (Lamna ditropis) also has a dark blue to grayish-black back with a white underside that often features dark blotches. These heavy-bodied sharks, typically 1.8 to 2.1 meters (5.9 to 6.9 feet) long, are found in the subarctic and temperate waters of the North Pacific Ocean, preying on fish like salmon and herring.
The Science Behind Blue Coloration
The blue appearance in sharks is primarily due to a form of camouflage known as countershading, where the dorsal (upper) side is dark and the ventral (lower) side is light. When viewed from above, the dark blue back of a shark blends with the deeper, darker ocean waters, making it difficult for predators or prey to spot.
Conversely, when seen from below, the shark’s white underside merges with the bright, sunlit surface waters, rendering it nearly invisible to prey looking upwards. This coloration is not produced by blue pigments in the skin but rather by structural color. Specialized cells called iridophores, which contain highly reflective guanine crystals, scatter blue light. These crystals, combined with melanin-filled vesicles (melanosomes) that absorb other wavelengths, create the vivid blue hue.