Bluntnose Sixgill Shark

Fascinating facts about the Bluntnose Sixgill Shark

• A 19th-century record from Portugal reports a bluntnose sixgill measuring 9 m (30 ft).
• Adult males average 3.1–3.3 m (10–11 ft) while females average 3.5–4.2 m (11–14 ft); the biggest recorded sharks reach 6 m (20 ft) and weigh 1,000 kg (2,200 lb).
• These sharks perform a nightly vertical migration, swimming up to about 300 m (980 ft) after midnight and descending to 600–700 m (2,000–2,300 ft) around noon.
• With litters of 22–108 pups born 60–75 cm (24–30 in) long, females do not mature until they reach 4.5 m (15 ft) and are 18–35 years old.
• Positive buoyancy lets sixgills glide upward for minutes during their night-time ascent, letting them sneak up on prey from below with minimal swimming effort; this physical trick helps explain how a sluggish-looking shark can still be an effective predator in the deep sea.

At a glance

About the Bluntnose Sixgill Shark

The bluntnose sixgill shark, Hexanchus griseus, commands attention with its massive, torpedo-shaped body that can reach 5.5 m (18 ft) and weigh up to 500 kg, though exceptional individuals have been recorded at 6 m (20 ft) and 1,000 kg. Its blunt, wide snout and small, fluorescent blue-green eyes sit above six rows of saw-like lower teeth and smaller upper teeth, while a light-colored lateral line runs the length of its sides, punctuated by darker spots that increase with age. Its skin shifts from tan to black, and the shark’s single dorsal fin sits near the caudal fin, complemented by broad, rounded pectoral fins. Found from 65° N to 48° S across the Atlantic, Indian, and Pacific oceans, it roams the outer continental shelf at depths of 180–1,100 m but can dive to 2,500 m or rise to the surface at night, performing a striking diel vertical migration that sees it ascend to as shallow as 300 m after dark to forage before slipping back to deeper, colder waters by noon. A generalist predator, it devours bony fish, cephalopods, crustaceans, rays, chimaeras, seals, cetaceans, carrion, and even smaller sharks, using protrusible jaws, sawing bites, and a unique pre-strike fin-lowering maneuver to capture prey. One of its most surprising traits is its positive buoyancy, allowing it to glide upward for minutes during night-time migrations, a rare adaptation that lets it stalk prey from below with minimal effort.

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