Bluntnose sixgill shark

What it is

This species belongs to the family Hexanchidae and represents the largest member of its group. It possesses a robust body, a long tail, and a wide, blunt snout. The skin varies from tan to black, marked by light lateral lines and spots that increase with age. A key feature is the presence of six gill slits on each side, unlike most modern sharks which have five. Adults typically measure between three and four metres, though specimens can exceed five metres. The eyes are small with fluorescent blue-green irises and black pupils.

Where it lives

Found globally in tropical and temperate zones, this shark spans latitudes from 65°N to 48°S. Sightings occur off the Americas, Europe, Africa, Asia, and Australia. It inhabits the outer continental shelf and deeper slopes, usually between 180 and 1,100 metres below the surface. Juveniles may venture into shallower coastal waters near shorelines, while adults prefer depths exceeding one hundred metres. Fossil evidence suggests historical presence in regions like South Korea.

How it lives

These sharks act as generalists, consuming a wide variety of prey including fish, squid, marine mammals, and carrion. They exhibit diel vertical migration, rising to shallower depths at night to feed before returning to colder, deeper waters during the day. This movement helps conserve energy due to their positive buoyancy. Their sluggish nature belies bursts of speed used to chase prey. They utilize sawing and tearing motions with their jaws and lower pectoral fins to strike effectively.

Breeding and life cycle

Reproduction is ovoviviparous, meaning embryos develop inside eggs that remain within the mother until hatching. Litters are large, containing twenty-two to one-hundred-and-eight pups measuring sixty to seventy-five centimetres at birth. Females mature later than males, reaching sexual size at four-and-a-half metres around eighteen to thirty-five years of age. Males mature earlier at roughly three metres. Courtship involves males nipping female gill slits, leaving seasonal scars.

Fish and people

Although generally harmless to humans unless provoked, this species faces pressure from fishing activities. It is caught both as bycatch and targeted for food and sport. Its slow growth and late maturity make populations vulnerable to overexploitation. Conservation bodies list it as Near Threatened due to these biological traits. Regional assessments vary, with some areas classifying stocks as data poor but secure overseas. Historical encounters may have inspired local folklore regarding dangerous sea creatures.

Status and threats

The International Union for Conservation of Nature lists this species as Near Threatened. Its extensive range does not fully protect it from exploitation due to its longevity and appeal to sport fishermen. Population data remains scarce in many regions, but certain local stocks show severe depletion. The New Zealand Department of Conservation categorizes it as Not Threatened with qualifiers indicating data limitations. Conservation efforts focus on monitoring these vulnerable populations amidst increasing human activity.

Relatives and look-alikes

It shares the genus Hexanchus with the bigeye sixgill shark and the Atlantic sixgill shark. These species can be distinguished through mitochondrial gene analysis. The bluntnose sixgill also has close fossil relatives, such as Hexanchus gigas, known from Miocene teeth. Living relatives include other six- and seven-gilled sharks, dogfish, and Greenland sharks. Some fossil lineages date back two hundred million years, highlighting its primitive status among modern sharks.

Questions people ask about Bluntnose sixgill shark

Good reading and sources

• Blue Planet II: The moment giant sharks attack crew submarineBBC, Article

• Bluntnose sixgill shark on WikipediaEncyclopedia
• More photos on Wikimedia CommonsPhotos
• Wikidata recordOpen data