- Scientific name: Hexanchus griseus
- Also know as: Cow Shark
- Size: Thought to grow to over 20ft in length
- UK minimum size: N/a
- UK shore caught record: N/a
- IUCN Status: NT (Near Threatened)
- Distribution: Widespread but sparse distribution in deep seas all around the world.
- Feeds on: Predator which will feed on all manner of fish and squid, will also take smaller shark and marine mammal species such as seals.
- Description: Unsurprisingly, this species has a rounded nose and six long gill slits. Eyes are located close to the edge of the snout and mouth is full of multiple rows of large teeth. Body is relatively slim and streamlined with large pectoral fins and a single dorsal fin located far back on the back. Tail is elongated and has a white/light lateral line running from the tip to the middle of the body.
The bluntnose sixgill shark is a very large shark species which is present in UK and Irish waters, although in low numbers. Bluntnose sixgill sharks are a poorly understood species, with little being known about their behaviour, feeding or reproduction. Its name comes from the fact that it has six gill slits on each side of the body – the majority of shark species have five.
Bluntnose six gill sharks are found all around the world with the waters of America, Canada, Brazil, Chile and parts of Africa and Central America all holding populations of this species. As well as this bluntnose sixgill sharks are also found of the coasts of Australia and Newzealand and throughout Asian waters around Indonesia, China and Japan. Within Europe the bluntnose sixgill shark can be found throughout the Mediterranean to Scandinavian waters, although numbers are dispersed and sparse. This species can be found all around the British Isles, although in very low and diffuse numbers, with the west coast of Ireland and parts of the North Sea holding the most significant populations.
Bluntnose six gilled shark are thought to be solitary fish which only join other members of their species to reproduce. They generally live at depths of 700 – 800 metres but can be found all of the way down to depths of over 2000 metres. However, this species is thought to come into shallower water to feed if food sources are abundant there – in the Mediterranean this species has been observed in less than 40 metres of water. Fully grown bluntnose sixgill shark are thought to take part in vertical migrations where they spend daylight hours at great depths and then swim upwards towards the surface at night. The reasons for this may be linked to feeding but this is yet to be confirmed by the scientific community. The six pairs of gills are thought to be an adaptation to living in the oxygen-poor depths. Bluntnpse six gill sharks featured in the BBC documentary Legends of the Deep: Deep Sea Sharks which was narrated by David Attenborough. In the programme a research project led by Japanese shark expert Dr. Sho Tanaka placed a sperm whale carcass on the bottom on the ocean to attract and film deep sea sharks and study their behaviour. The project found that a bluntnose sixgill shark would swim around the whale carcass but only eat tiny amounts of the whale flesh. It was concluded that the shark was displaying territorial behaviour, a theory strengthened by the fact that no other large sharks were spotted near the whale carcass.
Bluntnose sixgill sharks have been present in the earths seas and oceans for at least 200 million years, and are therefore sometimes referred to as a ‘living fossil’.
Although bluntnose sixgill shark are generally slow-moving they are powerful predators which are capable of reaching high speeds over short distances when they need to. They feed on fish and squid, but may also take crustaceans such as crabs and lobster, especially when young. When fully grown large fish will form part of the bluntnose sixgill shark’s diet, with hake, cod, pollock and larger shark species such as spurdog, smooth-hound and similar species all being eaten, with even seals and sea lions also being taken by the larges bluntnose sixgill sharks.
Despite their size there has never been a report of a bluntnose sixgill shark attacking a human. Bluntnose six gilled shark are not fished for commercially but are inadvertently caught by trawlers. This was seen in the ITV series Trawlermen Tales which was shown in 2016. The flesh is edible and is mostly eaten in southern European countries. The liver is also valued for its oil and the carcass of a bluntnose six gilled shark can also be utilised as fishmeal. The bluntnose sixgill shark is a prized catch for boat anglers and there are recreational boats fishing in a number of locations in America (mostly California) which specialise in catching this species. There is, however, evidence that in certain areas this species has had its numbers seriously reduced by recreational boat anglers. There is no British shore caught record for this species, with the qualifying weight set at 5lbs. The boat caught record was set by F. Beeton with a 9lb 8oz specimen which was caught off Penlee Point, Plymouth in 1976 but this record was broken by Chris Rogers who caught a bluntnose sixgill shark triple this size in 2012 when fishing out of Halsar Gosport near Portsmouth. However, a this fish is completely overshadowed by the Irish record – a 12ft 9in, 1,056lb bluntnose sixgill shark caught by 70-year-old Swiss tourist Joe Waldis off the coast of County Clare in 2009.
The fish was reeled in after a thirty-fve minute battle and is the largest ever caught on rod and line in British or Irish waters. However, there was controversy as the fish was killed to be taken back to shore to be weighed, rather then returned to the sea.
Bluntnose six gilled shark are currently classed as Near Threatened by the IUCN (International Union for the Conservation of Nature) on a global basis, but numbers in Europe appear to be in somewhat better condition with European Union-wide limits of fishing for deep-sea sharks appearing to have allowed populations to stabalise. Like most shark species they are slow growing and late maturing, with females possibly having to reach the age of around thirty years old before they can reproduce. This low fecundity means that the numbers of bluntnose six gilled shark can be badly hit by both commercial and recreational fishing.
Another Species of Six Gilled Shark
There is also the bigeye six gilled shark (Hexanchus nakamurai). This is a warm water species which is not found in British waters and is limited in its distribution to the seas and oceans around the equator. This species is much smaller than its bluntnose relation, growing to a maximum of around 6ft in length