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July Elasmobranch of the Month: Bluntnose Sixgill


Author: Linda Weiss


Bluntnose Sixgill Shark

Hexanchus griseus

Key Features/Appearance

As the name implies, bluntnose sixgill sharks have a large, bluntly rounded head and 6 long gill slits, while most sharks have 5. They are a large species, reaching lengths of 4.8 m (16 ft) and weighing 590 kg (1,300 pounds). Their mouth is also wide and rounded. Each side of their lower jaw contains six broad, multi-cusped teeth, resembling a saw blade. Their upper jaw contains nine smaller, single-cusped serrated teeth on each side. Their topside coloration is brown, gray, or olive green, fading to a paler underside. On each side of their body, they have a cream or white colored stripe which runs close to their lateral line. They have only one dorsal fin, which is rounded and located further down its back than most sharks, between the pelvic and anal fins. The edges of this shark’s fins are sometimes cream-white in color. They have large green eyes.


Habitat and Distribution

The bluntnose sixgill shark is found in tropical and temperate waters around the globe. Its range includes the western Atlantic in the USA from Florida to North Carolina and the Gulf of Mexico from the United States to Argentina. In the eastern Atlantic, bluntnose sixgill’s can be found from Iceland south to Namibia, including parts of the Mediterranean Sea. In the Indian Ocean, it ranges from Mozambique to Madagascar. Range in the Western Pacific Ocean is from Japan to Australia and New Zealand, north to Hawaii. In the eastern Pacific, this shark has been seen from the Aleutian Islands to Alaska, to Baja California, Mexico as well as Chile. A deep-water species, it rests during daytime at depths around 2,000 m (6,500 ft), moving into shallow waters at night to hunt.

Diet

Nocturnal hunters, the bluntnose sixgill’s diet consists of a wide range of prey items including, but not limited to; billfish, cod, flounder, mahi-mahi, hagfish, dogfish, stingrays, squid, crabs, shrimp and snails. It will also eat the carcasses of mammal such as sea lions, whales and seals.

Reproduction

Bluntnose sixgill reproduce through aplacental viviparity ( live birth). Fertilized eggs hatch inside the female where the embryos develop until they are ready to be born. During gestation, embryos are nourished by yolk sacs, then consume other unfertilized eggs and sometimes their embryo siblings. Litter sizes range from 22-108 pups, each measuring approximately 60-75cm (23-30 inches) long.

Status

The IUCN Red List of Threatened Species currently lists the Bluntnose Sixgill shark as Near Threatened, with a decreasing population trend.

Threats

Bluntnose sixgill sharks are targeted by the commercial fishing industry for their liver and meat. The meat is sold fresh, frozen and dried. This species is also used to produce oil and fishmeal. Bluntnose sixgills are also killed as bycatch when other ocean animals are hunted. Some regional populations of the species have been depleted due to overfishing. Potential natural predators of the bluntnose sixgill shark are the great white shark, orcas, and sea lions.


Incredible footage of a bluntnose sixgill from a submarine- Research done by Florida Statue University and OceanX




Learn more about Dr. Dean Grubbs and his deep sea shark research




References

Florida Museum

https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/hexanchus-griseus/

Marine Bio

https://www.marinebio.org/species/sixgill-sharks/hexanchus-griseus/

Washing Department of Fish and Wildlife

https://wdfw.wa.gov/species-habitats/species/hexanchus-griseus#desc-range

The IUCN Red List of Threatened Species

https://www.iucnredlist.org/search?query=bluntnose%20sixgill&searchType=species

Finucci, B., Barnett, A., Bineesh, K.K., Cheok, J., Cotton, C.F., Dharmadi, Graham, K.J., Kulka, D.W., Neat, F.C., Pacoureau, N., Rigby, C.L., Tanaka, S. & Walker, T.I. 2020. Hexanchus griseus. The IUCN Red List of Threatened Species 2020: e.T10030A495630. https://dx.doi.org/10.2305/IUCN.UK.2020-3.RLTS.T10030A495630.en. Downloaded on 11 July 2021.

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