Bluntnose sixgill shark
Encyclopedia
The bluntnose sixgill shark, Hexanchus griseus, often simply called the cow shark, is the largest hexanchoid shark
, growing to more than 5.4 m (18 ft) in length.
. Many of its relatives are extinct. The living species that are closest genetically include the dogfish
, the Greenland shark
, as well as other six- and sevengilled sharks. There are more closely related relatives in the fossil record than living species. Some of the shark's relatives date back to 200 million years ago. This shark is a notable species due to both its primitive and current physical characteristics.
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Skin color ranges from tan to brown, or as dark as black. It has a light colored lateral line
down the sides and on the fins' edges. There are darker colored spots on the sides. The general body shape is a heavy, powerful body with a broad head with small eyes. The pupils are black and the eye color is a fluorescent blue green. As an adult the bluntnose sixgill shark can grow to a massive size. True body length is determined by the gender of the individual. Males generally average between 309 and 330 cm. Females tend to be larger, averaging between 350 and 420 cm. This shark can attain a length of up to 550 cm.
The bluntnose sixgill shark resembles many of the fossil sharks from the Triassic
period. This could be because there are a greater number of Hexicanus relatives in the fossil record than there are left alive today. They have one dorsal fin
located near the caudal fin. The pectoral fins are broad with rounded edges. There are six gill slits which gives the shark its name. Most common sharks today have only 5 gill slits.
(travelling surfaceward at night, returning to the depths before dawn).
The bluntnose sixgill shark can be seen at depths of 30 m (100 ft) and shallower during parts of the year in some specific places e.g. Flora Islet, near Hornby Island
, Sightings during shallow evening dives in Whytecliff Park West Vancouver in British Columbia
, in Puget Sound
, Monterey Canyon
off Monterey, California
and in fjord
s in Norway
.
The sharks are deepsea sharks, but like most fish that prefer the deep, they come to the shallower depths to feed
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Although sluggish in nature, the bluntnose sixgill shark is capable of attaining high speeds for chasing and catching its prey. Because of the bluntnose sixgill shark's large and diverse range they have a wide variety of prey items. Their diet consists of a variety of mollusks, crustaceans, and Agnatha
ns (hagfish
and sea lamprey
s). They also dine on Cape anchovies, Pacific salmon, various species of hake
. There are also many more species that are eaten depending upon the shark's home range.
Despite its size, the shark is not known to have eaten any humans.
, which means that the young are carried within the mother's body until the eggs hatch. They develop without a placenta
to provide nourishment. The pups are born at a fairly large and developed stage at 65 to 74 cm. New pups are also born with a lighter belly than adults. This is a form of cryptic coloration or camouflage
that is used to disguise the pup's appearance. The litter size ranges from 22 to 108 pups. It is presumed that there is a high mortality rate of the young pups, owing to the large litter size.
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
, growing to more than 5.4 m (18 ft) in length.
Taxonomy
The bluntnose sixgill shark is a member of the Hexanchidae familyFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
. Many of its relatives are extinct. The living species that are closest genetically include the dogfish
Squaliformes
Squaliformes is an order of sharks that includes about 97 species in seven families.Members of the order have two dorsal fins, which usually possess spines, no anal fin or nictitating membrane, and five gill slits. In most other respects, however, they are quite variable in form and size...
, the Greenland shark
Greenland shark
The Greenland shark, Somniosus microcephalus, also known as the sleeper shark, gurry shark, ground shark, grey shark, or by the Inuit languages name Eqalussuaq, is a large shark native to the waters of the North Atlantic Ocean around Greenland and Iceland. These sharks live farther north than any...
, as well as other six- and sevengilled sharks. There are more closely related relatives in the fossil record than living species. Some of the shark's relatives date back to 200 million years ago. This shark is a notable species due to both its primitive and current physical characteristics.
Description
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
down the sides and on the fins' edges. There are darker colored spots on the sides. The general body shape is a heavy, powerful body with a broad head with small eyes. The pupils are black and the eye color is a fluorescent blue green. As an adult the bluntnose sixgill shark can grow to a massive size. True body length is determined by the gender of the individual. Males generally average between 309 and 330 cm. Females tend to be larger, averaging between 350 and 420 cm. This shark can attain a length of up to 550 cm.
The bluntnose sixgill shark resembles many of the fossil sharks from the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period. This could be because there are a greater number of Hexicanus relatives in the fossil record than there are left alive today. They have one dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
located near the caudal fin. The pectoral fins are broad with rounded edges. There are six gill slits which gives the shark its name. Most common sharks today have only 5 gill slits.
Habitat
This species typically inhabits depths greater than 90 m (300 ft), and has been recorded as deep as 1,875 m (6,150 ft). Like many deep-sea creatures, the bluntnose sixgill shark is known to undertake nightly vertical migrationsDiel vertical migration
Diel vertical migration, also known as diurnal vertical migration, is a pattern of movement that some organisms living in the ocean and in lakes undertake each day. Usually organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone...
(travelling surfaceward at night, returning to the depths before dawn).
The bluntnose sixgill shark can be seen at depths of 30 m (100 ft) and shallower during parts of the year in some specific places e.g. Flora Islet, near Hornby Island
Hornby Island
Hornby Island of British Columbia, Canada, is a Northern Gulf Island parallel with Vancouver Island's Comox Valley.A small community of 1,074 residents is distributed across the island. The island is culturally distinctive as it was the site of a large immigration of American draft dodgers during...
, Sightings during shallow evening dives in Whytecliff Park West Vancouver in British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, in Puget Sound
Puget Sound
Puget Sound is a sound in the U.S. state of Washington. It is a complex estuarine system of interconnected marine waterways and basins, with one major and one minor connection to the Strait of Juan de Fuca and the Pacific Ocean — Admiralty Inlet being the major connection and...
, Monterey Canyon
Monterey Canyon
Monterey Canyon, or Monterey Submarine Canyon, is a submarine canyon in Monterey Bay, California. It is the subject of ongoing study by the scientists at the Monterey Bay Aquarium Research Institute, the Moss Landing Marine Laboratories, and other oceanographic institutions.Monterey Canyon begins...
off Monterey, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
and in fjord
Fjord
Geologically, a fjord is a long, narrow inlet with steep sides or cliffs, created in a valley carved by glacial activity.-Formation:A fjord is formed when a glacier cuts a U-shaped valley by abrasion of the surrounding bedrock. Glacial melting is accompanied by rebound of Earth's crust as the ice...
s in Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
.
The sharks are deepsea sharks, but like most fish that prefer the deep, they come to the shallower depths to feed
Feeding patterns
Agnatha
Agnatha is a superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. The group excludes all vertebrates with jaws, known as gnathostomes....
ns (hagfish
Hagfish
Hagfish, the clade Myxini , are eel-shaped slime-producing marine animals . They are the only living animals that have a skull but not a vertebral column. Along with lampreys, hagfish are jawless and are living fossils whose next nearest relatives include all vertebrates...
and sea lamprey
Lamprey
Lampreys are a family of jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from an admixture of Latin and Greek, lamprey means stone lickers...
s). They also dine on Cape anchovies, Pacific salmon, various species of hake
Hake
The term hake refers to fish in either of:* family Phycidae of the northern oceans* family Merlucciidae of the southern oceans-Hake fish:...
. There are also many more species that are eaten depending upon the shark's home range.
Despite its size, the shark is not known to have eaten any humans.
Reproduction
Very little is known about the reproductive process of bluntnose sixgill sharks. What little is known is actually scientific speculation. Many biologists believe that the male bluntnose sixgill shark's teeth are specially adapted to the courtship ritual. The male will nip at the female's gill slits using its longer-cusped teeth. This action is thought to entice the female into mating. Evidence of this theory is that female bluntnose sixgill sharks show up with seasonal scars around their gill slits, which apparently is from breeding with males. The female bluntnose sixgill shark reaches sexual maturity between the ages of 18 and 35 years. Males usually reach sexual maturity much younger, between the ages of 11 and 14 years old. Scientists are unsure of how the bluntnose sixgill shark reproduces but it is thought that males and females meet seasonally between the months of May and November. The gestation period is unknown but scientists believe that it is longer than 2 years. The bluntnose sixgill shark is ovoviviparousOvoviviparity
Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animals in which embryos develop inside eggs that are retained within the mother's body until they are ready to hatch...
, which means that the young are carried within the mother's body until the eggs hatch. They develop without a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
to provide nourishment. The pups are born at a fairly large and developed stage at 65 to 74 cm. New pups are also born with a lighter belly than adults. This is a form of cryptic coloration or camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
that is used to disguise the pup's appearance. The litter size ranges from 22 to 108 pups. It is presumed that there is a high mortality rate of the young pups, owing to the large litter size.
External links
- Information on H. griseus from ReefQuest Center for Shark Research
- YouTube video (1:17) - 18' specimen filmed at 1000m in Molokai, HI.