The
bluntnose sixgill shark,
Hexanchus griseus, often simply called the
cow shark, is the largest hexanchoid
sharkSharks 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, before the time of the dinosaurs....
, growing to more than 5.4 m (18 ft) in length.
The bluntnose sixgill shark is a member of the Hexanchidae
familyIn 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...
. Many of its relatives are extinct. The living species that are closest genetically include the
dogfishDogfish can have many meanings, but usually refers to a type of shark:* A shark belonging to the order Squaliformes, or to one of its constituent families:* Family Centrophoridae * Family Dalatiidae...
, the
Greenland sharkThe Greenland shark, Somniosus microcephalus, also known as the sleeper shark, gurry shark, ground shark, grey shark, or by the Inuit Eqalussuaq, is a large shark native to the waters of the North Atlantic Ocean around Greenland and Iceland. These sharks live further north than any other shark...
, as well as other six- and sevengilled sharks.
The
bluntnose sixgill shark,
Hexanchus griseus, often simply called the
cow shark, is the largest hexanchoid
sharkSharks 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, before the time of the dinosaurs....
, growing to more than 5.4 m (18 ft) in length.
Taxonomy
The bluntnose sixgill shark is a member of the Hexanchidae
familyIn 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...
. Many of its relatives are extinct. The living species that are closest genetically include the
dogfishDogfish can have many meanings, but usually refers to a type of shark:* A shark belonging to the order Squaliformes, or to one of its constituent families:* Family Centrophoridae * Family Dalatiidae...
, the
Greenland sharkThe Greenland shark, Somniosus microcephalus, also known as the sleeper shark, gurry shark, ground shark, grey shark, or by the Inuit Eqalussuaq, is a large shark native to the waters of the North Atlantic Ocean around Greenland and Iceland. These sharks live further north than any other 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.
Description
Skin color ranges from tan to brown, or as dark as black. It has a light colored
lateral lineIn aquatic organisms , the lateral line is a sense organ 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
TriassicThe Triassic is a geologic period and system that extends from about 251 to 199 Ma . 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 finA dorsal fin is a fin located on the backs of some fish, whales, dolphins, and porpoises, as well as the ichthyosaurs. Depending on the species, an animal can have up to three of them. Its main purpose is to stabilize the animal against rolling and assist in sudden turns...
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 refers to a pattern of movement that some organisms living in the ocean's photic zone undertake each day. The word diel comes from the Latin dies , and means a 24-hour period....
(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 IslandHornby Island of British Columbia, Canada, is a Northern Gulf Island parallel with Vancouver Island's Comox Valley.A small community of 1074 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 ColumbiaBritish Columbia is the westernmost of Canada's provinces and is famed for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . In 1871, it became the sixth province of Canada.The capital of British Columbia is Victoria, the 15th largest metropolitan region in Canada...
, in
Puget SoundPuget Sound is a sound or complex of inland marine waterways in the northwestern part of Washington, United States, extending from the eastern end of the Strait of Juan de Fuca south to the head of the sound at the state capital of Olympia. It branches out from Admiralty Inlet and Deception Pass...
,
Monterey CanyonMonterey 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 at...
off Monterey,
CaliforniaCalifornia is the most populous state in the United States, and the third largest by area. California is the second most populous sub-national entity in the Americas, behind only São Paulo, Brazil...
and in
fjordGeologically, a fjord is a long, narrow inlet with steep sides, created in a valley carved by glacial activity.-Formation:Fjords are formed when a glacier cuts a v-shaped valley by abrasion of the surrounding bedrock. Many such valleys were formed during the recent ice age...
s in
NorwayNorway , officially the Kingdom of Norway, is a country in Northern Europe occupying the western portion of the Scandinavian Peninsula, as well as Jan Mayen and the Arctic archipelago of Svalbard under the Spitsbergen Treaty...
.
The sharks are deepsea sharks, but like most fish that prefer the deep, they come to the shallower depths to feed
Feeding patterns
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,
AgnathaAgnatha is a superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. The group excludes all vertebrates with jaws, known as gnathostomes....
ns (which is a family consisting of
hagfishHagfish are marine craniates of the class Myxini, also known as Hyperotreti. Myxini is the only class in the clade Craniata that does not also belong to the subphylum Vertebrata...
), and sea
lampreyA lamprey is a parasitic marine animal with a toothed, funnel-like sucking mouth. Translated directly, their name means stone lickers . While lampreys are well known for those species which bore into the flesh of other fish to suck their blood, these species make up the minority...
s. They also dine on Cape anchovies, Pacific salmon, various species of
hakeThe term hake refers to fish in either of:* family Gadidae * family Merlucciidae .An old European source mentions a hake that was transplanted from the coast of Ireland to Cape Cod...
. 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. 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, 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
placentaThe placenta is an organ unique to mammals that connects the developing fetus to the uterine wall. The placenta supplies the fetus with oxygen and food, and allows fetal waste to be disposed of via the maternal kidneys...
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
camouflageCamouflage is a method of crypsis that allows an otherwise visible organism or object to remain indiscernible from the surrounding environment through deception. Examples include a tiger's stripes and the battledress of a modern soldier...
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.
Biggest catch
On June 16, 2009 the hobby angler Joe Waldis from Aargau Canton, Switzerland, created a sensation: Off the coast of South West Ireland he caught a 480 kilogram and 3.9 meter specimen of the bluntnose sixgill with rod and line. Experts say that this is the world record catch with a fishing rod.
External links