Friday, July 29, 2011

Life of Bluntnose Sixgill Shark

Life of Sea | Bluntnose Sixgill Shark (Hexanchus griseus)Bluntnose Sixgill shark lives in dark waters at depths down to 5900 ft (1800 m), in dark or dim waters. It has been seen in coastal waters, usually below 330 ft (100 m). It has also been see by the surface of open waters at night. They do this probably or hunting. This shark is also called Cow shark.  Bluntnose Sixgill shark is found worldwide from tropical seas to northern temperate seas. The bluntnose sixgill shark is a member of the Hexanchidae family. 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.
 
Bluntnose Sixgill shark is a primitive, common, and distinctive shark that has six gills on each side of the body (most sharks have five pairs on each side of the face). These sharks are also known as the Cow shark, the Grey shark, the mud shark and the Bulldog shark. They have a single (and small) dorsal fin near the end of the body, a blunt snout, and small eyes in front of the mouth.They are gray-brown in color and are paler underneath. It has a toxic liver but edible flesh. It is fished by man for its oil and meat. Bluntnose Sixgill shark has six rows of saw-like teeth positioned in the side of the lower jaw. The upper jaw has smaller, curved, single-cusped teeth.  Bluntnose Sixgill shark averages about 16 ft (4.8 m) long. It ranges from 5 to 16.5 ft (1.5 to 5 m) long.

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, Agnathans (which is a family consisting of hagfish), and sea lampreys. 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.

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 ovoviviparous, 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.

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.


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