The Sixgill shark is one of the primitive species of sharks with close relatives that dated back to roughly 200 million years ago. They are known as Sixgill sharks because unlike most sharks with typical five gill slits, they have six gill slits. They generally are powerfully built and have a characteristic round, blunt snout, which earned them the additional name Bluntnose Sixgill sharks. They can grow up to a length of 18 feet and are usually not dangerous to humans if they are not provoked.
The Sixgill shark lives a solitary lifestyle, making their reproductive lifecycle difficult to ascertain. However, they are believed to have low reproductive rate. They tend to move into shallow water, hence making them easy targets for fishermen. The Sixgill shark is currently listed among species branded near threatened. The expected life span of the Sixgill shark is believed to be 80 years in the wild.
Taxonomy
The scientific name of the Sixgill shark is Hexanchus griseus. They belong to the family of Hexanchidae. They are relative to present day dogfish and Greenland shark.
Morphology
The Sixgill shark has a powerful body with a round, blunt nose. Another prominent feature of the Sixgill shark is the presence of only one dorsal fin located close to the tail. The color of the shark varies from tan or brown to gray or black in some cases. The females are usually bigger than the males. The Sixgill shark can grow up to a length of 18 feet. They have small and fluorescent green eyes with a black pupil.
Adaptation
Although the shark is a slow swimmer, its powerfully built body lend it the ability to achieve sharp burst of speed to catch prey. The young ones are lighter in color which make them to blend well with the environment and thus avoid predators. Their fluorescent green eyes are well suited to see in the very dark environment of the ocean depth.
Feeding
The Sixgill is a carnivorous shark that feeds on many things and do not have a specific diet. However, it tends to feed on a wide range of marine organisms. Examples include dead pig and horse carcasses from submarine, bony fish, squids, crabs, shrimp etc. Hunting typically occurs at night.
Habitat
This species of shark is among the most widely distributed sharks across the world. They are found in both the tropical and temperate oceans worldwide. The Sixgill shark has preference for deep water environment at the depth of 300 feet or even more below the sea. Nonetheless, they can venture up to areas of shallow water. They live a solitary life and are not social in behavior. Juveniles remain in shallow water until they are old enough to move down the slopes on the ocean floor into deeper water.
Reproduction
An adult male Sixgill shark attains maturity when they grow to 10 feet in length. The females attain maturity around body size of 13 feet, which means that in years, it takes the males about 11-14 years before maturity, and the females about 18-35 years. Courtship and mating are believed to take place in deep water environment, although actual observation of these reproductive behaviors has not been carried out. The Sixgill shark engages in an ovoviviparous mode of reproduction. The gestation period of the shark is from 12-24 months. At birth, the sizes of the pups are about 22-30 inches at birth. The litter is unusually large, as a single litter can contain around 22 to 108 pups. Although these pups tend to feed upon one another, thus cannibalism is high at this stage.
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References
IUCN Redlist (2019). Bluntnose Sixgill Shark. Hexanchus griseus. Retrieved from https://www.iucnredlist.org/species/10030/3155348
Kaufman, M (2019). A dominant shark lurks in the deep, dark ocean. Meet the sixgill. Mashable. Retrieved from https://mashable.com/article/sixgill-shark-deep-sea-oceanx/
SHARK sider (2019). Bluntnose Sixgill shark (Hexanchus griseus). Retrieved from https://www.sharksider.com/bluntnose-sixgill-shark/
The sea (2019). Sixgill Shark (Hexanchus griseus). Retrieved from http://www.seasky.org/deep-sea/sixgill-shark.html
UntamedScience (2019). Blunt Nosed Sixgill shark. Hexanchus griseus. Retrieved from https://untamedscience.com/biodiversity/sixgill-shark/