Sixgill Shark - Hexanchus griseus

Sixgill Shark 

View all Sixgill Shark Images in the Pacific Marine Index

Nicknamed cow sharks for their large size, Sixgill Sharks can reach a length of 18 ft. (5 m.), and weigh as much as 1300 lbs. (570 kg.) These sharks appear to lumber through the water and can be identified by a dark brown to grey colouration, and a pale underside. Having a single dorsal fin and elongated tail also separates this species of shark from others.  

Although Sixgill Sharks are usually slow and sluggish, their body structure allows them to attain high bursts of speed when chasing and catching their prey. They are carnivorous predators, feeding mostly on cephalopods, crustaceans, fish, and rays, along with some marine mammals. These sharks spend most of their time in deep water during the day, and at night, they undertake vertical migrations up to shallower waters to feed. During this time, it is not uncommon for them to come in contact with divers, but they are not usually dangerous to humans unless provoked.

The Bluntnose Sixgill Shark is a member of the Hexanchidae family, and is one of the few remaining members, as the majority of this shark’s ancestors are now extinct. Some of these shark's relatives date back to 200 million years ago. The living species of shark that are the closest genetically include the dogfish, the Greenland shark, and the Sevengilled Shark.

Due to the solitary lifestyle of Sixgill Sharks, very little is known about their reproductive behavior. Many biologists believe that they meet seasonally, moving to shallower waters between May and November to mate. Sixgill Sharks are ovoviviparous, meaning that the eggs are carried within the mother's body until they hatch. After hatching, still within the mother's body, the young have been known to eat any unfertilized eggs and even each other. These young sharks, known as pups, are a little more than two feet (about 70 centimeters) in length when they are born. The color of the pups is lighter than that of the adults, allowing them a certain amount of camouflage to help hide them from predators. There are between 22 and 108 pups born at any given time. Because of these large numbers, it is thought that there is an extremely high mortality rate among the pups, with not many surviving to maturity. Those that do survive are believed to live about 80 years in the wild.

Sixgill Sharks have the widest distribution of all sharks, except for possibly the Great White. They are found all over the world in temperate and tropical regions, where they have been known to dive as deep as 6,000 feet (over 1,800 meters), although they are more typically found at depths of about 300 feet (90 meters). These sharks have been observed moving into water as shallow as 100 feet (30 meters) during parts of the year in certain locations, although is not yet known why they do this. Since they do venture into shall water, fishermen are killing them for sport and food, and because of their low reproductive rate, they can easily be overfished. This has achieved them a near-threatened status on the global list of endangered species. But because we know so little about their populations, many scientists believe they could be in even more danger of extinction.

Encountering a Sixgill Shark as a diver and underwater photographer is an event to remember. Getting an image and having the memories to have seen one of these rare fish is true a feat in itself. Due to the Sixgill generally swimming at a slow rate, capturing an image is quite easy to accomplish, however these are large predatory animals and any type of sudden movement may be construed by the shark as a threat. Their behavior is unpredictable, so use caution when interacting with these unique fish.