The sixgill shark: Finding an old friend

We never know what deep-sea creatures will find our drop-cameras. When the cameras return to the surface and we check the results it’s always a period of patience combined with eager anticipation and the hope of something exciting. Last night our patience was rewarded when our camera returned from a depth of 2,100 feet (700 meters) here on Unnamed Seamount with footage of a beautiful sixgill shark!

The bluntnose sixgill shark (Hexanchus griseus) is a primitive and distinctive shark. The sixgill gets its name from a physical feature that sets it apart from other sharks: Instead of the more advanced five-gill arrangement which has evolved in most sharks, the sixgill has six gill slits. The sixgill shark that exists today is virtually unchanged from fossil forms dating back 200 million years.

They can reach a length of 16 feet (4.8 meters), which means that the one documented last night was likely to be one of the largest! Because this species has a very wide body, it is also called “cow shark” and “bulldog shark”. They have a blunt snout, small eyes in front of the mouth, and a jaw that contains two different types of teeth. These sharks’ upper teeth are triangular in shape, and the lower ones are edged with saw-like serrations.

Sixgills are found at depths reaching 8,000 feet (2,500 meters), so they are inaccessible to humans unless we use submarines or find them with our drop-cameras. Since they spend most of their time in deep water, very little is known about their behaviour. Although they are generally slow moving, sixgills can move with incredible speed for short periods, and may use this ability coupled with their drab coloration to capture their prey using an element of surprise. They are not usually dangerous to humans unless provoked.

It is also one of the largest sharks that feed on prey other than plankton. The sixgill shark eats large fish like other sharks, billfish, dolphin, flounder, spurdogs, rays, and cod. Even sea lions and whale have been reported in the sixgill’s gut. But they also eat crabs, shrimp, smaller fish, and squid with their very sharp, saw-like teeth.

I’ve been lucky enough to dive with a large six-gill shark in the Straits of Messina, and last night’s encounter felt like seeing an old friend. This is truly a large and beautiful “monster” of the deep!

The Pristine Seas team is currently conducting an expedition to the remote island of Ascension, in partnership with the Ascension Island Conservation Department, the British Antarctic Survey, the Royal Society for the Protection of Birds, and The Blue Marine Foundation.

Read all Ascension Island 2017 expedition posts.

Changing Planet


Meet the Author
Paul Rose is an ardent explorer, television presenter, journalist, author, and Vice President of the Royal Geographical Society, and an Expedition Leader on the Pristine Seas team.