Sixgill Shark Shark Bites

My name's Steve Backshall. Self-confessed shark-obsessed.

This is Shark Bites.

This time, we meet a shark that's positively prehistoric.

The sixgill shark.

It's changed little in 200 million years,

and is the ultimate super survivor.

True to their name, they've evolved an extra, sixth gill,

and can live nearly 2km deep where there's less oxygen to breathe.

For any shark, it's a tough place, but having changed little since

the time of the dinosaurs, these sharks thrive in their hostile home.

But what is their secret to survival?

The waters of Vancouver Island, off Canada's mainland,

are where they've been spotted.

Living in deep water during the day and only entering

the shallows at night, they're incredibly rare to see.

To increase our chances, we rigged an underwater camera,

and to attract them in, some smelly bait.

This shark bait here... These crates are filled with old fish heads...

..and lots of blood is floating up into the water.

You can't see it, but the sharks can smell it.

After a long wait back on the boat, we finally struck sixgill gold.

What was that?

That was definitely a shark tail.

It's a sixgill!

We've got a sixgill shark!

Fantastic.

This awesome animal that's been around since before the

dinosaurs is, for me, one of the most exciting animals on Earth.

And it's an ancient adaptation that enables them

to survive their hostile home.

Sharks use their gills to breathe underwater,

and while most shark species have five pairs of gills,

the sixgill has... Well, six.

And as water passes through them, it goes through tiny gill filaments.

These gill filaments have microscopic blood vessels which have

a lower oxygen content than the water around them.

This causes oxygen in the sea water to diffuse into the shark's

bloodstream where it can be distributed throughout the body.

It's thought that having an extra pair of gills allows this

shark to survive in harsh, low-oxygen, deep waters.

Using this extra set of gills,

they can take advantage of deeper waters...

ambushing prey in the darkness...

..and scavenging from the sea floor.

The sixgill shark. A colossal deep-sea giant,

armed with an extra set of gills and barely changed in 200 million years.

It is, without a doubt, positively prehistoric.