[chime]
[beeping]
- Off the coast of North Carolina
lies a treacherous stretch of water
with strong currents and shifting sands.
With the remains of up to 5,000 ships,
it's known as the graveyard of the Atlantic.
Hidden within this eerie resting place for lost souls
are gangs of Sand Tiger sharks.
Photographer and conservationist Tanya Houppermans
has spent over a decade documenting the shark
gang phenomenon occurring here.
- I started diving around 2009.
Came down here to North Carolina,
and that was the first time that I saw the Sand Tiger sharks.
It literally changed my life.
I walked into work and quit.
I left the corporate world behind
and decided to devote my life to spending time with sharks.
- Working with Spot A Shark USA, Tanya
is studying the thousands of sharks that have made
these shipwrecks their home.
These rusting hulks provide the perfect conditions
for marine life to grow and for predators to hunt.
But why Sand Tiger sharks congregate here
in such large gangs is still a mystery.
- There are times that we could see a hundred and maybe even
more sharks in an aggregation.
They really seem to prefer to be around other Sand Tiger sharks.
We're not quite sure why yet.
- Today, Tanya and her husband Scott
are looking for answers by diving a wreck
known for large groups of Sand Tiger sharks.
- Today were heading out to the wreck of the Caribsea.
This is a freighter that was sunk by a u-boat
during World War II.
Right now, she lies about 90 feet underwater.
That's where we tend to see a lot of Sand
Tiger sharks hanging out.
- Tanya is on the front line, trying to discover the secret
that unites these sharks.
She's taking photographs so scientists
can study them for vital clues.
- Inside this housing is the camera that I
use to photograph the sharks.
And we have two lasers here on each side.
When I take a picture of a shark,
these two green dots will show up on the side of the shark.
We can then actually calculate the length of that shark
just from the photograph itself.
And then we can go in and identify
each individual shark based on its unique spot patterns.
It's like a fingerprint is to a person.
I want to kind of give each other's gear a look over, too.
[puff]
All right.
Looks good.
Every dive, there's the possibility
of learning something new about these animals.
There really hasn't been a lot of research done on them,
compared to a lot of other species such as Great Whites,
so any time we get in the water with them
and bring back any information for the researchers
that I work with, it's a great day.
Good, then.
Right.
Let's go find some sharks.
[splash]
[air hissing]
We have 100 feet of visibility, clear blue water.
A lot of the wreckage still intact--
you can see the big bow structure.
It never gets old.
There are just sharks as far as I can see all around me.
- These sharks are named after tigers because
of their voracious appetite.
But to Tanya, they're gentle giants.
- They have these raggedy teeth that
makes them look really fierce, but these sharks
are full of personality.
Sand Tiger sharks are probably about six or seven feet,
the female being a little bit bigger than the male.
- Surrounded by a swarm of sharks,
Tanya begins her search for evidence
as to why so many are here.
- There are a lot of females.
Every so often, you see a few males, but it's mostly females.
Why is that?
- With her laser guided camera, Tanya captures her first clue
to solving this mystery.
- Some of the females do have scars from mating.
When sharks mate, the male actually holds
on the female with his teeth.
If we see fresh mating scars, that female may be pregnant.
We're finding several pregnant females.
Why are they grouping together?
- After photographing the girl gang--
- That was amazing.
There was a lot of sharks.
- Tanya tries to make sense of this incredible spectacle.
- So what we're seeing is a big gang of Sand Tiger sharks,
mostly females.
We have so many unanswered questions.
But what we're thinking is that maybe these females
are aggregating together during pregnancy
so that the males don't try to mate with them again.
It could be possible that the females are banding together
as kind of a support network.
They are choosing to group together like this.
And so not all sharks are just solo predators.
Sharks could have a social life, just like humans.
[gentle music]