- [Announcer] Funding for this episode of "Sci NC" is provided by the PATH Initiative a project of the North Carolina Department of Natural and Cultural Resources.

- [Frank Graff] No creature likely conjures up more emotions than the shark.

Fear, awe, foreboding, wonder.

The reality is most sharks are not a threat to people.

- It's far more dangerous to go for a walk in Chicago, New York or LA than to worry about a white shark when you go surfing.

- [Frank] As it turns out, North Carolina's coast is a pretty sharky place.

And as climate change transforms its ecosystem, sharks are given an even bigger role to play.

What scientists are learning about sharks coming up on "Sci NC."

[gentle music] ♪ Great white sharks aren't new to North Carolina's coast but now great whites are visiting in greater numbers and greater frequency.

No research organization has done more to increase our understanding of these predators and share their work on social media than OCEARCH.

It's springtime off the coast of North Carolina and the OCEARCH team is trying to solve one of the biggest mysteries of the great white shark, where the sharks mate?

- We're talking about an ancient secret.

This is a 400 million year old secret that the ocean is deciding whether or not it wants to reveal to us or not.

- [Frank] It's a daunting task in the face of North Carolina's turbulent seas.

- In this time of year in this area when these big mature animals are here the weather's tough.

It's super dynamic, you got the Gulf Stream colliding with Hatteras just north of us it's windy and maybe you're able to work one in four days across a 22 to 25 day trip and then you have to catch the right shark.

This is just a test, a test of endurance, a test of tenacity, a test of stamina, if it was easy it would've been done right now.

- [Frank] Since 2012, OCEARCH has tagged 84 sharks and mapped their range across the world using a gentle catch and release method that leaves the animal unharmed and outfitted with a tracker.

They discovered where the great white sharks nurseries are, where they feed and forage, and this is the last piece of the puzzle.

The team suspects that sharks are mating off the coast of North Carolina because they've seen adults converging here.

- And then all of a sudden, the males just continue their sort of dumb male thing of going back and forth, but then the females all of a sudden shoot offshore from here and they make these enormous loops out into the open ocean.

I mean way past Bermuda, all the way out to the what's called the Mid-Atlantic Ridge.

Why would they do that?

And why just the mature adult females?

Well, we think that the best explanation is that's when they're pregnant and they're getting away from the rest of the population, getting away from any more harassment by males.

- [Frank] Knowing where great white sharks mate is important.

- So if we can understand the entire life of a white shark, which might run 80 years from birth to old age and death, then we can know where those critical places are in each step of the way.

So these animals have been severely depleted over the last three or four decades and now they're making a return.

And our work is laying out a path for that return to abundance and also showing us where the critical habitats are, where these animals face threats that we need to take into consideration.

- [Frank] 97% of the more than 100 shark centered movies produced since "Jaws" have featured sharks threatening humans and the antagonist in most of the films have been great white sharks.

Despite our anxiety around sharks, those sharks have more to fear from us than we have from them.

Overfishing and by-catch or getting caught accidentally in fishing nets are the biggest threats to great white sharks globally and we're discovering that their presence in the ocean is crucial.

- And what we see when we lose our large sharks is we see the entire food web collapse.

Things like seals and squid and other things that sharks really keep under control begin to wipe out all our fry, all our baby fish, and the seals will wipe out all the stripers, all the cod, all the red fish.

And so with sharks and our large sharks at such low levels, we were in a situation where if we don't find out how to bring them back, how to manage them back, we were gonna really struggle to deliver a working abundant ocean to the future.

And that's why the white shark, things within their life history that are hugely important to make sure they return because they have a lot of challenges.

These animals aren't sexually mature until they're 20 so they have to live 20 years just to replace themselves.

- [Frank] That's why OCEARCH has crossed the globe tracking great white sharks revealing the secrets of how and where they spend their lives.

But it's not just OCEARCH scientists that use this data.

At least 45 researchers from around the world rely on samples from the OCEARCH team to conduct critical shark research.

- We have to touch far less sharks than if all those 45 scientists were to go out and working on the white shark for example, and have to collect the sample size they needed it would be potentially 45 times bigger sample size so it's a beautiful thing.

- [Frank] The team found two males with elevated sperm counts off the coast of North Carolina, but they want a larger sample size to confirm this last life cycle mystery so they'll be back to brave North Carolina's weather.

- Now we're really ocean people and we are trying to get involved with things that help make sure our kids could go out and see an ocean full of fish.

Our mission is to return our world's oceans to abundance.

It just happens that one of the primary paths to abundance happens to go through the white shark, our apex predator and the balance keeper.

- [Frank] Sand tiger sharks are now the top predator living on shipwrecks off North Carolina's coast and that's not a bad thing.

On wrecks where sand tiger sharks hold sentinel, there's a greater variety of reef fish.

- You can't swim with a shark without just being fascinated by how this animal has evolved over the years of their tremendous success story and to see how they've adapted in so many ways.

There's so many species of sharks that it's just to me, a subject that there's no end of questions to ask.

- [Frank] And to answer some of those shark questions, I'm in the ocean tank at the North Carolina Aquarium on Roanoke Island.

Yep that's me, and that's Shawn Harper the aquarium's dive safety officer and those are sand tiger, nurse and sandbar sharks.

Harper says the shark's behavior in the tank mimics their behavior on the wrecks off the North Carolina coast.

- Very indicative of what you would see here the sand tigers, other shark species such as the sandbar sharks are swimming around the wrecks.

- [Frank] And that's why I'm in the ocean tank.

More on that in a moment.

But first let's go off the North Carolina coast where more than 3000 shipwrecks dating back to the first English settlements are found on the ocean floor.

Treacherous weather, ocean currents, shifting sandbars, and even world wars gave the North Carolina coast the nickname, the Graveyard of the Atlantic.

But those wrecks have become havens of ocean life especially for sharks.

- The history of the wrecks is one very cool aspect of it the marine life that are associated with the wrecks.

I'm a biologist so that really attracts me and the fact that you can see these natural aggregations of large numbers of large sharks and be swimming shoulder to shoulder with them, there's not many places in the world where you get to do that.

- [Frank] There are about 73 species of sharks that live or pass through North Carolina waters every year.

- So it's not a scary aspect for me.

I'm always aware of their space and try to not encroach on them, to startle them or to make them aggravated in any way.

- [Frank] But it's the sand tiger sharks that really intrigue scientists and it's not just because sand tiger sharks are the predominant species on the wrecks.

- Where these sharks go, when they come back, how long they hang out, do they move from wreck to wreck or stay?

We do know just from where sand tiger sharks tend to aggregate and even watching their behavior in our aquariums and stuff that they do like to be near structure.

They don't seem to like to be out in the wide open ocean.

- [Frank] It turns out sand tiger sharks not only like to hang out on the shipwrecks off North Carolina's coast, scientists say the wrecks appear to play an important role in a sand tiger shark's life cycle.

- We're catching almost all big females on these shipwrecks off of North Carolina.

This is interesting.

I'm actually a veterinarian and so one of the tools that we use a lot for aquatic animals is ultrasound 'cause ultrasound relies upon sound rays, it works really well in water, we ultrasound fish and sharks all the time in our care, in our aquariums.

So we were ultrasounding them and not only are most of these sharks that we're catching off the wrecks in North Carolina big females, but most of them were pregnant.

So now we have all other big question okay, why are they all pregnant?

And why are we not catching females that aren't pregnant?

Why aren't we catching males?

- Some of these females that are just dating are potentially hanging out on these wrecks for longer periods, whereas the males might be passing through seasonally.

And then other females that are taking their break from pupping might be also migrating through.

- [Frank] Female sand tiger sharks give birth after a 12 month pregnancy.

The eggs hatch inside the mother they are normally two offspring.

- There's two big questions we don't really know where they mate and possibly even more importance from a species standpoint is we don't know where they pup.

It appears that these wrecks are what you might call a gestation ground.

So for whatever reason this is where these pregnant females, one of the things we have learned we do know about sand tiger sharks is that they have a biennial or triennial reproductive cycle so they get pregnant one year then they take one or two years off to resume their energy stores.

So those non-pregnant females are living somewhere else in those off years.

- [Frank] North Carolina Aquarium researchers are joining with scientists at aquariums and universities along the East coast to better understand sand tiger shark behavior.

Part of that research involves catching the sharks and inserting a tiny tracking device into the shark's underbelly.

Receivers to record the sharks movements are attached to shipwrecks.

There are 39 receivers on coastal shipwrecks off the North Carolina coast.

Some early findings indicate sand tiger sharks are migratory with a range from Georgia to New York, and they swim from structure to structure.

- They also tend to follow temperatures a lot so we don't know if it's something that has to do with the thermoclines in North Carolina we're very close to the Gulf Stream here in this area where these wrecks are, we don't know exactly but that's part of the things that we're trying to tease out.

- The sand tiger sharks have been a staple of public aquariums for as long as I can remember.

They do well in aquariums but for as long as we've worked with them there's still gaps in our knowledge about these animals and so I feel like it's kind of a way that public aquariums can return the favor.

- [Frank] Which brings us back to the aquarium's ocean tank.

I'll admit I was a little nervous even with Shawn diving with me but I was mostly in awe watching a creature so graceful, so powerful, so beautiful despite the teeth and so mysterious.

Well, some sharks visit and leave the coast and others live on shipwrecks.

There are some shark species that simply migrate along the coast.

That's the story of the blacktip shark.

- Four beach approach Skyhawk flight 280 Delta checking with you northbound along the shoreline 500 feet.

Got beautiful clear water today.

Great visibility we can easily see the sharks.

There's a bunch of sharks right there.

A dozen or more right there.

There's another shark southbound along the beach.

Oh, there is a bunch of sharks here and they're all going south that's cool.

A bunch of people in the water with the sharks.

People have no idea there's sharks there.

- [Frank] It's winter in South Florida and along with the tourists, blacktip sharks are flocking to the shore.

These sharks move up and down the Eastern Seaboard every year passing through North Carolina's coastal waters every spring.

And Dr. Stephen Kajiura has been studying this migration for 12 years.

- We're flying down here along the beach in South Florida, and we're nice and low 500 feet off the water and we're flying fairly close to the beach here simply because that's where the sharks are.

So we're seeing sharks here but it's in the range of a few to maybe dozens.

It's certainly not in the range of hundreds to thousands like we've seen in the past.

- [Frank] The clear waters of South Florida's coast allow researchers to count blacktip sharks by flying a small plane from Miami up to Jupiter with a high definition camera mounted out the window.

- The blacktip sharks that we've worked with down here are an average sort of shark what you typically think of when you think of a shark.

They have a maximum size of about two meters or so, and they are fast sharks.

These sharks are feeding primarily on little bait fish.

They have sharp pointy teeth which are very good for grasping slippery fish and they're making these long distance migrations along the coast and that's what we're interested in looking at.

What are these sharks doing after they leave South Florida as they're migrating all the way up the U.S. Eastern Seaboard.

- [Frank] Blacktip sharks are social creatures and they migrate and hang out in groups.

Usually those groups are in the shallow waters near shore right where beach goers like to swim.

- And that's what was sort of the impetus for this whole study why are there so many sharks right where the swimmers are?

- [Frank] It turns out blacktip sharks have several reasons to hug the coast as they migrate north and south.

They particularly eat small bait fish and those fish like to hang out in the shallows.

Also being a shark doesn't automatically put you at the top of the food chain.

Blacktips are a tasty meal for larger sharks like hammerheads so by staying near the shore, they can often dart into shallow waters.

Predators can't follow them.

- It's a good place for the sharks to be.

They can eat and they can avoid being eaten.

- [Frank] But we don't know all of this just from aerial surveys.

- The aerial surveys are great because it gives us the big picture what's happening along the whole coast of Southeast Florida here.

But then you need to get down on the water to actually work directly with the sharks.

- [Frank] First, you have to find the sharks.

- I see a shark 1, 2, 3, whole bunch of sharks right here cool.

We're gonna go right up here, we're gonna start dropping blocks in and we're gonna catch some.

- [Frank] Researchers deploy baited hooks attached to concrete blocks in floats in a line along the shore.

They then wait for the shark to take the bait.

[upbeat music] ♪ - Does it look healthy?

- Yeah, it looks healthy.

- Sex?

- Nice big male.

Male okay.

- [Frank] Once the shark is secure alongside the boat, they take measurements.

Make a small tissue sample for DNA analysis and attach an identifying tag before releasing the shark.

- If you were to just look at the aerial survey data you only get data for a few months when the sharks are here but we don't know what happens after they leave.

- [Frank] Using satellite or acoustic transmitters, Dr. Kajiura and his team can track individual sharks for years collecting valuable data about their migratory patterns.

Satellite tags are fixed to a shark's dorsal fin communicate with an orbiting satellite every time that fin breaks the oceans surface.

Listening stations up and down the coast, picked up signals from acoustic transmitters, a network of scientists along the coast share the data.

- For this sort of work where you're talking about movements along an entire Eastern Seaboard of the United States, this is well beyond the range of what one lab can handle.

But with so many individual labs all the way along and all pooling our data together, it enables everyone to benefit.

And we're able to look at these long distance migrations that would simply be impossible to study any other way.

And we have long term data sets going back 50 years or more and what this enables us to do is look at the effects of things like global climate change on the distribution of these animals.

- [Frank] And all that data reveals that blacktip sharks follow temperatures.

They spend the winter in Florida and migrate all the way to New York in the summer to mate and give birth.

- And remember, these sharks are both the same size as us.

They're about the same size as a human that's a long haul for us to walk that far.

And these guys are doing it twice a year so it's a long migration and they do it on mass huge numbers of them all swimming together up the coast and then back down again.

That's what makes this so interesting.

- [Frank] But the data also shows as climate change warms ocean waters, the migration patterns for blacktip sharks are changing.

Fewer sharks are migrating so far South to Florida.

More are staying north.

It seems blacktip sharks enjoy living in a particular water temperature range.

- And if you look at the historic range, they used to go from South Florida up to about Cape Hatteras North Carolina in the summertime.

But now their current range is extending much farther than that and now it's extending all the way up to New York.

So we're going to eventually see this shift where we won't see them coming as far south, and we'll see them going farther and farther north.

- [Frank] But thousands of sharks moving into different coastal territories is likely to have an impact on coastal ecosystems and their inhabitants, human and fish alike.

- When you think of these sharks going farther north than they have historically they're gonna be encountering different fish up there, and the fish are not accustomed to having literally thousands of these blacktips coming in every summer.

And so it's gonna be a dramatic change to the ecosystems farther north, it's gonna be a change to the ecosystems farther south here.

If you don't have that annual influx of these top level predators taking advantage of the little bait fish buffet, you don't know what's going to happen to the animals that are down here that are not being eaten.

So there's a lot of potential for cascading effects through multiple ecosystems and multiple trophic levels and it's just gonna be interesting to see what actually happens.

- [Frank] While scientists are learning more about the important role sharks play in the healthy ocean of today, a massive creature from the past is still worth exploring, the megalodon.

We're 100 feet underwater of the coast of North Carolina.

That may look like a pointy rock but it's actually a multimillion year old megalodon shark tooth fossil.

- Yeah so here in NC this is meg country, I mean, this is one of the top spots on earth for finding megalodon teeth.

Megalodon is probably the most famous extinct group of shark it's clear it was a carnivore, it's clear it was a predator, you don't have giant steak knife teeth with serrated edges if you're not eating meat.

So they were these extremely large, probably the biggest macro predatory sharks that ever lived.

- Megalodon has to eat a metric ton of food every day.

That's like having to eat your Ford F-150 every other day.

- [Frank] Paleontologists look to fossils to learn about how extinct megalodon lived.

But for sharks, the fossil record is a little different.

- Well, one of the big differences between sharks and other animals is that they have no bones.

Their bodies are composed of cartilage which is like a styrofoam frame for the body.

It's strong, it's bendable, but the second that they die those cartilage prisms they just detach and everything disintegrates.

- The only really hard part of a shark is the teeth.

Teeth are really, really good at fossilizing.

- [Frank] And sharks lose a lot of teeth during their lifetime.

- It's been estimated that sharks can lose as many as 35,000 teeth during the course of their lifespan.

So because of that we have an incredibly rich, incredibly dense fossil record of sharks' teeth but that's it.

We don't have the bodies, we don't have the rest of the skeletons for the most part.

The jaws we have at this museum teeth are real, the jaws are reconstructions.

Basically all that we know is based on this tooth record.

- [Frank] And coastal North Carolina is one of the best places in the world to find megalodon teeth.

- Now is that a result of prehistoric North Carolina just having been swarming with megalodons to the exclusion of other places, no.

The megalodon was a globally distributed species we know it was living in oceans probably mostly in equatorial regions around the world in the late age of mammals.

- [Frank] Fossils aren't easy to find.

A lot of the fossiliferous rock in the world has been destroyed by natural processes and existing fossils are often buried deep underground.

- So you need to have rocks of the right age that one, still exist.

Two, are exposed at the surface and three, are the right kinds of rock.

- [Frank] Costal North Carolina checks all of the boxes.

- There are two major sources of megalodon fossils in the state.

The biggest one historically was these giant phosphate mines out east near Aurora.

- [Frank] The layer of rock being mined is from the nearshore marine environments.

That's where a lot of biodiversity occurred so it contains a dense concentration of marine fossils.

- So a lot of this megalodon bearing rock is not at the surface, but just below it.

And so how can we get at it?

The wave action on the coast is eroding the edges of those fossiliferous layers which we call the strata and washing them then into the ocean.

- [Frank] Skilled divers like Shane head out to those eroding underwater ledges to find shark teeth and other fossils.

- Where we are in North Carolina it's typically pretty far offshore and on average 100 feet of water.

It's very rare that you see a whole tooth laying exposed.

It's typically, pretend my thumb is black that's all you see of that tooth but that sixth sense kicks in and you investigate and you find a true tooth.

Let's see what we got.

So we got at least one really good, that is a megalodon you'll clean it up nice.

This is a broad tooth mako.

- [Frank] Since fossils are the only remnants of megalodon we have, studying them helps researchers understand more about these massive ancient predators especially what they ate.

And fossil donations to the museum allowed new discoveries about megalodon to be made.

A donated megalodon tooth with a unique split down the middle prompted Haviv to dig over 200 years deep into the literature to find an explanation.

- On most megalodon teeth right here in this surface right here it's curved, it's convex or it's flat.

But on this tooth and if I can get the lighting right you can maybe see it goes in right there.

That makes us think that whatever caused this deformation, it started early on at the base of the tooth when it was still forming.

- [Frank] Those historical records helped Haviv decide the trauma was likely caused by something spiky that the megalodon ate.

- It would make sense that they weren't just eating whales but they probably ate a plethora of different animals.

If they found a meal they were gonna eat it they had to because they had to eat a metric ton every day.

- [Frank] Specimen donations like this are critical for future discoveries.

- We are reliant on partnerships with the broader community of anyone who is out there looking for fossils.

As a state paleontologist in North Carolina I can't be at every river cut every day where there was a rainstorm and maybe a new fossil washed out of a river bank.

- And so donations like this are really vital towards allowing us to share with you and unravel the mysteries of our natural world.

[gentle music] ♪