- Palm beach approached, 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.

Those a bunch of sharks here.

They're all going south.

That's cool.

A bunch of people in the water with the sharks.

People that have no idea there's sharks there.

- [Narrator] It's winter in south Florida.

And along with the tourists, Black Tip Sharks are flocking to the shore.

These sharks migrate up and down the Eastern seaboard, each year, passing through north Carolina's coastal waters in the spring.

And Dr. Stephen Kajiura has been setting 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.

It's 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 that we've seen in the past.

- [Narrator] The clear waters off south Florida's coast allowed Dr. Kajiura and his students to count Black Tip Sharks by flying a small plane from Miami up to Jupiter, with a high definition camera mounted out the window.

- The Black Tip Sharks that we work 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.

They have a sharp pointy nose.

They're very smooth and streamlined 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 us Eastern seaboard?

- [Narrator] Black Tip Sharks or Carcharhinus Limbatus are social and they migrate and hang out in groups, usually in the shallow waters near shore, right where beach goers like to swim.

- [Dr. Kajiura] And that's what was, sort of the impetus for this whole study.

Why are there so many sharks, right where the swimmers are?

- [Narrator] It turns out, Black Tip Sharks have several reasons to hug the coast as they migrate north and south.

They primarily eat small bait fish, and these fish like to hang out in the shallows.

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

Black tips make a tasty meal for other larger sharks like hammerheads.

By staying near the shore, they can often dart into shallow waters where their predators can't follow.

- [Dr. Kajiura] It's a good place for the sharks to be.

They can eat and they can avoid being eaten.

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

- The aerial surveys are great because it gives us the big picture of 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.

[upbeat music] - [Narrator] First, you have to find them.

[drone buzzing] - I see a shark 1, 2, 3, the 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.

- [Narrator] Dr. Kajiura and his team of students and volunteers deploy beaded hooks, attached to concrete blocks and floats in a line along the shore and wait for a shark to take the bait.

[crowd murmuring] - [Dr. Kajiura] You got a tension?

All right.

We gotta a shark.

- Right here, under, can you get the tail air?

- [Dr. Kajiura] Is it look healthy?

- Yeah, it looks healthy.

- [Dr. Kajiura] Sex?

- Average male.

- [Dr. Kajiura] Male.

Okay.

[upbeat music] - [Narrator] Once the shark is secure alongside the boat, they quickly take measurements, a small tissue sample for DNA analysis, and attach an identifying tag, sorry buddy, 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.

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

Satellite tags, affixed to a shark's Dorsal fin, communicate with an orbiting satellite every time that fin breaks the ocean's surface.

- And so you can literally get an email to say tag number 123 was detected at this latitude and longitude, and you're able to track the movements of these sharks in real time.

- [Narrator] Listening stations up and down the coast, pick up signals from acoustic transmitters.

A network of scientists 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.

[soothing music] Really fortunate that shark research has been conducted along the east coast of the us for many decades now.

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.

And we know now that these sharks are spending the winter down here and then as the water temperature starts to warm up, they'll migrate their way farther up the coast.

They get as far north, as about long island, by September.

So they're making this long distance migration from south Florida, all the way up to New York, and then back again.

And remember these sharks are built the same size as us, right?

They're about the same size as the human.

That's a long haul for us to walk that far.

And these guys are doing it twice a year.

- [Narrator] A long term data set like this, allows researchers like Dr. Kajiura to see patterns and shifts in the migration.

- Even in maybe a 10 years' span.

We've seen a dramatic decline in the number of sharks that are coming down here every winter.

And it's tightly correlated to water temperature.

What you'll see here is that half that 50% of their time is spent at a temperature between 22 and 23 Celsius.

And like 85% of their time is spent in just a three degree temperature band.

So they have a very narrow thermal preference.

They really like that particular range of temperatures.

And that's what they're following.

They used to go from south Florida up to about Cape Hatteras, North Carolina in the summertime and now it's extending all the way up to New York.

- [Narrator] It's not clear yet, what this change in Black Tip Shark distribution will mean?

Overall even though their migration pattern has shifted northward, the Black Tip Shark population is stable.

In fact, they're even fish commercially 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 Black Tips 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.

[slow background music] What I would like people to remember, is that there are literally thousands of sharks right in our beaches.

And very few people get bitten.

And so these sharks are not out to get you the sharks are there, they're doing their own thing.

You're in the water as well.

And you're having a good time and I encourage you to keep going in the water and having a good time.

Don't be afraid of the fact that there's sharks in the water.

You've probably been swimming with sharks before and just didn't know it.

[calm music]