JOHN YANG: Environmental efforts to protect sharks in recent years has resulted in a huge increase in the great white shark population off the New England coast.

It's a conservation success story, with potentially unnerving implications for beach goers.

David Wright of Rhode Island PBS Weekly went out with one conservation group, which is tracking the rise of the world's biggest known predatory fish.

DAVID WRIGHT (voice-over): Just when you thought it was safe to go back in the water.

MAN: It's not that little.

DAVID WRIGHT (voice-over): Comes up pointed reminder that you might want to think twice at least in Cape Cod.

DAVID WRIGHT: I guess the headline is, there are lots of sharks here more than we thought.

MEGHAN WINTON, Atlantic White Shark Conservancy: Yes.

DAVID WRIGHT (voice-over): Meghan Winton of the Atlantic white shark Conservancy is one of the authors of a new study documenting a surge in the population of great white sharks here in recent years.

DAVID WRIGHT: And what's your best testimony?

MEGHAN WINTON: So the best estimate is over that four-year period that 800 individual white sharks visited the waters off of Cape Cod.

DAVID WRIGHT (voice-over): She and her colleagues have spent years patrolling these waters tracking every shark they encounter.

They recently let us tag along.

MEGHAN WINTON: We did just get one.

Okay, so it says white shark spotted 100 yards off southern most part of Nasik ORV.

DAVID WRIGHT (voice-over): Overhead they have a spotter plane the pilot Wayne keeps a sharp eye.

On the boat, they have underwater cameras and microphones and a ready supply of these things.

MEGHAN WINTON: It's just kind of like an easy pass for sharks.

The simplest way to explain it.

DAVID WRIGHT: You're charged call.

MEGHAN WINTON: We should start.

DAVID WRIGHT (voice-over): A radio beacon with batteries that last 10 years.

Every time a tag shark swims past one of these yellow buoys it sends out a ping you conservancy relies on citizen sightings to from a growing number of eco tour boats.

DAVID WRIGHT: You got to see some?

MAN: Yeah.

WOMAN: Yeah, I saw one.

Supper shallow here.

I saw 14 feet it wasn't tagged.

DAVID WRIGHT (voice-over): People on that boat tell us they us they saw a 14 footer here moments ago.

Every sighting from people or pings gets relayed to an app you can download, sharktivity.

They've identified more than 600 individual sharks here over the past 10 years.

DAVID WRIGHT: As I bet your app is fairly popular among beachgoers.

MEGHAN WINTON: I mean, I'd like to think so it is.

It's been downloaded over 100,000 times at this point.

And it's a great platform for us to report sightings.

Oh, we're out on the water for eco tour boats to report sightings and for anybody.

DAVID WRIGHT (voice-over): It may come as a surprise to know that nearly 50 years ago, when Steven Spielberg scared the pants off just about everybody with his iconic movie about sharks in this part of the Atlantic.

The population of great whites here was in danger of dying out.

MAN: You're going to need a bigger coach.

DAVID WRIGHT: Greg Skomal was still in grade school when Jaws came out.

The movie caught his imagination in the best possible way.

GREG SKOMAL, Director, Massachusetts Shark Research Program: I was motivated by the scientist in the film, as were a lot of colleagues of mine at the time to become sharp biologists, you know, so as a young kid watching that, I was thinking, wow, this is a really cool job.

DAVID WRIGHT (voice-over): Skomal has personally tagged more than 300 sharks, fulfilling his dream at a time when Cape Cod is finally beginning to see the dividends of decades of marine conservation efforts.

Over the last 50 years, the Marine Mammal Protection Act gradually helped bring back the seals and the sharks who prey on them.

GREG SKOMAL: We think about it in the time that both sharks and seals were gone, you know, Cape Cod has exploded as an area that draws people to enjoy this environment.

And so now, the predators coming back to feed on its prey, but it's overlapping with human activities.

And certainly humans are not used to that.

And so you know, but they're coming to grips with it.

DAVID WRIGHT (voice-over): The team deploys a drone for a bird's eye view of the water.

What they tend to find is that the sharks spend about half their time and water that's less than 15 feet deep.

MEGHAN WINTON: We've got the seals which love the beautiful beaches of Cape Cod, so do people and the sharks are coming in close to shore to hunt for seal.

So there is an overlap of these three species.

MAN: It has a tag.

DAVID WRIGHT (voice-over): finally, late in the day, a bonafide sighting.

Greg Skomal climbs out onto the pulpit, like a friendly Captain Ahab, armed, not with a harpoon, but a GoPro camera.

A 14 footer, a teenager, not yet fully grown.

Great white sharks are four feet long when they're born, they can grow up to 20 feet long their lifespan more than 70 years.

GREG SKOMAL: So that shark right there is one that we tagged a few weeks ago, you know, right in this exact same area.

So clearly, he's been sticking around.

And I think the only reason they stick around is if they're successfully feeding, because no point in staying in an area where you're not having any success.

DAVID WRIGHT (voice-over): Most of the regulars have nicknames, not this one yet.

DAVID WRIGHT: Who gets to name it?

MEGHAN WINTON: We've got a donor in the queue, who gets to name that shark, and that program helps us fund the cost of research trips.

DAVID WRIGHT: So you contribute a little to the work that you guys are doing.

MEGHAN WINTON: Yes.

Yes.

DAVID WRIGHT: And you got to name a shark.

MEGHAN WINTON: Exactly.

It's a pretty cool thing.

DAVID WRIGHT: How much is sharks name go for these days?

MEGHAN WINTON: $2,500.

DAVID WRIGHT (voice-over): That nickname will pay for another day out on the water like this one.

For PBS News Weekend, I'm David Wright in Chatham, Massachusetts.