♪ ♪ DANNI WASHINGTON: An invasion that spans continents.

♪ ♪ Triggered by humans.

They didn't choose to be released in an entirely different environment, but they're here.

♪ ♪ WASHINGTON: The lionfish.

Along the Atlantic coast, they've gone from population: zero to top predator in mere decades.

I'm talking about, in some cases, 100 lionfish on one reef site that may be the size of your car.

We constantly go back and forth from being appalled at what we see, but being excited by our ability to witness those things.

WASHINGTON: What has made them so successful?

TICO CHRISTIAAN: Copy that, be advised, we are heading up for lionfish.

Yeah, yeah, yeah, yeah, that's it-- all right.

All right, keep it there, keep it there, yeah, bring it up.

WASHINGTON: And what, if anything, can stop them?

FARRA FIGAROA: We bring it to a restaurant where they sell them, where they sell the lionfish.

WASHINGTON: What's the average depth that you normally put this down in?

Truly out of recreational diving limits, in deep water.

There we go.

Nice.

We're ready to go.

WASHINGTON: "Ocean Invaders," right now, on "NOVA."

♪ ♪ ♪ ♪ WASHINGTON: The Argentine black and white tegu in Florida.

African hippos in Colombia.

South American cane toads in Australia.

Species are being introduced to new places like never before.

The Asian giant hornet is so much bigger and faster and stronger.

WASHINGTON: Some are harmless and actually make our lives better, while others become invasive, causing harm and spreading uncontrollably.

We short-circuit the geographic barriers between these species.

WASHINGTON: But it's in the ocean where an invasive species has wreaked so much havoc, it's considered one of the most successful of them all.

The lionfish.

And the ocean, well, that's my territory.

I'm Danni Washington, an ocean explorer and science communicator.

I've always been drawn to the mysteries of the underwater world.

So when I learned that an invasion of epic proportions, spanning continents, was happening below the surface, I had to investigate.

What I really want to know is, why are lionfish a threat?

What makes them so invasive?

And what can be done about it?

The Gulf of Mexico is one of the regions that has been hit hardest by the invasion.

So today, I've come to participate in a fish survey to get a closer look at these "Ocean Invaders."

♪ ♪ My mission is to find lionfish during this survey, so I'm really looking forward to that.

I know that they love to hang around wrecks or any type of structure underwater, so I'm curious to see how many we'll find.

WASHINGTON: I join coastal resource manager Alex Fogg at the Big Dawg, a U.S. Air Force vessel sunk in 2021.

So where maybe there's a staircase, or maybe an open door where there are some nooks and crannies for them to hang out, that's where you want to be looking for them.

Okay.

We'll help if we can.

All right, cool.

And I think the universal signal for lionfish, I mean, if I remember correctly, it's this one right here?

Correct, yep.

FOGG: You got it, yep, yep.

Pretty easy one to pick out.

WASHINGTON: Great.

So if you can point 'em out to me, let me know when you see some, and I'll make sure to tally it down.

WASHINGTON: Okay, well, I think we should get suited up.

♪ ♪ ♪ ♪ WASHINGTON: The Big Dawg was not a casualty of a hurricane or torpedo.

It was intentionally sunk as a part of an artificial reef program.

♪ ♪ As it comes into view, I'm blown away by its massive size.

♪ ♪ In regions with featureless sea floors, like the Gulf, structures are sunk as artificial reefs to promote marine life.

Like this huge roughtail stingray, one of the first creatures we encounter.

♪ ♪ We see several species that people depend on for food, including grouper and red snapper.

So reefs like this don't only support biodiversity, they support us.

While artificial reefs here are havens for native fish, they've also become buffet grounds for the invasive lionfish.

♪ ♪ To start our survey, we head into the ghostly wreck.

It really doesn't take long to spot my first lionfish.

Three of them, actually.

At a distance, their striped bodies blend in with the mangled metal.

But up close, they are striking, hypnotic, and unlike any other fish on the reef.

♪ ♪ As I continue the dive, I tally up more and more invasive lionfish.

I'm careful to keep my distance.

They're venomous, and capable of delivering a potent sting with their spines, so I'm extra-wary when checking different compartments and swim-throughs.

Turns out they're not at all hard to find here-- which is exactly the problem.

There are dozens of lionfish down here.

♪ ♪ FOGG: In some cases, more than 100 lionfish on one reef site that may be the size of your car.

It's unsustainable for a lot of the species that are on those reefs or were on those reefs prior to lionfish showing up.

(breathing heavily) Well, that was cold.

(laughs) FOGG: Yeah, a little bit!

It's a little chilly.

Good vis, though!

Yeah, great visibility.

All right, well, that was a great dive.

Yeah, it was killer.

Yeah... We absolutely had lionfish down there.

Yes, we did.

We didn't have lionfish ten, 15 years ago.

So just adding lionfish to the system totally changes things.

They may be preying on fish, like red snapper and grouper, that we really depend on.

WASHINGTON: Scientists say that on some reefs, lionfish are killing off up to 80% of young fish.

And in some Atlantic waters, they make up nearly 40% of the total predator biomass.

Not long ago, they made up zero percent.

This leads us to the question, how did lionfish end up so successful here, where they don't belong?

And where did they come from?

LUKE TORNABENE: Lionfish occur throughout the Indo-Pacific oceans, basically from the Red Sea and Indian Ocean throughout the Central Pacific, all the way out to French Polynesia.

They have a number of predators in their native range.

So no one, no one looks at, as lionfish as a nuisance.

They look at them as this beautiful ornamental species that everyone wants to have in their fish tank.

WASHINGTON: The lionfish's strange beauty makes them popular in home aquariums around the world, and most scientists believe that is what led to the Atlantic invasion.

Here, we're talking about something that happened just like that.

WASHINGTON: The theory is, in the 1980s, lionfish living in home aquariums were released off the coast of Florida.

Somebody took this species that had never, you know, been found naturally in the Atlantic Ocean and dumped it in, and it just took off.

WASHINGTON: Over the past few decades, they've spread up and down the Atlantic coast and Caribbean, from North America all the way down to Brazil.

And there are records of lionfish in the Mediterranean, introduced separately via the Suez Canal.

SHARLENE SANTANA: Our ability to move species from one place to another is, uh, over very large distances, is much greater than what many of those species would be able to accomplish by their own means.

FRANK MAZZOTTI: We short-circuit the geographic barriers between these species, through things like the pet trade, and so things that would have kept these species apart, you know, essentially forever, for millennia, we've done away with that barrier.

CAROLE BALDWIN: Other, you know, aquarium species have been released into the open ocean, and they don't, you know, do well-- you might have a small local population, or they may just, you know, die out completely, but you take a, a fish like a lionfish, that just has all the characteristics that make it a hardy survivor, and, you know, it can wreak havoc.

WASHINGTON: Humans manage to move plenty of animals to opposite ends of the Earth.

So, what sets lionfish apart?

What allows them to proliferate so successfully in their new territories?

As a fish biologist, someone who loves studying these species, we're often drawn towards the evolutionary novelties or the oddities-- the weirdos in the fish world.

And lionfish are definitely one of them.

Most fish don't have frilly moving appendages on the outside of their body.

Most fish look like a torpedo, essentially, with some short fins on the top and the bottom.

The lionfish seems to have a suite of characteristics that make it a particularly great invasive species, or terrible invasive species, depending on your perspective.

Their appetite is seemingly endless, and they digest food very quickly, too.

WASHINGTON: A lionfish can eat 90% of its body weight in a day.

In fact, a lionfish's stomach can expand up to 30 times in size.

TORNABENE: They will not chase down a food item across the reef and eat it.

That's just not how they work.

They're, they're smarter than that.

And in some ways, they're lazier than that.

So, their approach is definitely a slow approach to targeting their prey, getting them in an opportunistic position where they can ambush it, and developing an easy, an easy meal.

WASHINGTON: Lionfish eat over 100 different species, one of the reasons they are such destructive invaders.

But that's not all.

They're also very good at reproducing.

While most native fish only reproduce for a few months, female lionfish can produce millions of eggs over the entire year.

This relentless multiplication leads their populations to skyrocket.

They release the eggs into the water column, thousands of them at a time, and they're fertilized and they drift.

And so that makes it really hard to contain, you know, an invasive species to any one area.

WASHINGTON: And crucially, in their original habitat, lionfish have predators.

In the Atlantic, there aren't really any animals that see them as food yet.

Organisms are highly adapted to their environments and to the species that they interact with because of this process of natural selection.

Within an ecosystem, you have species that have been interacting for millions of years, probably, right?

And it's a network of very intricate interactions.

Pattern recognition between predator and prey, and, and it's sort of this evolutionary arms race.

And in the lionfish's native range, we can imagine that the predators there have had much longer time to recognize this otherwise unique pattern, and recognize that that is actually a prey item.

Whereas in their introduced range, they've only been here for 30 years.

So most of the species here have no idea what this pattern is at all.

WASHINGTON: Without predators to keep them in check, invasive lionfish have an advantage over native species that have evolved together.

But humans have moved species around the globe for millennia.

So how bad can an invasive species really be?

On the other side of North America, another animal is just starting its invasion.

One that scientists think could be catastrophic.

♪ ♪ TED MCFALL: It was a, it was a morning almost exactly like today.

And I saw, in front of one of the hives, a black area of, of what looked to be maybe a bunch of dead bees.

And, and that's when I opened up the hive.

And there was nothing, nothing less, left to save.

All of the bees had been beheaded.

WASHINGTON: Beekeepers Ted and Dorothy McFall were the first to be hit by this invasion.

In all my decades of beekeeping, I've never seen anything like it.

DOROTHY MCFALL: So a few weeks later, I was at a winter market and a couple said, "I don't want to alarm you," but they found some, some-- and she said the name, and I had no idea what she just told me.

And then I asked her again, "What is that called?"

And she said, "Asian giant hornet."

TELISSA WILSON: Vespa mandarinia.

The Asian giant hornet, yeah.

MAN: That's the Asian giant hornet, okay.

That's what it's commonly called here.

WASHINGTON: A.K.A.

the yak killer, the murder hornet, and officially named the northern giant hornet.

So the first nest was actually found in Nanaimo, British Columbia.

Come to now, we have found four nests in Washington state.

Nobody really knows how the first introduction happened.

It's plausible that it came in on shipments, or cargo containers.

TED MCCALL: The goal right now is to try to stop this Asian giant hornet problem from continuing, because it only takes somewhere between five and two dozen Asian giant hornets to come in and slaughter thousands.

And they do it in a matter of hours.

60,000 versus five.

WILSON: It kills people every year.

I think about 50 people in Asia die annually from stings.

It delivers more venom than any other hornet.

It's a cytolic venom.

It basically, like, breaks open your cells and degrades your tissue.

I know it sounds crazy, but the Asian giant hornet, they can sting multiple times.

And if you pick up a couple dozen stings, you're either gonna be, wind up in the hospital or in the cemetery.

WASHINGTON: But the danger they pose to humans is nothing compared to what they do to honeybees.

Giant hornet scouts roam, looking for beehives, so they can steal nutrient-rich baby bees and feed them to their own young.

When a scout finds a hive, it injects a pheromone onto it to signal this colony is a target.

This is like a pin marked on a GPS.

(buzzing) When the rest of the hornets arrive, there's little hope for the bees.

They call it the slaughter phase, 'cause that's exactly what they're doing.

They literally will park up on the honeybee nest and just tear the workers apart.

WASHINGTON: Back in the hornet's native range in Asia, the most common honeybee has evolved a very effective defense-- kill the scout.

When the hornet scout shows up, the Asian bees ball around it and beat their wings.

This not only allows them to pierce the hornet's armor, but also suffocate it to death.

This is possible because Asian honeybees evolved alongside the giant hornet.

The honeybee colonies that were able to defend themselves triumphed.

Meanwhile, the honeybees far away in North America did not participate in this evolutionary arms race.

WILSON: Honeybees here don't have a defense mechanism.

They haven't co-evolved with the Asian giant hornet, and so that's a really scary thought when you think about all of the pollination that our honeybees do.

WASHINGTON: And there's the big problem.

Honeybees are the most productive pollinator in the U.S. A third of all food produced in the country depends on these bees.

So, if the honeybees have a major problem, the food supply has a major problem.

TED MCCALL: Food prices will go up.

Berries, vegetables, nuts, you know, all these things are dependent on honeybees.

Coffee-- you know, without, without the honeybees, we're gonna be eating a lot of potatoes, eating a lot of corn, and...

I guess we'll always have corn syrup.

WASHINGTON: At the Washington State Department of Agriculture, the recently discovered giant hornet nests are being studied.

Scientists like Telissa Wilson are working against the clock to understand the hornet's presence and future in North America.

WILSON: So here is the part, just part of the nest number four that we found last year.

And just for comparison, here's another nest I found outside of my lab in the parking lot, of another hymenoptera.

It's pretty crazy.

(chuckles) I mean, they're, they're unmistakable when you see 'em.

They're the largest hornet.

They have two big black eyes with three little eyes in the middle.

Five total eyes.

Which is just too much.

(laughs) We do stand a chance of eradicating it, and we're throwing a lot of people at it and a lot of time and resources, and we're collaborating with a lot of citizen scientists.

MAZZOTTI: Early detection and rapid response.

Almost all of the examples, when we have successfully dealt with an invasive species, has been something that was detected early, responded to rapidly, with brute force-- just go in and get it out.

WASHINGTON: Over the spring, Ted and Dorothy set traps with their local bee club in hopes of catching any emerging hornet queens before they can reproduce.

RUTHIE DANIELSON: The first year, we had about 18 to 20 Asian giant hornets caught in traps?

Last year, we had 14, wasn't it?

DOROTHY MCCALL: Oh, yes, 14, I think.

DANIELSON: 14?

Yeah, yeah.

So every time you catch an Asian giant hornet in a trap, what that says is, there's a nest in the area.

And so then the, the scientists, the entomologists, will saturate the area in a grid pattern with live traps that they will check daily.

♪ ♪ TED MCCALL: None of these hornets or other vespas are even close to the size of the Asian giant hornet.

The Asian giant hornet is so much bigger and faster and stronger.

It's pretty incredible.

TED MCCALL: But hopefully, if we can stop it, then we're not gonna have to deal with it, but... We can stop it, of course we can.

Yeah.

We're, we're trying like heck, aren't we?

Of course we can.

(both laugh) WILSON: Once an invasive species is endemic or established, the amount of money and resources you would have to use to eradicate it are just too much.

Once it gets to a certain point, all hope is lost.

WASHINGTON: It is undeniable that invasive giant hornets are a threat.

We still don't know if they can be eradicated in North America, but the clock is ticking, driving scientists and locals to take action, because we not only love, but depend on the native honeybee.

The honeybee is non-native.

(tape player stops) WASHINGTON: Wait, what?

(tape player starts) Well, in some of these species, that gets to another end of a definition.

Some non-native species become naturalized, and that is, that's kind of the opposite of invasive, and that is, they become part of the ecosystem that they've been introduced to and fit into the ecosystem.

And so there are naturalized non-native species, as well as invasive non-native species.

WASHINGTON: Okay, so let's get this straight.

Non-native species are the ones that have moved into new ecosystems.

And like Frank says, such species can become either naturalized as a part of the ecosystem, or invasive and disrupt the ecosystem.

But species have been moving around the world for millions of years.

So does that mean every plant and animal could have been considered non-native and potentially invasive at some point in Earth's history?

Could North America's beloved honeybees have been, for a time, invasive, and out-competing native pollinators?

What else?

Cats.

(tape player stops) WASHINGTON: You're killing me, Frank.

(tape player resumes) Cats eat birds, eat small mammals, eat reptiles, and, and are responsible for (wild cat growling) hundreds of millions, if not billions, of birds being eaten every year.

Cats are the, one of the most invasive species.

Cats get a pass because people do like them.

(cat meows) They shouldn't get a pass.

Gonna anger all the cat people.

(laughing) It's okay, I'm a dog person, I own it.

(laughs) WASHINGTON: So, invasive giant hornets are a problem because they could potentially wipe out honeybees and impact America's food supply.

Outdoor cats are a problem because they kill billions of birds.

But what about lionfish?

In some parts of the Atlantic, the populations of dozens of fish species have plummeted.

And many scientists believe lionfish are to blame.

Those fish are crucial to the survival of corals.

For instance, some fish help control algae growth on coral reefs.

If lionfish overconsume algae-eaters, reefs could suffocate.

Countless coastal communities in the Western Atlantic depend on these coral reefs for everything from fishing to tourism.

But lionfish populations can be managed-- sort of.

Currently, the most effective way to do this is through spearfishing.

(boat motor revving) Tim Shivers and John Kidd compete in lionfish derbies.

These competitions can award big prizes for catching the most lionfish and can temporarily decrease populations.

SHIVERS: So I've lived here pretty much all my life.

And we really didn't start seeing many lionfish in this area until about '08, '09, somewhere around in that time.

SHIVERS: Shortly thereafter, there was, like, a large boom of them that just seemed to keep coming in and coming in, and...

The lionfish don't tend to run off, as you imagine they would, when being shot with a, a spear.

They don't even see us as a predator when we go down there.

They, there's no recognition that we're even there.

They just tend to keep on doing what they do.

FOGG: They're not very active hunters.

So, when you drop down a bait to fish for your snapper and grouper, lionfish are generally not going to eat that hook.

So, it really comes down to divers going out and harvesting lionfish with a spear.

KIDD: You don't spear lionfish like you would spear any other fish.

We take down something called a zookeeper, which is just basically a PVC tube with a, a funnel on, in the top of it.

And we also use this much shorter Hawaiian sling-style spear with a paralyzer tip at the end, with three barbs.

You can basically use the structure to push against it and push the elastic band back, and hold it here, point, and release to shoot the spear.

WASHINGTON: But spearfishing doesn't come without its risks.

As I learned on my dive with lionfish, you have to be very careful around them.

With 18 loaded venomous spines, they have a very dangerous side.

The venom is a defense mechanism.

One slip of the hand could lead to an intolerable pain, with symptoms remaining for weeks.

And it's probably, maybe like a jellyfish times 5,000-- I mean, it's, it's very painful.

Have you ever been hit by a stingray?

I got hit by a stingray in my foot, and that was, I thought, the most painful experience of my life until I got hit by a lionfish.

It was six hours of the most excruciating pain I have ever experienced.

SHIVERS: One of them actually went under my ring, and by the time we could get me back in to land, it was two-and-a-half hours later, and you couldn't even see my ring.

It was swollen up so bad, I had to be taken in to the hospital and they had to cut it off.

And it took about two weeks for it to really get back to the normal size.

WASHINGTON: Despite the danger, spearfishing could make managing lionfish populations possible, down to about 130 feet.

But scientists have made a troubling discovery.

Lionfish seem to be venturing beyond the diving range for spearfishing-- to deeper, darker depths.

What damage could they be doing down there, out of human sight?

♪ ♪ BALDWIN: Over the past ten years, we have been exploring the deep-reef areas from about 200 feet down to 1,000 feet.

Initially, when we started the sub diving, we didn't know half of what we were seeing, partly because none of these things had ever been seen alive, but more importantly, most of them had never been discovered before.

WASHINGTON: Marine biologists Carole Baldwin and Luke Tornabene have discovered over 30 new deep-reef species during their decade of research off the Caribbean island of Curaçao.

But then, they saw something they never expected.

We saw the first record of, of lionfish consuming a species that we didn't even have a name for yet.

So that kind of switched the, the lights on in our brains to say, "We gotta start catching these things."

WASHINGTON: But why lionfish would be hanging out deep is a mystery.

There's less food down there, it's barren, and cold, so it's a bit of a paradox, considering lionfish's relentless appetite and its many adaptations for complex reef ecosystems.

TORNABENE: The number-one priority right now is understanding the extinction risk that lionfish pose to deep-reef native fishes.

And to do that, our major goal is to collect as many lionfish from deep reefs as possible.

WASHINGTON: Each dive is six to eight hours long.

They'll descend down to 1,000 feet, searching for lionfish along the way.

The goal is to collect deep-dwelling lionfish to later analyze their gut contents.

But it won't be easy.

No one has ever done this before.

TORNABENE: Lionfish didn't choose to be captured by people selling them for the aquarium trade, and they didn't choose to be released in an entirely different environment, but they're here.

So it's not, not so much that we have a personal vendetta against these species, but lionfish are a threat.

And we're just beginning to understand how big of a threat that is, especially to these really sensitive deep-reef environments.

Yeah, so right now, we're descending to about 160 feet, making our way down to around 600 feet.

So this is all skeleton of old, old ancient reefs that are now home to a community of fishes that live only in this narrow slice of the ocean.

(man speaking on radio) Copy that, be advised, we are heading to, uh, around 600?

To around 600, 500, 600 feet for lionfish.

TORNABENE: Let's shoot some lionfish.

(machine whirring) TORNABENE (grunts): I don't know where the lionfish went, but he's around here somewhere.

MAN: Yeah, and we'll be here to find him.

TORNABENE: There he is, right there, right there.

CHRISTIAAN: Where?

TORNABENE: Down, straight down.

CHRISTIAAN: All right.

TORNABENE: All right, so we've got a lionfish here at 513 feet, and he's corralling some... One of the more common species down here, a rough-tongued bass.

Spearing a lionfish with a six-and-a-half-ton submersible, pulling it off the spear, putting it into a basket, reloading the spear, and firing again to shoot multiple lionfish on a dive was something that we were unsure if we were gonna be able to do.

TORNABENE: Right, right, right, right, right, right.

No, you're too high, you're too high, you're too high.

Right, we're right there, though.

He's, he's not moving.

To your right.

Now.

(machine whirrs) (whirring) Okay, I will now apply the anesthetic.

WASHINGTON: The anesthetic is used to numb and knock out the fish, preventing them from wriggling their way to escape.

They are tough, so it sometimes takes a few tries.

TORNABENE: Oh, there he goes.

(machine whirring) I forgot how hard this was.

If you're spearing when you're on scuba, and you, your, your spear gets stuck in the reef, you just grab it and pull it out, or if you miss a lionfish, you can reload in a second and fire again.

And once you've got it on the end of your spear, you just literally push it into a bucket.

Every step of that process, from finding the lionfish, to approaching it, to spearing it, to getting it off the reef and getting it to the surface, is exponentially harder with a submarine.

BRUCE BRANDT: Oh...

There you go, right.

That's the next one.

What the (bleep).

TORNABENE: (bleep) hell.

Nice shot-- straight back now, straight out.

CHRISTIAAN: Awesome shot.

TORNABENE: Okay, great shot.

Oh-- he's okay, we're going to have to do it again.

I'm going to get ready to reload.

WASHINGTON: The whole process is a precise unchoreographed waltz between piloting the sub and operating its robotic arms.

(machine whirring) ♪ ♪ TORNABENE: There he goes.

Oh, it bounced off.

WASHINGTON: Adding to the extreme challenge, the spear gun mechanism is starting to act up, which could compromise the whole dive, leaving the team with only one more day to get the samples they need to figure out what these lionfish are doing down there.

The spear gun isn't cocking very well right now.

Bent prongs are okay, we can fix that.

But if we can't reload it, then we're kind of screwed.

MAN: Those barbs are... MAN: Too good.

TORNABENE: Yeah.

MAN: Yeah, pretty good.

TORNABENE: Okay.

Good, okay.

(machine whirring) CHRISTIAAN: Yeah, yeah, yeah, yeah, that's it-- all right.

All right, keep it there, keep it there.

Yeah, bring it up, bring him up, bring him up-- yeah.

TORNABENE: Well, get out, get out in open water-- oh... (machine whirring) CHRISTIAAN: All right, oh, oh, oh... TORNABENE: Oh, good, good, good, good, good, good, good.

Good, head first-- swish.

CHRISTIAAN: Yeah, I'm going, I'm going, I'm going.

TORNABENE: Whoo!

(laughs) CHRISTIAAN: Nice job!

MATT GIRARD: That's one.

(all laughing) It's okay, we got one.

Whew!

(laughs) Hey, if this was easy, everybody with a submarine would be doing it, right?

CHRISTIAAN: Yeah, that's true.

Wow, all right!

I hope his stomach is full of important information, 'cause... CHRISTIAAN: What depth was that?

Uh, what did we start with?

You wrote it down, right?

GIRARD: We started with 564.

CHRISTIAAN: Oh, 564, okay.

WASHINGTON: After hours in the submersible, Luke and his team collected only one lionfish due to the malfunctioning spear.

If they can't fix the spear for the final dive tomorrow, they won't have enough samples to effectively analyze deep-water invasive lionfish.

Rallying hard against the clock, that night, they work on modifying the entire spear mechanism before morning.

♪ ♪ CHRISTIAAN: Port side is 2,000.

Starboard side same, 2,000.

And current depth is 475.

All starboards functioning.

Closer.

TORNABENE: Left, up.

Up, up, up, up-- there.

(machine whirrs) Nice.

WASHINGTON: The modifications to the spear gun pay off.

The sub becomes like the lionfish itself, and slowly creeps up on its prey.

When the moment is right, it pounces.

This time, the team is able to reload the spear easily and continue the hunt.

MAZZOTTI: As wildlife biologists, I can tell you that we did not become wildlife biologists to kill wildlife, but we realize the importance of doing that because of the other impacts that these species are going to have.

It's not something that we enjoy, but it is something, as biologists, we simply realize the necessity of doing.

TORNABENE: What's the count, Sarah, seven?

SARAH YERRACE: I believe it's seven.

All right.

I'll call that a victory for a dive.

♪ ♪ ♪ ♪ TORNABENE: Behaviorally, you know, when we find them in the shallows, they're doing a really great job at camouflaging themselves and ambushing prey.

Whereas when we look at them in the deep reefs, they're out in the middle of nowhere, just wandering out the open plains, hunting.

So, we already see some behavioral differences between shallow and deepwater lionfish.

So hopefully we'll see some diet differences, as well.

WASHINGTON: Luke will return to his lab to analyze the guts of these lionfish.

He's now seen firsthand how lionfish have infiltrated deep-sea ecosystems.

TORNABENE: Managing lionfish below scuba diving depth is gonna be a challenge.

It's a challenge that welcomes innovation.

So far, lionfish have been shown to not respond very well to many of the traps that are used to catch other fishes.

So, how do we remove deep-reef lionfish?

♪ ♪ WASHINGTON: Back in Florida, I join some researchers who are taking on this challenge.

They're testing a new lionfish trap, the Gittings trap.

It could be the next frontier in managing deep-sea lionfish.

♪ ♪ So this is a trap, the Gittings trap.

Gittings trap.

Let's get some of this gear out first.

Make sure everything is ready to go before we get on the boat.

There we go.

It's a lot easier to fix something in the parking lot, then fix it on a moving vessel.

Exactly.

We're gonna open it up.

There it is.

Wow.

Awesome, great.

So is this the future?

Is this what deepwater, you know, collection of these lionfish looks like?

So that's exactly the research that we're trying to find out right now.

We are currently in the beginning of those research processes in the Florida Keys to try to contain this invasive species in deeper depths.

WASHINGTON: What's the average depth that you normally put this down at?

BRYANT: So the goal to put, for these traps, is gonna be 200 to 300 feet of water.

So this is truly deep water.

Truly out of recreational diving limits, and deep water.

WASHINGTON: I help Alexa Bryant and Madalyn Mussey, A.K.A.

Moose, gear up the boat to test some traps.

The ultimate goal of their research is to make a trap that fishers can consistently use.

(chuckling) Sweet-- that was actually great.

Then you're just gonna lay that on top of here.

WASHINGTON: So it's gonna lay on here?

MUSSEY: Yep.

Legs out, there we go.

Perfect.

And just like that.

That was all it took!

That was it.

(laughing) WASHINGTON: In the final step before deployment, Lex attaches a sound recorder to the trap.

Why?

Apparently, lionfish make sounds.

Lex and Moose are experimenting with this device to get an understanding of their presence at depths too deep for cameras.

WASHINGTON: And how sensitive is the recorder?

They have to be pretty close to be able to record the sound, which is okay, because what we realistically want to have is them near the trap or on the trap.

So we'll be able to know if they're on the trap because they can't record super-far away.

Can you mimic a lionfish sound?

Oh, man-- Moose probably can.

(laughing) How do they do?

I don't know, I'm trying to think of the best way to imitate it-- like I said, it's like a purring, grunting, almost... Yeah.

It's like... Purring, grunting?

It's like a cat.

(hooting) I don't know how to say, it's, like, but it's more purring than that.

(tape player stops) WASHINGTON: A lionfish actually sounds like this.

(lionfish making pulsing sound) (tape player resumes) All we gotta do is just lift it into the water and let it drop... BRYANT: All right, Moose, you ready to go?

Yep!

Sweet, you guys got it.

MUSSEY: Just lift it.

BRYANT: Drop it over the side.

WASHINGTON: There we go, in the water.

MUSSEY: In the water, there it goes.

BRYANT: Awesome, that's it.

Let this out, let this out.

I just felt it hit the bottom.

Great.

WASHINGTON: There we go.

WASHINGTON: The trap is like a hula hoop with hinges that allow it to open and close.

Made with materials that can be found at the local hardware store, its simple engineering is impressive.

BRYANT: And I'm gonna let that over.

Throw that bullet, buoy in, toss it in.

Bye-bye.

Nice, there we go.

Nice.

We're ready to go.

WASHINGTON: As I witnessed in the Gulf of Mexico, lionfish cannot resist structure, so while other fish come and go, they stay.

It becomes a trap only when it's pulled up to the surface.

The net base closes around the congregated lionfish, taking them with it.

So far, they've caught as many as 20 lionfish in a trap, but the overall effectiveness of these traps remains to be seen.

Understanding the fish's deepwater behavior will help researchers continue to tweak the design or come up with new ideas altogether.

At the University of Washington, Luke Tornabene continues his investigation of Curaçao deepwater lionfish.

DNA analysis of their gut contents might give Luke and lab assistant Megan Ewing a clearer understanding of these deep-roaming invaders.

All right.

Here are the beauties.

(sniffs) First up is... Let's do this guy first.

Oh, that's a, that's a chunky belly.

That's a chunky belly.

That's a chunky belly-- all right.

WASHINGTON: Megan cuts open a lionfish stomach to scoop out the gut contents and puts them into a petri dish.

TORNABENE: Okay, so this is a fish.

Can't tell what type of fish it is, but you can still see the backbone.

So this might be one fish.

This could be ten fish, could be four fish.

Um, we'll know once we get the DNA sequence data back.

This is all gonna get ground up into a mortar and pestle and be put into a tube to be extracted.

It's like lionfish guacamole.

Mm-hmm.

While you're doing that, I'm gonna rinse out the stuff.

(chuckling): Lionfish guacamole?

I'm just registering now what you said.

(laughing) WASHINGTON: Over years of research, Luke has contributed to a large database of fish DNA.

He can cross-reference the species he finds in the lionfish's stomach with the depth of where that fish lives.

This means he can figure out not only what lionfish are eating, but where they're eating it.

After a week, Luke gets his first batch of data and takes the first look at what's inside the guts of a deep-reef lionfish caught at 574 feet.

There were two species inside of its guts that jumped out at me.

The first one was this species of soldierfish, which occurs at around 500 or 600 feet.

So that's not a surprise.

So that tells me that the lionfish down deep are eating species that live down deep.

Now, the cool thing that we found, though, was that one of the species inside of the lionfish's gut was this species of damselfish.

These damselfish are probably the most common fish you'll see snorkeling, uh, on a coral reef.

So to find them inside of the stomach of a fish at 574 feet is, uh, pretty surprising.

So right off the bat, we know that this deepwater lionfish is eating both shallow-water prey and deepwater prey.

WASHINGTON: Lionfish digest their food extremely fast.

So Luke's eye-opening discovery means that this deep-reef lionfish came up to the shallows to feed and then traveled back down within a matter of hours.

TORNABENE: In my eyes, it's actually a better thing that the lionfish are coming up, because it gives them a chance to get removed by recreational fishermen or commercial fishermen.

If we start sequencing the guts of all of these dozens and dozens of deepwater lionfish, and every one of them has something shallow in its stomach, that's good news.

WASHINGTON: This is just the beginning of the research, and if this data trend continues, it unlocks many more questions.

Like, why don't the lionfish just stay in shallow water?

Why go down deep at all if there is less food there?

No matter what, invasive lionfish have the potential to impact hundreds of thousands of people who make a living through fisheries in the Caribbean.

But some countries, like Curaçao, might be flipping the script on the invader.

Without traps, boats, or even scuba gear, two local free divers start their evening along the rocky coast.

♪ ♪ Joline ten Haken and Farra Figaroa have taken up hunting lionfish for side income.

I know Joline from my swimming club.

And, yeah, we met there, and one time she asked me, "Oh, do you want to go hunt lionfish with me a day?"

I was, like, "Okay, we can try one day."

And then I started doing it.

Almost every weekend, we catch lionfish, yeah.

♪ ♪ TEN HAKEN: You feel very free because you're without any equipment.

It's just ourselves and our, our bodies and our stamina.

♪ ♪ There's sea all around the island, and if there's something that Curaçao has, it's sea and fish, so it's really good to go out here and, and fish.

♪ ♪ ♪ ♪ One of us has got the zookeeper, and the other one went looking for fish.

And as soon as we saw one, we just go down and we, we try to catch him.

FIGAROA: Yeah.

♪ ♪ Yeah, I also do it as a side job.

I'm 15 and I always wanted to have a side job and get a lot of, a little bit of money to buy things.

♪ ♪ No, it's a really good day.

TEN HAKEN: Yeah.

FIGAROA: Yeah, like, nine kilos?

TEN HAKEN: I guess.

FIGAROA: It's, yeah, I think it's nine kilos-- it's a lot.

♪ ♪ ♪ ♪ Now we're going to put 'em in a... (speaks world language) TEN HAKEN: Cooler.

Cooler, and then we, we bring it to a restaurant where they sell them, where they sell the lionfish, and they make a lot of dishes.

TEN HAKEN: It's very funny story.

In fact, Farra actually didn't eat fish before she started hunting lionfish.

And now she, she hunted, hunts lionfish, she had to start eating them, and she actually really likes them.

WASHINGTON: Farra and Joline are two of the many divers on the island who have helped turn the lionfish's Atlantic invasion into a commercial opportunity.

As awareness builds, invasive lionfish are becoming an increasingly popular local dish.

The fish can be used to create island favorites, whether it's ceviche or fried whole.

And the lionfish are not just caught for eating.

Some businesses are finding creative ways of using every part of the lionfish's body, like the venomous spines, to create jewelry and other products.

Hola!

WOMEN: Hola!

Todos bien?

Sí.

Pescado.

When I was a kid and was snorkeling and diving here, there were so many fish, and also a lot of big fish.

And when I returned after ten, 15 years, you didn't see as much fish anymore.

You saw the damage on the reef, on the coral reefs.

From there, I got into catching the lionfish, first to control the population.

And from there, selling it to restaurants.

And from there, the jewelry to, to make a real life out of that.

I definitely see that it can be commercialized, especially if you use more of the fish, and I definitely see a future there, yeah.

Maybe even a franchise, you never know.

(laughs) WASHINGTON: The key to lionfish management might be, turn them into menu items, earrings, sneakers, whatever people buy-- because businesses that revolve around invasive lionfish not only support the ecosystem, but the local economies, too.

VALEK: It is so fresh.

I don't think it gets fresher than what we... FOGG: Nature tends to find a way of figuring things out.

While lionfish may be here to stay, they're going to find their place in the ecosystem.

The ecosystem could not support 200 or 300 lionfish on a single reef site, but it certainly can support maybe ten or 20.

WASHINGTON: There's no debating that lionfish have disrupted the current balance of biodiversity along the Atlantic coast.

Is it being destructive to ecosystems because it's a villain?

No, the lionfish is just being... a fish.

MAZZOTTI: A lot of people want to say or, or ask the question, "Well," you know, "aren't these things going to, to balance themselves out?"

Probably, but at what cost?

We could be losing a native species that have very important roles in the environment that are not replaced by a non-native species.

SANTANA: Biodiversity can be valuable because of its aesthetic value, or by the appreciation that we have over this, all these life forms that have evolved over millions and millions of years.

If we value that, then I think we have still the responsibility to do something about this invasive species.

TORNABENE: It's crazy to think that one species can have such a huge impact in such a short period of time, but then there are parallels.

It's not unprecedented, what we're seeing, but it's certainly alarming.

MAZZOTTI: You know, "The biggest invasive species are humans."

Ooh-- maybe we are.

Pretty much everywhere where humans are now, they're not native to.

It spreads.

Well, we sure spread.

Has negative impacts...

I don't know.

Should human beings consider themselves above these other species, or are we part of the ecosystem and realize that yes, we have our impacts, but we like each other, and so the rules are different for us?

WASHINGTON: Humans have moved so many species all over the world for millennia, like the cherished non-native honeybee.

We now rely on it.

So 500 years from now, will people embrace the lionfish as critical to the Atlantic and Mediterranean ecosystems?

Will it become a beloved fish for its beauty and taste?

The lines that divide invasive, non-native, and native can be blurred.

And for better or worse, invasions are now part of the global ecosystem.

But with each invasion comes a new discovery of how nature endures, and adapts, shining a light into uncharted waters.

♪ ♪ ♪ ♪ ANNOUNCER: This program is available with PBS Passport and on Amazon Prime Video.

♪ ♪ ♪ ♪