(mellow music) - [Narrator] Florida.

It's nearly 1,400 miles of coastline, support a diverse variety of fish, making the Sunshine State a saltwater angler's dream.

- [Mike] It's the saltwater fishing capital of the world, is how Florida touts itself.

It's definitely a big economic driver within the state.

- [Narrator] Saltwater recreational fishing has a $9.2 billion annual impact and supports more than 88,000 jobs in Florida.

But there's trouble in paradise.

- [Angler] Aw, that's not nice!

- [Stephen] Increasingly in the last several years, recreational fishermen have noted that a lot of the fish that they're bringing up are getting hit by sharks on the way up.

- [Narrator] Researchers call this depredation.

- [Rick] The shark encounters now are on a daily basis, and in my career, it wasn't that way up until two or three years ago.

There's times where I won't go to a spot because I know from three days before, "Oh man, the sharks were so bad there."

I believe that now, the shark numbers are outta control with certain species.

- [Demian] Sharks in the U.S.

Atlantic and Gulf have increased in the past two decades, and that's a great thing because that was by design where there's a lot of management being put in place.

- [Marcus] We've done a really good job of protecting and rebuilding these populations after they were historically overfished.

It's a conservation success.

However, there are consequences for these increases in predator population.

- [Narrator] Now, scientists are testing shark repellents to see if they can help minimize this human-wildlife conflict.

- [Demian] We've got the brains as humans to outsmart the sharks, at least some of the time.

- [Laura] There are a few different kinds of repellents.

There are some that will emit electrical pulses and then there's the idea of the permanent magnets.

- [Jack] If we can find a way to deter the sharks from actually coming up too close, I think that's gonna benefit everybody.

(light pensive music) - [Narrator] How do these shark repellents work?

And how are researchers evaluating their effectiveness?

(mellow moving music) (mellow moving music continues) - [Announcer] Major funding for this program was provided by The Batchelor Foundation, encouraging people to preserve and protect America's underwater resources.

Additional funding was provided by the Parrot Family Endowment for Environmental Education.

(pensive music) - [Narrator] Sharks, the ultimate apex predators.

Loved by some, loathed by others.

These keen hunters illicit strong emotions among conservationists and anglers.

- There was a major escalation in shark fishing in the U.S.

in the 1980s.

And that was largely a response to the opening of the Chinese economy and sort of a boom in demand for shark fin soup.

- It drove down a lot of shark populations dramatically.

By some estimates, shark populations declined by 50%, 60, up to 90%.

- And it took until the early 1990s for the federal government to develop a management plan for sharks.

And the idea there was to make sure that these populations would be sustainable.

- [Narrator] Sharks reproduce slowly, and it takes decades for populations to recover.

- [Demian] We are now seeing in the mid-2020s, a positive trend, which is what we want to see.

There's a recovery happening.

- We're probably still nowhere near what the historic levels were a hundred years ago, but we're getting there.

And at least for some species that have a faster generation time, the populations are coming back more rapidly.

Others have a very slow population regrowth time.

(pensive music) - A lot of the species, I believe now, are out of balance.

What I've seen happen, years and years of being on the water, you would see sharks, but those sharks were really afraid of the boats.

Now they hear the outboard, "Oh, that's the dinner bell."

(light pensive music) - [Narrator] Aware of the problem, scientists are now independently testing commercially available repellents that promise to be effective.

- There's a company called Sharkbanz that makes bracelets for surfers.

And the idea is that it deters sharks from biting surfers.

They have now taken that same technology and made it into a depredation deterrent called the Zeppelin.

- [Narrator] The Zeppelin is a magnet that's meant to irritate the sharks' unique ability to sense electrical fields.

- If you look at the head of a shark, you'll see that there are little pores scattered all over the surface of the head.

And each of those pores leads down through a thin tube that's filled with a jelly-like material.

It's a highly conductive gel that will conduct an electric signal from the outside environment and the seawater into the head of the animal.

When they're sensing prey, they're sensing the actual electric field produced by the prey because the concentration of ions in the body of the prey is different than the seawater.

And so as a result of that, the little prey fish is constantly leaking little ions into the water.

Basically, what's happening is that fish becomes a little battery.

And that voltage can be tiny, microscopic, like a billionth of a volt per centimeter.

- [Narrator] When a shark approaches a magnet, it induces an electric field around its own body that's stronger than the electric fields of its prey.

- And it's enough to say, "Whoa, what is that?

I don't know, and I'm gonna leave now."

- It kind of is supposed to basically overwhelm that sensory system because it's not a stimulus that they would normally detect.

- [Narrator] While still a master's student at Florida Atlantic University in Boca Raton, Laura Jones tested how well the magnet can deter sharks in the presence of bait.

- Because obviously a shark, you would think, there's a fish here, I'm going to eat it.

- [Narrator] The research team went offshore with Florida Shark Diving, a tour operator in Jupiter, Florida.

- They're accustomed to chumming up sharks and bringing them up to the surface for their clients to jump in the water and snorkel and then see the sharks.

These sharks are right on the reef ledge.

It's where a lot of the recreational fishermen are out there.

And so we know that we're in the same place dealing with the same sorts of species that these recreational fishermen are gonna be encountering.

- [Narrator] To observe the sharks' reactions to the magnet, Laura deployed what is known as a BRUV, which is short for baited remote underwater video.

- [Laura] We have a long piece of PVC that's wrapped in pipe insulation to allow it to float.

And then one arm has a camera, which is recording the interactions of the sharks with the deterrent, and the other arm has a mesh bag with the bait and the deterrent.

- [Narrator] Laura also tested the same setup with an identical, non-magnetic control device to see if the sharks reacted differently.

- Sure enough, what we found is the sharks would bite at the mimic, the non-magnet, significantly more than they would bite at the actual magnet.

They were repulsed by the magnet significantly more than they were by the control treatment.

So this indicates that, at least for this particular scenario, the magnet seemed to work, it seemed to keep the sharks away from the bait.

- The four species that I was able to study were the sandbar shark, the bull shark, the lemon shark, and the silky sharks.

The most sample size that I got were with the sandbars.

And so although the other species, we didn't have enough numbers to really statistically say this is effective, with the sandbars, we were able to.

It isn't effective 100% of the time, but a majority were deterred away from it.

(pensive music) - [Narrator] Up the coast, colleagues at FAU Harbor Branch in Fort Pierce decided to test the magnet while fishing in areas where depredation is a problem.

- So we have our rod set up here.

We have a inline camera that is going to be looking down and filming everything that happens at depth.

So we put this in line and this comes down to our hook, which we'll attach our bait to, and then below that is the deterrent here.

- [Mike] It's basically meant to take the place of a sinker that you would incorporate in your fishing gear.

It's about six ounces.

- And when your fish gets caught and you're retrieving it and pulling it back to the surface, the Zeppelin hangs in front of the shark, between the shark and your fish, and the idea is the shark would encounter that field and get repelled before getting to your fish.

- We fish with an active deterrent, and then we have somebody fishing with a dummy or control device that looks exactly the same, same size, same shape, same weight, no magnet, so it doesn't have any electrical field associated with it.

You fish those for the same amount of time, fish at the same spot at the same time.

- [Narrator] Each time the anglers catch or lose a fish, they review the camera footage to see what happened beneath the surface.

- Look at the bull shark.

- [Mike] Oh my god, this footage is great.

Did you get eaten by a shark?

Did your fish get eaten by another fish?

Did you get snagged on the reef or the wreck and that's how you lost your gear?

- In addition to sharks that we have out there, we have large Goliath grouper, which are known to depredate reef fish.

We have barracudas out there.

And for those species, the device is not intended to deter them.

We have a few indicators that suggest that it is going to be an effective deterrent.

For example, we haven't caught a single shark using the Zeppelin yet.

To me, that indicates that, you know, the sharks, they're not comfortable enough to bite the hook.

We have caught several sharks using the control device.

- Oh, two of 'em!

- Oh man, look at that!

Well that explains it.

- And there goes the fish.

- As far as its behavior against struggling fish, it's a lot more complicated than we originally thought.

So we've seen other species depredating the catch.

Over half of our videos, we see sharks, of those, a quarter of the time they seem interested in the catch.

And then we've had just a few depredations, mostly on the control device.

But we have recorded, I think, one or two on the Zeppelin.

So it's not a hundred percent effective tool, but we think it's effective enough that it can make a long-term difference.

- [Mike] It's not meant to be a silver bullet solution.

There is no one silver bullet solution to the depredation challenge.

It's one more tool in the tackle box.

- [Narrator] To gain a more in-depth understanding of what anglers are experiencing, the researchers analyzed posts in the Facebook group Sportsmen Fighting for Marine Balance.

- Which was started by a group of local anglers here in the Jupiter, Stuart area.

They were just frustrated with losing their catch.

They gave us access to the Facebook group, and so we used that to get a broad qualitative characterization of what's kind of going on with depredation in these fisheries.

- [Narrator] Next, the team designed a quarterly survey that went out to all saltwater fishing license holders in the state of Florida.

- [Mike] We received over 2,200 responses.

About 98% of the people who responded to the survey agreed to participate, which is incredible.

- And that in and of itself is, I think, an indication of how motivated people are to talk about this topic and how important it is to them.

- [Mike] We had a couple overarching trends that we saw.

Just under 50% of anglers had said that they had experienced depredation in the past three months while they were fishing.

There were hotspots both regionally and temporally.

We saw a high number of respondents experience depredation in the spring and summer.

- It was a lot more common for individuals fishing deep water, a snapper and grouper as well as pelagics.

- [Narrator] And certain shark species are causing more problems than others.

- [Mike] By and large, bull sharks and sandbar sharks were the two most frequently reported depredating species.

- [Narrator] This finding was further confirmed with genetic testing.

- We trained anglers and showed them how to take a genetic swab of the bite wound.

- And we would run DNA analysis on those similar to like a crime scene, trace DNA.

It was good to take these accounts and get them into the scientific literature.

And it has actually led to some favorable outcomes.

- [Narrator] NOAA Fisheries is currently conducting a sandbar shark stock assessment and planning to do the same for bull sharks starting in late 2027.

- To see if there are management changes that could be implemented.

So, you know, that data that the fishermen had plus the data that we obtained from the surveys and the genetics really kind of was an impetus for this, you know, push to assess those two stocks.

- I think folks are energized that this challenge to them is being recognized at a national level.

And we're just here to help understand the problem and seek solutions so that we can support sustainable fisheries but also conserve highly susceptible species like sharks.

- Anglers might think, well, there's an overpopulation of sharks now that it's way over what it should be.

Whereas as scientists, we know that they don't really overpopulate.

They're not like cockroaches.

They reproduce very, very slowly.

- [Narrator] Researchers say there are several factors that exacerbate the perception that certain shark species are out of control.

- We have a slightly increasing population of sharks, a increasing population of anglers and boats and availability to get to areas where we never used to be able to get to before, coupled with a struggling fish population.

- [Narrator] The state of Florida issued more than 2 1/2 million saltwater fishing licenses in fiscal year 2025, an increase of more than 231,000 licenses over a 10-year period.

- And the compounding factor to that is that we now have social media which allows these interactions to be widely disseminated very quickly.

And so whereas before someone lost their snapper to a shark, it was a story they told their two closest friends.

Now they post it on Instagram or Facebook, and now it's seen by thousands of people instantly.

- I think it's very likely that people that have been fishing for much longer remember a time when depredation was a common event, and they probably noticed a bit of a lull when the shark populations went down.

And so now, if they're still fishing, they're just going, "Oh, this just got back to how it used to be."

Whereas younger people didn't necessarily experience that.

Their perception of it is that this is this big new thing which in fact it's not.

(lively music) - [Narrator] Ernest Hemingway wrote about depredation nearly a hundred years ago.

- He was a great outdoorsman and a great fisherman.

And so he's documented the ways in which he dealt with depredation, particularly back in the 1930s around Bimini in The Bahamas.

Now, this was a time when no one had been able to land intact bluefin tuna in that region, but anglers had just figured out, there was a certain time of year where those fish were moving through and they were susceptible to capture on hook and line.

And so Ernest Hemingway set out to do that.

And he failed multiple times.

Like he'd bring up these massive bluefin that had just been completely chomped by sharks until he figured out, "Okay, I need stronger gear," and he needed to fight the fish really quick.

And that's fascinating 'cause you fast forward almost a hundred years, we're like refiguring out the same sorts of things.

If anglers can change some of their behaviors and some of their angling techniques, that's one way that we can sort of get around this issue.

- Certainly fishing heavier tackle, heavier line is helping.

When you're a professional fisherman like myself, we have to lead the charge in some form or another, whether it's conservation, whether it's trying new products.

And I think of course I'd be open to seeing if these repellents work.

- [Angler] Oh, I'm getting eaten.

Uh-oh, I'm getting eaten.

(cheerful music) - [Narrator] Shark repellents were first developed in the U.S.

during World War II to protect sailors and pilots from shark attacks.

- Probably the earliest scientific attempts to develop shark repellents was through the Navy when they realized that they needed to have some way to protect their downed pilots, adrift in shark-infested waters.

So they tested lots of different kinds of chemicals.

The two most effective compounds were copper sulfate, and believe it or not, the compounds from decomposing shark meat, ammonium acetate.

So, they decided to use a copper acetate, combined with a dye called nigrosin.

The combination provided an olfactory inhibition to repel sharks and a visual way to protect the downed pilot from being seen by the shark.

It was called Shark Chaser, and it was packaged in neat units such as this and were applied to the jackets of pilots.

And on life jackets that only had pouches, they had a repellent package with the same compound in it.

The Shark Chaser was effective in close proximity to the diver, but once it started to spread and become diluted, then its effectiveness decreased drastically.

It was more effective as a psychological support mechanism for the downed pilots.

- [Narrator] In later years, the Navy tasked Mote Marine Laboratory in Sarasota to continue research into shark repellents.

- [Carl] Perry Gilbert, who was director of Mote Marine Laboratory from 1967 to 1978, was one of the early pioneers in research to develop shark repellents.

- [Narrator] Dr.

Gilbert designed shark tanks with channels that had electrical shields across them.

- Sharks would come to the shield and turn around and go the other way.

The problem is it's really restricted to the size of the shield, and may really have only effective application to fishing trawls and things like that as opposed to large beach areas.

- [Narrator] Perry, together with collaborators, also explored the idea of different body armor, including a suit made of Kevlar.

- Kevlar, at that time, was being used in bulletproof vests.

So they studied whether the Kevlar could protect a diver.

Turns out the sharks tore right through the Kevlar like it was butter.

So the Kevlar, even though it stops a bullet, it couldn't stop the shark from ripping through the Kevlar material.

And they developed a bag-like device where a downed pilot could get in the bag, which would then keep any body fluids, blood, sweat, whatever, from getting out into the water to attract the shark.

It also protected him visually from the shark because the part underwater was a drab color and not attractive.

This was called the Johnson Shark Screen and proved to be very effective and was used for, for many, many years by the Navy.

- [Narrator] Today, shark researchers at Mote are investigating an electrical pulse device that anglers can attach to their rod and reel.

- The product we're currently testing is called the Shark Guard, and it is manufactured by Fish Tech Marine.

You attach it maybe 25 centimeters away from whatever you don't want the shark to bite.

This thing fires periodically every second.

- [Jack] It's similar to a static shock that you might do as a kid dragging your feet on the carpet and then just touching your friend, and they get a little, little jolt.

- [Demian] But to a shark that's very sensitive to electric fields, it's much more annoying.

They really don't like that sensation.

- [Narrator] To test the effectiveness of the device, the shark researchers set up an experiment with sandbar sharks in Mote Marine Laboratory's Marine Experimental Research facility.

- Which houses two very large 60 and a 40,000 gallon tank.

So that enables us to keep large and small sharks in captivity.

We have a fishing rod.

We tie the device to that, and we tie the bait to the recommended distance that the manufacturer has suggested.

And then we wait for the animals to settle, and we just lower it on the opposite side of the tank where the animal's at and slowly drag that device into the middle.

We're really just looking for them to come in, seek food, and encounter the device.

And basically, we record all the stuff with overhead cameras and in-water cameras.

And then we write down each interaction that we've seen from the animal.

- [Demian] The device will, sometimes it'll be on and then sometimes it'll be off.

And essentially what we are trying to see is what's the difference between when it's off, which is the control and on, which is the treatment.

When the device is off in these experiments, what typically happens is the shark just, as soon as it perceives the bait that it wants, it just comes in and takes it.

It's just like bam.

Absolutely no stop to it.

When the device is on, the sharks, when they encounter the pulse, they will typically turn away hard.

They really don't like it.

They turn, come back around.

Eventually they might get the bait, but the idea is, is that they turn away several times.

The first species we worked testing the Shark Guard was the bonnethead shark.

That's a small species of hammerhead.

- At the time, there was a two-second delay between each pulse.

And we saw them turn and quickly come back in-between pulses and take the actual prey that we were offering.

So we had made a recommendation to shorten that time to one second, and it changed things immensely.

It will buy you three to four times the amount of time before the animal actually can acquire that bait.

What that means is up to one to two minutes in some cases.

That's plenty of time for any angler to really land their catch before the shark comes and takes it away.

- [Narrator] Early field tests of the device are showing promise as well.

- We have a line, and we send a piece of bait down, and we have the device positioned close to it.

We'll put that in for 10 minutes, which should be more than enough time for a shark to sweep in and take that bait.

We have a camera positioned on the line so we can see if that happens.

- [Narrator] It didn't take long for a sandbar shark to come in and investigate.

- What we saw in the video is that the animal encountered that pulse device, did not like it, kept trying a few more times and finally gave up.

Said, "This is not worth the effort," and it sank back down into the depths.

So we were crazy excited to see that because that's the first time we've had an interaction with a shark in the wild with this device, and it showed a very positive result for us in terms of mitigating any type of deprivation from sharks.

- [Angler] American red snapper!

- [Angler] Whoo!

- [Angler] Nice work!

(mellow music) - [Narrator] Researchers say they are encouraged to see shark repellents showing promise at addressing depredation.

But they also acknowledge that this complex issue will likely take multiple approaches to keep anglers happy and sharks thriving.

- Scientists like myself and others, we're gonna keep working on solutions.

- Fortunately, we're being heard, and I think we all are coming together, science and recreational, about what are we going to do about this?

- Finding all the different tools that could be available to anglers, scientists, and managers to address and mitigate this problem is the ultimate goal.

(mellow moving music) (mellow moving music continues) (mellow moving music continues, then fades) - [Announcer] Major funding for this program was provided by The Batchelor Foundation, encouraging people to preserve and protect America's underwater resources.

Additional funding was provided by the Parrot Family Endowment for Environmental Education.

(energetic music)