NARRATOR: Locals are still talking about what happened here last spring. It was a perfect day for fishing. MAN (off screen): Whoo! That's a big one. NARRATOR: But below the surface, two heavyweights of the shark world were on a collision course. MAN (off screen): That's insane! NARRATOR: It's a rare face-off between a bull shark and a great hammerhead prompting a team of experts to dig deeper into the encounter... MAN: One, two, three. NARRATOR: ...in the hope to uncover surprising behaviors... VALERIE HAGAN: We might have a predation. DR. YANNIS PAPASTAMATIOU: I have no idea what is going on here. NARRATOR: ...and come face-to-face with two of the biggest... MAN: NARRATOR: ...baddest... DR. MIKE HEITHAUS: Look out! Look out! NARRATOR: ...super predators on the planet. But which one takes the crown? Several people captured the event in the spring of 2021. MAN (off screen): That's insane! NARRATOR: The video quickly went viral. A bull shark chases a monster great hammerhead and pins it to the beach. There's no escape. The bull shark circles... followed by a second. Then the hammerhead is ripped to pieces. Marine biologist Dr. Mike Heithaus was floored. DR. HEITHAUS: I've never seen anything like this. A lot of times, we've got these big, top predators but they don't usually pay much attention to one another. In this case, it was a head-to-head battle. We had a winner and a loser. NARRATOR: An encounter of this magnitude is rare. It provides the perfect opportunity to understand how these apex predators stack up in a one-on-one battle. Fishing Charter Captain Mike Myers saw the whole thing. CAPT. MIKE MYERS (off screen): Oh, my gosh. DR. HEITHAUS: Can you walk me through what happened that day? CAPT. MYERS: I had clients onboard. I just saw it. "Oh, my gosh, a huge hammerhead." DR. HEITHAUS: How big do you think that hammerhead was? CAPT. MYERS: I'm estimating somewhere around 12 to 13 foot. They kinda swam up towards the beach and people were over there screaming and hollering because he kept beaching himself. Every once in a while, one of the bull sharks would come up and grab 'em by the tail and jerk it and then swim up real fast. And all of a sudden, you look down... and then... the sand just exploded. We looked as hard as we could after that whole mess happened. There wasn't a fin on the ground. There wasn't anything in the water. He was gone. DR. HEITHAUS: You've been out here a long time. CAPT. MYERS: I've seen a lot of bizarre things with these sharks over the years. Oh, my gosh. I've never seen anything close to that. NARRATOR: Big sharks are known to attack and eat smaller sharks. But these two apex predators are powerful equals. The hammerhead, sleek, massive, and can turn on a dime. In a one-on-one fight, they are fearsome opponents. Great hammerheads can grow to be nearly 20 feet long, almost twice as big as the bull shark. Bull sharks may be in a different weight class, but they pack a lot of punch for their size. Stocky with a superior jaw strength. Bull sharks have a bad reputation for a good reason. DR. HEITHAUS: Lots of questions come out of this video. CAPT. MYERS (off screen): Oh, my gosh. DR. HEITHAUS: They're both top predators. You don't really think about one going after the other. So to see them battling it out is incredibly unique. If these sharks are going head-to-head, who's gonna come out on top? When top predators battle it out with one another or have interactions that can cascade through the rest of the ecosystem. So learning about the interactions among top predators is really important. NARRATOR: To investigate this surprising new dynamic, Mike has assembled a team of experts. DR. HEITHAUS: We're gonna try to get to the bottom of this by first studying bull sharks and great hammerheads separately and then going to a place where they might come together to see if it's a collision or if they go their separate ways. NARRATOR: First up, the great hammerhead. Team member Erin Spencer leads this part of the investigation. ERIN SPENCER: They're one of the most recognizable sharks in the ocean. When you see that cephalofoil and just see the eyes and how big that head can get, it really kinda takes your breath away. NARRATOR: Famous for its elongated head extensions called cephalofoils, the great hammerhead has an advantage over the bull shark in its uniquely positioned eyes. With a nearly 360-degree field of vision, it has the best depth perception of any shark, giving it pinpoint accuracy on attack. Its wide head also contains more electrosensory receptors than other sharks. SPENCER: All of these pieces come together to make them as good a predators as they are. But because they're so big and wide ranging, they're really difficult to study. We use something called biologgers which are essentially animal mounted data collecting devices. And the biologgers are like Fitbits for sharks. DR. HEITHAUS: So by putting that on the back of the shark, it can give you a three-dimensional path of how it's moving through its environment, how it's speeding up, slowing down, pitching, rolling. We just gotta get out there, catch a hammerhead and get one of our accelerometer tags on its dorsal fin. NARRATOR: While Erin readies a hammerhead 3D biologger, Mike heads back out to the scene of the crime... to look for more clues with Captain Myers. For a few months a year, this relatively deep channel west of Fort Myers is a fisherman's paradise. MAN: I told you it's a big one. DR. HEITHAUS: It is packed full of these giant fish called tarpon. They could be more than 200 pounds and they're one of the world's most coveted game fish. NARRATOR: As the water warms each spring, thousands upon thousands of tarpon migrate north to Boca Grande to spawn. Anglers come from all over the world to try their luck. As they fight these mammoth fish, bull sharks and hammerheads cross paths in their quest for easy prey. Over the years, Captain Myers who captured the video of the attack has observed both predators on a daily basis. DR. HEITHAUS: Have you ever seen the bull sharks or hammerheads go after tarpon that aren't hooked up? -So-- -CAPT. MYERS: Oh, God, yeah. The bull sharks will get around these schools. That's 10,000 fish running up and down this beach. I have seen numerous, numerous times the hammerheads come in. People don't realize how agile that fish actually is. NARRATOR: What Captain Myers recalls next intrigues Mike. CAPT. MYERS: And what's really cool, when a hammerhead comes, bulls aren't around. They don't want nothing to do with it. NARRATOR: It contradicts the behavior Captain Myers captured on video a year earlier. CAPT. MYERS: The hammerheads come in and there's no more bull sharks. What I saw floored me. NARRATOR: The team decides to deploy the hammerhead tag right here in Boca Grande Pass. But the next morning, Mike gets some bad news. (sighs) DR. HEITHAUS: Unfortunately, we just heard from Erin and she's been exposed to COVID, so she can't make it out today. But she's programmed the tag for us and we've got a crew. So we're gonna go out and try to catch a great hammerhead. Anything we need to be thinking of to get this on for you? Not having her on the boat is gonna be a big challenge 'cause that's one less experienced person to handle a shark. But hopefully we can get it done and get some great data for. NARRATOR: Mike will work with Mote Marine Laboratory biologists Valerie Hagan and Jack Morris to see if they can get the tag on a hammerhead by themselves. HAGAN: Jack and I work with one another for most of our field work. JACK MORRIS: That's fishing, right? So you always come up with the expectation that you hope you're gonna get what you want. And when you do, it's amazing. NARRATOR: They set ten fishing lines along the mouth of Boca Grande Pass, its prime hammerhead territory. DR. HEITHAUS: That is a piece of stingray. And a hammerhead loves stingrays. They'll actually use their head to pin 'em to the bottom to hold them down so they can get a bite. NARRATOR: While they wait for a catch, Mike preps Erin's 3D biologger. DR. HEITHAUS: What it can do is help us recreate a three-dimensional track of the hammerhead. And it samples at such a fast rate. We can see if they're doing burst swims to try to catch something. And you're out here in Boca Grande, we know that bull sharks and hammerheads can be on a collision course. So learning more about each is really important to understand how they're going after a prey or are they maybe eating one another? NARRATOR: By the time the last line is in the water, it's time to circle back and check the first where something is already on. DR. HEITHAUS: So, this is a blacktip shark and they're one of the more common species along the coast of Florida. And these are snacks for great hammerheads. NARRATOR: Catching the hammerhead's prey is a good sign for the mission. MORRIS: Here goes. Okay. Oh, there it goes. DR. HEITHAUS (off screen): And away. NARRATOR: The next hook looks more promising. DR. HEITHAUS (off screen): Yeah, it's dragging it. HAGAN: I saw the buoy actually made a splash. DR. HEITHAUS: Yeah. This is not nurse shark, not blacktip. -Yes! Hammerhead! -HAGAN (off screen): Whoo! -DR. HEITHAUS: Whoo! -HAGAN: That's a biggun. DR. HEITHAUS: Two of 'em. There's another one right here. -HAGAN: What? -DR. HEITHAUS (off screen): We got two hammerheads. NARRATOR: The second hammer is free swimming, analyzing the situation. Hammerheads are known to eat their own when the opportunity arises. HAGAN (off screen): We might have a predation about to happen. NARRATOR: They need to secure the hooked shark as quickly as possible. But there's another problem. HAGAN: I tried to pull on that, but there's no give. DR. HEITHAUS: We've got a hammerhead here wrapped up in a crab pot. NARRATOR: Until they untangle it, the hammerhead is a sitting duck. And the second hammerhead circles closer and closer. DR. HEITHAUS: Okay. You gotta go to the right. -You gotta get reverse. -HAGAN (off screen): Port side? MORRIS (off screen): We gotta get him away from that other shark. DR. HEITHAUS: I know. Ahh! Look out! Look out! Look out! Look out! MORRIS (off screen): How about we swing it out? NARRATOR: The team struggles to untangle the line before the great hammerhead becomes shark bait. DR. HEITHAUS: (grunts) Forward. Let go. Let go. Let go. -Yes, free! -HAGAN (off screen): Oh. -DR. HEITHAUS: Nice job. -HAGAN: Yeah. (laughs) DR. HEITHAUS: Okay, we just have the shark now. -HAGAN: Holy cow. -DR. HEITHAUS: That is a big animal. Well, we got a really nice 10-foot-plus great hammerhead. We have another slightly smaller one around. This is the exact size we want for this tag. Oh, beautiful. I don't see the other one now. HAGAN (off screen): We probably spooked the other one off. NARRATOR: But the battle to subdue the shark is only beginning. MORRIS: You know, the hairs on your skin start to stand up a little bit. Once you get what you want, you wanna keep it. DR. HEITHAUS (off screen): Look out. Look out. Look out. -Don't try this at home, kids. -MORRIS: Nicely done. HAGAN (off screen): Definitely female. Hello, gorgeous. NARRATOR: Val attempts to secure the shark's powerful tail. -DR. HEITHAUS: Get it? -HAGAN (off screen): No. I couldn't get that lower lobe. It was close. NARRATOR: Handling a shark this big is proving difficult without the help of their teammate Erin. -(Hagan grunts) -DR. HEITHAUS: We're gonna move the top lobe. (grunts) We're gonna lose this shark. -HAGAN (off screen): Okay. -(grunts sharply) NARRATOR: The urgency is compounded by the fact that great hammerheads are fragile. MORRIS: There's theories that they fight an awful lot when they're on a hook and they overexert themselves and they run out of energy very quickly. HAGAN: It's wearing us out. It's wearing her out. And we want this animal to survive. DR. HEITHAUS: Hey, slow it, slow it. NARRATOR: The shark zooms around to the other side of the boat, trying to throw the hook. DR. HEITHAUS: Jack, can you come back? MORRIS: Yeah. Okay, what do you want me to do? DR. HEITHAUS: I want you to get the dorsal. Let's clamp this thing on and get it. Otherwise we are gonna lose this animal. -MORRIS: Alright. NARRATOR: Finally, the tail rope is secured. HAGAN: Come on. DR. HEITHAUS: Put the tag on. Get it as far as you can. Excellent. HAGAN: I was very focused on the tail and then I looked up and I saw that the tag was on. DR. HEITHAUS: Good. Let's get a quick measurement and go. Fast, fast, fast, fast. HAGAN (off screen): 345. DR. HEITHAUS: The hook is bent and out. You gotta get that tail rope up fast. -Good swim. -HAGAN: Whoo! NARRATOR: The biologging tag will capture 3D data, providing valuable insight into how great hammerheads move through the water. And help the team see how these giants stack up against bull sharks. With the tag finally recovered and a clean bill of health, Erin's back on board to walk Mike through the hammerhead data. DR. HEITHAUS (off screen): She can build a computer model so we can see not just how it navigates and where it went, but maybe how it's attacking its prey. SPENCER: This is when the hammerhead is released. We start at the surface and then just go straight down. And then we can actually see how the animal starts to move around. NARRATOR: The shark heads down to a depth of about 40 feet. It swims away from the boat in sweeping lateral movements. SPENCER: Here, we see that the shark is kind of meandering down a little bit slower and is kinda midrange, and then there's a really quick turnaround. NARRATOR: It cuts through the water with its hydrodynamic head, making several tight, very rapid turns. SPENCER: And then there's a really quick bolt up to the surface, almost a vertical line. DR. HEITHAUS: There's probably a reason for that because why else would you burn that energy -if you didn't have to? -SPENCER: Yeah. We can say, okay, using the mathematical models, actually how many calories would a shark need to consume to sustain that sort of movement pattern? DR. HEITHAUS: If you need a lot of energy, you gotta eat that bigger prey to get you more energy like other sharks. NARRATOR: Erin's tags were only beginning to reveal the secret abilities of the great hammerhead. When it tilts its head, the hydrodynamic potential of the great hammerhead cephalofoil is unleashed, allowing the shark to move and turn with rapid precision. And this makes hammerheads more nimble and agile than other sharks, including bulls. DR. HEITHAUS: If you combine the speed, the size, and maneuverability, I mean, that's an impressive predator. Bull shark versus hammerhead, who wins? SPENCER: I vote hammerhead. DR. HEITHAUS: One for team hammerhead. NARRATOR: The awesome power of the great hammerhead is coming into focus. But Mike and the team are no closer to understanding why the hammerhead was attacked by bull sharks at Boca Grande. NARRATOR: The team has proven that great hammerheads are formidable opponents, but what about the other contender in the battle? DR. HEITHAUS: Now it's time to investigate the other species in this matchup. Bull sharks. NARRATOR: Maxing out at around ten feet, the bull shark is smaller than the great hammerhead. But what it lacks in size, it makes up for it elsewhere. It's thick with a broad head and big mouth, built for taking out large prey. The bull shark is super adaptable. It has a reputation for being aggressive. DR. HEITHAUS: Seeing that video really shows us that bull sharks might attack great hammerheads and kill 'em. But the question is, is this a common event that's happening more often when they're out there coming into contact? NARRATOR: To dig deeper into the bull shark component of this matchup, Mike enlists Dr. Yannis Papastamatiou. DR. HEITHAUS: Yannis is one of the top shark scientists in the world, and has helped developed new technologies to get more insights into their behavior. For this project, we're gonna try something that's never been done before. We wanna put a camera on the back of a bull shark. And until now, that's only been done with sharks that have been caught, and that might really change the behavior of the shark, so we're gonna go out there and try to put a camera on a bull shark without catching it. NARRATOR: Along the southeast coast of Florida, there's a thin band of warm, shallow water. It creates a shark super highway, bringing all sorts of species in contact with one another, including lots of bull sharks. DR. PAPASTAMATIOU: I'm really hopeful we'll get this tag on, but I, you know, I'm also a little bit nervous because it's going to be somewhat challenging to get a tag on a free-swimming bull shark in blue water, in a current. I'm hopeful. But it's going to require a well-behaved shark. And I also hope she won't bite me. DR. HEITHAUS: We're heading about four miles offshore, and that's where we should be able to find bull sharks. DR. PAPASTAMATIOU: We should get about ten hours of video footage. DR. HEITHAUS: Then that dissolves in a couple days, -there's nothing left on it. -DR. PAPASTAMATIOU: Yep, yep. So within a week, there'll be nothing on the shark's fin at all. NARRATOR: To keep the shark at arm's length, they'll use a spring-loaded pole to snap the tag on the shark's fin. -DR. PAPASTAMATIOU: Okay, so that's now primed. -DR. HEITHAUS: Right. DR. PAPASTAMATIOU: If you now click the small trigger... -DR. HEITHAUS (off screen): Watch your fingers. -DR. PAPASTAMATIOU: Yep. DR. HEITHAUS: One, two, three. -DR. PAPASTAMATIOU: And that'll pop. -DR. HEITHAUS: Yeah. DR. PAPASTAMATIOU: We just need one to behave the right way and we'll get it on. DR. HEITHAUS: If we pull this off, it'll be a world first. DR. PAPASTAMATIOU: No pressure. (laughs) DR. HEITHAUS (off screen): No one's ever done it. There's no pressure. Just go do it. NARRATOR: If bull sharks are hunting hammerheads more commonly than thought, this camera could pick up hard evidence. To bring a bull shark in and keep it close enough for a tag deployment, bait is needed. It injects a constant scent trail into the current, drawing a roadmap directly to the divers. DR. PAPASTAMATIOU: NARRATOR: It's a silky shark. She makes tight circles, sniffing out the food and sizing up the human competition. Silky sharks are a bold species that spend a lot of time in the open ocean, where food is scarce. The bait is working... but it's not the species they're after. DR. HEITHAUS: Silky sharks don't really have a sense of personal space, especially if you have a camera in your hand. NARRATOR: Then as quickly as they came, the silkies disappear. DR. PAPASTAMATIOU: NARRATOR: The bull shark zeroes in on the bait. It's a big female. In order to tag a free-swimming bull, they'll need the most bold and inquisitive shark they can find. Experts generally agree that bulls are one of the most dangerous shark species. Most bull shark-human interactions take place in murky water, where biting is the only way to identify possible prey. In clear open water, the team and the bull shark can see one another and maintain healthy boundaries. She's a good candidate for the camera tag. DR. HEITHAUS: We got the bull sharks we wanted. If this goes well, the shark's gonna swim away with the camera on it, and we will be done. NARRATOR: With daylight fading, the team has limited time to pull this off. It's a deployment that's never been done before. The big female comes in closer. She's curious. Confident. The perfect shark. Yannis readies the trigger. He needs to slip the opening of the clamp over the dorsal fin of the shark. It's a game of inches. One miss and the shark will be spooked. NARRATOR: Clamping the tag on a free-swimming bull shark is a cat-and-mouse game. Every time he gets close, the bull changes direction. DR. PAPASTAMATIOU: NARRATOR: Success. DR. HEITHAUS: NARRATOR: In a first for science, the bull shark swims off, unfazed by its new bling. DR. PAPASTAMATIOU: So the tag is on an animal. First part is done. She's the perfect size, she came in close and took my shot, and, uh, it worked. In the end, she responded perfectly, didn't seem to bother her much at all, she just slowly swam off. DR. HEITHAUS: Camera on. Everybody's okay. -DR. PAPASTAMATIOU: Yeah. -DR. HEITHAUS: Now, one more step. -Get the camera back. -DR. PAPASTAMATIOU: Getting the camera back. NARRATOR: The tag will remain on the shark for two days. Tracking one bull will allow the team to see everything from the shark's point of view. But camera tags only tell one part of the story. To see if hammerheads are on the bull shark menu like in the video, the team has to take a cloacal swab, otherwise known as a fecal sample. DR. HEITHAUS: One of the most important things we need to know about predators is what they eat. Usually, that's been figured out by looking at the stomachs of dead sharks. DR. HEITHAUS: It turns out, if you just get a little swab and collect shark poop, you can run that through a DNA test and see what had been in its stomach. This cloacal swabs are gonna help us figure out if these bull sharks are eating a lot of other sharks and may even go after great hammerheads. NARRATOR: The next morning, Mike and PhD student Davon Strickland head off shore to swab bull sharks. Davon is part of the next generation of marine biologists trying to unravel the mystery of how sharks interact with one another. DR. HEITHAUS: He also happens to be a co-captain of FIU's football team. DAVON STRICKLAND: With football being a game of inches, how that's translated in the shark work is you gotta make sure you know your role, because there's so many things that could go wrong, you gotta be able to work as a team. DR. HEITHAUS: He also is a pretty good person to have on the boat when we're handling big sharks. We need those long arms. (indistinct chatter) Oh, my gosh. The visibility here is insane. NARRATOR: They set their lines just at the edge of deep water. DR. HEITHAUS: So we are right where we'd expect to find bull sharks, the perfect depth range, so that's why we're just gonna drift along here with the bait. I thought I saw a shadow there. Oh, there's a shark right there. NARRATOR: It's an eight- to nine-foot bull shark. STRICKLAND: Let me take it, let me take it. -DR. HEITHAUS: Yeah. -STRICKLAND: Oh, there's two of 'em. DR. HEITHAUS (off screen): Okay, that should help. NARRATOR: The larger shark makes the first move. DR. HEITHAUS: There, it's right, it's right next to the bait, it's taking a look at it. Take it, take it, take it. Oh, oh, oh. Yup. It took it. Okay, get ready. Watch your feet. Okay, I think we're in business. Careful, careful. Yup, slow, slow. Heads up, heads up. Clear, clear, clear. Move, move, move, move, move. That is a big bull shark. Neutral. Heads up now. Oh! DR. PAPASTAMATIOU: He go? DR. HEITHAUS: Bit the line. STRICKLAND: So close, but yet so far. DR. HEITHAUS: Bummer. DR. PAPASTAMATIOU: The shark actually bit through the mono. She was fresh, so she was really strong. So we got out to the surface, but she had the mono in her mouth. That tooth just sliced through it. It's the way it goes. NARRATOR: It's not long before they have another curious shark. DR. PAPASTAMATIOU (off screen): Shark. NARRATOR: A big female. DR. HEITHAUS: Back up, back up, back up! Oh, damn! DR. PAPASTAMATIOU (off screen): Okay. Pull the line. DR. HEITHAUS: Nice. Yes. Okay. Whoo! Good job. NARRATOR: The team makes sure she is calm and getting water through her gills. DR. HEITHAUS: This is perfect. NARRATOR: Then they take a measurement. -DR. PAPASTAMATIOU: 187. -DR. HEITHAUS: Yup. It probably outweighs you by a hundred pounds. STRICKLAND (off screen): Oh. And this fish is longer than I am tall. -DR. HEITHAUS: Okay. -DR. PAPASTAMATIOU: Alright. DR. HEITHAUS: So what we need to do is get her upside down, we're gonna do this cloacal swab, we need to try to keep it out of the water. NARRATOR: Flipping the shark on its back puts it into tonic immobility, a relaxed, trance-like state. It helps keep everyone safe during workups. They'll send the swab off to be analyzed for hammerhead DNA. While they have the shark, they will also implant a permanent tracking transmitter in her belly. DR. HEITHAUS: Right there? DR. PAPASTAMATIOU: Yeah, that's fine. NARRATOR: The shark will now alert the team any time it passes a receiver in a network along the coast of Florida and beyond. DR. HEITHAUS: We can follow them for years, so using the transmitters, video cameras, and the DNA techniques, we can start to piece together a much better picture of bull shark life in general. NARRATOR: The acoustic tags can help the team see where and when bull sharks may overlap with great hammerhead habitat. It could also reveal whether bull sharks are gathering in groups. DR. HEITHAUS: Okay, it's in. NARRATOR: All that's left is to suture the wound and release the shark. Everything's in place. STRICKLAND: Let me know when you're ready. DR. PAPASTAMATIOU: Okay. STRICKLAND: It's out. Nice! NARRATOR: The team is confident. If these bulls are hunting hammerheads, evidence will be with them soon. Two days later, the bull shark's fin cam surfaces. DR. PAPASTAMATIOU: It did pop off about six miles offshore. but then we had a pretty strong current, so it was very rapidly moving offshore. NARRATOR: When they finally catch up to it, it's in deep water, way out in the Gulf Stream. DR. PAPASTAMATIOU: I was really, really happy when that tag was in my hands. NARRATOR: Back at the lab, the team discovers the tag captured hours of video. DR. PAPASTAMATIOU: This is the first time that one of these camera tags is being put on a free-swimming bull shark, and so I'm really excited to see what the tag is going to show. NARRATOR: The shark swims away as if nothing happened. It's proof their tagging technique is minimally stressful to the animal. It cruises alone for hours. -Then... -DR. HEITHAUS (off screen): Whoa. DR. PAPASTAMATIOU (off screen): So, there's another shark came right over it. -DR. HEITHAUS: Yeah. -DR. PAPASTAMATIOU: There's another one. That's one, two, three, four, five, six, seven. NARRATOR: It's a gang of bull sharks. DR. HEITHAUS: Yeah, look at that. DR. PAPASTAMATIOU: I mean, that's right on top of each other. There's a lot of sharks here. DR. HEITHAUS (off screen): One there. -DR. PAPASTAMATIOU: There's another one there. -DR. HEITHAUS: Look at that. DR. PAPASTAMATIOU (off screen): It's just bull sharks all over the place. And we're seeing at least six, seven, eight individuals in frame. -Camera's only pointing forward. -DR. HEITHAUS: Yeah. DR. PAPASTAMATIOU: It tells nothing about on the sides or behind. DR. PAPASTAMATIOU (off screen): So whatever number we calculate, the group size will be larger. DR. HEITHAUS: And these are big animals. DR. PAPASTAMATIOU: I have no idea what is going on here. I mean, a lot of this is just not known. You know, why are all these sharks hanging out in these regions? NARRATOR: The footage didn't show any interactions with great hammerheads, but it has confirmed a remarkable social life between bull sharks. DR. HEITHAUS: Are they feeding in groups? Maybe these bull sharks are actually maintaining relationships with other sharks or working together when they're hunting. NARRATOR: And the results from the cloacal swabs also arrived. DR. HEITHAUS: It turns out that these bull sharks were eating other sharks. We didn't get any great hammerheads, but it does show that these bull sharks are eating big prey and it's plausible that they could go after other larger sharks. NARRATOR: Scientists already know that sharks are hesitant to take on the risk of a one-on-one fight with an equal. It's possible the video evidence points towards something scientists haven't considered before, multiple sharks using their collective strength to take down another apex predator. In order to see whether this dynamic exists between multiple bulls and hammerheads, Mike jumps into the ring himself. The Bahamian islands of Bimini are only 50 miles east of Florida. But worlds away in terms of shark activity. Bulls regularly patrol these waters and great hammerheads visit in the winter. It's a prime location to observe them up close. DR. HEITHAUS: That water is crystal clear and so you can actually get in the water with the great hammerheads in a way that you couldn't in Boca Grande. It's also an area where both of them are coming into at least some semblance of proximity, but are they actually battling it out? Or do they give each other space? NARRATOR: It's the ideal spot to witness these two predators coming head-to-head. Local scientist Candace Fields will lead this leg of the expedition. CANDACE FIELDS: I'm from Nassau, Bahamas, so Bimini is an absolutely amazing place for great hammerhead sharks, mainly because of the fact that there's so much prey available for these guys. NARRATOR: Candace brings Mike to a dive site known for hammerhead aggregations. But the occasional bull shows up here, too. When they arrive, a swarm of nurse sharks is already on patrol. DR. HEITHAUS: We're really interested to see if, like, one bull shark comes in or if maybe a group shows up because it sure is seeming like -bull sharks may not be as solitary as we used to think. -FIELDS: Mm-hmm. Hopefully we'll see both hammerheads and maybe bull sharks. And so I'm just super pumped to get in the water and just see what we got. NARRATOR: They don't have to wait long. -DR. HEITHAUS: Got one? -FIELDS (off screen): Yeah. DR. HEITHAUS: Oh. Oh, yup. Hammer. Time to get geared up. NARRATOR: The team drops to the bottom and camps out next to the chum crate. It's not long before the great hammerhead comes in to investigate. It's a nine-foot male. His body posture is relaxed as he circles closer. They watch the great hammerhead make sharp, agile turns. Just like what Erin is seeing in her data. Then a second hammerhead enters, a female, about the same size as the male. She's no threat to the other shark. They're solitary individuals here investigating the bait. DR. HEITHAUS: Candace and I could see that maneuverability they have, you know, how they're able to move up and down, and also how they interact with one another. NARRATOR: Both hammerheads look strong and healthy. DR. HEITHAUS: It's really awe-inspiring to be so close to such big animals. NARRATOR: Then shadows appear from the surface. Bull sharks. They glide in to survey the scene below. Three of them. A potential gang. DR. HEITHAUS: Here's our opportunity to see how these sharks interact when they get together. NARRATOR: The bulls descend, swimming a wide, careful arc around the two hammerheads. They size each other up, pushing in closer. The bulls are smaller but they have numbers. A challenge over bait could happen at any second. Then they move in to investigate the humans. DR. HEITHAUS: They seem to be a little less focused on what's going on, kind of out front of us and more, "How do I get close when you don't see me?" NARRATOR: The hammerheads are dominant, showing no sign of fear. The body language of the bulls is relaxed and confident. It's a bull versus hammerhead standoff. Suddenly, a game-changer appears on the horizon. DR. HEITHAUS: NARRATOR: The new hammerhead on the scene dwarfs the other sharks. It's a 13-foot female. Now, it's a three-on-three showdown between bull sharks and hammerheads. The imposing shark works her way to the center of the group. DR. HEITHAUS: NARRATOR: She's about the same size as the hammerhead attacked in Boca Grande Pass. MAN (off screen): That's insane. NARRATOR: But this super predator brings a completely different power dynamic to the face-off. FIELDS: It felt as though she was running the show. She was making much closer passes to us than the other sharks were, perhaps because she feels far less threatened by us as potential predators. NARRATOR: The bull sharks circle, sizing her up. The hammerhead makes quick turns, possibly bracing for a three-on-one fight. DR. HEITHAUS: NARRATOR: The bull sharks take turns coming in... closer and closer. The 13-foot great hammerhead stands her ground. The bull flinches first. As the hammerhead approaches, the bull gets a sense of her true size... and retreats. FIELDS: Things underwater kind of changed. The dynamic changed a bit. So it was really cool to see that she kind of made everybody else clear out a little bit. NARRATOR: The team has now seen first-hand the power and dominance a giant great hammerhead has over bull sharks. DR. HEITHAUS: Bull shark kinda gave way first. They both turned, but it's like that bull shark was kinda, "You can have the swim lane first." FIELDS: Exactly. Unlike most people think that all sharks are at the top of the food chain, but that's obviously not the case, right? DR. HEITHAUS: Yeah, you can really see the difference in maneuverability. Those bull sharks are, like, a tank trying to get turned around and the hammerheads just spin on a dime. FIELDS: Absolutely. I mean, maybe that's another reason why the bulls aren't coming in as much. You know, the hammerheads have so much body and so much capacity to move around, whereas the bulls don't. DR. HEITHAUS: That's just what we were looking for, an opportunity to see these two big predators together, but it doesn't mean when they get together, it's gonna be one eating the other. It might actually take special situations for bull sharks to go after hammerheads or vice versa. NARRATOR: After bearing witness to the head-to-head showdown, Mike believes there's an answer to which shark would come out on top. DR. HEITHAUS: Based on what we've seen, I think if it actually came down to a battle and you had a bull shark and a great hammerhead, the great hammerhead's gonna come out on top. They are bigger, they are fast, they are maneuverable. NARRATOR: So how did the hammerhead become a victim in Boca Grande? Back in Florida, Mike sits down with the video one more time. Instead of focusing on the aggressive behavior of the bull sharks, he takes a closer look at the hammerhead. DR. HEITHAUS: The thing that I noticed is that the hammerhead's not really swimming quite right. Think about that 3D track from Erin, those sharks are able to turn on a dime. NARRATOR: Unlike the giant great hammerhead in Bimini, when faced with a threat, these sharks swim stiffly in a straight line. DR. HEITHAUS: I would've expected it to be accelerating rapidly, turning quickly, or even turning the tables 'cause that hammerhead was bigger than the biggest bull shark that's there. That suggest to me that that was a hammerhead that was in trouble. NARRATOR: The great hammerhead may have been injured before the attack. It was the height of tarpon season. It's possible the hammerhead was hit by a boat or accidentally hooked on a fishing line while pursuing a tarpon. It's likely the bulls sensed that it was compromised and went in for the attack. DR. HEITHAUS: And the bull sharks were then able to just follow it and wait for the hammerhead to be too exhausted or injured to fight back. And then they finished it off. This video is amazing, but probably the exception to the rule. In the end, bull sharks and great hammerheads are both amazing top predators in their own right, but when it comes to bull shark versus great hammerhead, they probably don't go after one another unless the scales are really unbalanced. But if a great hammerhead or a bull shark's in trouble, they can become dinner. Captioned by Point.360