Why Are Record-Breaking Bull Sharks Moving From Saltwater To Freshwater? | River Monsters

Added: 2026-05-08

[00:00:00]I've been given a second chance.

[00:00:02]>> Anchor up, please. Anchor up.

[00:00:03]>> And I'm not going to let this one get away.

[00:00:06]>> And it's running. That's running. It's running.

[00:00:10]Tightening up. Tightening up. Tightening up. Tightening up. Okay. Right. We're on. We're on. We're on. We're on.

[00:00:16]Look at that. It's really cutting sideways. They're really cutting sideways.

[00:00:24]Oh, that was it's really heart stopping when the it suddenly goes slack and you think it's off and then it's there's tension there again. It's probably kicking or rolling on the line even.

[00:00:39]This apex predator is not accustomed to this kind of treatment.

[00:00:46]There he is.

[00:00:48]Instead of running away, it's coming in to check me out.

[00:00:55]I can't imagine what the shark is making of this experience.

[00:01:03]It's gone again.

[00:01:06]With a lot of fish, you see them up on the surface, you see them close in, you think that's it. They're nearly done there. I think this one was just coming up partly out of curiosity. What's all this? What's happening?

[00:01:17]Now he's checked me out. He's not coming anywhere near again.

[00:01:21]>> Last time the shark brought things to an early end by rolling on the line. This one seems set for the long hall. 2 hours.

[00:01:31]2 hours.

[00:01:34]It's a different phase of the fight now.

[00:01:36]It was tearing around, you know, using speed in the early stages.

[00:01:42]There it is again. There it is again.

[00:01:43]There it is again.

[00:01:45]Yeah, there's definitely some tactics going on. The speed didn't work, so now just uh a bit of a war of attrition.

[00:01:54]>> Ah, this is punishment.

[00:01:57]2 hours into the fight, the shark begins pulling the boat towards some shallows.

[00:02:02]>> Under 3 m now.

[00:02:05]>> By now, the battle is beginning to attract attention.

[00:02:09]This is turning into an event. Everyone wants to see this shark.

[00:02:16]I can see the fish. I can see the fish.

[00:02:19]>> Back to 2 m.

[00:02:20]>> If my line catches a rock down there, it could cut through and the shark will be gone.

[00:02:25]>> We got to get away from the rocks. We're still in 2 m now.

[00:02:29]>> I've got a boat full of scientists relying on me to get this shark in. The tension on board is palpable.

[00:02:37]>> 4 m. Yeah.

[00:02:43]Okay, I've got Right. I've got the line.

[00:02:45]If it goes, it can go without the line catching anybody.

[00:02:48]>> Got that line around the Right. Have you got the tow strap around?

[00:02:52]>> Yeah.

[00:02:52]>> Good. Okay. Brilliant. Got a good hold.

[00:02:55]>> Okay.

[00:02:57]>> This is my biggest catch ever. And 2 and 1/2 hours is by far my longest fight.

[00:03:02]It's astonishing to think that I've hauled this beast from a river.

[00:03:09]But I was lucky to get it in at all because it was foul hooked in the side, snagged on a flap of skin between the gill slits.

[00:03:24]The scientists want to know why the sharks are here.

[00:03:28]>> Right, this is like sort of time is of the essence >> and they're actually they're starting to pump water to irrigate the gills. That buys a little bit more time.

[00:03:37]Last year's giant catch was a heavily pregnant female, which led the scientists to assume she was in this river to deliver her two foot long pups.

[00:03:45]Our expectation is that this fish too is female.

[00:03:51]>> One, >> it's a male.

[00:03:57]>> Our first catch and we have answered one of our questions. It looks like the Bria River is a place where sharks come to feed.

[00:04:06]3 2 1 >> 9 and 1/2 ft and with an estimated weight near 500 lb, he's one of the largest bull sharks ever caught anywhere, and I'm returning him back into the river.

[00:04:25]I've just caught a giant, but I'm not off the hook. The scientists want me to try for another, and this time even bigger.

[00:04:38]There is heated controversy about returning the sharks to the river where people swim and play.

[00:04:44]But unlike bull sharks elsewhere in the world, these bull sharks have never attacked a person.

[00:04:52]So what makes the Bria River sharks so unusual?

[00:04:59]Hunting for clues, I talk to local fishermen who fish these waters for grunt and cobb.

[00:05:05]>> Do they weigh it?

[00:05:06]>> There's one here.

[00:05:08]>> Kobus Vid is a fisherman and a kite surfer. He's been here for 50 years and has had his fair share of shark encounters.

[00:05:17]>> Every year there's a swim gala over here over there. And and I mean we're not not scared of the of the sharks actually because they don't attack people. I've never never heard of a of a a bull shark attacking anybody. So, actually, we're very lucky.

[00:05:33]>> Any any thoughts why that might be?

[00:05:35]>> Maybe they don't like the taste of of human blood.

[00:05:40]>> And you're confident that if you just take basic precautions, you're perfectly happy about going in the water yourself.

[00:05:45]>> Yes, absolutely. Although, when you're down in the current, you know, and you fall down, then for for a fraction of a second, you're thinking, "Oh, I better get up."

[00:05:56]This is my >> Eugene Boyas is one of only a handful of commercial fishermen left in Vitzand.

[00:06:02]>> His knowledge of sharks has been passed down through his family.

[00:06:07]>> Are you surprised that no no people have been attacked?

[00:06:11]>> Yeah. You know, there's such a lot of food in this river. It's it's it's it's such a healthy system. I think that's that's why they're not going to be interested. Obviously, when somebody's standing in the water, there's a vibration there. you will come and investigate and you'll see, okay, this is not what I want, you know, then you'll just swim off type of thing. But maybe when there's a year where there's not not such a lot of food in the in the river and all that, there could be an attack.

[00:06:35]You never know.

[00:06:39]Just had a call from Paul, one of the team, that there's been a shark attack right off the harbor wall.

[00:06:52]This this is the victim, is it?

[00:06:53]>> It was incredible. I just I just put the boat alongside and um heard a giant splash about 20 yards off off the harbor wall here. There was a giant pool of blood. The fish floated up to the surface.

[00:07:06]>> One of the reasons bull sharks got their name is because they are known to ram their prey before they kill it.

[00:07:15]This can clearly be seen by the marks along the side of this cob.

[00:07:20]>> So you reckon it's actually just hit it from the side? Yes sir.

[00:07:23]>> And then when it's and then when it's floundering the water just came along and just >> I mean that I mean that is just muscle but that's that's a killer blow isn't it? I mean the fish >> straight through >> a battering ram armed with razor sharp teeth.

[00:07:37]>> That's about the thickness of my leg which is quite disconcerting. And it's gone right through the backbone as well.

[00:07:42]Just clean through.

[00:07:46]This is actually the biggest cob that I've seen so far. And that is without the final third, which is out there somewhere inside a shark.

[00:07:53]Witnessing how they hit monsterized prey makes me even more determined to land a monsterized bull shark.

[00:08:04]Before I try again, I have the opportunity to discover exactly what the Brietta River bull sharks are doing that sets them apart from bull sharks in other rivers.

[00:08:19]We head out to track the shark that I caught and released.

[00:08:24]The acoustic tag, which we secured to the back of the shark, transmits a signal, which we hear as a ping on our hydrophone.

[00:08:32]The clearer the sound, the closer the shark.

[00:08:37]>> Yeah. So, a bit further up here.

[00:08:41]>> Maybe the hint of something. We might be just out of the main range.

[00:08:52]>> We end up 20 m up river in search of a tagged shark.

[00:09:06]Apparently the guy there just said you mustn't catch sharks here cuz we swim here. Um I'm not quite sure what the logic of of that is. Um I think you know whether we catch them or not, they're here. Apparently the big one last year was tracked right past these houses on several occasions.

[00:09:26]Yeah. Meanwhile, the one that we're looking for at the moment. No, no sign, or should I say no sound of it.

[00:09:37]We turn and retrace our steps back down river. Searching as we go.

[00:09:43]Eventually, we come across a group of fishing boats just off Fit Sand.

[00:09:48]>> A couple of fishermen have just had a very close encounter with a shark.

[00:09:52]>> Teeth marks there. Teeth there, teeth there. Just trying to get a a look at that.

[00:09:57]>> He had him in his mouth.

[00:10:01]>> The shark tried to steal their catch as they brought it in.

[00:10:05]So, I know there's a shark here and it's hungry.

[00:10:17]>> Oh, there's a beep already. Yeah, >> we found the tagged shark that I released yesterday.

[00:10:22]>> 87 81. That's sort of straight ahead.

[00:10:25]So, it's actually 9. Oh. Oh, and 98.

[00:10:29]>> The hydrophone signal peaks at 100. So, 98 means the shark is within yards of our boat.

[00:10:37]Slightly worried about my hands close to the water. Now, 83. There we go. That's like 1:00.

[00:10:51]According to the hydrophone, the fish has been, you know, right under that boat.

[00:10:58]And I'm just I'm just listening to the beeps and looking at the screen. And then when I get the strongest signal, I hold it here. I look up and look, it's just pointing straight at the boat.

[00:11:10]The Breeda River bull sharks have leared to shadow fishing boats, waiting for fish to be hooked, then taking them off the line.

[00:11:24]It's very specific, systematic behavior.

[00:11:27]There are no records of bull sharks doing this anywhere else in the world.

[00:11:32]And I just witnessed it firsthand. It's like a protection payment. The sharks steal a percentage of the fisherman's catch and in exchange they leave humans alone. At least for now. Normally, one of the first things you've got to do is actually locate the fish. But it appears that here, even though we got a lot of water, I don't have to go looking for the shark. They're going to come looking for me.

[00:11:55]To many, it's the stuff of nightmares. A heavily populated river that's also home to massive hungry bull sharks.

[00:12:11]Leaving the tagged shark behind, we move on. Mark points out areas that we have to avoid.

[00:12:19]There's been some very big floods on the river in the last few years, which washed in, I think, 70 odd of these jetties here.

[00:12:27]Catching a shark is going to be challenging enough anyway, but if my line under tension touches anything like that, that shark is gone.

[00:12:38]I head to a spot where the big female was tracked several times last year.

[00:12:48]I'm actually now about 12 mi up river, but this is a good spot. Um, very deep hole there, about 90 foot. Perfect sort of lurking place. And they actually tracked the fish last year in this spot several times.

[00:13:12]It's very, very quiet up here. I've had the bait swimming around here for well over an hour now and there's just nothing doing at all. You know, it's very attractive. It's just, you know, about 10 or 12 feet down, very, very visible to anything.

[00:13:31]Nothing doing. So I head back down stream.

[00:13:39]She'd doing the opposite to what I'd normally do if I was fishing. Normally I'd be very very quiet and I'd normally be fishing quite a long way from the boat.

[00:13:47]But from what the local fisherman say and from what the science team are finding out with the tags, you know, these fish will actually come close to the boats and check them out. They could be right underneath. And because the water is, you know, not very clear, we wouldn't even know they're they're there.

[00:14:06]I think something's actually taking that bait, but it's not actually running at the moment.

[00:14:11]Here it goes. Four, five, six, 7, 8.

[00:14:17]Oh, here we go. Here we go. Here we go.

[00:14:19]Here we go. Here we go. Here we go. Here we go. Here we go. Oh, what happened there?

[00:14:26]line went.

[00:14:33]That looks like that line's been rubbed.

[00:14:35]It might have gone around a a snag, you know. So close. That was a take.

[00:14:41]That was a definite shark.

[00:14:43]>> Catching another shark is proving tricky. Uh >> far more difficult than I imagined.

[00:14:55]I'm going to have to get into the mind of the sharks.

[00:15:01]I know that the Bria River sharks have leared to steal fisherman's catches from their lines. Unique behavior not recorded in bull sharks in any other river in the world, which may explain why they grow so big.

[00:15:15]They will actively hunt down fishing boats, lie and wait until the fisherman make a catch, and then bolt in to take an easy meal.

[00:15:29]My plan is to position myself right next to the fisherman and let the sharks come to me.

[00:15:36]Yeah, lots of activity on the river today. That's going to get the sharks quite excited.

[00:15:42]I set up seven miles up river in a spot close to where the team landed the big female shark last year but well away from this year's tagged shark which was last located near the river mouth. The tracking team are out searching for him right now.

[00:16:01]There's boats generally around the river. I think that you know the sharks are going to be are going to be active.

[00:16:04]This is this is their big feeding day.

[00:16:06]This is when the humans come and do do the work for them.

[00:16:13]The biggest bull shark ever recorded was caught in this river, and I'm determined to catch another.

[00:16:22]Then the tracking boat appears. Oh no.

[00:16:25]Right. Megan's making signs like this.

[00:16:28]It's checking us out. Yeah. It looks like the tag shark is actually around the boat. And I had no awareness of that at all until the tracking boat turned up. There's actually been a shark circling the boat for quite a few minutes apparently and we were just totally unaware of it. We're being shadowed by a giant shark which is clearly hunting.

[00:16:48]From now on, we'll keep Megan on board with the tracking equipment.

[00:16:53]This way, I'll know exactly when the tagged shark is nearby so I can get my bait out of the water before it strikes.

[00:17:03]It's close.

[00:17:05]This is just really frustrating. It's just proving so hard to keep away from that that tag shark. It's just covering such an area of water.

[00:17:12]>> It's right behind us now.

[00:17:17]>> And we just popped it in when we arrived here. This is actually one of the favored spots. All clear. And you know, about five minutes after anchoring, we're getting a signal.

[00:17:25]>> The shark's right under the boat.

[00:17:32]catching again would not be a good idea because at the moment we've got a a stable situation. It it comes along, it's taking fish from fisherman's boats and everybody's happy. Okay, the fisherman aren't too happy, but you know that is its main or important source of food. If anything actually makes the sharks wary of fish near boats, they could start feeding in a more opportunistic way, which, you know, might not be good news for the people around here. So very important to uh avoid hooking that fish again.

[00:18:04]>> If I hook the same shark again or if anyone else does, it may become wary of its normal food source and start searching for other prey.

[00:18:18]We move on once again. We're learning so much about the behavior of the bull sharks in this river that the scientists are desperate for me to make another catch.

[00:18:29]The capture of the male shark told us that they're probably here to feed.

[00:18:34]And the tracking showed us that they're actively following fishing boats for an easy supply of food.

[00:18:41]Catching another big one would confirm the Bria River as home of the monster sharks.

[00:18:55]I've left the tagged shark several miles up river and set up just off the town of Bitsand.

[00:19:02]This is what I use for glass tiger fish, Nile perch, things like that. 80 lb line. So, a big shark on here would be very interesting.

[00:19:16]I might as well just try pulling the bait a little bit. You know, if there's a predator watching, sometimes just a little bit of movement. You know, it's thinking about it. It's thinking, do I want it? Don't I want it? But it's got time to think about it. If you move it, suddenly it can be like a reflex.

[00:19:28]They'll just bang. They'll hit it.

[00:19:31]Something had a go. Yeah. Wait a minute.

[00:19:33]The balloon's gone. One, two, three.

[00:19:37]This could be the monster I came here for. It knows it's hooked now. This feels a good size fish.

[00:19:45]It's running. It's running. It's running. Only a shark in this river runs with this power and speed. But I've got a problem.

[00:19:55]>> Oh, wait a minute. What's happened there? Suddenly went slack. Oh, that No, that's round something. That's round something. Ah, that is actually snagged.

[00:20:04]>> I've already lost one shark to a broken line. I don't want to lose another.

[00:20:10]>> I can still feel the fish. If we can go back, let's get it off that snag. Whatever it is, this is not good.

[00:20:24]I think we're clear. I think we're clear.

[00:20:28]Oh, that's the line is a bit shredded there. Oh, that line is in a bad way.

[00:20:35]>> This shark has taken the line around some debris on the bottom. And even though it hasn't gone through, it's very badly frayed. I'm only on about I don't know, might only be 50% strength on the line.

[00:20:49]>> My line is wearing through. But if I try to bring the shark in too quickly, I could lose it.

[00:20:56]>> I'm just so nervous cuz I know the line's not in a good way.

[00:21:03]>> 1 hour and one mile further up river.

[00:21:07]Friend of mine who's caught bull shark said to me, "Bull shark's full, you know, they're not like sound like a makeo shark, which is a real speed merchant."

[00:21:13]A bull shark is very solid, very muscular. It was just like, "Take you for a walk." I feel like a six-year-old child taking a a rock violet for a walk.

[00:21:22]>> It feels bigger and stronger than the other shark.

[00:21:26]>> It's just getting more lively all of a sudden. It's right under the bow. If we can go left. All right. Okay.

[00:21:35]3 miles from where I hooked the shark and it's still pulling the boat. People who say catching fish doesn't cause any pain, which they're wrong. My back is killing me.

[00:21:46]Not to mention where the rod butt is jammed. Oh dear. It's going to be an interesting color, I think, after the end of all this.

[00:21:54]As the hours pass, the shark continues to drag the boat up the river.

[00:22:04]This is totally not normal in a river.

[00:22:07]Uh I had a giant stingray on for two hours, but we've gone past that. It must be like 2 and 3/4 now.

[00:22:17]The fight is now heading towards its third hour.

[00:22:21]The shark has taken the boat and me four miles up river.

[00:22:28]>> It might come up. It might come up.

[00:22:30]Coming towards the surface.

[00:22:33]That's a tail. That's a That's That's a fish. Dorsal and tail. Dorsal and tail.

[00:22:37]First time it's broken the surface. It's going to show again.

[00:22:42]That's a dorsal. Oh.

[00:22:46]Ah. Wait. It's under the boat. It's under the boat. Back. Please. Back.

[00:22:49]Back. Back. Back. Back. Back. Back. So, last. Here we go.

[00:22:55]Right now. Absolute concentration. If I say let go, just let go. All right.

[00:23:12]The gaff is necessary to hold the head up, but it barely punctures the tough skin.

[00:23:18]>> Bloody hell.

[00:23:20]>> It's not really that, is it? This is going to break the gap. It's going to break the bloody gap.

[00:23:25]This shark has battled with me for 3 and 1/2 hours and dragged the boat 5 miles up the river.

[00:23:32]>> Get to the bank. I think >> we just need to get to the bank. You guys need to get off.

[00:23:38]>> Never had a fight anywhere like that long before. That's almost double the longest fight I had with a freshwater stingray. And those things just glue themselves to the bottom.

[00:23:48]Wow.

[00:23:53]The gap's now out.

[00:23:55]>> This bull shark is definitely larger than the last one I caught. We'll keep it alive while the team take samples, measure it, and insert the acoustic tag, then get it back into the river.

[00:24:07]>> Shark's going to actually pump water over the gills. So, uh, I'm wedging the the mouth open with a bit of wood and just shoving water in its mouth. Yeah, >> it's another male bull shark. 9 ft 10 in long and more than 500 lb. The biggest fish I've ever caught and one of the largest male bull sharks ever landed.

[00:24:29]Tags are there, samples taken, parasites, all the rest of it. Very quick operation. But this thing, having been so strong for so long, is now just feeling a bit like I am. So, we just need to get it uh get it revived.

[00:24:46]Sharks trigger a primal fear like no other. And even though it's utterly exhausted after fighting with me for nearly 4 hours, this bull shark can still prompt a nervous run for land.

[00:25:02]Two catches proving that last year's shark was not a fluke and that the Bria River is home to some of the largest bull sharks anywhere in the world.

[00:25:13]When I first came here, I never imagined that what we would find out would take the investigation so far forward and actually provide likely answers to some of the big questions about the sharks in this river.

[00:25:25]It seems that they come here during the warmer months of the year to feed, but it's not a random feeding strategy.

[00:25:33]Instead of wasting energy by chasing free swimming fish, they're actually taking their food from anglers lines, like plucking fruit from a tree.

[00:25:46]It's a very efficient way of feeding.

[00:25:48]And perhaps this explains why the sharks in this river are so big.

[00:25:55]This easy food source also possibly explains why there have never been any attacks on humans. And as long as the numbers of those small fish remain healthy, this remarkable coexistence between humans and potential man-eaters should continue.

[00:26:13]Ah, that is a very, very strange sensation. Very strange. And it's looking me right in the eye. Ah, that's a good way to good that's a good way to calm them down.