(soft music) ♪ (intense music) (narrator) The great white shark.

The perfect predator.

(man) Push it down!

Push it down!

♪ (narrator) One of the least understood creatures of the deep.

♪ (man) Ah!

Jesus Christ!

♪ (narrator) In 2003, an electronic tag recorded the sudden death of one of these feared sharks.

♪ This three-meter animal had been chased and devoured by an unknown predator.

(splashing) (David) The mission to uncover what took out our shark has overtaken my life.

It's almost like a drug.

(narrator) This is the story of how one man's obsession to find the shark's killer... (David) We're on 'em, we've got something.

(narrator) ...has uncovered an even greater mystery of the deep.

♪ (somber music) ♪ (waves whooshing) ♪ (David) In Bremer Bay, in late 2003, I heard of a sperm whale stranding.

It was the most amazing, raw natural history event I've ever seen.

(dark music) ♪ (narrator) Along West Australia's remote southern coastline, a herd of sperm whales had beached themselves after being chased ashore by an unknown threat.

♪ All of the whales were pregnant and slowly dying.

(David) When we first turned up at the site where the sperm whales beached, we were only in 20 feet of water out the front.

We had 13 great whites circling our boat.

It was seriously awesome.

The vibe of the whole place was just really, really buzzing.

(shouting) (dramatic music) (narrator) Dave Riggs had been contracted to document Australia's first large-scale great white shark tagging project.

With whale blood streaming into the notoriously sharky waters, Riggs had chanced upon the perfect tagging scenario.

(David) We pulled up right in front of the whales.

We anchored, which in hindsight was a mistake.

And instantly, we had two three-meter great whites nudging the boat.

(splashing, thumping) It wasn't frightening at that stage, it was just intense.

There were sharks everywhere, big sharks.

(narrator) The team's aim was to tag adult great white sharks so they could study their patterns of movement along Australia's coast.

(eerie music) (David) I remember looking at one of them, thinking, "Wow, she's just a magnificent-looking animal."

It was only three meters long.

Didn't have a mark on her.

When she first came in, she came in with a real swagger, like a real confident, bold move, and then just pushed up against the dinghy and gave us the opportunity to tag her, and he placed his tag perfectly.

(whooshing) (beeping) (narrator) Designed to stay attached to the shark for up to 12 months, multiple sensors inside the tag were set to constantly record and store data.

The tag's information was programmed to transmit back to scientists only once it had automatically released and floated to the surface.

♪ (David) They're seriously streamlined.

They can dive down as deep as 2,000 meters on the back of the animal.

I think it was the perfect system to have on this shark.

(dark music) (narrator) Code named Shark Alpha, the healthy female left the scene without any sign of distress.

♪ Moments later, a male shark with a different attitude approached the team.

♪ (David) Within three or four minutes, a big shark came in really angry, was swimming around our boat with his head out of the water physically looking at us.

It was really unnerving, but I didn't think anything of it more than, "Wow, let's get some shots."

-Around the back of the boat.

-Coming your way.

(ominous music) ♪ Ah!

Jesus Christ!

(indistinct chatter) (splashing) ♪ (David) This animal circled our boat three or four times, dived to the seafloor which was only 20 feet down, turned around and powered up straight into us.

(tense music) ♪ (slamming) ♪ (grunting) ♪ (slamming continues) As soon as the shark smashed into the boat, it was just mayhem.

I thought the boat was gonna flip straight over.

We then grabbed the side of the boat... ♪ I thought we were gone for all money.

It was absolutely terrifying, to be honest.

(grunting, smacking) This thing was trying to physically get us in the water.

(slamming) So, we had to use our oars and let go, but it swam away and then charged the boat.

It slammed into us three times.

(slamming) ♪ We ended up cutting the anchor rope and ran for shore.

(dramatic music) ♪ I always had a really healthy respect for great whites, but to see this animal so angry caught me off guard.

I had no idea.

(indistinct chatter) (eerie music) ♪ (narrator) Four months later, Shark Alpha's tag was found by a beachcomber.

♪ It had washed ashore four kilometers from where it had been attached to the shark.

♪ Its data revealed an incredible story.

(ominous music) Over the four months since Shark Alpha was tagged, she traveled 4,000 kilometers up and then back down the West Australian coastline, but her final recordings captured 70 kilometers offshore from Bremer Bay were unlike anything known to science.

(soft, tense music) (David) When I was first told about the data that came back from the tag that was on the shark, I was absolutely blown away.

(dark music) (narrator) At 4:00 a.m. on Christmas Eve, the shark suddenly plunged at high speed straight down the edge of the continental shelf.

♪ (David) It showed this profile going down the shelf to 580 meters and then a huge temperature change.

(narrator) Within seconds, the shark's external tag recorded a dramatic shift from the sea's temperature of 8 degrees to 26 degrees, a temperature that could only be achieved inside the belly of another living animal.

♪ (David) The question that not only came to my mind but everyone's mind who was involved was, "What did that?"

It was obviously eaten.

♪ What's going to eat a shark that big?

What could kill a three-meter great white?

♪ (narrator) The tag recorded 26 degrees for eight days, moving between the sea's surface and 100 meters of depth before it was released and floated to the waves above.

(beeping) There was no doubt, the seemingly indomitable Shark Alpha had been attacked and eaten by a super predator of the deep.

(David) Why did it happen in this location?

And what else could be out there?

I mean, it was just straight away I had to know.

♪ (tense music) ♪ (narrator) Haunted by the mystery of Shark Alpha, Dave spent a decade obsessed with finding the shark's killer... ♪ ...taking on any type of job that would bring him close to where the shark had perished.

He soon became a man of the sea.

♪ (David) Some of the occupations that I've had to take up to get out there: working on shark boats, working on crab boats, working on different sorts of surveys to allow me to get out into this zone.

They're difficult jobs.

It's kind of frightening sometimes, but it's worth it.

To get out to this location, it's become something I have to do.

There is no choice.

(whirring) (narrator) To explore beneath the waves, Dave designed camera systems that could capture the behavior of unpredictable marine predators.

(driving music) (David) It's become an obsession, and I think lots of people go through that, where something happens in your life that makes you change.

You can't let it go.

(dark music) (narrator) Each year, he gathered more evidence of highly unusual marine activity.

(splashing) He soon discovered a pattern.

♪ Marine predators gathered in a small oceanic zone for just six weeks each year, close to where Shark Alpha had disappeared.

♪ Out of the blue, he had discovered a hot spot.

♪ Oil and gas survey maps of the seafloor revealed an incredible underwater world.

Directly beneath the hot spot is the Bremer Canyon, a vast rift twice as deep as the Grand Canyon that sweeps up from the ocean floor to the edge of the continental shelf.

♪ (David) When I first got this bit of information, it was, "Wow, here we go.

This is the spot.

There could be animals here that are capable of taking out our shark."

(narrator) Dave believes there are three predators that patrol this zone which could've taken down the great white shark.

(David) Suspect number one would be a killer whale.

We've noticed a lot of these animals out in the canyon over the years.

Same time of year as our animal was taken out.

You can probably imagine a white shark straying into his turf could be in trouble.

Suspect number two, giant squid.

We've seen evidence by way of sperm whales that have washed up dead on the beach around here with huge sucker marks on their heads.

That's indicating squid in excess of six-meter range.

They're aggressive, they hunt by stealth.

It's a possibility.

Suspect number three would be a white shark.

They're in the area, they're large, they can be aggressive.

They are known to be cannibalistic.

A large shark could be motivated to take out another of its own kind.

(bird squawking) (tense music) (narrator) Joining this list of suspects is another entirely more mysterious perpetrator.

(bird squawking) Tales of an unknown creature of the deep have echoed for decades across the Port of Albany, once the home of Australia's largest whaling fleet.

♪ Mick Stubbs and Kees Vander Geeg work together hunting sperm whales along the continental shelf.

♪ (David) So you used sonar to pick up whales.

While you were doing that, did you ever pick up anything mysterious?

(Kees) Yeah, we get every now and then a good, strong echo.

And because you didn't know what it was, you used to follow it for about an hour, an hour and a half.

Used to come up close to the surface, but it never broke.

-And what would happen then?

-Nothing.

It would swim down again without seeing it.

-And how big was it?

-Big as a whale.

(David) As big as a whale?

So it was sort of coming up near the surface, -but it wouldn't breathe air.

-No.

(David) You have any idea what it could've been?

-Pfft, no, we never knew.

-It'd still be there, I reckon, even now, 35 years later.

-Yeah, laughing its head off.

-Yeah.

(David) And, then, once or twice you came across a whale that you came back to pick up.

There was a big shark on it.

(Mick) The whale was 30-odd foot.

The shark was equally as big as the whale.

Huge, I've never seen anything so big.

I really haven't.

Don't go for a swim there.

I don't intend to.

(dark music) (narrator) Are these just tall tales about the one that got away?

♪ Dave is determined to find out.

♪ (dramatic music) ♪ After ten years of self-funded research, Dave used his mounting evidence of an offshore hot spot to drum up support for his search for Shark Alpha's killer.

♪ (David) Little bit of work going on at the moment to demobilize this vessel we're using.

So we're gonna remove all the seats and then put TVs on an expedition vessel.

Here we go.

There's four of them leaning up just behind the shark cage.

You'll see them sitting there.

(narrator) One of the first Dave signed on was Peter Hudson, a local tour operator.

(Peter) I'd be interested to see what we find.

You know, obviously, that's part of being on the trip and being involved, that's why I sort of was prepared to do what I am doing to the boat, because you only get opportunities like this once in a while.

-Just get one each side of it.

-Yeah.

(narrator) To catch a killer in the treacherous waters of the Southern Ocean, Dave has had to assemble some serious kit.

(David) The different sorts of things I'm having to think about range from nuts and bolts and toilet paper right up to three-ton winch spools for the tow camera system.

(Peter) That's it!

That's it!

Beautiful.

-Well done, buddy.

-Thank you, man.

(narrator) Accompanying Dave across the three-week expedition are specialist marine scientists.

Everything on board is designed to find the ocean's super predator.

(David) We've got a lot of different scientific experiments happening, and it's critical that we get all of the components now for each experiment.

(man) It should be wiggling from side to side now.

Ask Dave if he can see it.

(David) Yeah.

(intense music) (narrator) Dr. Michelle Blewitt and Scott Sheehan have spent decades studying whales around Australia's coast.

(camera shutter clicking) Their target species is the first animal suspected of devouring Shark Alpha... ♪ ...the killer whale.

♪ (tense music) ♪ (David) So this is a key piece of data that we've got.

This basically shows the tag when it was on the animal... ♪ ...and the tag when it was in the animal that ate it.

What do you make of that?

(Michelle) I mean, the depth profile of whatever this tag was consumed by is consistent with the depth of killer whale diving unlike these other profiles that show it going much deeper when it was on the shark.

However, the temperature gradient is a little bit different and it's staying around a mid- to high-twenties.

I mean, being a mammalian species, a warm-blooded species, their internal temperature would be somewhat similar to ours.

But it has been suggested also that that can fluctuate with the geographic location that the animals are in.

And there is evidence in other parts of the world to suggest that killer whales do predate on sharks.

♪ (David) I guess I'm feeling the pressure, but it's an exciting pressure.

This is something that I've wanted to do for a long time.

So, I guess, bring it on.

♪ (dramatic music) ♪ (narrator) The expedition's target is 70 kilometers offshore, directly above the Bremer Canyon.

♪ This is the hot spot of marine predator activity and close to where Shark Alpha disappeared.

♪ With the wilderness of the Southern Ocean surrounding them, the team's mission is to identify what species are out here and who is the most likely killer of Shark Alpha.

(David) How far to go -do you think we've got?

-We've got 4.5 nautical miles.

What I'm thinking is we should continue on this kind of trajectory, if you will, between these two contour lines.

It's a bit difficult to see what's going on at the moment.

A little bit bumpy.

(Peter) Well, there's plenty of birds working, so we'll just keep our eyes open and hope.

(driving music) ♪ (birds squawking) ♪ (shouting) (man) Count the waves, come with the waters.

Two lines.

♪ (narrator) Within minutes of reaching the Bremer Canyon hot spot, the team is surrounded by a pack of marine mammals.

(Michelle) Yeah, below it, straight ahead.

Hundred meters.

(Peter) They're up on our port side again.

♪ (David) We've come across the killer whales.

They've come up to have a look at us.

The main herd are off behind us, but we'll try and get some ID shots of these guys initially.

Yeah, it's really exciting.

(tense music) (narrator) To find out what's happening beneath the waves, Dave prepares one of his own inventions.

♪ (David) Put this tow video camera system in the water.

It's got a camera facing forwards and one facing backwards.

We'll see if we can see what they're eating.

(water bubbling) ♪ That's amazing, isn't it?

(narrator) But deploying the system while the boat is underway isn't a straightforward task.

(David) It's completely upside down for some reason.

That's not good.

Why is it doing that?

(intense music) (staticky crackling) (soft music) (sighing) Just killed two cameras.

Flooded them straight up.

Unbelievable.

♪ (narrator) Killer whales have rarely been sighted in Australia's waters.

With the cameras replaced, Dave hopes to capture a glimpse of their underwater world.

(splashing) (energetic music) Thought to travel thousands of kilometers across the Southern Ocean in fast-moving family groups, no one has managed to document them along this coastline before.

♪ (David) This is nerve-racking.

(Michelle) Look at them, there they go!

Whoa!

Look at the body!

(David) Ah, look at this!

♪ Oh, look at this one, look at this one!

He came right up.

(Michelle) Scott, here, here, they're chasing fish.

Quick!

Under the boat!

Yeah!

Woo-hoo!

They're all around us.

It's amazing.

(dramatic music) (David) Is that one recording still?

It is.

(sighing) ♪ (whales vocalizing) ♪ (narrator) Dave's underwater camera system has opened a magic window into another world.

(whales vocalizing) ♪ (whales vocalizing) ♪ -Wow.

-What do you think?

(Michelle) Amazing.

You were right on.

I mean, this is the spot.

I mean, at least we've seen at least one female and a very small calf.

One larger animal, that could be a sub adult bull, I would expect.

And like two little groups here.

And you said there's more further this way.

(whales vocalizing) (narrator) Could these magnificent creatures be the killers of Shark Alpha?

♪ Are they the super predators of the deep?

(whales vocalizing) ♪ (soft music) ♪ (Michelle) We haven't seen this congregation of killer whales in Australian waters anywhere else really.

It's remarkable.

I mean, it's right here and where you said is in these canyon's areas.

They're not just traveling through this area, you know, there's something going on here.

We've seen them feeding, we've seen them chasing things through the water.

What that is, we don't know yet.

We saw a young calf, so it could be a really important area for breeding and mating as well.

It's obviously a really great spot, a hot spot.

(Scott) Okay, you can see here the two calves were playing and interacting and lying on their back.

(narrator) This photographic evidence provides a vital clue.

♪ Killer whales are known to behave aggressively when protecting their young.

If this is killer whale calving territory, few marine animals would be able to stand their ground.

(Michelle) And, see, I mean, look at that, that's a big dorsal when you look at it like that.

(David) Oh, he's massive.

This is him here swimming with a female, but I imagine that if a great white turned up in his vicinity, he would be the sort of animal that could take it down.

(Michelle) He's a big enough animal.

Absolutely.

(ambient music) (narrator) After four days of tracking killer whales, their movement above the Bremer Canyon proves they're concentrating on specific activity at the center of the hot spot.

♪ Dave needs to find out what's keeping them here.

(dramatic music) ♪ Taking advantage of the calmer seas, the team prepare to launch a remotely controlled -deep-sea glider.

-It's a thumb thing, push the little button on the end and then the pin will come out.

(narrator) Designed to search for clues in the depths of the canyon, it's looking for readings out of the ordinary.

(David) Are we gonna deploy into the wind, or are we gonna swing it around into the lee?

(man) Into the wind side of the boat, blows away from it.

(David) Ah, that's--yeah, right, learned that the hard way.

(laughing) Here we go.

♪ (splashing) ♪ Off she goes.

It's in there.

Classic.

♪ We're gonna run it straight through the area overnight, right through where the killer whales are actively feeding.

We'll send it down to around a thousand somewhere.

At the end of the day, this device is designed to pick up any sort of nutrients, any sorts of hydrocarbons, fuel, things that are leaking that could possibly be causing the congregation of marine life out here.

This is a great way to find out.

Poor thing, I feel horrified for it.

(clicking) (uplifting music) (water bubbling) ♪ (narrator) With the killer whales approaching and the engine switched off, Michelle uses an underwater microphone to eavesdrop for clues.

-Can you hear them?

-Clicks.

♪ (whales vocalizing) (ambient music) ♪ The great thing with acoustics is that you're able to get more of a 3D picture of what's going on 'cause you can see their surface behavior, but you can also hear and listen to what's going on under the water.

(whales vocalizing) (soft music) (narrator) As they approach the boat, the killer whales become wary and stop vocalizing.

(Michelle) And so they're using passive acoustics, so they're listening rather than using active acoustics unless they need to get each other together again.

(dramatic music) Ohh!

♪ (David) It seems they're just starting to fire up now.

We're coming up on quite a large flock of birds, and we've seen a lot of blows of killer whales, so it looks like they could be feeding, and with any luck, if they're feeding, there will be other species of animals there and that's particularly what we're interested in.

(Michelle) I was starting to feel a little bit skeptical this morning.

Change of weather.

(engine starting) (narrator) Now that they've got hunting killers in their sights, the team send a photographer to the scene for an aerial view.

(plane droning) (David) Yeah, copy, can you hear me loud and clear?

Over.

(David) John, it looks like we've got at least a dozen or so whales.

It'd be good to hear what you guys can see.

Maybe if you go up to a thousand or something, or 800.

Over.

♪ (Peter) Yeah, they're feeding here.

(David) Yeah, great.

Okay, thanks, mate.

(Peter) They're feeding on something up here.

-Oh, look.

-So did they say that there's something on the surface?

(David) Yeah, something that's belly-up.

-Large or small?

-Said quite large.

(indistinct chatter) I'll move down a little bit quicker.

I can't go too much faster.

(Michelle) Oh, feeding.

(Scott) They're feeding over here, look.

(Michelle) Oh, wow, look at that.

(plane droning) (narrator) Timing their mission perfectly, the aerial team captures this extraordinary event as it unfolds.

(camera shutter clicking) (dark music) (birds squawking) (Michelle) Look at all those birds.

I wonder what they've got.

Scott, can you get a photo of the birds?

We need to know what that is!

We need that bit of meat!

♪ Christian, do you have a net?

Scott, Scott, Scott!

(Scott) I can't, I got to focus.

The whale came up and turned on its side.

It had a chunk of flesh in its mouth.

I could see all the white flesh.

(Michelle) Lots of birds, they're all pulling at some sort of meat.

I mean, I could see it was white and blubberish.

What it was, I don't know.

♪ (narrator) Moments later, the killer whales' mysterious feeding event now over, their behavior suddenly changes and they head straight for the boat.

(David) Look at that.

(majestic music) ♪ -Oh!

-Oh, this is what we want.

(splashing) ♪ (Peter) They're all around us at the moment, so it's pretty hard to know where to go.

(Scott) There's mom with a nick.

We've got the first day with the calf.

(David) We're sitting on about 20 to 30 killer whales.

What's interesting with these guys is that they've got a tinge of yellow to them which apparently indicates they've recently come from the Antarctic.

(camera shutter clicking) ♪ What's this tail-slapping all about?

Could it be directed towards us, you think, or do you think it's just them-- (Michelle) Oh, there's a head slap.

No, well, I mean, you're seeing the behaviors outside of where we are, so it's towards each other.

Now, I mean, it could be mating behavior.

The tail slapping is more likely to be aggression towards each other or--whoa!

Just right there!

(camera shutter clicking) ♪ Absolutely incredible.

I mean, they're just being really social with us and each other.

Look, you can see their calves, and look.

♪ -That's a calf.

-That's a calf playing with another one.

I've started crying, that's how emotional I'm getting right now.

(narrator) These spectacular interactions indicate that this hot spot, if not a breeding ground for killer whales, could be a type of nursery where the young learn the ways of the old.

If a great white shark entered this territory unannounced, its chance of survival would be slim at best.

♪ (Michelle) It's just an area that we have to learn more about, because this doesn't happen in the Southern Hemisphere.

It hasn't to this date.

It's groundbreaking.

It's never been documented like this.

It's just incredible.

♪ (mysterious music) (narrator) Back on dry land, one of Australia's foremost marine biologists, Dr. Mark Norman, has joined the team.

His first task is to try and identify the mysterious flesh that was consumed by the killer whales earlier in the day.

(anxious music) (man) So, here's the images, guys.

I think you've gotta have a look at this.

This is-- Keep in mind, we're up high.

Pete got us up quite low, but we didn't wanna spook anything, so I zoomed in on this.

Quality's not 100 percent, but, yeah.

(Mark) It's definitely a squid, and the skin color's-- What's the scale, can we get a sense of size?

The black of the killer whale is roughly four meters, and what you can see of the white is obviously a similar sort of a size.

To me, this just says, squid mantle.

A mantle is like the tube that they cut the rings out of when you have calamari rings.

That's an opening where the head would have attached from a squid.

The color really sits comfortably for one of the big squid species.

With the sort of red skin like that, it really looks like a big squid, which if it is, you guys are on such a hot spot.

'Cause the one thing that hasn't happened in Australia before, there's never been a connection of the whales feeding and the evidence of big squids brought to the surface.

Is that the only photo you've got?

(Dave) No.

-We have a couple more.

-We have a couple more.

(Mark) Now, what amazes me is that the head and arms are already gone, so these guys have been chewing on this somewhere else.

I'm startin' to see white under here, which looks a bit like torn-off fin on the edge of the mantle or something.

If that whale is four meters, we're talking a bloody big squid.

-Keep going, show me more.

-Show you more.

(David) The last image is this one.

(man) Oh, you can't make much of that, can you?

(Mark) No, but it's big.

It feels nervously big to me.

(Dave) Whatever this was, was basically eaten, like, killer whale fairy floss.

-It was that quick.

-Quick.

Well, if it went quick, that goes back to-- it's hard to eat a shark quick.

(Dave) Yeah.

(Mark) No, that looks significantly larger.

It's either the biggest giant squid on record, or I don't know what it is, which leaves a lot of other possibilities.

(David) That's very interesting.

(curious music) This was the easy phase.

Now we need to go deep.

(splashing) (narrator) To hunt for deep-water predators all the way to the seafloor, the team are assembling a remotely controlled camera sled.

Its four camera housings are designed to withstand undersea pressure that would crush a human being.

Their focus is to find the next suspect.

But first, Dr. Mark Norman needs to hit Dave with some cold, hard facts.

(Mark) Okay, Dave, I've got something to show you that proves that it wasn't a giant squid that ate your shark.

No matter how big a giant squid might be, they've got a mouth end that is very strange.

This is the exact replica of a mouth end of a giant squid -that was 15 meters long.

-Wow.

(Mark) So, it's got a beak in two halves, and then underneath, it's got a tongue covered in sharp teeth.

And the whole point of that whole front end is to chew the food into the finest kind of liquid they can.

The reason is that all the squid, and octopus, and cuttlefish evolved with a doughnut-shaped brain.

Their brain evolved around their food tube, -around their esophagus.

-Right.

(Mark) So, they've gotta turn everything into a thick shake to squeeze through the middle of their brain, which means it couldn't possibly have swallowed an intact receiver into its stomach.

It's just not physically capable of it.

Take your arm off easy enough -wouldn't it?

-Totally.

(intriguing music) (narrator) The giant squid might not have the weaponry to take out Shark Alpha, but they are high-energy prey items for other large marine predators.

If they can find further proof that giant squid populate the canyon, it would explain why big animals are targeting this location.

♪ (Peter) Well, actually, they're coming in on us again now.

We're just trying to drift down towards them and watch them feeding.

(water splashing) (whales calling) (Mark) They're right under us!

♪ Got 'em?

-Look at that!

-Comin' up for a look.

(Mark) Isn't that the stuff?

(Dave) Look, right there!

(Mark) They're going between the hulls, unbelievable.

But you gotta have a boat that whales love.

(mysterious music) (narrator) Moments later, the ocean sends the team a sign that something is stirring deep below.

(Mark) You smellin' that?

(Dave) What is that?

(Mark) That's another mystery!

I don't know.

What's leaking that much liquid, or that much oil, this isn't a cupful.

-No.

-That's a huge amount.

Maybe we're seeing the edges of a feeding frenzy down there -that's bubbling to the surface.

-Yeah.

(Mark) Maybe the smells in those slicks are what's in the water columns bringing animals in from everywhere.

So, who knows what's goin' on?

(energetic music) (Dave) Just running straight up the oil slick into the wind, and, of course, straight up the head of the oil slick are the killer whales, so.

The birds are all congregating around them, as usual.

♪ (narrator) As soon as the killer whales dive, birds fight for the scraps left at the surface.

(birds calling) -It's a squid tentacle.

-Yup!

(Mark) It's a squid tentacle, -can you get it?

-I reckon.

I need to get up on it, I'll grab it.

(birds chirping) Ah, off it goes.

♪ Mark's got some photographs close-up from the top, and it was definitely a squid tentacle about this long, but unfortunately, it sunk, so we didn't get a sample of it.

(Mark) What I like is a squid has just been killed in this area.

We don't know how big that squid was.

It might be the tip of a big arm, or it might be that was the full arm, and it's a smaller squid.

But I think you couple that with some activity showing on the depth sounder, and all of a sudden, we're getting really interesting-- Something's going on here, it's really, it's starting to hop.

So, sooner we get that deep-tow camera in, the sooner we can see what's goin' on at 200 meters.

(mysterious music) ♪ (narrator) The team call in the deep sea glider to interpret its water column data.

They want to know where they're most likely to find deep sea predators.

(man) We have, uh, it's showin' up two areas of interest for us to look at.

There's a chlorophyll maximum at about 70 meters.

(Mark) So, this is an indication of plant activity.

Where food's being made, and other creatures come to it to feed.

(Dave) That'll be our first point that we'd like to get our drop cameras to.

We might see some interspecies interaction.

And it looks like we've got another point at 700 meters.

(man) Yeah, what we're getting is the signal off the sensor, which is sensitive to hydrocarbons.

-Hydrocarbons, as in oils.

-Yeah, yeah.

Quite a broad band, about 50 meters thick.

But, yeah, that's quite anomalous, and pretty exciting.

You've got a theory about hydrocarbons, haven't you?

(Dave) I'm thinking there could be some sort of a leakage of some description in the mouth of this canyon that's providing a vertical source of nutrition for this water column activity that we're observing.

That could be the reason for this for this congregation -of life we're seeing out there.

-This hot spot -we're seeing here.

-Yeah, the hot spot.

(foreboding music) (narrator) The glider's data has identified two separate targets for the camera sled.

The first is at 70 meters, a sunlight-fueled depth zone.

The second is 700 meters down, pitch dark and freezing cold.

It's here, in two different sub-surface worlds, the team are hoping to catch sight of a predator capable of taking out a great white shark.

(Peter) Soon as this goes out, we'll strap these back.

Oh, and you clipped on?

(Mark) Let me just check everything's working.

(man) Hold it!

Hold it!

(indistinct speaking) Right-o, start feedin' her out!

Keep feeding it!

♪ (narrator) The camera sled is fitted out with a sonar system that's capable of detecting the movement of large creatures within a 500-meter radius.

♪ Tethered to the vessel by kilometer-long steel cable, the system feeds live images to the team above.

(anxious music) (Dave) Ugh, nerve-racking.

So, why have we got two dead?

Hm.

(computers beeping) Two tellies aren't working, so we need to come up.

May mean that we've had a flood.

(Mark) Yeah, that should have-- (Dave) Ugh!

Oh, smoky, smoky!

(Mark) One down.

(Dave) You're just gonna get the housing off, -run with three, dump it in.

-Yeah.

(Dave) Oh, well.

(tense music) ♪ (Peter) Lower it down, mate!

♪ (narrator) After two long hours, the team finally guide the deep-sea camera beneath the waves.

-Beautiful!

-Well done.

♪ (Mark) See?

Comb jelly.

Comb jelly, look at that!

(laughing) -There's a lot of life there.

-It's pretty busy.

Let's sit down over here.

(Mark) Bremer Bay Canyon reality TV.

(Dave) Yeah.

(Mark) I think we try this at a couple of different depths and see what we can see.

So this is at 70 meters, where that sort of plant matter productivity, the phytoplankton is.

So it looks pretty dense.

There's a lot of things goin' on there.

This is encouraging.

(captivating music) Bigger animals would be there, especially at night, they'd be feeding in this sort of territory.

It's just, yeah, the luck of getting them into frame, I suppose, seeing what comes into the cameras.

Hopefully, something very big will come through, but that might be deeper down.

(Dave) Mark suggested that he was gonna stay awake for 48 hours straight.

(laughing) (narrator) Slowly falling three meters every minute, the camera sled descends towards the seafloor.

(suspenseful music) ♪ (Mark) What I really like about this is all these little bright dots, most of them are living creatures, but I always think it looks like you're traveling through outer space, and then these alien creatures come through.

So that weird-looking thing, this is a free-swimming oceanic worm.

There's stuff everywhere.

Here, at 500 meters, we're still finding heaps of critters.

Another prawn.

And we know we're in deeper water now because it's red.

It takes less energy to make red pigment than it does to make black pigment, so you find a lot of deep-sea creatures are bright red.

♪ So, the other thing you get a lot of in this deep water is jellyfish.

But every now and then, we're getting fish coming through.

So, they're all kind of going up the steps of the food chain from the smallest, simplest things, up to our big munchers, like the sharks and the killer whales.

(ominous music) ♪ (beeping) You've got squid here.

You're gonna have all sorts of squid in this system from the tiniest ones, through to the big giant squid.

But you can see how fast they are, and how they're darting around -in the lights of the camera... -Yeah.

(Mark) ...grabbin' food and shooting out.

In searching for things like giant squid, it's like you're shooting blind in this huge area of ocean.

Anything we get is an absolute win.

And you never know what's gonna turn up.

All you can do is cross your fingers, and hope that it's one of the big ones.

♪ (narrator) In the early hours of the morning, a fast-moving mass briefly appears on the sonar right before the camera signal cuts out.

(banging) (static) (eerie music) ♪ After a three-hour ascent, the team wake to see that the sled has been hit with brute force.

(Dave) That's not good.

Somehow, the whole sled has turned, and it's put a full kink in the fiber-optic cable, so no more using the drop camera.

(dispirited music) (narrator) It's the end of the story for the underwater camera.

But incredibly, new evidence from the deep appears before their eyes.

(Peter) What is it?

-What's that?

-I don't know!

-Slime?

-It's not sand.

Doesn't feel gritty.

(curious music) (narrator) Surrounding the boat and stretching kilometers out to sea, an unknown bloom appears on the water's surface.

(exciting music) ♪ (David) So, where's that coming from?

We need to follow it.

(Mark) Can we drive along it?

(David) Can we follow this slick up, Peter?

Thanks, mate!

♪ (Mark) Look out from the nose, and see where it goes.

(David) Yeah, yup, I'll head up.

(Mark) Yeah, I wanna scoop more of this if I can.

-Looks pretty new, eh?

-Yeah.

When you get these sort of smooth patches, they get called Langmuir slicks, and it's where a little bit of current concentrates things.

(narrator) To discover the identity of the bloom, the team needs samples.

♪ (David) Just in here, go right.

Under that bird, kinda.

There's a couple of bits and bobs in there, actually.

(Mark) Well, we're gonna try and scoop up as much of it as we can.

(narrator) Dave believes this bloom signifies the end of the seasonal surge of marine life at the hot spot.

Initial tests reveal an ancient toxic bacteria that thrives when nutrient levels are depleted.

With killer whales nowhere to be seen, the water column has now effectively become a dead zone.

(David) I guess we're launching into the next phase now.

(narrator) The story of Bremer's seasonal food chain event begins at the edge of the canyon, one kilometer below.

Here, hydrocarbon seeps, first discovered by oil and gas prospectors, could be the instigators of life.

(eerie music) At these seeps, oil, methane, and nutrients surge up from deep within the Earth's crust.

(bubbling) These effectively act as organic engines in the cold, dark depths of the ocean.

♪ Surrounding these seeps, an amazing abundance of life flourishes... (wondrous music) ♪ ...from deep-water tube worms to armies of Yeti crabs, to schooling fish circling above.

At the height of summer each year, a surge of spawn rises to the surface, providing a rich source of food for all marine species.

Dave believes this is the secret of the hot spot and explains why so many large predators annually gather here.

♪ (anxious music) (wind gusting) ♪ Dr. Martin Hovland, an expert investigator of the world's most dynamic seafloor systems, has a theory that supports this idea.

-Hey!

-How you doin'?

(Martin) Good!

-Really good to see you.

-Yeah!

-Fully.

Finally.

-Fantastic.

(mysterious music) (narrator) Martin believes that the Bremer Canyon seeps reach the seafloor via a giant underground tunnel of salt, a geological phenomenon that supercharges the hot spot area with fertilizer.

(David) So here we are, this is where we are now.

-Bremer.

-Okay.

(David) And this is the area that we've been operating in.

(Martin) Yeah, you're seeing the canyons here.

-Yeah.

-So, you're sitting -between two canyons.

-Yes.

(Martin) To me, they tell that there is a weakness spot in the Earth here.

And any river pointing in the same direction will be the same weakness spot in the crust on land.

So, you see that the Bremer River is actually pointing right at this canyon, which is adjacent to your site.

-Yes.

-If there is seepage on the seafloor, there may often also be evidence of seepage on land.

(upbeat music) ♪ (narrator) Martin is targeting evidence of a specific type of seepage.

(Martin) Okay, so we come down to this small lake here, which is one of the mysterious brine lakes, like these.

(David) Hang on, everybody.

(indistinct speaking) (Martin) It should be in here, here it is.

-There it is.

-I see it.

-That's the lake.

-That's great.

(Dave) Let's just find somewhere to get in.

There'll be snakes in here, -tiger snakes, no doubt.

-Really?

Yeah, I'd say so.

(Martin) So this is the lake.

So, wow, look at this.

Let's taste it.

(David) I'll let you go first, you're the expert.

-It's really salt.

-Is it?

(Martin) But I don't know which type of salt.

(David) This isn't poisonous, I mean, look at this biodiversity.

(Martin) Yeah, but you see, it has to do with the degrees of poison.

The fact with seeps in the ocean, in the middle, there may be too much of it, so it'll be poisonous.

But when it disperses, and is eaten by the bacteria, that's when it's a nutrition.

Then you have to think up, 200, 300 meters up, and that's where the killer whales are swimming... -Yeah, yeah.

-...at the same spot all the time.

So, I've started calling it the tree in the ocean.

(David) Yeah!

(narrator) This theory of a super-fertilized water column explains the density of apex predator activity at the hot spot.

(water splashing) (curious music) It also explains why one suspect has remained elusive-- the great white shark.

♪ With multiple herds of killer whales patrolling the sea's surface, and vast amounts of prey below, great white sharks have stayed deep.

(dramatic music) More than ten years of tracking data proves they utilize the Bremer oceanic area.

♪ To Dave, these tracks offer a further vital clue.

The data shows there is a direct link to an infamous shark haunt to the east, the Neptune Islands.

♪ (foreboding music) ♪ Dave has joined one of the first research expeditions to the Neptune Islands of the winter season.

The Fox Shark Research Foundation has been studying great white sharks here for more than 40 years.

♪ Dr. Rachel Robbins is the team's lead shark biologist.

Andrew Fox is the expedition's leader.

(gate sliding) Their first mission is to retrieve a shark monitoring device that's been on the seafloor for the past 18 months.

(David) They'll rip the door open, one of them will jump out, run across the seafloor, grab this listening station.

It's potentially a little dangerous.

The guys have seen some, in excess of, five-meter sharks here.

While this person's out of the cage, there could be a big one come in.

(uneasy music) ♪ (narrator) No sharks have been detected in the area for two days... ♪ ...but this is no guarantee of safety.

♪ With the device located below, a lone diver races for the seafloor.

♪ Moving quickly, the device is tied to a rope, and hauled to the surface.

♪ (Rachel) We went down, and we managed to find the receiver.

And then we can get the receiver off, download the data.

I can't wait, this has been in the water for nearly 18 months now.

(indistinct speaking) (narrator) Data contained inside this device could reveal if extremely large sharks target the Bremer oceanic hot spot.

(Rachel) We know that the sharks that we tag at the Neptunes often travel west, and we know that some of our sharks have been detected on receivers in Western Australia.

So it's just as likely that sharks tagged over in Western Australia will travel back here and be detected on these receivers too.

(indistinct speaking) (narrator) This data, coupled with ten years of archive, shows that a super-sized five-meter-plus male has traveled between the Neptune Islands and the Bremer oceanic zone.

It's proof that huge great white sharks utilize the same area as killer whales and giant squid.

(tense music) (splashing) Within three minutes of the device being downloaded, the boat is surrounded by great white sharks.

♪ Dave wants to capture hard data of a white shark's body temperature to see if it matches the profile of the killer.

♪ (David) We're using this thermal imaging camera to show that when these animals come out of the water, they've got an elevated body temperature, and this can show us what that body temperature is.

♪ (narrator) Only when the shark breaks the surface can the thermal imaging camera pick up the body heat signal.

(David) All right, up you come.

♪ When they are coming out of the water, it's really distinctive that they've got an elevated temperature, roughly right about 26, 27 degrees, which is the same as what the tag showed the animal that ingested our animal was.

(narrator) The killer of Shark Alpha dived to a depth of 580 meters.

The tag's temperature stayed at 26 degrees in cold, ambient water.

This data profile fits the great white shark.

The shark's body heat profile now adds to the proof.

♪ (David) I guess the next question is what could motivate a large great white to eat this sub-adult white shark that we tagged?

(Andrew) There's a variety of reasons why it may have been attacked.

It may have just been a territorial dispute.

It could be hunger-induced.

Big sharks eat little sharks.

(ominous music) (narrator) The combined evidence places another great white shark front and center as the perpetrator, a cannibal.

But the speed of the attack is suspicious.

A shark capable of taking out a three-meter great white would have to be lightning-fast and of colossal size.

Tomorrow, the team are hoping to come face to face with such a creature.

(banging) (chain clinking) (Rachel) Keep your arms in, and stay in the cage.

(indistinct speaking) (narrator) It's been ten years since Dave was attacked in his boat by the great white during the tagging of Shark Alpha.

(David) Yeah, I haven't actually been in the water with great whites before, and here's is the first time.

So, there's a big animal down here.

His name's Mulga.

These guys have seen him a bunch of years in a row, so he's well big enough to have taken out this animal that we've seen in Bremer.

I guess I'm a little apprehensive.

They're pretty serious machines.

At the end of the day, I'm not a hero.

(anxious music) ♪ (narrator) Immediately, the cage is surrounded by half a dozen great white sharks.

♪ These animals are classified as sub-adults.

♪ They've reached a tipping point where their diet of fish changes to include mammals.

♪ Unusually, they appear to be moving as a pack.

♪ But something scares them off.

♪ (bubbling) ♪ Then suddenly, out of the blue, Mulga arrives.

(majestic music) Measuring more than five meters in length and weighing in at two tons, this is as big as male great white sharks get.

♪ Capable of attack speeds bursting to 50 kilometers an hour, Mulga's sheer size underlines his survival skills.

Sharks don't grow this big unless they're able to dominate other animals.

There can be no doubt that this is a super-predator capable of devouring a three-meter shark.

♪ (splashing) ♪ (David) Had a couple of nice, big four and a half, five meter sharks around the boat, so bit nerve-racking when you get in the water, but now that I've been in there with 'em, they're really interacting, and then one would take off up.

(Andrew) And then Mulga was pretty big, as well, wasn't he?

(Dave) Yeah, beautiful.

Yeah, he's got a real presence, doesn't he?

(narrator) These sharks, and generations before them, have likely targeted the Bremer hot spot through millennia, attracted by the huge reserves of seasonal prey on offer.

There, in the hydrocarbon-fueled ecosystem of the deep, is a place that harbors what could be the largest giant squid on record, an ocean zone so productive that it supports Australia's biggest seasonal killer whale population.

But in his search for the killer of Shark Alpha, the weight of evidence points clearly to one species.

(David) At the end of the day, I think we can conclude that the mostly likely candidate is a white shark.

There's no doubt about that.

As you saw, they're definitely capable.

They do interact with each other.

They can be aggressive.

(narrator) What remains unknown is the extent of aggression between species at the Bremer hot spot.

(captivating music) Could it be the realm of the marine world's most dominant apex hunters?

A place where the ocean's super-predators must compete to survive at the top of one of the world's most dynamic food chains.

(David) The plan is to continue heading out to this location.

There's a lot of secrets to be learned out off this canyon.

And the ultimate goal here is to protect the place.

It's that important.

♪ (energetic music)