Steve Backshall: I'm Steve Backshall, a naturalist and explorer.

There are still dark, wild, and beautiful corners of our planet about which we know nothing, but now more than ever, the most important thing is finding ways to protect them before it's too late.

In the last year, I've headed to some of the most remote parts of the planet in search of precious natural wonders.

Look, look.

Bear.

Backshall, voice-over: I've attempted to unearth the secrets on an ancient civilization...

It's the stairway to heaven.

Backshall, voice-over: and to discover extraordinary wildlife... Backshall: This is amazing.

♪ Backshall, voice-over: wildlife more at risk than ever before.

[Gorilla bellows] Backshall: Wow.

Those sounds, they just put the hairs up on the back of your neck.

Backshall, voice-over: Only by understanding the world around us can we preserve it for generations to come.

I've never been anywhere like this before in my life.

♪ Backshall, voice-over: Saudi Arabia is a land of unsolved mysteries.

Ancient cites left virtually untouched for thousands of years still hold undiscovered secrets.

Now it's a race to find and record places like these before they're worn away by time.

♪ The Arabian Peninsula was once a major trade route from Southern Arabia up to the Mediterranean and beyond.

♪ We're headed to Al-'Ula.

♪ 2,500 years ago, this was a thriving city, the capital of the ancient Dedanite and Lihyanite kingdoms.

♪ Our goal is a series of 3 giant rock pinnacles.

♪ Specialist Dedan archeologists believe the third and highest pinnacle was held sacred and have been studying it to discover what this ancient site was used for.

♪ We've been give special permission to free-climb the unexplored western face.

♪ To take it on, I'm teaming up with one of the world's best rock climbers-- Leo Houlding.

Is that where we're headed?

Backshall: Yeah.

[Scoffs] Look formidable.

Backshall, voice-over: Archeologists have been to the summit, but where we're going no one has set foot for centuries.

♪ We want to follow the pathway used by these ancient civilizations up staircases carved 2,500 years ago.

♪ We hope our climb will reveal new secrets from this long-gone era.

♪ Local guide Ahmed Aliman is taking us to the base of the first pinnacle, where we'll start our climb.

Oh, that is really beautiful.

Look at that.

[Panting] [Exhales] It's just ancient, ancient rock.

♪ How do you think the ancients would have accessed this peak?

Aliman: They don't want people to reach easily, only the people who's allowed to reach there.

That's why there are stairs, there are bridges between rocks, nothing anyone can pass by.

♪ Backshall, voice-over: To reach this sacred peak, ancient stonemasons carved staircases into the rock and built bridges to link all 3 pinnacles.

After centuries of erosion, many of the staircases have disappeared, and the last bridge has collapsed, cutting off our route to the summit.

♪ No one has climbed these ancient, carved staircases for hundreds of years.

♪ Do you know what's on top of this peak?

I reach the first and the second rock.

The third one, never been there.

♪ Backshall, voice-over: To reach this elusive third pinnacle, we're relying on Leo's world-class climbing skills.

That looks incredibly loose.

I'm no archeologist, but it looks to me like this bit's eroded away quite significantly.

I would suggest we rope up now.

Backshall, voice-over: This ascent is beyond most climbers' limits, so Ahmed and the rest of the team are staying behind.

[Carabiners clattering] Backshall: Every time I end up climbing anything with Leo, at the end, I say to myself, "I'm never doing that again," because I've been frightened silly, and yet somehow here we are.

We don't normally have 3,000-year-old ruins at the end of the day, though, do we, Steve?

No, but there's an extra added element.

You've also got to be careful because what you're touching is history and you could destroy something of absolute significance.

Yeah.

Remind me of that if you see anything because I'm gonna be focused on getting us up there as safely as possible.

Backshall, voice-over: We'll keep Ahmed across everything we find over the radio.

Good luck, and thank you so much.

Backshall: And thank you for giving us the great privilege of doing this.

♪ Come on, then.

Let's do it.

♪ Right, so just watch out.

I'm just gonna do a rock test to see how loose it is.

♪ Yeah.

That's loose.

♪ Backshall, voice-over: Climbing alongside Leo and me is ropes expert Aldo Kane.

Kane: First impressions?

It's hollow, very hollow... ♪ and it's quite difficult to trust.

There's a lot of loose ones here.

♪ Backshall: There's that tense moment before you start anything like this of focusing your mind, trying to think about all the simple tasks of making sure that you've got everything in place that you need, and having seen Leo, one of the best climbers in the world, going up that gingerly, I'd be lying if I wasn't a little bit on edge already.

[Inhales] Backshall, voice-over: With Leo safely on the first ledge, it's my turn.

♪ Uh!

♪ Oh, wow.

That is amazing.

You wait till you see this.

Is that all carved out above you and behind you?

Yeah.

Yeah, the whole thing, the whole face.

Backshall, voice-over: Unraveling the mysteries of these rocks will take archeologists years.

♪ This mountain is a sacred place for Dedanite.

They have many secrets still hidden.

They don't want anyone to reach it.

Backshall, voice-over: 30 meters up, we've reached the start of a long, carved staircase.

Houlding: Oh, ha ha!

Wow!

All right.

Come on.

Let's go.

Let's go.

Huh huh huh huh!

That is one very, very excited Leo Houlding.

[Laughter] Backshall, voice-over: On each step, there are chisel marks still visible.

We're walking in the footsteps of the ancients.

It's the stairway to heaven.

♪ Oh, this is the top of the first one.

Backshall, voice-over: From here, the route gets tougher.

We must cross the first stone bridge to access the second pinnacle, but the rocks have crumbled away.

♪ Leo crosses first to secure a safety rope.

♪ Ready, Steve?

Ready, mate.

OK. ♪ Ahh, thanks, buddy.

Backshall, voice-over: From the bridge, we can see our next hurdle.

Backshall: We've got a traverse here which is almost impossible to protect, so the only thing to really do is just go for it and just walk and try not to think of quite how far down it is.

Kane: You walk like that.

[Shudders] Backshall: Nice work.

Backshall, voice-over: With the traverse behind us, we can now head to the top of the second pinnacle.

Houlding: Ooh, hello.

We've got an obstacle, boys.

♪ Houlding: Pretty serious one.

♪ Backshall: The face has fallen away below us as well as there, so there's no staircase here.

We're gonna need to abseil down to even access it.

Houlding: All right, full concentration, boys.

Kane: Yep.

We're in a death position now.

Backshall, voice-over: Leo rigs ropes so we can abseil to the base of the bridge and walk around it.

Beauty.

Backshall: How happy are you with that, Leo?

Happy.

♪ Backshall: It's tiptoeing around on ledges, lots and lots of slippy stuff.

I have to admit, I'm really quite scared, but the potential for what's up top makes it very, very difficult to turn back.

♪ [Breathes deeply] OK. Ready?

Yep.

How's that feel, Steve?

Uh, sketchy as-- Looks like you're going over an overhang.

♪ Backshall, voice-over: We navigate our way around the bridge only to realize that was the least of our worries.

Oh, my goodness.

That is a pretty severe obstacle.

It's probably only 10 meters to the start of the staircase, but it's overhanging, featureless, and loose.

I can't quite see how we're gonna get up it just yet.

♪ Backshall, voice-over: We can see the staircase above us, but blocking our path is a sheer rock wall with no obvious foot or handholds.

There's only one of us capable of attempting this, and that's Leo.

♪ OK.

It's a little bit complicated, but I'll tell you what we're gonna do.

We're gonna create a baby bouncer.

We're gonna use two ropes, so one of the ropes is gonna go to that piece of protection over there, and then the other rope is gonna go into that piece over there, and I'm gonna try and climb directly up there, which means if I fall off, "A," less of the load's going onto that one, and, "B," if that one pops out, I'll swing over into this, which would be a less bad fall than going all the way down there.

By less bad, you mean smashed legs.

Well, exactly.

I mean, you know, legs heal.

Necks don't.

♪ OK. No mistakes.

♪ Backshall, voice-over: As Leo climbs, he fixes small anchors for the safety rope.

All we can do is watch and hope.

Backshall: It makes me feel sick.

Just look at what he's walking on and look at the drop below, and he's not even on a rope.

♪ I mean, I love working with Leo, seeing someone who just kind of looks at rock in a totally different way and risk, as well, but there are times that he does things that just make me feel physically sick, and this is one of them.

Kane: Need a bit of slack on that?

Yeah.

[Blows] ♪ Backshall, voice-over: Leo climbs with the lightest of touches using delicate fingerholds to scale the sheer rock wall.

♪ There's nothing for your feet at all, and it's slightly overhanging.

♪ Uh!

Backshall: Leo's pushing through some really hard stuff.

It just looks like you couldn't climb there.

♪ All right.

I'm at the ledge, boys.

Backshall: Roger.

Whoo!

Wowsers.

That was unbelievable.

If that was one meter taller, that blank section, I wouldn't have been able to do it.

As it was, it was right at my limit.

I was holding on to the tiniest, little chip marks from the chisels of our ancient masonry friends.

99.9% of the population would not be able to climb up there now that the wall is demolished.

♪ Backshall, voice-over: This sheer rock face has stopped anyone from climbing this route until now.

♪ Leo has unlocked the pathway to the highest pinnacle.

We're now treading in ancient footsteps for the first time in hundreds of years.

Backshall: There's something spine-tingling about this, about looking at every single one of these cut marks, and it's soft rock, but it is still rock, and every single one of these scrapes represents the graft of someone way back in time.

They've come up on a mountaintop, and they've carved away the cliff face to create this perfect stairway.

♪ I was so curious what can be found up there to complete the story of Dedan, why they are using this mountain, what's at the top.

♪ Backshall: Whoa ho ho ho!

Wow!

The rock is covered with inscriptions.

Almost every single hand's breadth of rock is carved.

Be quite careful where I put my hands and my feet because it is everywhere... ♪ and all of this would have been carved at least 2,100 years ago.

Backshall, voice-over: We can't show these inscriptions because the archeologists want to protect this discovery.

Once deciphered, they could revolutionize our understanding of this ancient world.

We film them to add to the ongoing study of this sacred site.

Backshall: Ahmed, there's so much evidence up here.

What evidence?

What kind of things?

There is writing everywhere, all over the rock walls, on some of the tumbled slabs.

Like full sentences or just words?

Some of the things that I'm looking at look like they are sentences, but there's so much of it, you know, it's covering all of the walls above my head, in front of my face, down on the floor, and some of it stretches for quite long distances, so it looks like sentences... Wow.

so if this was a sacred place, what do you think would have happened here?

Aliman: Maybe it is for meditation or for sacrificing animals, sacrificing something for their god.

Well, they've certainly picked a very, very dramatic spot for it.

You couldn't wish for somewhere that feels closer to the heavens than this.

♪ Backshall, voice-over: On our way to the summit, there are more clues to the purpose of this site.

Backshall: These furrows in the sandstone-- I've seen these before-- these are where people have been sharpening their tools.

Can you imagine someone coming up here and sharpening their blade before using it to sacrifice an animal, uh, possibly even a person, to the gods?

That puts a chill up my spine.

♪ Backshall, voice-over: With one last push, we summit the final pinnacle, possibly the most significant point of this ancient kingdom.

♪ Thank you, mate.

Awesome adventure.

What a privilege.

♪ Backshall: Back through time, peoples have always given their effort, their blood, sweat, and tears to the gods, and in making an effort to get somewhere like here, the bravery, the manhours of work to get up here, that in itself is a sacrifice.

♪ What we can see all around are fortifications, walls, inscriptions, carvings.

♪ This was somewhere that meant everything to the Dedanites, and eventually, their civilization disappeared, and we may never know that much about it, but up here, you can feel something of their spirit, something of what was special to them.

♪ What a place.

Backshall, voice-over: If understanding our past before it's lost forever is important, preserving the world we live in today is crucial.

♪ The Sea of Cortez stretches 1,000 kilometers along the Mexican coastline.

It renowned for its rich marine life.

Our journey starts on the Baja Peninsula in the harbor of La Paz.

♪ Backshall: We're leaving port in La Paz and heading out into the Sea of Cortez, which is the place that Jacques Cousteau referred to as being "the world's aquarium," but in the 1980s, industrial fishing was allowed in the Sea of Cortez.

It had a devastating effect on marine life.

The good news is that the Mexican government created 11 marine protected areas, and life here is recovering, but the mobula, a species of ray, is still struggling.

The Mexican government fears it could go extinct and has recently placed it under special protection.

♪ I've come here to find out whether they're bouncing back.

Our secret weapon is the Peregrine spotter plane.

Man: Peregrino, Peregrino... [Speaking Spanish] Backshall: For our first two days, we have a spotter plane that's gonna be flying around close by to us looking out for mobula rays.

They're kind of like a mini manta ray, but they occur in huge squadrons hundreds of animals strong, and to find and locate those right now would be really special.

Backshall, voice-over: Pilot Siddartha Velasquez is scanning the ocean.

It's April, and at this time of year, mobula rays migrate through the Sea of Cortez, but no one has seen them yet.

Backshall: Sid, hola.

Hola.

¿Como esta?

Muy bien.

¿Y tu?

Muy bien.

Your plane is amazing.

Thank you.

Did you make it yourself?

Yeah.

You did?

Yes.

I did.

That's unbelievable.

You've been up flying this morning?

Yeah.

And what have you seen, anything good?

I saw whale, humpback whale.

I saw two big pods of dolphins, common dolphin.

We don't see-- I don't see too much of mobula munkiana... Yep.

so seems like the mobulas munkiana, you are gonna begin to see it from Ensenada de Muertos all the way to Los Barriles, La Ribera, and Cabo Pulmo.

So that's south.

Yes.

Backshall, voice-over: We follow Sid's directions and head 4 hours and 200 kilometers south, anchoring in a large bay just outside Cabo Pulmo National Park.

♪ At night, we have a much better chance of tracking down mobula, but we're not going to them.

Backshall: The sun has dropped down below the mountains.

It's starting to get dark, and now we have a way of attracting the mobula to come to us, so they are plankton feeders, and by putting light in the water like this, we can create an artificial bloom of plankton, and with a little luck, that will draw in all of the rays from this bay.

Backshall, voice-over: It's not long before the plankton starts working its magic.

Look at that on the surface of the water over there.

That's amazing, so that is the top of a squadron of mobula heading straight towards us.

Mobula are nervous, but while they're distracted feasting on plankton, I hope they'll tolerate us being in the water with them.

♪ You can see just by simply putting a light down into the water, we've attracted in the plankton, and that's brought in loads and loads of fish, but so far, not our mobula.

♪ Wow.

What are those big fish?

♪ Holy moly, look at the size of those.

♪ Backshall, voice-over: The giant shoal of smaller fish is drawing in jacks, and who knows what else might be lurking in the darkness?

Backshall: You have this many fish flashing around your ears by night, it's impossible not to start thinking of predators.

Certainly, there are lots of bull sharks in this area, and while I quite like to see them by day, I wouldn't be quite so happy right now.

Backshall, voice-over: With this much plankton in the water, the fish are in a frenzy.

Backshall: This is the weirdest sensation.

♪ I'm being physically assaulted by random f-- Oh!

Right to the-- I wasn't expecting that.

You'd think they'd be able to perceive where I am, but they don't seem to care.

Backshall, voice-over: There are plenty of fish here, but the group of mobula we saw earlier have still not shown up.

From her vantage point on the boat, marine biologist Frida Lara has spotted the issue.

Lara: There is a lot of plankton, anyway, so the light is just gonna concentrate plankton, but if they can find food in other places, they might just not come.

Backshall, voice-over: With plankton carpeting the entire area, this bay is a giant marine canteen.

The mobula could be anywhere.

Backshall: Well, we may not seen any mobulas tonight, but there's certainly no doubting the amount to life in these seas, and being in the midst of this predatory frenzy has been, well, frankly, a little intimidating.

Backshall, voice-over: Time for me to get out, but I'm hoping the high levels of plankton keep the mobula here until morning.

♪ We can see splashes at the surface, and it looks like animals breaching out of the water, almost certainly mobula rays, so our best course of action is to send the drone over in that direction and look straight down at them.

♪ All yours, Maru.

♪ Backshall, voice-over: Drone pilot Maru Brito scouts the area.

Backshall: Right.

Let's see what we've got.

♪ Backshall, voice-over: With a 360-degree view of the ocean, Maru spots what we've all been hoping for.

Backshall: Oh, that is beautiful.

♪ Whoa, that is a lot of animals.

Man: Yeah.

What, so every one of those is a mobula?

Si.

Ah, that's huge.

♪ That is beautiful.

It's like a billowing clouds of, well, leaves.

They look like leaves, but every single one of those is a mobula-- that's breathtaking-- and then every once in a while, it's kind of punctuated by this explosion like cannon fire at the surface as they leap up from below the water and then crash back down again.

♪ Backshall, voice-over: This is a giant squadron, the biggest that I've ever seen.

♪ You think we'll be able to get in with them?

Hopefully.

Sure.

We're gonna try hard, no?

♪ Backshall, voice-over: Even in a feeding frenzy, these rays are likely to be wary.

Maru and Frida track them carefully with the drone.

♪ How many do you think they are, Frida?

Lara: I think they could be hundreds or thousands, even... Wow.

because you see the top, but there are layers of them under, so it's so many.

Where are we right now?

Are we on the group?

Contreras: They're forward of your position.

They're coming in the direction of the bow of our main boat.

♪ Backshall, voice-over: I want to see whether this giant squadron will let me free-dive with them.

♪ Ah... this is amazing.

♪ We are sitting almost on top of a squadron of hundreds, possibly even thousands, of mobulas, and right now, they're doing what mobulas do.

They're breaching.

They're leaping.

They're jumping out of the water.

♪ [Gasps] There's lots and lots of reasons why these animals breach.

One of them could be to get rid of parasites and dead skin from their bodies.

Another way could be to evade the attention of predators, or it could be for communication.

There's one other intriguing idea, which is that this could be a way of demonstrating strength.

It's a way of showing that you're fit, that you have powerful genetics, and that could be a really important tool when it comes to breeding.

♪ Backshall, voice-over: Free-diving gets me closer to the mobula than I'd ever thought possible.

♪ I'm treated to a marine spectacle beyond my dreams.

♪ Backshall: It's one of the most beautiful, most balletic forms of movement in the entire aquatic world, and to see one single mobula ray is a special day.

Seeing thousands of them like this, it completely blows your mind.

♪ Backshall, voice-over: Mexico's special protective measures are paying off.

The mobulas are coming back in big numbers.

♪ Animals are resilient.

With protection, they can recover.

They just need a helping hand.

Other places on the planet are harder to protect.

In the jungles of West Africa, wildlife is under threat from poaching.

♪ Gabon's Moukalaba-Doudou National Park is home to one of the highest densities of great apes in Africa.

♪ I'm heading to Doussala Research Centre to meet a special group of gorillas.

♪ Outside the park, gorillas across West and Central Africa are under severe threat from hunting, habitat destruction, and disease.

♪ Here, they're protected, and I want to find out whether this troop is thriving.

♪ Biologist Alessandra Mascaro has worked on primate conservation projects across Gabon.

Mascaro: [Speaking French] Backshall, voice-over: The Research Institute for Tropical Ecology has been running a gorilla conservation project here for 10 years.

Lead researcher Etienne Akomu is allowing me to join his team of trackers.

We look for some traces and find the direction, where are they going, Yep.

and after that, we will try to follow traces.

Backshall, voice-over: Etienne and his team spent a decade tracking these gorillas until their funding ran out.

♪ Now for the first time in over a year, we're going back in, but we have to keep our numbers down.

♪ Backshall: So from here on in, I have to stick with the trackers and sadly leave Alessanda and the team behind, and as soon as we get close to the gorillas, I'm gonna get on the radio and give you guys a call, bring you in.

OK.

I'll see you guys soon.

Mascaro: Good luck.

Enjoy.

Merci.

I'm gonna be filming myself, got a couple cameras, just trying to follow the process of actually tracking gorillas through their natural terrain, and these guys are obviously the master.

I'm with this guy here.

Comment vous appelles?

Stephen.

Stephen.

Ah.

Moi aussi.

Oh.

Ha ha ha!

Two Steves in the forest together.

How about that?

Backshall, voice-over: Etienne leads us through the village plantations to the edge of the national park.

♪ Backshall: I've tracked gorillas lots of times over the years, and you just never know.

Sometimes you can find them within an hour or so, and sometimes you can go all day and not find anything.

Backshall, voice-over: Western lowland gorillas are notoriously shy and difficult to track in dense rainforest, but Etienne and the trackers can read this jungle like no one else.

Backshall: We're making our way across the Moukalaba River, and on the other side is the protected park and where we're likely to be able to pick up track of our gorillas, so once we reach the other side, we're gonna have to wear our face masks because we can pass on our pathogens to them, we're such close relatives.

Backshall, voice-over: In jungle this dense, we must stay on high alert.

Backshall: You don't need to be a tracker to recognize these giant, crater-shaped footprints that we're following.

Forest elephant.

The area is thick with sign of them, and that is by far the most dangerous animal in this part of the world.

♪ Some of these footprints are super, super fresh.

Stephen: Come on.

Look.

Oui, oui.

Oh, oui.

So the tree here is still wet where they've scraped past it as they've gone through.

If we were tracking elephants, I'd be delighted, but we're not.

We really don't want to be walking into them in this forest.

Backshall, voice-over: We're not the only ones using these elephant trails.

Backshall: Chimp poo.

This forest really is incredibly rich with wildlife-- chimps, gorillas, buffalo, elephant.

There's really nowhere else quite like it on Earth.

♪ Backshall, voice-over: Etienne spots our first sign of gorillas.

♪ Backshall, voice-over: To cover ground more quickly, we split up.

Stephen and I take one path.

Etienne takes the other.

♪ Backshall: We're finding more and more gorilla poo.

It's mostly plant material.

There's a few fruit seeds in here, as well, but it kind of shows that we're on the right track.

♪ Backshall, voice-over: After 3 hours, it looks as if we're getting close.

Backshall: Our first feeding signs.

The gorillas have been eating here.

♪ Backshall, voice-over: 500 meters away, Etienne radios in.

Akomu, on radio: [Speaks French] Backshall: [Speaks French] [Speaks French] Ah, we have them.

Yes.

Hello.

Etienne?

Akomu, on radio: We already found gorillas.

Ah, amazing news, amazing.

We will be with you very shortly.

Backshall, voice-over: I'm a complete stranger to these gorillas, and it's been a year since they've seen the trackers.

How they'll react is anyone's guess.

♪ Backshall: [Whispering] We found our gorillas.

We have two in the swamp just in front of me, a large animal just behind them, and another two or 3 feeding above our heads.

♪ See how cautious they are, how wary.

Any noise they're not expecting, and the eyes flit around, and they stop dead.

♪ Backshall, voice-over: The gorillas are on guard, but they're not showing any signs of aggression.

They've accepted me.

We call in Alessandra and the film crew.

Backshall: [Whispering] Oh, glad to see you.

How is going?

Amazing, amazing.

The silverback is above our heads.

There is a blackback just over here and a couple of smaller animals-- this one just there and another in the tree just here, and they seem pretty chill.

Backshall, voice-over: These gorillas are known as Groupe Gentil, the kind ones.

The trackers recognize each gorilla by its unique face markings.

Alessandra uses the cameraman's zoom lens to see the silverback close up.

Mascaro: Can you see the two stripes that he has on the sides?

They use them to recognize him and he should also have cuts on the ears.

Backshall: Oh, yes.

Yeah.

I seen the cuts.

It's a way to identify.

Uh-huh.

Backshall, voice-over: As the dominant male, the silverback is responsible for the group's protection.

♪ From his vantage point, he's keeping a close eye on us.

He's looking at us.

♪ Backshall: There are so many more animals up there than I realized.

Mascaro: Yes.

♪ There are not many places in the world that you can get a sight like this, are there?

No, absolutely not.

It's quite rare.

♪ Backshall, voice-over: It is the perfect opportunity to count them and, after a year without human contact, find out how healthy the troop is.

♪ Mascaro: In general, in terms of how many individuals can be found in a group, the minimum, like I mentioned, is around 10, 11, something like this, but here, they have around 19.

Backshall, voice-over: With such a large number of individuals, Groupe Gentil is going strong.

♪ [Gorilla screeching] Backshall: Wow.

Those sounds, they just put the hairs up on the back of your neck.

It just transports you back more than 6 million years when we shared a common ancestor with these animals.

See, he's using that drumming, chest-beating display as a way of both exerting his dominance and also kind of saying he'd rather we weren't here... [Bellows] so it looks like what we best do is move off and leave them well alone.

It has been an extraordinary experience, you know, this animal that faces so many threats from us as human beings but here has a future.

♪ Backshall, voice-over: Back in the village, the local community welcomes us with a traditional ceremony.

[Women singing] Backshall, voice-over: Our guide Rodrigue is passionate about these gorillas.

Protecting them is an age-old family tradition.

[Singing continues] Backshall: The Punu as a group not only hang on to their culture fiercely with a determination that's just extraordinary to see, but they also value nature tremendously, and they're a huge part of the reason why gorillas still remain safe here in this area.

[Singing continues] Backshall, voice-over: Here in Gabon, gorillas and humans are finding a way to live in harmony, but elsewhere on the planet, there are still places where wildlife and people never even need to meet.

♪ I'm heading to the Kamchatka Peninsula in the far east of Russia to the Kronotsky Reserve.

The Kronotsky River is the lifeblood of the reserve and home to one of the world's last truly wild salmon runs.

This vast, untouched wilderness has Russia's highest level of environmental protection.

Backshall: I can see the salmon.

I can't believe it.

I can actually see the salmon from up here.

They're so big and there are so many of them that they are clearly visible from several hundred meters up.

♪ Backshall, voice-over: I want to explore this pristine ecosystem, a place where animals have remained untouched by humans.

♪ For the next few days, we're gonna be based at this area of tundra.

It should be much easier here for us to explore and have a really good chance of finding some of the wildlife that makes Kamchatka so special.

Backshall, voice-over: Alexey Maslov, the reserve inspector, will be my host.

♪ Backshall: Hello.

I'm Steve.

Alexey.

Very nice to meet you, Alexey.

Backshall, voice-over: Alexey's ranger station sits on the Kronotsky River in the heart of brown bear habitat, the end point of the salmon run.

Backshall: When you look down the river, even for a few minutes, you start to see the scale of migration of salmon here.

The water is just thick with them.

Backshall, voice-over: Each one of these salmon has swum thousands of kilometers across the Pacific Ocean to return to the exact spot where it was born.

♪ Backshall: The riverside is key bear feeding habitat.

This is where you get a real sense of why the salmon are so critical to this whole environment, so you can see the littered remnants of the fish here and, of course, loads of bear scat and poo, and what's essentially happening is that you're getting all of this protein.

These nutrients which have been formed out at sea when these animals were out there feeding has now come back inland.

The fish themselves will die at the river's edge, or they get dragged up onto the land, and all of the nutrients get returned to the soil, and they help all of this environment to grow.

In actual fact, everything here, from the predators to the trees, it all relies on the salmon.

♪ Backshall: [Whispering] Bear, bear.

Oh, whoa, it's some bear.

It's coming our way.

♪ So he's seen us, and he's lifting his snout up to the air to get a bit of a scent of us.

♪ I am absolutely blown away by how big the bears are here.

I would not be surprised if the biggest brown bears in the world are right here in Kamchatka.

Certainly, they have everything they need in terms of an extraordinary amount of food.

♪ Maslov: Amazing animals.

It's my totem.

Your totem, your spirit animal.

Yeah.

I can see that.

♪ Oh, look, look, look.

Look.

Ohh... Oh, ha ha ha!

♪ There's a lot of talk about this possibly being the place on the planet that has the highest density of bears, and it certainly feels like that.

Backshall, voice-over: The bears are not just here because of the abundance of salmon.

They're here because of the lack of humans.

♪ Backshall: That's 4 bears in 10 minutes.

I've never been anywhere like this before in my life.

♪ Our bear is at present in search of breakfast.

♪ It is such easy pickings for them, I mean, they don't have to put any effort into hunting at all.

They can just wander around, dip their nose in, come out with a fish the size of my leg, and they take what they want, leave the rest because another fish is gonna be right next to it.

♪ Backshall, voice-over: I've seen bears all over the world, but this is the first time I've seen then so relaxed and unaffected by humans.

This is nature as it should be.

♪ Backshall: One of the first things you learn in biology is the idea of food pyramids, so that the bottom, you've got all the stuff that gets eaten by things as you go successively higher up the pyramid until you get to the apex predators at the top, and usually, there are very, very few of those.

To have lots of predators, you need to have an immense amount of food.

This amount of predators, you need a stratospheric amount of food.

♪ Backshall, voice-over: 13 kilometers downstream, where the river meets the ocean, the salmon attracts predators in their thousands.

So we go?

We go.

OK. Backshall, voice-over: There's another top predator I'm dying to see-- the Steller's sea eagle.

Our best chance of seeing it is at dawn.

Mm mm mm.

In Kamchatka, do you ever have a meal that doesn't have fish?

[Laughter] ♪ Backshall, voice-over: The Steller's sea eagle is my all-time favorite bird, and a salmon run this huge will be a magnet for them.

♪ That giant, black shape flying just below the moon is our sea eagle, and it's heading down towards the estuary, where all the salmon are gonna be congregated.

I reckon, follow that bird.

♪ [Gulls squawking] ♪ Backshall: Right here at the mouth, the estuary, of the river is where all the salmon are focused as they're starting to head upriver to spawn, and because of that, the amount of life here is just mind-blowing.

♪ Backshall, voice-over: And a little further down the coastline, we catch up with the eagle.

♪ What a sight.

Backshall, voice-over: Anywhere else on the planet, you'd struggle to see a single one of these rare birds.

Here, there are Steller's sea eagles dotted all along the beach, drawn to the salmon run.

♪ Backshall: They are the biggest, the grandest of all of the eagles, and this-- this is the best place on the planet to find them.

♪ They're so energy-efficient, just a couple of flaps of the wings to get them airborne, and they find a thermal, rising current of warm air, and just get higher and higher and higher.

Backshall, voice-over: Joining them are thousands of sea birds feasting on the salmon.

♪ The air is thick with birds... ♪ and in the water, there's loads of seal heads bobbing around, watching us curiously... ♪ and walking down the surf-- a giant brown bear.

♪ Backshall, voice-over: This magnificent, untouched coastline has one more surprise.

Sea otter.

♪ Backshall, voice-over: Sea otters are an endangered species, and elsewhere in the world, their numbers are dropping fast.

♪ I was not expecting that.

That's great.

♪ Backshall, voice-over: This reserve is a glimpse into the world as it once was, a world before humans.

Left well alone, it's a near-perfect ecosystem, and it's thriving... ♪ but our window of opportunity to preserve precious places like this is closing.

Backshall: All over the world, our wilderness areas are in big trouble.

Our forests are on fire.

The icecaps are falling apart.

To come somewhere like here that's still absolutely perfect, it strengthens the resolve.

It forces you to remember what it is we have to lose and all there is that's worth fighting for.

♪ Backshall, voice-over: As the human and natural worlds continue to collide, we have to identify the pristine places we still have left.

♪ The need for exploration has never been more urgent.

Backshall: What we've learned more than anything from these expeditions is that there is still so much out there to be done, so many mountains to be climbed and rivers to be paddled, but now more than ever, the most important thing is the conservation of these few perfect, pristine parts of our planet.

♪ Announcer: "Expedition with Steve Backshall" is available on Amazon Prime Video.

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