Giants of the West Britain's Secret Seas

The waters around the UK hide treasures

and surprises we rarely get to see.

Powered by Arctic currents to the north,

and the Gulf Stream to the south,

our island occupies a unique position in the Atlantic Ocean.

'I'm explorer Paul Rose.

'I was base commander of the British Antarctic survey for ten years

'and I've scuba-dived all around the world.'

I've found one! That's a bomb.

'But now I've come home to lead a team of specialists,

'to uncover the secrets beneath our seas.'

-Divers up!

-'Joining me is marine biologist Tooni Mahto.

'Her underwater expertise will reveal

'the unexpected riches of British marine life.'

See the size difference between

the giant male and the much smaller female.

'Journalist and underwater archaeologist Frank Pope

'will examine the bigger picture

'of our relationship with the sea and explore our maritime history.'

Even if we make one tiny deviation, we could easily end up grounded.

This series will take us on a journey

right around our British seas

to uncover the most startling underwater wonders.

This week, we're exploring Britain's west coast.

We're going in search of the UK's biggest marine animals,

the biggest ships and its biggest wreck.

The seas of the west coast of Britain

are cram-packed full of giants.

Beneath our waves is a world of secrets.

Our expedition begins in Cornwall,

down at the very bottom of the west coast of Britain.

It's here we hope to investigate our nation's largest native animal -

the mighty basking shark.

The west coast of Britain has got many giants,

but none greater than the basking shark.

They grow to an astonishing 11 metres long,

weighing in at seven tonnes.

It's the second largest fish in the world -

only the whale shark is bigger.

And in the summer months, the basking sharks can be seen

along the entire west coast of Britain

from Cornwall right up to Scotland.

But what is it about our waters that attract these mighty leviathans?

Look at that!

It's hard to believe that these things live in British waters.

They're huge, great things.

There's a real element of mystery about these sharks.

So little is actually known about their biology, where they spend their winters,

what their reproductive cycle is,

there's all this sort of list of unknowns

about this giant, giant creature.

They're listed as vulnerable, aren't they?

Listed as vulnerable and endangered in the north-east Atlantic.

Sharks, in particular, are in real trouble,

because they grow so slowly and they don't give millions of eggs

like other species, so if you start hammering sharks,

you very, very quickly send a population into trouble.

'Across the globe, sharks are in decline.

'We want to find out if the giant basking sharks

'that visit our shores are also under threat.

'From mid-May onwards,

'it's here in Cornwall they first begin to appear off our shores.

'They might be giants,

'but basking sharks can be notoriously difficult to find.

'We're going out with experienced shark spotter Charlie Hood.'

Whereabouts are we likely to see them? Is there only one area or...?

Where we have been seeing them is very close in shore.

So we're going to hug the coastline

and get everybody spotting at the same time.

We're looking for the telltale sign

of the little black fin skimming the surface,

just like you see in the Jaws film.

Close to shore? How close?

Oh, they can be within ten yards. Yeah.

'We hope to find out what's so special

'about the sea off the Cornish coast

'that draws these giant fish so close inshore.

'And we're in luck!'

There we go. That's the first one!

-Yeah!

-Holy smokes, there's two there!

That's it's caudal fin, that's it's tail fin.

It's doing what it's meant to be doing, which is basking.

I can see there's a couple of fins there. There's two separate.

'To investigate why the sharks are here,

'we need to closely observe their behaviour underwater.

'But these giant fish can get easily spooked.'

The basking sharks don't like the bubbles. We'll disturb them

if we use scuba gear, so we're just going to use snorkelling gear

and stay right at the surface.

'Sliding into the water as quietly as possible,

'we make our first tentative approach.'

Woohoo-hoo-hoo!

That is so much bigger than I was expecting.

You can see those fins lopping around on the surface of the water.

More over here as well. All around us.

-All over the place. Look at these guys over there as well.

-They're huge!

'Tooni has advised us to get ahead of the sharks

'and stay floating at the surface, as diving down can disturb them.

'They can swim up to four knots, so there's no point trying to keep up.'

I've never seen anything like this.

Just being surrounded by dorsal fins.

'The key to why the sharks are here is in those giant open mouths.

'They've come into the shallows to feed.'

These basking sharks have absolutely enormous mouths -

up to about 1.5 metres wide.

But though their mouths might be big, they really are gentle giants.

All they are doing is drifting through the water,

feeding on zooplankton, these tiny, tiny particles in the water.

'The tiny animals that make up the zooplankton

'thrive here during the summer months.

'We're actually swimming in a living soup of basking shark food.'

The basking sharks are at the surface of the water,

because they are filtering plankton through their gills,

and they filter the equivalent

of an Olympic-sized swimming pool of water every hour.

That translates into about 30kg of zooplankton -

microscopic animals that they are consuming every day.

Even though we know these are harmless feeders,

there's something about something that weighs seven tonnes

with a mouth that big coming towards you, it just has an effect.

Then that giant tail just flicking past!

When they close their mouths,

it looks as if they are kind of...

Yeah, they do, they close their gullet and,

as they ram through the water,

the plankton goes onto their gill rakers,

and then they shut their mouth every minute or so

and literally gulp all that plankton back.

'It's the plankton that's making the water appear cloudy.

'To get a close up view of these tiny animals,

'Frank's going to try and take a sample.'

Got a plankton trawl, which just funnels

the plankton down and gets caught in the sieve here.

If I do it here where the basking sharks are feeding,

we'll get a little sample of what they're feeding on.

It took us two minutes to get this,

and we've got a dish full of plankton.

As you can see through the lens, it's just teeming.

Plankton is made up of a range of miniature plant and animal species, plus the larvae of larger animals.

These microscopic organisms are key to life on our planet, forming the basis of our oceans' food chains.

Each year, the plankton bloom appears off the Cornish coast from mid-May

but lasts only a few short months.

By the end of June, the bloom will have disappeared, and so will the sharks.

So the west of England juts out into the North Atlantic, and all of the south-westerly currents come up

and hit it, and they bring the nutrients

that fuel the plankton blooms, that the basking sharks are here to eat.

Today, we've seen why the sharks come in so close to our shores.

But to assess the long-term future of our resident giants,

we're going to continue our expedition further north along the west coast.

Later on, we'll be joining a team of scientists

working at the forefront of research into these extraordinary fish.

I was hoping to see one basking shark, but to be surrounded

by eight or ten of these great creatures was pretty spectacular.

And every time I kept looking up at the shore and thinking, "I'm in Cornwall, this is unbelievable."

Sharks aren't the only giants in our waters.

Earlier this month, Tooni went to South Wales where she investigated quite a different migration.

I've come to Stackpole Quay, an 18th-century fishing harbour tucked away along the Pembrokeshire coast.

You don't always need to go far offshore in order to witness some spectacular underwater events.

Once a year during May and June, vast numbers of one of the UK's largest crab species

migrate from the deep waters of the Atlantic into the shallower waters of the coast of South Wales.

This bay here at Stackpole Quay becomes the focus of an orgy of activity.

But what are they coming here for?

'Beneath the waves, thousands of giant crustaceans are on the move.

'The event I've come to see is the annual migration of spiny spider crabs.

'But they're proving a little tricky to locate.'

So we're a few metres down now in Stackpole Quay, and I'm looking

for the spider crabs, but the problem is they're masters of camouflage.

They're especially difficult to find in amongst these giant swathes of floating kelp.

Perfect hiding place.

Oh, there's one.

SHE LAUGHS He's a tiny little one!

Oh, wow!

That is just an amazingly camouflaged little thing.

Look at that!

'It's not quite the giant I was after, but this tiddler is showing off some fantastic exterior design.'

These spider crabs actually cement bits of algae and small marine animals

onto their carapaces, the bit on their back.

Absolutely brilliantly decorated to look like a small rock.

Beautiful watching them move across the sand.

They really do dance.

Looks like he has literally done himself up for Saturday night out.

What's so incredible though is that you take one look at them,

then you look away and you look back

and you can't see them, because he's so well camouflaged.

'With a little more searching, I find the giant I was looking for.'

Look at the size of him!

He's kind of hunkered down there, doesn't want to come out

but I'll try and get him out from underneath this rock.

Here's a really good example of why they are called the spiny spider crab.

They have these spines here and two horns at the front of the carapace.

He's hanging on pretty tight to that rock.

And he's got me with his claws.

Luckily, I've got the gloves.

Now, you can tell he's a male because of these giant claws

that he is gesticulating at the camera very magnificently.

They can grow to about one and a half metres across,

which is about another that much on him, which is a phenomenal size.

Ooh!

Ow!

Argh! SHE LAUGHS

Oh, I tell you what,

even through a set of gloves, that's a pretty good pinch on him.

'Once a year, thousands of spider crabs are drawn to the shallow waters of South Wales.

'And here's the reason why.'

Ah. Look at this...

Oh, goodness me - there's two of them.

So this is a big male, and he's gripped onto a smaller female.

This is the start of mating. This is the reason why they come into these waters, to actually breed.

Normally, you find them out in much deeper Atlantic waters,

in about 120m depth,

but the problem with being in deep water and a solitary individual is that it's hard to find a mate,

so by coming into shallow waters all at the same time,

you can indulge in a mating frenzy.

He's grabbed hold of her, he'll turn her over

so they're abdomen to abdomen, and that's when breeding will occur.

See the size difference between the giant male

and the much smaller female.

Ooh!

I feel a bit bad that I've broken up the mating ritual.

Here we go.

'This is the one time of the year that you can see so many of these monster crabs in shallow water.

'In a month's time, they will return to the deep.'

That was fantastic!

There are a lot of spider crabs down there - there's kind of individuals and pairs -

and we found some males and females together,

so it very much feels like the start of the mating season.

They're definitely starting to come up from the deeper water into the shallows,

but they are just the most phenomenal creatures.

They're real...alien invaders of the shallow waters.

I love them, I think they're fantastic.

British waters are full of a rich diversity of wildlife, and it's in our interests to keep it that way.

Frank went to our country's first marine reserve

to see if it could be used as a template for the future conservation of our seas.

Located 18km off the coast of North Devon, this is Lundy Island.

Once ruled by a self-proclaimed king,

Lundy is a remote 5km chunk of ancient granite rock perched out in the Celtic Sea.

With one side of the island exposed to the Atlantic currents

and the other a sheltered refuge, Lundy is uniquely placed to attract a wide range of wildlife.

In 1971, Lundy became Britain's first marine reserve.

There are now plans afoot to have many more of these marine nature reserves around the nation.

But has Lundy itself been a success?

The island is owned by the National Trust.

Along with the wild Sika deer, there's an amazing abundance of birdlife.

From April to July, the cliffs of Lundy's west coast

are filled with sea birds, returning to the island to breed.

But it's beneath the waves that Lundy really comes into its own.

We're used to the idea of nature reserves and national parks on land, but what's different about Lundy

is that it's taken the concept of protecting the environment from the land out into the ocean.

'The marine environment around Lundy is now legally protected.

'Biologist Dr Keith Hiscock has been closely studying the underwater life here for the last 40 years.'

What was it that made you realise this is a special place?

I dived on Lundy in 1969.

You could just tell that there was lots of spectacular, rare species which we hadn't seen before.

You've got extensive, very rich sediments off the east coast here.

The granite rocks themselves have got lots of nooks, crannies, overhangs.

As soon as you get a wide range of habitats, you get a wide range

of communities of wildlife colonising those habitats.

'In 2003, a section of Lundy's marine reserve became Britain's first "No Take Zone".

'Here, all forms of fishing are banned.

'I want to find out what this level of protection can achieve.'

There's a rather beautiful - but very poisonous - blue jellyfish.

Wow, look at him. He's a big fella.

The blue jellyfish that we're seeing do seem to come in with the more oceanic water.

There's a small-spotted catshark, which, for a long time, has been known incorrectly as a dogfish.

'Safe from man-made disturbances, many fragile species are able to flourish here.

'This branching sponge grows less than a millimetre a year.

'Its size alone suggests it could be nearly 200 years old.'

There are some of the very common sea urchins over here.

They actually eat away at animals and algae which might otherwise become dominant.

So this is an animal that most people think of only as being a pain

in the foot, but in fact it opens up the environment for others.

Yes, the sea urchins have a very important role in policing the diversity of species on the seabed.

'The variety of underwater habitats encourages a wide range of species.'

You get a lot of these cup corals along the wall here.

There are some nice sea fans over here.

Oh, look, there's a seal. A seal right below us.

Thank you very much(!) Really stirring up the visibility in the canyon.

Here are these absolutely fabulous rock walls of jewel anemones.

The jewel anemones just here have caught a blue jellyfish.

It's going to be consumed.

Jewel anemones are absolutely fabulous - they're really pretty, but also absolutely deadly.

So we're in a forest,

but this is not a forest of plants, it's a forest of animals.

'Lundy's No Take Zone doesn't just benefit Lundy.

'It has the ability to increase the abundance

'and species richness of marine life up to 50km beyond the boundaries of the reserve.'

Lundy ends up functioning like a giant seed bank,

to disperse larvae and eggs of all the different species that live here,

and that way, Lundy can repopulate areas that have been over-exploited by man's activities.

Divers up!

How much can the Lundy model be taken as a template for the rest of Britain?

Well, that model has actually been shown to be true throughout the world, not just at Lundy.

So, if you take the pressure off, then the fish stocks increase.

So, in fact, No Take Zones are a service, if you like,

to the commercial fishing industry,

because they are creating more fish stocks to be caught for us to consume.

'In 2009, Parliament passed a bill

'that paves the way for marine reserves to be set up all around the UK.

'But what works for an isolated island like Lundy

'might not be as popular when it affects tourism and commercial fishing across on the mainland.'

To try and use this concept around Britain is fraught with problems

because of all the vested interest and the amount of money people are making from the way things are.

If we can overcome those challenges, we can roll out a whole network of marine reserves around the country,

and if we do that, I think we'll look back and see that Lundy was a great start.

'Back on our basking shark expedition, we've travelled north from Cornwall,

'up the west coast of Britain, to the Isle of Man.'

'Located in the middle of the Irish Sea, the Isle of Man is a hot spot for basking shark activity.

'The long-term future of these giant fish is still uncertain.

'We've come to work alongside marine biologists Jackie and Graham Hall

'to find out the extent to which our basking sharks are still vulnerable.'

Permission to come aboard?

'These scientists are involved in a worldwide project,

'studying basking shark populations and their migration patterns.'

-Pleased to meet you, Frank.

-Hi.

When you see a basking shark, they are big, beautiful, charismatic animals.

They fill you with enthusiasm and passion,

especially when you realise that they are so endangered,

and that we... we can make a difference.

'Today, we're hoping to collect shark DNA,

'as part of a global study, assessing the health of the sharks' gene pool.'

Maintaining a healthy gene pool is all about good breeding.

If the local shark population only breed amongst themselves,

that could narrow down their mix of genes.

If, on the other hand, sharks come in from miles away,

this could introduce a healthy injection of new genes to the local population.

'Getting a sample of DNA from a giant fish is not an easy task.

'For such state-of-the-art science, Jackie and Graham use a somewhat basic approach.'

Ah, that's the one!

-Just have a look at that - that is the thing.

-You can see these very expensive paper clips.

-But actually it's cheap and it works.

-Brilliant.

And all this is is a pan scrubber, a plastic pan scrub,

and we extend the pole as far as we can

and then we just use this and we brush it against the shark's fin.

'Well, that's the plan, anyway!

'But finding the giant fish is proving much harder than it was in Cornwall.

'After several hours searching...'

We've got one right here! He's about 20 yards over there just off our port quarter.

Can you see him? It's a small one.

-Don't you think, Tooni?

-Yes, he's small, the boat went right by him.

Now, he's turning round, cos he's feeding, he's following the food, he's following the plankton line.

'While Tooni and I work from the science boat...

Coming to you!

'..Frank and Gavin, our underwater cameramen, prepare to get in the water and get some close-up shots.'

What the director's handed me is this fantastic-looking mask camera.

And what you do is you put it on, and it takes the images here.

He's right here, he's about 35 metres away now.

Just gone under.

'The shark's large dorsal fins often have small injuries along the outer edges.

'This can create a unique pattern and provide a quick way to identify individuals.'

Almost a textbook dorsal fin, I'd say.

'Although the fins can acquire more scars over time,

'by building up a catalogue of photos,

'individual sharks can be tracked around Britain - and even across the world.

'The shark doesn't seem bothered by our presence, so we're now going to try and take a DNA sample.

'As Jackie slowly manoeuvres the boat into position, Graham gets ready at the bow with the scourer.'

-Damn near.

-Ah, couldn't get it.

'It's a tricky operation.

'Jackie takes us round for a second attempt.'

All right. OK. Now, then, where's he gone?

'This technique doesn't harm the shark in any way.'

Got it?

Yes, he's got it!

'We're actually taking a swab of a slimy coating

'that naturally occurs all over the shark's body.'

He's got it. That's there. Shark goo.

Well done!

'The black shark goo will now be sent off to have the DNA extracted.

'By collecting hundreds of different samples,

'scientists can begin to assess the health of the sharks' gene pool.

'They can find out whether isolated populations are interbreeding

'and even estimate the total number of basking sharks in the global population.'

Did you get a size estimate?

-Three and a half, I think.

-Three and a half metres.

-Small fellow, but nice - nice condition.

-Yeah, I'll say.

'The DNA work is still in its infancy

'but combined with other research around the world,

'we believe some of our local animals ARE going on long migrations in order to breed.

'This mixing of genes will help our sharks maintain a healthy and robust gene pool.'

What are the implications of those findings?

They're huge, from the point of view of management.

We're not doing blue skies research here.

We're doing it so that we can manage these animals effectively.

If it's a global population, they need global protection.

There are still more secrets to uncover about our basking sharks -

but for the moment, it's back into port.

When you witness such thriving wildlife, it's easy to forget just how vulnerable our seas are.

I went back to Cornwall,

to the scene of the biggest ever environmental disaster to affect our shores.

The Cornish coastline is full of picture-postcard views,

with quaint fishing villages and beautiful beaches.

But just over 40 years ago, the scene looked very different.

On the morning of 18th March 1967, the largest oil tanker of its time,

the Torrey Canyon, ran aground off the Cornish coast.

She was carrying 119,000 tonnes of crude oil,

which began gushing out in the Atlantic.

The Torrey Canyon remains one of the worst ecological disasters in British maritime history,

but what is its legacy 40 years on?

Built in 1959 and measuring nearly 300 metres long,

the Torrey Canyon transported crude oil from Kuwait to the oil refinery at Milford Haven.

But 24km off Land's End, disaster struck.

The tanker hit a huge offshore reef called the Seven Stones.

The authorities at the time didn't really know how best to deal with the disaster.

The RAF were scrambled,

unleashing wave after wave of bombs to sink the wreck,

and napalm to burn off the oil.

Despite the bombing campaign, the oil slick washed up on the Cornish coast,

killing much of the local bird and marine life.

Over the course of the next 12 months, the oil that had blackened our pristine beaches

and decimated the ocean wildlife was slowly cleaned up.

But what about the tanker itself?

The Torrey Canyon is the largest shipwreck in British waters,

but one that very few people have seen.

And getting to the wreck is quite a challenge.

I want to see for myself what remains at the actual scene of the disaster.

Setting off from Penzance harbour,

we're heading out to the treacherous Seven Stones reef.

We have to be very careful,

as the rocks lying just beneath the waves could do us some serious damage,

just as they did to the Torrey Canyon.

So you can just see, out here, the tops of the Seven Stones.

And here they are. It's a very complex little area.

We can take our small orange boat, our inflatable, right inside the Seven Stones,

and if we're careful, we can get right over the Torrey Canyon.

'This is a dive loaded with difficulties.

'Dive Supervisor Richard Bull has his concerns.'

This is serious diving.

We are a long way offshore.

If we want help, it will be a long time getting here.

What's it got on it? Bombs. Unexploded bombs.

We're all school boys at heart, we all like things that go bang.

But let's not make them go bang today. OK?

Big swell, big wreck, bombs.

How much more do you want?

All around us, patches of white water are breaking over the rocks.

Three, two, one, go!

We've come at slack water,

the calmest time of the day, but the sea's still quite choppy.

Paul Rose, comms check. Over.

'Loud and clear to me, over.'

Enjoy your dive, guys!

'I'm not quite sure what we'll see down here.

'We believe the wreck is lying 30 metres beneath the surface.'

Wow!

Hard to tell what's rock and what's shipwreck.

Cos it looks nothing like a ship.

It's just so overtaken with this beautiful marine growth, it's hardly recognisable.

Here's a patch of exposed Torrey Canyon.

The rusty bit gives the game away.

But for that clean patch,

you could be excused for thinking it was just a load of seaweed-covered rock.

This is quite obviously the shipwreck.

It's worth coming underneath the wreck here,

because you can see this is the bottom, these are all rocks.

But above me is a great pile of the plates of the Torrey Canyon itself.

'It looks like all that's left of the ship is giant sheets of mangled metal.'

We've got to be very careful.

Got myself tangled up on some bits of wreckage there.

Quite a gloomy feeling in here.

Hey, what the heck is this?

Oh, it looks like a bomb.

What did they say they've found?

They've found a bomb.

-'That's a bomb!'

-It's a bomb.

I've found one. That's a bomb.

Luckily, it's one that's already exploded.

'This is just one of the many bombs

'dropped by the RAF to sink the stricken vessel.

'A few minutes later, we come across something I wasn't expecting to find.'

This is the bridge!

This is the main control centre of the ship.

Have a look down there, through this hole. I'll have to be careful.

But if you look down there, you get a sense that this really is a ship.

Bloomin' great, this. Fantastic!

Can you just imagine what it must have felt like to be on the bridge of the Torrey Canyon?

Things were probably pretty calm.

You're cruising along having a cup of coffee, talking to your mates,

and then the unthinkable sound and feeling of "bang!" -

this huge thing running aground.

You come up from being underneath the wreck and you come into this burst of life.

It's just teeming and thriving with life.

The sea is finally taking over the Torrey Canyon, isn't it?

There's no sign of the oil and the ship looks beautiful.

Let's face it, the sea wins.

'This may be Britain's biggest shipwreck and the site of our worst-ever oil spill,

'but even after 40 years, I'm surprised how well the sea has healed itself.'

The wreckage of the giant tanker might now be consumed by the sea,

but 270km away on the Channel Island of Guernsey,

Tooni went to see how the legacy of the Torrey Canyon disaster lives on.

19 days after the Torrey Canyon ran aground,

its huge oil slick hit the western coast of Guernsey.

Then, as now, tourism was a major source of income for the island

and the authorities knew they had to act quickly in order to save their beaches.

They came up with a plan to gather the thick layer of oil

from the surface of the sea and store it in a disused quarry.

That was 43 years ago and, sadly, it's still here today.

Tucked away in the far north-east of Guernsey, this quarry isn't on the tourist route.

Yet here sits a piece of British maritime history.

The quarry is a really weird, quite eerie place.

And there is an all-pervading, overwhelming stench of oil

that hits you literally as you just draw up.

In the past 30 years, several attempts have been made to clear the oil.

But modern technology may now provide the answer.

Rob Roussel is in charge of the current clean-up operation.

The line that's all around. The black line that's all around -

-that was a previous level of where the oil was?

-It is, yeah.

In the 1980s, they pumped a lot of oil off the surface.

We're probably talking about a metre thick of oil on the surface of the water,

and it built up again, so we pumped it out.

A lot of that oil was used locally in the power station, to generate electricity.

Recently, Guernsey's government voted to try and completely remove

this stain from its otherwise pristine landscape.

But pumping out the remaining oil is no longer an option.

Basically, a lot of the oil is tied up in the sediment at the bottom of the quarry.

There's also unexploded ordnance from the Second World War in there.

It's a fairly hazardous environment.

In a final bid to rid the island of the last vestiges of the oil from the Torrey Canyon spill,

Rob and his team are using a process called bioremediation.

This is a biological approach using bacteria to literally munch their way through the oil.

This is the first large-scale use of these micro-organisms anywhere in the British Isles.

Technician Phil Ledger is on hand to supervise.

In this jug, there is a million, trillion bacteria.

And once we put the bacteria plus the nutrients into the water,

that whole soup will create the solution to the oil in there.

'The tank sits for 24 hours and then the bacteria are ready for action.'

From their dehydrated state, they are now fully active and functional?

Fully active,

swimming around quite happily ready for their job, to eat the oil.

Open the valve, you'll hear them going down the pipe.

Looking down at the surface, you can see patches of oil

simply disappearing into nothing as the bacteria munch away.

The bio-remediation process has been working so well, the team hope to

have the quarry pretty much cleared of oil in just a few short months.

Some 40-odd years after our coastline suffered such a

catastrophic ecological disaster, we've now found the solution to removing the remaining oil.

Here on Guernsey, we might at last be able to write the final chapter

in the disastrous story of the oil tanker Torrey Canyon.

Oil tankers and container ships are still key to our survival as an island nation.

And to make the ships more cost effective,

they're being built even bigger, presenting challenges to our ports that are hundreds of years old.

Frank went to Liverpool Docks, to see how our busiest port on the west coast

deals with these man-made giants.

The port of Liverpool handles over 40 million tonnes of imported cargo

every year, from fruit and veg to recycled metal.

But getting gigantic container ships safely into dock is quite a challenge.

It's a job that begins way out west in North Wales, at the small harbour of Amlwch, in Anglesey.

I'm being taken out to meet one of the biggest transatlantic container ships in the world.

Making its monthly voyage from Nova Scotia in Canada, this is the 52,000-tonne Atlantic Companion.

I want to see how this vast ship gets its precious cargo safely into Liverpool Docks.

Captain Veeger has agreed to take me on a quick tour.

We have a sports room in here.

Oh, my Lord!

Today, this ship is carrying everything from wine and cereal to beans and steel.

Down below, they're also hauling some classic merchandise.

Ships like this carry millions of pounds' worth of cargo.

While we're all very aware of air travel, it's actually

imports coming in by sea that our island really relies on.

But getting a ship this size into Liverpool Docks is no easy matter.

What you really need is an experienced and, above all,

local pilot.

Mersey, Companion.

Just approaching south of the bar inbound, with no known defects and some hazardous cargo.

Today, pilot David Boardman is the man who will take the helm for the final critical miles into port.

You have to be trustworthy enough for the Captain to say, OK,

take control of my enormous vessel and its priceless cargo.

A lot of it is on trust and experience, and

confidence as well in your own ability, but training as well.

To become a first-class pilot in Liverpool is five and half years

of experience and training.

Do excuse me one moment.

Mersey, Companion.

David's job is to navigate the ship through the narrow Mersey Estuary.

Each journey presents unique challenges.

David's got to balance the effects of wind speed, tides and currents,

plus the estuary itself has its own inherent hazards.

Right now, we're in the middle of a specially dredged channel in the Mersey Estuary.

But even that only gives a ship of this size about half a metre of bottom clearance.

That makes navigation really, really tight and

even if we make one tiny deviation, we could easily end up grounded.

With only 50 centimetres between the bottom of the boat and the sea floor,

this is a real test of skill and timing.

3.97. OK, thank you.

So, at the moment, we're still pretty much short of water.

We're looking for another metre of water.

So what we don't want to do is be too early.

Barbados, the Companion.

Channel Six for me, please.

David times his progress up the estuary to cross the shallowest point at the highest tide.

He's fast approaching the point of no return,

beyond which he can't turn back, and is committed to getting into dock.

What we'd call the abort position now is the next buoy.

Once I get past that buoy...

-This buoy here?

-Yes. ..I am committed then.

Shouldn't you be sort of gripping the controls at this point?

Not at all, not at all.

I'll put it down, and hopefully, we'll see years of experience at doing this.

I hope we don't catch the one time you mess it up.

No, well, I hope that as well.

Entry to the port is via a sea lock.

To protect the lock from damage by tidal surges, it was built facing up-river.

But that means David now has to make the maritime equivalent of

a handbrake turn to be able to enter port.

So what we're doing now is spinning round and trying to line ourselves up for the lock.

We've only got a two-hour window to get in, at which point,

they shut the doors and we've got enough water under our hull.

It doesn't look like we are going to make it at all.

But he's bargaining on the tide carrying us,

so we get to line up with it.

But at the moment, it doesn't even look close.

Getting into the lock is a tight fit.

There's just two metres spare on either side of the ship.

West-side man, we've got the greens. OK, thank you.

You can see the docking signals now, they've given us the green light.

Tell me how you work out where you are?

When I'm looking down the south side of these sheds

and that quay wall there now,

that tells me that our bow is 60 metres south of the entrance,

so I pretty much know

that I'm clear to drop in and slide past the entrance there.

Slowly, we creep in.

With the back gate shut, the lock is filled.

The giant ship can then move into the dock itself.

The ship's owners get charged by the hour for the time they

spend at the dockside, so they really don't want to hang around.

Nor do they want to miss their next exit window out to the ocean, which

is the next high tide, so it's all a bit of a race against time.

In just a few hours, around 15,000 tonnes of cargo will be offloaded from this one container ship.

It then gets reloaded with British exports.

I've been counting and I can see about 15 people on the dockside,

and that's all that is required to offload this massive cargo.

The innovation of containerisation has

revolutionised the speed with which these giant ships can return to sea.

As an island nation, we've always relied on our docks,

and the port of Liverpool, and these vast container ships,

will continue to play a key role in our future.

Out in the Irish Sea, off the Isle of Man,

we're coming to the end of our basking shark expedition.

But there's one last secret to explore.

Many of the basking sharks spotted off the Isle of Man seem to be quite young.

Graham has spotted a shark, he thinks it's a very small one,

so we're just going to creep closer and try and get some photographs

and collect our data.

It's quite a small shark, you can see its little nose...

Could this area potentially be a breeding ground?

Very little is known about basking shark reproduction.

What is known is that when a female was caught in 1936, as she was towed

into a Norwegian fjord, she gave birth to five live 1.5-metre pups.

Marine Biologist Jackie Hall has evidence

that the Isle of Man is a special place for these astonishing fish.

We realised we were getting a lot of newborns, which is 1.5, 1.8 metres long,

here on the Isle of Man.

We have far more newborn sharks in this 40-kilometre stretch than in the whole of the rest of Britain.

-So this could be a bit of a nursery?

-If they're not being born here, they're being born very close by.

Wow. Fantastic.

So that would mean it would be a very important area for protection.

Very. We know it's special for newborns, we know it's special

for feeding, we know it's very special for courtship behaviour.

For a small shark, that was a nice experience.

He was beautiful!

So not only do these giant fish come close into our

western shores to feed, but it looks like they also come here to breed.

With our expedition coming to a close, the day holds one last surprise.

On the way back to port, we come across something I've never seen before.

A giant swarm of jellyfish.

So we're right in a swarm of moon jellies at the moment,

which are these incredibly beautiful jellyfish.

They've got sort of an iridescent top,

which is basically their gonads, and it seems to vibrate with colour.

These creatures are related to corals and sea anemones.

Just like the basking sharks, they are here to eat the plankton.

Jellyfish are predators, so they have stinging cells

called nematocysts that hang down on their tentacles.

If you swim through a swarm of moon jellies, you feel a sting,

but it's very, very slight.

So they're not these monstrous jellyfish that you sometimes find.

The swarm is strung out, forming a line hugging the coast,

stretching as far as the eye can see.

Fantastic. There were so many jellyfish in there.

Thousands and thousands of them, snacking on exactly the same food

that our basking sharks will be after.

With the sun going down, and no more sharks spotted,

our voyage of discovery along Britain's west coast is over.

We've found some astonishing giants,

from the spider crabs of Wales and the wreck of the Torrey Canyon,

to the container ships squeezing into Liverpool Docks.

But for me, the basking sharks have been the highlight of the trip.

I'm hopeful they have a bright future ahead.

Interbreeding between transatlantic populations should be enough to

maintain the genetic health of our basking sharks.

But it does highlight the need for global

rather than just national protection for these astonishing animals.

And it has been a fabulous experience to swim

with these gigantic creatures.

Next time on Britain's Secret Seas, we uncover the wild North,

revealing creatures that glow in the dark.

Everything's fluorescing!

Witness the success of the magnificent gannet.

That is an incredible strength.

And get hands on with our underwater bomb disposal.

3, 2, 1, now.