The Power of the East 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...'

Right, let's go diving!

'..And I've scuba dived all around the world.'

Just look at that. It's so easy to take this kind of thing granted.

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.

I'm glad I've got my gloves on!

Journalist and underwater archaeologist Frank Pope

will examine the bigger picture of our relationship with the sea,

and explore our maritime history.

Ships like this can generate awesome power with the wind.

This series will take us on a journey right around

our British seas, to uncover the most startling underwater wonders.

This time we're exploring the sea off Britain's eastern shores.

To the east, we've got one of the youngest seas on the planet.

It was only formed 10,000 years ago at the end of the last Ice Age.

But that doesn't stop these shallow waters from being truly remarkable.

Beneath our waves is a world of secrets.

Our journey starts in the Farne Islands,

on the rocky shores of Northumberland.

It's here in these cold, harsh waters we'll be studying

our most powerful native marine mammal,

the grey seal.

This group of islands is home to the largest population

of grey seals in England.

There's probably over 1,000 of them on the islands right now,

and they're thriving.

We're going to try and find out what makes the grey seal

such a powerful and successful predator.

'The Farne Islands have been a national nature reserve since 1993.'

We should see some seals. There's stacks of them here.

'But the local population of these tough, adaptable animals

'has suffered a long history of human exploitation.'

Something like 100 years ago

there were about 500 seals here, and now there's over 150,000 of them.

One of the reasons they're doing so well is that we used to hunt them.

They were hunted for their blubber, their fat, which was used for oil.

-Yeah...

-Their skins were fairly useful as well,

and people used to eat them.

But now that's stopped,

the culls have stopped, and the numbers are increasing.

Actually they were the first mammal

to have been given full protection in the UK.

I mean, in 1914 they decided to protect the grey seal,

and that was following all the slaughter that happened

in the 19th century.

But the end of hunting alone isn't enough to explain

the dramatic success of the grey seal.

We're going to head out to the islands and figure out

why the grey seals have bounced back so strongly,

and why they've been such a success story.

Grey seals have to eat five kilos of fish a day to survive the cold temperatures of the North Sea.

Fish stocks in these waters are in decline

but these seals are still finding enough to eat.

The key to that is their amazing ability to dive.

I'm planning an experiment to find out how they do it

with Dave Thompson, a marine biologist

from the Sea Mammal Research Unit at St Andrews University.

As mammals, seals can't breathe under water

but they've evolved to maximise their use of oxygen.

One of the ways they do it is by something called

the mammalian dive reflex,

a reflex shared by many mammals, even humans.

'It's a survival mechanism that conserves oxygen

'by slowing your heart rate.

'It's triggered when your face is immersed in cold water.'

Right. I'm going to test this mammalian dive reflex here.

What you need is a bucket and some nicely cold water.

-Dave, have you got the heart monitor, mate? And we'll get set up here.

-Yes.

How are we going to hold that on? Oh, duck tape, great!

Yeah, OK. Putting it on's going to be all right...

Yeah, I've got my suit on, you see.

OK. Normally you'd try and get it down below your pecks.

That's all right.

You should be able to read that now on your machine.

Have you got me there?

OK, we're getting a heart rate of about 81 beats a minute.

OK. Right, shall we give it a go?

Yeah, let's give it a go.

'Sensing the cold water,

'nerves in the face instruct the brain to slow down the heart.'

An immediate drop. It's dropped from 85 to 74, 73...

'Just as in seals, the reflex saves oxygen by slowing the metabolism

'and diverting blood to the vital organs.'

65, 64.

So it's already dropped 20-odd beats per minute.

-Did it go down?

-Yeah, it did.

It dropped from mid-80s down to about 56.

-Wow, just in that...

-Over that period of time.

Rapid decline at the beginning and then a gradual decline after that.

So it proves the point - you get cold water...

So we still have that, within us, that mammalian dive reflex.

-It's a reflex. It's nothing you're consciously doing.

-No, for sure.

Dave's been studying the same reflex in grey seals

to find out how their physiology is adapted for life under water.

To see how much more effective grey seals are than humans at diving,

we've enlisted the help of an expert.

Emma Farrell's trained herself to dive to over

40 metres holding her breath, in a sport known as freediving.

So what sort of depths can seals dive to compared to humans?

OK, as a seal biologist, I'm going to say the seals win by a long way.

In the North Sea, they're going down to about 100-120 metres.

We've had some off the west coast going deeper.

How long are they under water? How long can seals hold their breath?

Grey seals can hold their breath for up to 40 minutes,

probably 45 minutes.

-Free divers, Emma?

-The record is 11 and a half minutes, which is completely phenomenal.

Only a few years ago, the record was six and a half, seven minutes

and people thought, "No way will anyone reach ten," and now it's eleven and a half.

We're going to measure Emma's heart rate while she dives,

and compare it with that of grey seals.

The sea here is 20 metres deep, and she'll be diving to the bottom on a single breath.

Free diving always carries a risk, even for the experts,

so we have safety divers standing by.

You can just see

the outline of Emma way up there on the surface.

It's quite an experience watching actually.

She just looks really, really relaxed. She's just laying there,

not using any energy whatsoever.

Here she comes.

You can see her pinching her nose.

That's so that she can equalise the spaces in her head.

You know, the ears and sinuses would be incredibly painful here.

She's holding her breath for a long time.

There's no way I could hold my breath for that length of time.

There she goes. Bye, Emma!

-We'll go and download this and see what's on it.

-Thanks.

This is the data from the heart rate monitor that we put on you before you went diving.

You've got a gradual reduction in heart rate,

from what was quite a high level before you went in, down to...

it's dropped you about 20 beats a minute, maybe, 15-20 beats a minute.

You can see where you came to the surface.

But gradually your heart rate was getting slower and slower

-and slower, where that mammalian reflex must have kicked in quite clearly.

-Yeah.

And it looks like the longer I'm in the water, the more it's becoming affected, so...

Starts to really kick in, yeah.

'Dave's done exactly the same experiment on grey seals.'

These are heart rate traces from a couple of grey seals.

As soon as his face goes in the water, his heart rate drops and it drops like a stone...

So this is 120 beats a minute?

Yes, at the surface, they're like a racehorse, breathing incredibly hard.

-Then very quickly down to five or ten or whatever that is.

-Yeah.

This one averaged about 15 beats a minute during the dive.

-Wow, look at that.

-It's amazing, absolutely amazing.

Emma's trained herself to hold her breath for over four and a half minutes.

Seals can go ten times longer and it's not just because their heart rate slows down more than hers.

They have twice as much blood as we do, and many more of the red blood cells that carry oxygen.

This means they can store far more oxygen in their bodies than we can.

With no sinus cavities, they don't suffer from changes in pressure like humans.

And they can dive to over 120 metres to catch their prey.

They swim in a highly energy efficient way.

'Even a top competitive free diver can learn a lot from the grey seal.'

That's what it's all about.

Just look at the smooth efficient way that she's moving.

Moving just as the seals do.

'The ability to dive so efficiently on a single breath

'is the key to their success as a top predator.'

Emma has trained for years to dive deeper and far longer than I could

even dream of but today even Emma has been outdone by the grey seals,

because they have evolved to become one of the most powerful diving mammals on our shores.

There's more to their success as predators than diving prowess.

They also have to become expert hunters.

Later on, Frank and Tooni will be diving with some young seals to see how they do it.

The whole of our eastern seaboard is flanked by the North Sea.

These are the shallowest waters around our shores, averaging less than 100 metres deep.

But these waters have provided us with some of our most valuable resources.

The east coast has played vital role in our industrial history, not least

because it's here that we first discovered offshore oil and gas.

For over 30 years they have kept us self-sufficient in energy but today, they're starting to run out.

However, it does look like there's another resource that might see the North Sea come to our rescue again.

Wind.

I'm on board the Pelican at the start of the annual Tall Ships Race.

This leg is an eastward dash to Holland.

Ships like this can generate awesome power with the wind.

And out here you can really see why they've been so successful.

The winds here are twice as strong as the global average.

Stand by to set the main topsail!

Haul away the sheet!

It's a magnificent sight, and a striking example

of the power of the wind.

With a full spread of sail up, the Pelican can generate 1,000 horsepower.

That's three times more than the engines can produce.

It's clean, there's no diesel fumes, there's no carbon footprint, nothing.

There's just the silent beauty of the wind.

Because of our position on the edge of the Atlantic,

the one thing we're not short of in the North Sea is wind.

Basically, you get wind because as the sun warms the air

at the equator it rises, and cool air blows in to take its place.

Now that means you get cool air coming in

from the north at low altitude, and then recirculating back up

when it's warm at high altitude.

Now that's the simple picture. Actually what happens is much more complex, because the earth

is spinning, and the land and the sea warm and cool at different rates,

and that creates all sorts of local variations in the strength

and the direction of the wind that we actually see.

Out here, we get a lot of south-westerly winds,

and that's been powering ships here for centuries.

And the wind might just be about to come to good use again.

No-one knows quite how much longer we'll be able to keep getting oil and gas out of the North Sea.

It's getting a little bit less every year and somehow we've got to make up that shortfall.

Wind farms like this one at Scroby Sands on the Norfolk coast could be the answer.

Scroby Sands, just two miles east of Great Yarmouth,

was the first offshore wind farm to get planning permission in Britain.

It produces enough electricity to power 40,000 homes.

The electricity from Scroby Sands comes ashore here in three cables, at 33,000 volts.

It comes all the way up the beach, under the promenade,

past Deb's Diner, then round the corner under three kilometres of streets

until it gets to here, the substation, where it feeds into the local network.

To meet our power needs and cut carbon emissions, the government's

earmarked an area of seabed big enough for 10,000 turbines.

It's the most ambitious plan for offshore wind power in the world.

But if we are going to build this number of wind farms, I think we

need to know what effect these are going to have on our marine life.

With only 30 turbines, Scroby Sands is a small wind farm compared

to the ones planned in the waters off Kent and the Thames estuary.

Although building wind farms is very disruptive to marine life,

some scientists argue once they're in place, they could be good for it.

You can see sort of classic zonation there.

Right at the top of that level there, that's where high tide is. We're at low tide now.

And that's a whole layer of barnacles and limpets growing on the metal there.

And as you get further down, there's some seaweed just where the water level is now.

Right down at the bottom of this steel shaft is a layer of boulders that have been put there

specifically to make sure the water currents dragging past the bottom don't scour the metal.

They are to protect the metal itself, and it's the bottom - it's these boulders

right at the bottom - that act like an artificial reef.

So they create extra habitat for marine wildlife.

Diving this industrial installation is going to be a tough technical challenge.

Dive supervisor Richard Bull has his concerns.

We've got vicious tides here.

We haven't got very long slack water.

If that tide takes off, you're going with it.

If ever there was a graphic demonstration of, "time and tide wait for no man," this is it.

-I can see you're looking forward to it after that. Fantastic.

-Can't wait.

It's not just the current we have to contend with.

The sea on this part of the east coast is infamous among divers for having terrible visibility.

I'm going to go right down to the base of this wind turbine

behind us to take a look at just what exactly is happening to the marine life down there.

As you come down the post you can see

plenty of barnacles, mussels...

..and a sort of band of seaweed.

As I feared, the water is thick with sediment.

It's so bad I can't even see where the camera is.

Ah, there you are.

This is one of the support structures

holding the actual main shaft of the turbine, which is over there.

It is literally covered with life that wouldn't normally be here

if it wasn't for these huge, man-made things in the sea.

So these are all filter feeders jutting out into the water column, picking up plankton as it comes.

So what these turbines have done is create a whole other food chain

in an area where it wouldn't normally exist.

'At the base of the turbine, there are piles of rocks placed there to protect it from erosion.'

What it's also done is create a habitat for a wide diversity of marine life.

Underneath here there are plenty of anemones.

There are crabs in the small nooks and crannies, lobsters.

There are even reports of octopus here as well.

These are incredibly pretty dahlia anemones.

This is exactly the kind of thing that you wouldn't normally find

in this environment were it not for these artificial, hard surfaces

that they can attach onto.

'The tide has started to turn and we have to get out

'to avoid being swept away.'

For me, the major positive of wind farms, aside from the fact that they're supplying renewable energy,

is the fact that you don't get any fishing trawlers going through here, so essentially it acts almost like

a marine reserve, a place where fish larvae can come, they can grow, and it acts like a refuge for them.

Hopefully that will have a sort of spill over effect so seeding other

fishing grounds around the North Sea with more fish, helping to create a really productive environment.

100 miles north of Great Yarmouth is Flamborough Head.

Here, warm water from the southern North Sea collides with cooler water from the North

to bring a wealth of nutrients to the surface,

providing food for a wonderful variety of marine life.

I'm here to explore a phenomenon I've never fully understood.

There's a blooming great shoal of fish down here. How cool is that?

'This shoal of fish is made up of whiting, pouting and bib.

'They've come together around this wreck of an old steamer, attracted by the density of food.'

And a shoal is a very relaxed group of fish.

It's where feeding and breeding occurs.

'But a shoal is transformed into a school if it detects the presence of a predator.'

As I start swimming towards them,

they'll get themselves more organised and you'll see they'll quickly turn into a school.

That's happening - they're starting to school now.

When they're in that school...

..they're much safer because if I really was a predator

I'd have too many targets.

Once they reach a safe distance, the fish will stop schooling and go back to being a loose feeding group.

This is a force of nature that is actually a work of art.

That was a great dive. It's a beautiful thing to see

thousands of fish in a relaxed shoal suddenly turn into a very organised school.

I can understand why they do it, but how?!

I went to see marine biologist Jens Krause to try and find out.

Jens has devised a pioneering experiment to figure out how fish swim in schools.

He's created a remote controlled imposter - Robofish.

-So here we have Robofish. The whole set-up.

-So this is it!

-The fish is actually over here.

-Oh, yeah. That looks great.

'By moving the robotic fish around the tank, Jens can observe

'how a school of live fish respond to the movement of an individual.'

In a moment I'll put some live fish in.

Then we can watch the interaction and then you can release them.

-Yes, please.

-You can pull the gate.

-OK, let's have a go.

The tank is a neutral environment where the fish have no reason to move in any particular direction.

I put in the fish so they're joining the Robofish now.

Let's give it a go. You tell me what to do and I'll do it.

OK, I'll give you a countdown and you pull the gate.

Okey-doke, I'm ready.

Three, two, one...

go.

-The gate's open.

-OK, so the Robofish is coming out.

-The live fish are following.

-Oh, yeah, look! They're making the turn.

They've made that turn, right over here.

Look at that - a lot of them have followed him even back into the trap!

-That's right.

-Kind of led them back home.

Jens' experiment has shown how a group of fish will tend to copy

the movements of whichever fish moves the most decisively.

In this case Robofish.

You can really see that this is local information transmission,

like a Mexican wave in a football stadium -

people are responding to their near neighbours.

They are getting up and the next one is getting up

and the wave travels through the stadium. The same thing happens here.

The closest fish copies the Robofish and the information is transmitted to the other individuals.

The other fish copy Robofish because they perceive its decisive movement

as being a response to a threat.

Jens has been working with sticklebacks to develop his theory

but the way they react is the same in many other species.

There are a number of different sensory organs that are involved in this.

There is first of all vision. Eyes are laterally positioned so fish have near round vision.

Some species have a small sort of blind spot at the back.

But they can see very far back.

But as you get closer, they can also feel you.

How do they do that?

This is usually done with a lateral line.

This is an organ that forms a canal alongside the body of the fish,

and inside are tiny sensors that are pressure sensitive.

The lateral line enables fish to detect exactly how close

they are to their neighbours and maintain their position.

When one fish moves to avoid a predator, the movement

is copied by its neighbours and ripples through the school.

This is one of the major advantages of schooling behaviour, that the fish on the outside of the school

work like an array of independent sensors and each individual will have its own information

about what's going on in the environment and can then alarm

other group members nearby and then the information

will spread from them to others and inform the entire group.

Individually these fish might have small brains

but they've evolved to share their collective intelligence.

I'm never going to look at a school of fish in the same way again.

Back on the Farne Islands, we're looking at how grey seals

recovered so well after being hunted almost to extinction.

I've seen how grey seals' physiology has evolved to make them formidable divers.

Tooni and Frank are off to observe how the young grey seals learn to become accomplished hunters.

Although grey seals spend most of their time at sea,

it's at places like the Farne Islands where they come ashore,

for breeding, pupping and rearing their young.

It's here that we can actually watch them both on the land and in the water,

how they interact with each other and, crucially, how they learn to hunt.

FRANK POPE: We're heading to the outer Farne Islands.

Grey seals spend two thirds of their life at sea.

With their thick blubber and short flippers, they're clumsy on land.

Out of the water, they're vulnerable and easily spooked.

We're getting in the boat to go and have a closer look at the seals' haul out site.

We don't want to approach them on land because we don't want to disturb them too much.

This group is mainly juveniles and females.

Most of the adult males are out at sea, hunting.

They just look like slugs on the surface, and you see them in the water, and they're beautiful.

The females up there will be quite heavily pregnant,

which obviously is another reason why they'll be sensitive to any kind of disturbance.

When grey seal pups are born. They're fed on a fat-rich milk to build up their strength

and help them put on weight quickly.

The mother gives them a very good start in life, then she heads off.

After three weeks, the pups are left to pretty much fend for themselves.

This is a much shorter period with their mothers

than most large mammals have.

So how do young grey seals master the hunting techniques they'll need to survive?

There's no point just seeing a seal on a rock.

You need to see a seal in the water.

Grey seals learn the skills they need through play,

like land-based carnivores such as fox or leopard cubs.

The Farne Islands are a great place for us to observe them.

With the rocky shores and seabed, the water is exceptionally clear.

This spot's perfect for the seals because they've got shallow rocks that they can haul out onto

and rest and digest, but also for the juveniles to learn to play in this very shallow, calm bay.

It's absolutely ideal for them to pick up the skills they'll need

for living their life further out to sea.

'At first, they seem to be avoiding us.'

Where are they?

Ah, here they all are!

'Their curiosity soon gets the better of them.'

These young seals aren't here to catch fish.

They do that much further out at sea. They're just here to play.

This is the perfect spot for them. It's very shallow, very calm here at the moment.

It's an ideal location for them to really learn how to hunt, to interact with each other,

to get those skills they'll need to survive.

'These seals are all juveniles. They can already feed themselves,

'but will continue to perfect their hunting skills

'in this underwater playground until they become sexually mature around the age of six.'

They learn through play exactly as toddlers do.

It's through this that they develop

their motor ability, their muscle tone and actually learn

how to forage and feed in the underwater environment.

'They also learn to master their whole range of senses,

'which include incredibly precise pressure sensors in their whiskers.'

These whiskers, they're not just decoration.

They're as important for the seal as their eyesight.

They use them to probe the water and sense the vibrations around them.

They can determine the direction in which a fish is swimming up to 50 metres away.

These complex and adaptable animals may also learn by copying the behaviour of others.

Look at that.

Is he copying me?

When I cross my arms, the seal crosses his flippers.

We know the seals mimic each other to learn.

It looks like this one has gone a step further.

They're so puppy-like. It's hard not to think of it as very puppy-like behaviour.

I'm glad I've got my gloves on because those claws...

But that certainly wasn't aggressive.

Well, this is a very playful gesture but it's very important to remember

that these are wild animals, and this seal's bite is in fact more powerful than a pit bull's.

Grey seals are solitary foragers, exploring the sea on their own,

often up to 100 kilometres offshore until they find a good place to fish.

As they grow up, these young seals will have to discover

their own hunting grounds if they're to survive.

When the one really inquisitive one comes up and actually jiggles with Frank's fins

or mimics him by lying in the seaweed, that's the point at which you

really begin to understand that they're truly learning about their environment by playing in that bay.

And hopefully that will help them

exist in the sea when they have to forage for food for the rest of their lives.

We'll be coming back to the Farne Islands to see how grey seals have benefited from their

hunting prowess and come to dominate their neighbours, the harbour seals.

For centuries, the shallow and productive waters to our east have provided us with fish

for our tables and supported a huge industry on our east coast.

But over the past 30 years, that industry has suffered.

Fish stocks in the North Sea collapsed in the 1970s and '80s, decimating our fishing fleet

and leaving harbours up and down the east coast struggling to survive.

But one North Sea fishing town has found a new lease of life.

FAIRGROUND MUSIC

Bridlington, on the coast of East Yorkshire, has a long and proud fishing tradition.

Bridlington used to be one of the busiest harbours on our east coast,

with trawlers landing hundreds of tons of cod and haddock every year.

But in the 1980s, this fishery collapsed when stocks of these lucrative white fish became scarce

and limits were placed on the total amount that fishermen were allowed to catch.

The town's ancient fishing tradition seemed to be at an end,

until fishermen realised there was a different catch right under their noses.

Last year they caught 350 tons of lobster.

But even under that intensive fishing pressure, numbers of lobsters are still going up.

Today in Bridlington, the entire fishing fleet of 40 boats has turned from catching white fish to lobsters.

But are lobsters going to go the same way the cod did?

Determined not to let that happen,

the Bridlington fishermen have launched a scheme to protect them.

I want to find out what effect this scheme is having on the lobster population.

I particularly love lobsters because I think they are the most curious,

archaic, alien creatures that we have around the British coastline.

I just think they're immensely likeable, actually,

rather bizarrely, in their strangeness.

It's like being born every time, isn't it?

There have been lobsters on the planet for at least 100 million years.

Individuals can live for up to a century.

They have eight legs for walking and two more that are adapted as pincers.

These wonderful pincers on the ends of his claws are different

on either side of his body.

This larger right one is for crushing.

So anything he finds on the sea floor

can literally be squished into oblivion, ready for eating.

The left pincer is for cutting, so it's more serrated and much finer.

But that means he's perfectly equipped

for taking on any bits and bobs he finds on the sea floor,

which is why they make such fantastic scavengers.

It's like they're just wielding these two massive boxing gloves

that are completely oversized and out of proportion

to the rest of the lobster.

Some scientists believe the recent rise in water temperature in the North Sea

has helped lobsters to thrive here.

The decline in cod stocks could also be helping them

as the cod would have eaten lobster larvae.

Now this male is sexually mature.

Lobsters have a slightly strange way of assessing

if another lobster is also sexually mature.

Basically, they pee in each others' faces

with a special gland that comes out from underneath here.

From the pheromones in that substance,

they can assess if the mate they find is prime for mating or not.

Each of the boats operating out of Bridlington

puts down over 400 lobster pots.

The way these cages work the lobsters enter through these funnels

that get narrower and narrower, so once they get inside,

they can't turn round and exit through the same way.

Essentially, you can get a lot of lobsters in just one pot.

Just the weirdest things in the world.

They've got a good catch today, I'll tell you that.

But they are just the weirdest, most curiously wonderful creatures

I think that you can find in these waters. I love them.

Despite the amount of fishing going on,

the lobster population appears to be stable.

I'm going to join the crew of the Kimberley

to find out how sustainable this fishery really is.

The secret might be in the way they're catching them.

Each lobster pot is hauled out about once a week.

The lobsters are taken out.

The old bait is discarded and fresh bait,

usually some scraps of mackerel, is added.

Today, scientist James Wood is on board the Kimberley.

He's been monitoring the Bridlington lobster stocks for three years.

Why are you doing this work with the lobsters?

We're trying to determine how sustainable they are

and whether we can gain a sustainable certification for them.

'Like everywhere in Europe, the Bridlington fishermen

'are only allowed by law to land mature lobsters.'

To measure a lobster,

you measure from the rear of the carapace,

follow it down the mid line to the rear there,

and we can see that individual is 106mm.

And the minimum size is?

87mm.

-So anything under 87mm has to be thrown back?

-Yes.

Because the young are thrown back,

the bait in the pots is giving them a free lunch

every time they're caught.

I've just been down diving, and whilst I saw an awful lot of lobsters

wandering around the sea floor,

there's also a lot of bait down there.

Is that in any way helping to sustain the population?

Yes, bait is probably having an impact

and sustaining a higher population than would naturally occur here.

Is that a little bit akin like almost farming free range,

organic lobsters in this area?

I'd prefer to think of it as a cultured stock.

You could consider it to be like a farm.

'The bait may be helping sustain the population,

'but the fishermen also have another method to help preserve their livelihood.

'Some of them have gone beyond European law

'to give added protection to fertile females

'carrying the tiny black eggs, known as berries.'

A lot of berries on there.

About that size, you're talking about 9,500 eggs.

The number of eggs increases exponentially with size.

'The fishermen have agreed to mark fertile females with a notch in the tail.

'And the council has made it illegal for anyone to land them.'

Due to a by-law that was introduced in our district in 1998,

this individual cannot be landed now. It's illegal to land it

and there's repercussions in the industry if you do.

-So we have to return them immediately by law.

-OK.

The V notch will take three years to grow out.

In that time, a fertile female could spawn hundreds

of young lobsters to replace the ones being caught.

With the numbers of lobsters that we've seen today

and the care they're taking to ensure this is a sustainable fishery,

I think they'll be fishing lobsters here for many years to come.

Unlike the rocky shores that surround much of Britain,

our east coast is mainly soft sediment.

In the sea, the sands are swept by the tide

to form an array of shifting sandbanks.

Down in the Thames Estuary, I took to the water

in my favourite form of transport

to uncover an intriguing part of our country's maritime history.

There's nothing more reassuring on a cold night at sea

than the familiar sight of a lighthouse flashing away in the darkness,

letting you know exactly where you are and keeping you off the rocks.

Out here on the east coast, the real problem isn't the rocky shores,

but it's these treacherous sandbanks.

They're just as dangerous, but you can't build a lighthouse on them.

So how do you stop ships from running aground when you can't see the danger?

You anchor a light ship over it.

A lightship is just that, a cross between a lighthouse and a ship.

They were invented 280 years ago.

Up until the 1980s,

they had a crew of hardy souls on board all year round.

These days, our light ships are all fully automated.

They're the only ships on our seas with no-one on board.

This is the Trinity House vessel alert.

They're responsible for all of our lightships and buoys at sea.

Today we're heading out to the Sunk Centre lightship.

It's a rare opportunity to see for myself how today's lightships work.

With Felixstowe on one side, Harwich on the other

and Tilbury just to the south,

this is one of the busiest shipping lanes in Britain.

Navigating round here is really quite complicated

cos there's these great sandbanks that run out

pretty much north east to south west.

It means the ships can't make a beeline for our important eastern ports.

Many of the sandbanks lie below the surface,

so it's vital they're clearly marked to stop ships running aground.

Captain of the Alert is Roger Swinney.

What fascinates me, Roger, is that in these days with all this modern technology -

look what we're surrounded with on this ship, radar, GPS, you name it -

that we still need lights to mark some of the most dangerous hazards at sea.

Do we still really need the lights?

Yes, certainly. There are dangerous banks round there.

They're very shallow.

You've only got to take your eye of the electronics for a little while.

There are so many other things, radios and faxes.

If you fail to make a course alteration it would be easy for a ship to run aground.

So you've always got that as a check to make sure you are where you think you are.

Roger remembers what it was like back in the days

when men had to live on lightships to keep the light burning.

It took a very special breed to go out there,

it's not like a lighthouse which is obviously pretty static,

you're out there leaping up and down in horrendous weather.

And you had to be able to get on with people.

If you're cramped up on the same boat

it's difficult to get away from each other

so you have to put up with people's little habits

that, after a few days, you might find quite irritating.

The crew of seven would live on board for a month at a time.

Now the ships are solar powered and fully automatic,

but they still need regular maintenance.

Bit tricky, this, we've come out here, and it's not that rough,

but the tide is on the turn.

So we stand a chance of just slewing round.

Roger's busy up there getting it right.

'Five metres off parallel. And two metres to come ahead.'

One metre to astern.

He's doing a good job, isn't he?

He is. In line fore and aft.

I've always wanted to do this. I've sailed past these things a lot

and there's always been that thing, "I wonder what it's like on there."

Looks like I'm going to get on. Great.

All right, James?

We'll get a bit closer, once we're happy she's steady we'll get across.

OK, she's gotten away so just hold fire till she's back.

All right.

Half a metre to come astern, if you can. Bow's starting to open. About a metre off.

It feels strange coming onto a completely empty ship.

Feels a bit wrong somehow.

James shows me inside where the crew of Sunk Centre lightship used to live.

Through one of the watertight doors,

just get that locked back cos it'll swing and smash us. OK.

This would have been part of the accommodation as well.

What would this have been?

An old mess room,

relaxation room, couple of sofas, maybe a little coal fire in the corner.

-Oh, that's nice.

-Yeah, little furnace.

Something to make it a bit like home.

Yeah, creature comforts of home, really.

The crews would spend a month at a time on the ships.

They did their best to keep morale up.

Too bad it's got such an empty feel about it.

Yeah, she does now.

-So what was this space then?.

-This is the old engine room.

It's so strange being in a place where this many men

spent months and years of their lives living here.

And it would have taken a really special breed of person

to have lived out here for all that time.

I just would have loved to have had a go at it myself.

The tour may be over, but we still have a job to do.

You got me set up, I've got me torch and me gas detector.

Gas detector there as well.

I've got a gas detector because it's an enclosed space

and this thing'll pick up any low oxygen readings

due to say, anything being rusty.

Lots of rust, eats up the oxygen.

There's lots of batteries in here, so this picks up any gases from the batteries.

The solar panels charge a bank of batteries during the day,

to power the light at night.

They need to be checked every six months.

These are standard lead acid batteries like you might have in your car.

-Yes, exactly the same.

-But there's a lot of them.

Yeah. A lot more of them.

-How is it?

-Dry on these two. See that, that's going off.

-Because of that?

-Coming out of that.

Yeah, picking up the hydrogen.

That's a signal for us to go out, we're getting too much bad gas

from these batteries so we'll step outside for a minute.

There you go, so they work.

All that is is the fumes coming from the battery.

'Once the gas has cleared,

'we head back in to top up the batteries with distilled water.'

-If you start pumping.

-Ready?

-Go on. Away you go.

-Good system that, James.

-Check another one.

That one's quite happy. That's going off.

-OK.

-BEEPING

That one's happy as well.

The light is mounted on a 12-metre tower

and it can be seen for 15-nautical miles.

Each lightship flashes at a different frequency

so they can all be identified by ships.

-So that is the light, the business end?

-That's the main light in there.

-It's huge.

-The optic is huge, but the bulb itself

-is probably no bigger than that.

-I see.

-Couple of inches.

This is where the light vessels come from,

from marking the sandbanks in the Thames estuary on the east coast.

Oh, I really like that, this was the birthplace of light vessels.

-Neat feeling, isn't it?

-Yeah, it's good.

We've stopped making light ships now.

In the future, the job will be done by a new generation

of cost-effective, hi-tech marker buoys.

I, for one, am going to miss them.

Our expedition to understand the secret of the grey seal's success

is coming to an end on the island of Lindisfarne.

Over the last decade, harbour seal numbers have plummeted

while grey seals have been going up.

They live in the same places, they're very closely related,

so what is it that makes grey seals so much more successful than harbour seals?

Tooni's joining a scientist who's trying to solve this puzzle.

There are a number of theories as to why grey seals are doing better than harbour seals.

Now, both species are hard to approach on land,

but in order to get more of an insight into their ecology,

I need to find a place where the two species co-exist.

I'm joining Ailsa Hall on a trip to a site near Lindisfarne

where we should be able to find both species.

Ailsa's been studying grey and harbour seals for over 20 years.

In that time, grey seal numbers have reached over 150,000

while harbour seals have fallen to less than 40,000.

What are the main differences between the grey seals and the harbour seals?

Well, the grey seals are a bigger mammal.

How big do they get?

Get up to 150 kilos for a female, 200 kilos for a male.

Two or three times your weight.

About your height! Whereas the harbour seal is much smaller.

As well as being smaller, harbour seals, like this one,

have wider eyes and shorter muzzles than the grey seal behind it.

They might both be seals, but these are separate species

and they can't interbreed.

Harbour seals are also known as common seals,

but they're far less common than greys in the North Sea.

Why do you think the grey seals are doing so well and the harbour seals not so much?

We've got a number of theories we've been looking at.

One of the things we're looking at here is what they eat.

And how the diet is the same or different between the two species.

So, the problem is we can't watch them eating,

but there are other ways we can see what they've been preying on.

I have a feeling I know what's coming.

Ailsa finds out what the seals have been eating

by examining their excrement, known as "skats".

Long before we get close to them, the grey seals and harbour seals scarper into the water.

What they've left behind is easy to identify.

Smell that.

Do you know what, I can smell it from here?

All right?

We think this is probably all one skat, actually.

-The whole of this.

-There's more there.

I think that's a separate one. This would be one, even that.

It's just like a pooper scooper.

Put your hand in the plastic bag. Scoop the skat together.

Not trying to miss any parts that might have the hard parts in.

Can you tell just from looking at these samples which species they've come from?

Not by looking at them no, obviously this region there were more grey seals

so these are likely to be grey seal skats.

But the size of these, looking at them, my guess would be that's it's a grey seal male.

Normally Ailsa would analyse the samples in the lab,

today we're going to have a preliminary look

to see what this grey seal has been eating.

We're looking for otoliths - the hard ear bones of fish

that pass through seals undigested.

In recent years, there's been a collapse in stocks

of the sand eels that both species prey on.

Ailsa's research suggests grey seals

have found a way to adapt to the change.

We do see differences between the two species.

The grey seals' diet seems to be dominated by the larger species,

the larger sand eels and cod, haddock, whiting, that kind of thing

and the harbour seals take smaller more localised prey

because their foraging areas are much closer in shore.

'If this theory is correct and the grey seals

'are going further to find new sources of food,

'we'd expect to find the bones of bigger fish species

'like cod and haddock in their skats.

'It's a painstaking business.'

When you pick up the skat, you want to get all the skat.

-Was that an otolith?

-I think it might be. That looks like an otolith to me.

We soon discover three ear bones in the skat.

What do these bones tell you about what the seals have been feeding on?

We know this was the skat we collected

that we think came from a grey seal and these are relatively large otoliths,

ear bones, possibly from a cod or a haddock, larger fish species.

So that tells us that these animals,

certainly the one that collected, are still preying on the larger fish.

If they're finding prey this large,

they must be foraging much further offshore than the harbour seals.

Being able to go further and find different sources of food

could be giving the grey seals their advantage.

Where both species live side by side like here at Lindisfarne,

the grey seals are out-hunting and out-competing their smaller neighbours.

On the face of it, it seems the bigger more physically robust grey seal

can adapt quicker to environmental change because it can forage

further afield than the much smaller harbour seal.

With its size, strength and ability to travel

hundreds of miles across the North Sea,

the grey seal is a formidable predator.

With our expedition at an end, we leave the Farne Islands behind us.

Well, for me the favourite thing was,

aside from the obvious sheer joy of diving with them,

which you can't deny, was just seeing how

they are so physiologically adapted for diving.

They're just such brilliant divers, absolutely great.

And you see them up close and they are just such chunky,

bulky, physically healthy animals.

They look like the ultimate survivor in the marine environment.

They're fantastically long-lived and sentient intelligent creatures

and you can see it in the way that they learn to forage.

Things that I might have taken for granted, to really study it

over these days has been a complete pleasure. Brilliant.

Next time on Britain's Secret Seas,

we reveal the mysteries of the south.

-Explore the secret life of our seahorses...

-I just think they're so magical.

Solve the puzzle of a 400-year-old shipwreck...

This is like finding a pharaoh's tomb.

And get up close with the fearsome conger eel.

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