0:00:05 > 0:00:09The waters around the UK hide treasures
0:00:09 > 0:00:12and surprises we rarely get to see.
0:00:13 > 0:00:16Powered by Arctic currents to the north,
0:00:16 > 0:00:19and the Gulf Stream to the south,
0:00:19 > 0:00:22our island occupies a unique position in the Atlantic Ocean.
0:00:26 > 0:00:27'I'm explorer Paul Rose.
0:00:27 > 0:00:31'I was base commander of the British Antarctic survey for ten years
0:00:31 > 0:00:35'and I've scuba-dived all around the world.'
0:00:35 > 0:00:38I've found one! That's a bomb.
0:00:41 > 0:00:45'But now I've come home to lead a team of specialists,
0:00:45 > 0:00:48'to uncover the secrets beneath our seas.'
0:00:50 > 0:00:55- Divers up!- 'Joining me is marine biologist Tooni Mahto.
0:00:55 > 0:00:57'Her underwater expertise will reveal
0:00:57 > 0:01:00'the unexpected riches of British marine life.'
0:01:00 > 0:01:02See the size difference between
0:01:02 > 0:01:05the giant male and the much smaller female.
0:01:05 > 0:01:09'Journalist and underwater archaeologist Frank Pope
0:01:09 > 0:01:11'will examine the bigger picture
0:01:11 > 0:01:15'of our relationship with the sea and explore our maritime history.'
0:01:15 > 0:01:20Even if we make one tiny deviation, we could easily end up grounded.
0:01:24 > 0:01:26This series will take us on a journey
0:01:26 > 0:01:28right around our British seas
0:01:28 > 0:01:33to uncover the most startling underwater wonders.
0:01:33 > 0:01:37This week, we're exploring Britain's west coast.
0:01:38 > 0:01:42We're going in search of the UK's biggest marine animals,
0:01:42 > 0:01:45the biggest ships and its biggest wreck.
0:01:45 > 0:01:47The seas of the west coast of Britain
0:01:47 > 0:01:49are cram-packed full of giants.
0:01:51 > 0:01:55Beneath our waves is a world of secrets.
0:02:07 > 0:02:09Our expedition begins in Cornwall,
0:02:09 > 0:02:12down at the very bottom of the west coast of Britain.
0:02:16 > 0:02:20It's here we hope to investigate our nation's largest native animal -
0:02:20 > 0:02:23the mighty basking shark.
0:02:25 > 0:02:28The west coast of Britain has got many giants,
0:02:28 > 0:02:30but none greater than the basking shark.
0:02:30 > 0:02:34They grow to an astonishing 11 metres long,
0:02:34 > 0:02:35weighing in at seven tonnes.
0:02:35 > 0:02:38It's the second largest fish in the world -
0:02:38 > 0:02:40only the whale shark is bigger.
0:02:40 > 0:02:43And in the summer months, the basking sharks can be seen
0:02:43 > 0:02:46along the entire west coast of Britain
0:02:46 > 0:02:48from Cornwall right up to Scotland.
0:02:48 > 0:02:54But what is it about our waters that attract these mighty leviathans?
0:02:54 > 0:02:55Look at that!
0:02:55 > 0:02:59It's hard to believe that these things live in British waters.
0:02:59 > 0:03:00They're huge, great things.
0:03:00 > 0:03:03There's a real element of mystery about these sharks.
0:03:03 > 0:03:07So little is actually known about their biology, where they spend their winters,
0:03:07 > 0:03:09what their reproductive cycle is,
0:03:09 > 0:03:11there's all this sort of list of unknowns
0:03:11 > 0:03:12about this giant, giant creature.
0:03:12 > 0:03:14They're listed as vulnerable, aren't they?
0:03:14 > 0:03:17Listed as vulnerable and endangered in the north-east Atlantic.
0:03:17 > 0:03:19Sharks, in particular, are in real trouble,
0:03:19 > 0:03:23because they grow so slowly and they don't give millions of eggs
0:03:23 > 0:03:26like other species, so if you start hammering sharks,
0:03:26 > 0:03:29you very, very quickly send a population into trouble.
0:03:34 > 0:03:36'Across the globe, sharks are in decline.
0:03:36 > 0:03:40'We want to find out if the giant basking sharks
0:03:40 > 0:03:44'that visit our shores are also under threat.
0:03:44 > 0:03:45'From mid-May onwards,
0:03:45 > 0:03:49'it's here in Cornwall they first begin to appear off our shores.
0:03:53 > 0:03:55'They might be giants,
0:03:55 > 0:03:59'but basking sharks can be notoriously difficult to find.
0:03:59 > 0:04:03'We're going out with experienced shark spotter Charlie Hood.'
0:04:03 > 0:04:07Whereabouts are we likely to see them? Is there only one area or...?
0:04:07 > 0:04:10Where we have been seeing them is very close in shore.
0:04:10 > 0:04:12So we're going to hug the coastline
0:04:12 > 0:04:14and get everybody spotting at the same time.
0:04:14 > 0:04:16We're looking for the telltale sign
0:04:16 > 0:04:19of the little black fin skimming the surface,
0:04:19 > 0:04:21just like you see in the Jaws film.
0:04:21 > 0:04:23Close to shore? How close?
0:04:23 > 0:04:27Oh, they can be within ten yards. Yeah.
0:04:30 > 0:04:33'We hope to find out what's so special
0:04:33 > 0:04:35'about the sea off the Cornish coast
0:04:35 > 0:04:39'that draws these giant fish so close inshore.
0:04:39 > 0:04:41'And we're in luck!'
0:04:41 > 0:04:43There we go. That's the first one!
0:04:43 > 0:04:46- Yeah!- Holy smokes, there's two there!
0:04:46 > 0:04:49That's it's caudal fin, that's it's tail fin.
0:04:49 > 0:04:53It's doing what it's meant to be doing, which is basking.
0:04:53 > 0:04:56I can see there's a couple of fins there. There's two separate.
0:04:58 > 0:05:01'To investigate why the sharks are here,
0:05:01 > 0:05:05'we need to closely observe their behaviour underwater.
0:05:05 > 0:05:08'But these giant fish can get easily spooked.'
0:05:08 > 0:05:12The basking sharks don't like the bubbles. We'll disturb them
0:05:12 > 0:05:15if we use scuba gear, so we're just going to use snorkelling gear
0:05:15 > 0:05:17and stay right at the surface.
0:05:17 > 0:05:21'Sliding into the water as quietly as possible,
0:05:21 > 0:05:24'we make our first tentative approach.'
0:06:20 > 0:06:21Woohoo-hoo-hoo!
0:06:21 > 0:06:26That is so much bigger than I was expecting.
0:06:26 > 0:06:30You can see those fins lopping around on the surface of the water.
0:06:30 > 0:06:32More over here as well. All around us.
0:06:32 > 0:06:36- All over the place. Look at these guys over there as well. - They're huge!
0:06:45 > 0:06:48'Tooni has advised us to get ahead of the sharks
0:06:48 > 0:06:53'and stay floating at the surface, as diving down can disturb them.
0:06:53 > 0:06:58'They can swim up to four knots, so there's no point trying to keep up.'
0:07:06 > 0:07:08I've never seen anything like this.
0:07:08 > 0:07:11Just being surrounded by dorsal fins.
0:07:21 > 0:07:26'The key to why the sharks are here is in those giant open mouths.
0:07:26 > 0:07:29'They've come into the shallows to feed.'
0:07:31 > 0:07:34These basking sharks have absolutely enormous mouths -
0:07:34 > 0:07:37up to about 1.5 metres wide.
0:07:37 > 0:07:41But though their mouths might be big, they really are gentle giants.
0:07:43 > 0:07:46All they are doing is drifting through the water,
0:07:46 > 0:07:50feeding on zooplankton, these tiny, tiny particles in the water.
0:07:53 > 0:07:56'The tiny animals that make up the zooplankton
0:07:56 > 0:07:59'thrive here during the summer months.
0:07:59 > 0:08:04'We're actually swimming in a living soup of basking shark food.'
0:08:08 > 0:08:10The basking sharks are at the surface of the water,
0:08:10 > 0:08:14because they are filtering plankton through their gills,
0:08:14 > 0:08:16and they filter the equivalent
0:08:16 > 0:08:19of an Olympic-sized swimming pool of water every hour.
0:08:22 > 0:08:26That translates into about 30kg of zooplankton -
0:08:26 > 0:08:31microscopic animals that they are consuming every day.
0:08:41 > 0:08:44Even though we know these are harmless feeders,
0:08:44 > 0:08:47there's something about something that weighs seven tonnes
0:08:47 > 0:08:51with a mouth that big coming towards you, it just has an effect.
0:08:51 > 0:08:56Then that giant tail just flicking past!
0:08:56 > 0:08:58When they close their mouths,
0:08:58 > 0:09:00it looks as if they are kind of...
0:09:00 > 0:09:02Yeah, they do, they close their gullet and,
0:09:02 > 0:09:04as they ram through the water,
0:09:04 > 0:09:07the plankton goes onto their gill rakers,
0:09:07 > 0:09:10and then they shut their mouth every minute or so
0:09:10 > 0:09:12and literally gulp all that plankton back.
0:09:17 > 0:09:21'It's the plankton that's making the water appear cloudy.
0:09:21 > 0:09:24'To get a close up view of these tiny animals,
0:09:24 > 0:09:27'Frank's going to try and take a sample.'
0:09:28 > 0:09:31Got a plankton trawl, which just funnels
0:09:31 > 0:09:34the plankton down and gets caught in the sieve here.
0:09:34 > 0:09:37If I do it here where the basking sharks are feeding,
0:09:37 > 0:09:41we'll get a little sample of what they're feeding on.
0:09:51 > 0:09:53It took us two minutes to get this,
0:09:53 > 0:09:56and we've got a dish full of plankton.
0:09:56 > 0:10:01As you can see through the lens, it's just teeming.
0:10:03 > 0:10:10Plankton is made up of a range of miniature plant and animal species, plus the larvae of larger animals.
0:10:10 > 0:10:18These microscopic organisms are key to life on our planet, forming the basis of our oceans' food chains.
0:10:22 > 0:10:28Each year, the plankton bloom appears off the Cornish coast from mid-May
0:10:28 > 0:10:30but lasts only a few short months.
0:10:30 > 0:10:35By the end of June, the bloom will have disappeared, and so will the sharks.
0:10:37 > 0:10:43So the west of England juts out into the North Atlantic, and all of the south-westerly currents come up
0:10:43 > 0:10:45and hit it, and they bring the nutrients
0:10:45 > 0:10:49that fuel the plankton blooms, that the basking sharks are here to eat.
0:10:55 > 0:10:59Today, we've seen why the sharks come in so close to our shores.
0:10:59 > 0:11:03But to assess the long-term future of our resident giants,
0:11:03 > 0:11:08we're going to continue our expedition further north along the west coast.
0:11:08 > 0:11:11Later on, we'll be joining a team of scientists
0:11:11 > 0:11:16working at the forefront of research into these extraordinary fish.
0:11:21 > 0:11:25I was hoping to see one basking shark, but to be surrounded
0:11:25 > 0:11:30by eight or ten of these great creatures was pretty spectacular.
0:11:30 > 0:11:36And every time I kept looking up at the shore and thinking, "I'm in Cornwall, this is unbelievable."
0:11:55 > 0:11:57Sharks aren't the only giants in our waters.
0:11:57 > 0:12:02Earlier this month, Tooni went to South Wales where she investigated quite a different migration.
0:12:09 > 0:12:15I've come to Stackpole Quay, an 18th-century fishing harbour tucked away along the Pembrokeshire coast.
0:12:18 > 0:12:24You don't always need to go far offshore in order to witness some spectacular underwater events.
0:12:24 > 0:12:29Once a year during May and June, vast numbers of one of the UK's largest crab species
0:12:29 > 0:12:35migrate from the deep waters of the Atlantic into the shallower waters of the coast of South Wales.
0:12:35 > 0:12:39This bay here at Stackpole Quay becomes the focus of an orgy of activity.
0:12:39 > 0:12:41But what are they coming here for?
0:12:51 > 0:12:57'Beneath the waves, thousands of giant crustaceans are on the move.
0:13:01 > 0:13:06'The event I've come to see is the annual migration of spiny spider crabs.
0:13:06 > 0:13:10'But they're proving a little tricky to locate.'
0:13:12 > 0:13:16So we're a few metres down now in Stackpole Quay, and I'm looking
0:13:16 > 0:13:21for the spider crabs, but the problem is they're masters of camouflage.
0:13:24 > 0:13:30They're especially difficult to find in amongst these giant swathes of floating kelp.
0:13:30 > 0:13:32Perfect hiding place.
0:13:38 > 0:13:40Oh, there's one.
0:13:40 > 0:13:44SHE LAUGHS He's a tiny little one!
0:13:44 > 0:13:46Oh, wow!
0:13:46 > 0:13:52That is just an amazingly camouflaged little thing.
0:13:52 > 0:13:54Look at that!
0:13:57 > 0:14:04'It's not quite the giant I was after, but this tiddler is showing off some fantastic exterior design.'
0:14:06 > 0:14:12These spider crabs actually cement bits of algae and small marine animals
0:14:12 > 0:14:15onto their carapaces, the bit on their back.
0:14:15 > 0:14:21Absolutely brilliantly decorated to look like a small rock.
0:14:21 > 0:14:23Beautiful watching them move across the sand.
0:14:23 > 0:14:25They really do dance.
0:14:28 > 0:14:32Looks like he has literally done himself up for Saturday night out.
0:14:35 > 0:14:39What's so incredible though is that you take one look at them,
0:14:39 > 0:14:41then you look away and you look back
0:14:41 > 0:14:44and you can't see them, because he's so well camouflaged.
0:14:52 > 0:14:57'With a little more searching, I find the giant I was looking for.'
0:14:59 > 0:15:02Look at the size of him!
0:15:03 > 0:15:06He's kind of hunkered down there, doesn't want to come out
0:15:06 > 0:15:09but I'll try and get him out from underneath this rock.
0:15:13 > 0:15:16Here's a really good example of why they are called the spiny spider crab.
0:15:16 > 0:15:21They have these spines here and two horns at the front of the carapace.
0:15:24 > 0:15:27He's hanging on pretty tight to that rock.
0:15:27 > 0:15:29And he's got me with his claws.
0:15:29 > 0:15:31Luckily, I've got the gloves.
0:15:38 > 0:15:41Now, you can tell he's a male because of these giant claws
0:15:41 > 0:15:45that he is gesticulating at the camera very magnificently.
0:15:45 > 0:15:47They can grow to about one and a half metres across,
0:15:47 > 0:15:52which is about another that much on him, which is a phenomenal size.
0:15:54 > 0:15:57Ooh!
0:15:57 > 0:15:58Ow!
0:15:58 > 0:16:01Argh! SHE LAUGHS
0:16:01 > 0:16:03Oh, I tell you what,
0:16:03 > 0:16:06even through a set of gloves, that's a pretty good pinch on him.
0:16:09 > 0:16:15'Once a year, thousands of spider crabs are drawn to the shallow waters of South Wales.
0:16:15 > 0:16:18'And here's the reason why.'
0:16:18 > 0:16:19Ah. Look at this...
0:16:19 > 0:16:21Oh, goodness me - there's two of them.
0:16:21 > 0:16:26So this is a big male, and he's gripped onto a smaller female.
0:16:26 > 0:16:32This is the start of mating. This is the reason why they come into these waters, to actually breed.
0:16:33 > 0:16:37Normally, you find them out in much deeper Atlantic waters,
0:16:37 > 0:16:39in about 120m depth,
0:16:39 > 0:16:46but the problem with being in deep water and a solitary individual is that it's hard to find a mate,
0:16:46 > 0:16:50so by coming into shallow waters all at the same time,
0:16:50 > 0:16:52you can indulge in a mating frenzy.
0:16:54 > 0:16:57He's grabbed hold of her, he'll turn her over
0:16:57 > 0:17:01so they're abdomen to abdomen, and that's when breeding will occur.
0:17:07 > 0:17:10See the size difference between the giant male
0:17:10 > 0:17:13and the much smaller female.
0:17:13 > 0:17:14Ooh!
0:17:14 > 0:17:18I feel a bit bad that I've broken up the mating ritual.
0:17:18 > 0:17:19Here we go.
0:17:21 > 0:17:26'This is the one time of the year that you can see so many of these monster crabs in shallow water.
0:17:26 > 0:17:30'In a month's time, they will return to the deep.'
0:17:39 > 0:17:41That was fantastic!
0:17:41 > 0:17:46There are a lot of spider crabs down there - there's kind of individuals and pairs -
0:17:46 > 0:17:49and we found some males and females together,
0:17:49 > 0:17:52so it very much feels like the start of the mating season.
0:17:52 > 0:17:56They're definitely starting to come up from the deeper water into the shallows,
0:17:56 > 0:17:59but they are just the most phenomenal creatures.
0:17:59 > 0:18:02They're real...alien invaders of the shallow waters.
0:18:02 > 0:18:04I love them, I think they're fantastic.
0:18:06 > 0:18:13British waters are full of a rich diversity of wildlife, and it's in our interests to keep it that way.
0:18:13 > 0:18:16Frank went to our country's first marine reserve
0:18:16 > 0:18:20to see if it could be used as a template for the future conservation of our seas.
0:18:31 > 0:18:38Located 18km off the coast of North Devon, this is Lundy Island.
0:18:40 > 0:18:43Once ruled by a self-proclaimed king,
0:18:43 > 0:18:50Lundy is a remote 5km chunk of ancient granite rock perched out in the Celtic Sea.
0:18:50 > 0:18:54With one side of the island exposed to the Atlantic currents
0:18:54 > 0:19:00and the other a sheltered refuge, Lundy is uniquely placed to attract a wide range of wildlife.
0:19:04 > 0:19:09In 1971, Lundy became Britain's first marine reserve.
0:19:09 > 0:19:14There are now plans afoot to have many more of these marine nature reserves around the nation.
0:19:14 > 0:19:17But has Lundy itself been a success?
0:19:27 > 0:19:30The island is owned by the National Trust.
0:19:30 > 0:19:35Along with the wild Sika deer, there's an amazing abundance of birdlife.
0:19:37 > 0:19:41From April to July, the cliffs of Lundy's west coast
0:19:41 > 0:19:45are filled with sea birds, returning to the island to breed.
0:19:45 > 0:19:50But it's beneath the waves that Lundy really comes into its own.
0:19:52 > 0:19:58We're used to the idea of nature reserves and national parks on land, but what's different about Lundy
0:19:58 > 0:20:03is that it's taken the concept of protecting the environment from the land out into the ocean.
0:20:07 > 0:20:13'The marine environment around Lundy is now legally protected.
0:20:13 > 0:20:21'Biologist Dr Keith Hiscock has been closely studying the underwater life here for the last 40 years.'
0:20:21 > 0:20:24What was it that made you realise this is a special place?
0:20:24 > 0:20:26I dived on Lundy in 1969.
0:20:26 > 0:20:32You could just tell that there was lots of spectacular, rare species which we hadn't seen before.
0:20:32 > 0:20:36You've got extensive, very rich sediments off the east coast here.
0:20:36 > 0:20:40The granite rocks themselves have got lots of nooks, crannies, overhangs.
0:20:40 > 0:20:44As soon as you get a wide range of habitats, you get a wide range
0:20:44 > 0:20:47of communities of wildlife colonising those habitats.
0:20:48 > 0:20:55'In 2003, a section of Lundy's marine reserve became Britain's first "No Take Zone".
0:20:55 > 0:20:58'Here, all forms of fishing are banned.
0:21:01 > 0:21:04'I want to find out what this level of protection can achieve.'
0:21:18 > 0:21:23There's a rather beautiful - but very poisonous - blue jellyfish.
0:21:23 > 0:21:25Wow, look at him. He's a big fella.
0:21:28 > 0:21:33The blue jellyfish that we're seeing do seem to come in with the more oceanic water.
0:21:40 > 0:21:47There's a small-spotted catshark, which, for a long time, has been known incorrectly as a dogfish.
0:21:53 > 0:21:59'Safe from man-made disturbances, many fragile species are able to flourish here.
0:21:59 > 0:22:03'This branching sponge grows less than a millimetre a year.
0:22:03 > 0:22:08'Its size alone suggests it could be nearly 200 years old.'
0:22:17 > 0:22:21There are some of the very common sea urchins over here.
0:22:21 > 0:22:28They actually eat away at animals and algae which might otherwise become dominant.
0:22:28 > 0:22:32So this is an animal that most people think of only as being a pain
0:22:32 > 0:22:36in the foot, but in fact it opens up the environment for others.
0:22:36 > 0:22:43Yes, the sea urchins have a very important role in policing the diversity of species on the seabed.
0:22:49 > 0:22:55'The variety of underwater habitats encourages a wide range of species.'
0:22:59 > 0:23:01You get a lot of these cup corals along the wall here.
0:23:04 > 0:23:06There are some nice sea fans over here.
0:23:12 > 0:23:16Oh, look, there's a seal. A seal right below us.
0:23:16 > 0:23:20Thank you very much(!) Really stirring up the visibility in the canyon.
0:23:26 > 0:23:31Here are these absolutely fabulous rock walls of jewel anemones.
0:23:38 > 0:23:43The jewel anemones just here have caught a blue jellyfish.
0:23:43 > 0:23:46It's going to be consumed.
0:23:46 > 0:23:52Jewel anemones are absolutely fabulous - they're really pretty, but also absolutely deadly.
0:23:52 > 0:23:54So we're in a forest,
0:23:54 > 0:23:59but this is not a forest of plants, it's a forest of animals.
0:24:06 > 0:24:11'Lundy's No Take Zone doesn't just benefit Lundy.
0:24:11 > 0:24:14'It has the ability to increase the abundance
0:24:14 > 0:24:20'and species richness of marine life up to 50km beyond the boundaries of the reserve.'
0:24:29 > 0:24:33Lundy ends up functioning like a giant seed bank,
0:24:33 > 0:24:38to disperse larvae and eggs of all the different species that live here,
0:24:38 > 0:24:45and that way, Lundy can repopulate areas that have been over-exploited by man's activities.
0:24:45 > 0:24:48Divers up!
0:24:53 > 0:24:59How much can the Lundy model be taken as a template for the rest of Britain?
0:24:59 > 0:25:04Well, that model has actually been shown to be true throughout the world, not just at Lundy.
0:25:04 > 0:25:07So, if you take the pressure off, then the fish stocks increase.
0:25:07 > 0:25:11So, in fact, No Take Zones are a service, if you like,
0:25:11 > 0:25:13to the commercial fishing industry,
0:25:13 > 0:25:18because they are creating more fish stocks to be caught for us to consume.
0:25:21 > 0:25:24'In 2009, Parliament passed a bill
0:25:24 > 0:25:30'that paves the way for marine reserves to be set up all around the UK.
0:25:30 > 0:25:32'But what works for an isolated island like Lundy
0:25:32 > 0:25:38'might not be as popular when it affects tourism and commercial fishing across on the mainland.'
0:25:41 > 0:25:45To try and use this concept around Britain is fraught with problems
0:25:45 > 0:25:49because of all the vested interest and the amount of money people are making from the way things are.
0:25:49 > 0:25:55If we can overcome those challenges, we can roll out a whole network of marine reserves around the country,
0:25:55 > 0:26:00and if we do that, I think we'll look back and see that Lundy was a great start.
0:26:06 > 0:26:10'Back on our basking shark expedition, we've travelled north from Cornwall,
0:26:10 > 0:26:13'up the west coast of Britain, to the Isle of Man.'
0:26:16 > 0:26:24'Located in the middle of the Irish Sea, the Isle of Man is a hot spot for basking shark activity.
0:26:24 > 0:26:28'The long-term future of these giant fish is still uncertain.
0:26:30 > 0:26:35'We've come to work alongside marine biologists Jackie and Graham Hall
0:26:35 > 0:26:39'to find out the extent to which our basking sharks are still vulnerable.'
0:26:39 > 0:26:41Permission to come aboard?
0:26:41 > 0:26:44'These scientists are involved in a worldwide project,
0:26:44 > 0:26:48'studying basking shark populations and their migration patterns.'
0:26:48 > 0:26:51- Pleased to meet you, Frank.- Hi.
0:26:51 > 0:26:59When you see a basking shark, they are big, beautiful, charismatic animals.
0:26:59 > 0:27:02They fill you with enthusiasm and passion,
0:27:02 > 0:27:06especially when you realise that they are so endangered,
0:27:06 > 0:27:09and that we... we can make a difference.
0:27:13 > 0:27:16'Today, we're hoping to collect shark DNA,
0:27:16 > 0:27:21'as part of a global study, assessing the health of the sharks' gene pool.'
0:27:24 > 0:27:28Maintaining a healthy gene pool is all about good breeding.
0:27:28 > 0:27:31If the local shark population only breed amongst themselves,
0:27:31 > 0:27:34that could narrow down their mix of genes.
0:27:34 > 0:27:37If, on the other hand, sharks come in from miles away,
0:27:37 > 0:27:41this could introduce a healthy injection of new genes to the local population.
0:27:43 > 0:27:48'Getting a sample of DNA from a giant fish is not an easy task.
0:27:48 > 0:27:54'For such state-of-the-art science, Jackie and Graham use a somewhat basic approach.'
0:27:54 > 0:27:55Ah, that's the one!
0:27:55 > 0:28:00- Just have a look at that - that is the thing.- You can see these very expensive paper clips.
0:28:00 > 0:28:02- But actually it's cheap and it works.- Brilliant.
0:28:02 > 0:28:06And all this is is a pan scrubber, a plastic pan scrub,
0:28:06 > 0:28:09and we extend the pole as far as we can
0:28:09 > 0:28:12and then we just use this and we brush it against the shark's fin.
0:28:15 > 0:28:16'Well, that's the plan, anyway!
0:28:16 > 0:28:22'But finding the giant fish is proving much harder than it was in Cornwall.
0:28:22 > 0:28:26'After several hours searching...'
0:28:26 > 0:28:31We've got one right here! He's about 20 yards over there just off our port quarter.
0:28:31 > 0:28:34Can you see him? It's a small one.
0:28:34 > 0:28:38- Don't you think, Tooni?- Yes, he's small, the boat went right by him.
0:28:38 > 0:28:44Now, he's turning round, cos he's feeding, he's following the food, he's following the plankton line.
0:28:44 > 0:28:47'While Tooni and I work from the science boat...
0:28:47 > 0:28:50Coming to you!
0:28:50 > 0:28:57'..Frank and Gavin, our underwater cameramen, prepare to get in the water and get some close-up shots.'
0:28:57 > 0:29:02What the director's handed me is this fantastic-looking mask camera.
0:29:02 > 0:29:06And what you do is you put it on, and it takes the images here.
0:29:11 > 0:29:16He's right here, he's about 35 metres away now.
0:29:16 > 0:29:17Just gone under.
0:29:29 > 0:29:34'The shark's large dorsal fins often have small injuries along the outer edges.
0:29:36 > 0:29:41'This can create a unique pattern and provide a quick way to identify individuals.'
0:29:41 > 0:29:46Almost a textbook dorsal fin, I'd say.
0:29:46 > 0:29:49'Although the fins can acquire more scars over time,
0:29:49 > 0:29:51'by building up a catalogue of photos,
0:29:51 > 0:29:56'individual sharks can be tracked around Britain - and even across the world.
0:30:00 > 0:30:06'The shark doesn't seem bothered by our presence, so we're now going to try and take a DNA sample.
0:30:06 > 0:30:12'As Jackie slowly manoeuvres the boat into position, Graham gets ready at the bow with the scourer.'
0:30:18 > 0:30:20- Damn near.- Ah, couldn't get it.
0:30:23 > 0:30:26'It's a tricky operation.
0:30:26 > 0:30:28'Jackie takes us round for a second attempt.'
0:30:28 > 0:30:30All right. OK. Now, then, where's he gone?
0:30:33 > 0:30:36'This technique doesn't harm the shark in any way.'
0:30:39 > 0:30:41Got it?
0:30:41 > 0:30:42Yes, he's got it!
0:30:42 > 0:30:45'We're actually taking a swab of a slimy coating
0:30:45 > 0:30:48'that naturally occurs all over the shark's body.'
0:30:48 > 0:30:51He's got it. That's there. Shark goo.
0:30:51 > 0:30:52Well done!
0:30:53 > 0:30:58'The black shark goo will now be sent off to have the DNA extracted.
0:30:58 > 0:31:01'By collecting hundreds of different samples,
0:31:01 > 0:31:06'scientists can begin to assess the health of the sharks' gene pool.
0:31:06 > 0:31:10'They can find out whether isolated populations are interbreeding
0:31:10 > 0:31:15'and even estimate the total number of basking sharks in the global population.'
0:31:16 > 0:31:18Did you get a size estimate?
0:31:18 > 0:31:21- Three and a half, I think. - Three and a half metres.
0:31:21 > 0:31:24- Small fellow, but nice - nice condition.- Yeah, I'll say.
0:31:27 > 0:31:30'The DNA work is still in its infancy
0:31:30 > 0:31:32'but combined with other research around the world,
0:31:32 > 0:31:38'we believe some of our local animals ARE going on long migrations in order to breed.
0:31:38 > 0:31:44'This mixing of genes will help our sharks maintain a healthy and robust gene pool.'
0:31:45 > 0:31:47What are the implications of those findings?
0:31:47 > 0:31:50They're huge, from the point of view of management.
0:31:50 > 0:31:53We're not doing blue skies research here.
0:31:53 > 0:31:57We're doing it so that we can manage these animals effectively.
0:31:57 > 0:32:00If it's a global population, they need global protection.
0:32:01 > 0:32:06There are still more secrets to uncover about our basking sharks -
0:32:06 > 0:32:09but for the moment, it's back into port.
0:32:10 > 0:32:16When you witness such thriving wildlife, it's easy to forget just how vulnerable our seas are.
0:32:16 > 0:32:18I went back to Cornwall,
0:32:18 > 0:32:23to the scene of the biggest ever environmental disaster to affect our shores.
0:32:30 > 0:32:34The Cornish coastline is full of picture-postcard views,
0:32:34 > 0:32:38with quaint fishing villages and beautiful beaches.
0:32:44 > 0:32:48But just over 40 years ago, the scene looked very different.
0:33:10 > 0:33:15On the morning of 18th March 1967, the largest oil tanker of its time,
0:33:15 > 0:33:19the Torrey Canyon, ran aground off the Cornish coast.
0:33:19 > 0:33:23She was carrying 119,000 tonnes of crude oil,
0:33:23 > 0:33:25which began gushing out in the Atlantic.
0:33:29 > 0:33:35The Torrey Canyon remains one of the worst ecological disasters in British maritime history,
0:33:35 > 0:33:37but what is its legacy 40 years on?
0:33:42 > 0:33:46Built in 1959 and measuring nearly 300 metres long,
0:33:46 > 0:33:53the Torrey Canyon transported crude oil from Kuwait to the oil refinery at Milford Haven.
0:33:57 > 0:34:02But 24km off Land's End, disaster struck.
0:34:02 > 0:34:06The tanker hit a huge offshore reef called the Seven Stones.
0:34:13 > 0:34:18The authorities at the time didn't really know how best to deal with the disaster.
0:34:18 > 0:34:19The RAF were scrambled,
0:34:19 > 0:34:23unleashing wave after wave of bombs to sink the wreck,
0:34:23 > 0:34:25and napalm to burn off the oil.
0:34:31 > 0:34:36Despite the bombing campaign, the oil slick washed up on the Cornish coast,
0:34:36 > 0:34:39killing much of the local bird and marine life.
0:34:41 > 0:34:46Over the course of the next 12 months, the oil that had blackened our pristine beaches
0:34:46 > 0:34:50and decimated the ocean wildlife was slowly cleaned up.
0:34:50 > 0:34:52But what about the tanker itself?
0:34:52 > 0:34:56The Torrey Canyon is the largest shipwreck in British waters,
0:34:56 > 0:34:59but one that very few people have seen.
0:34:59 > 0:35:02And getting to the wreck is quite a challenge.
0:35:04 > 0:35:11I want to see for myself what remains at the actual scene of the disaster.
0:35:11 > 0:35:13Setting off from Penzance harbour,
0:35:13 > 0:35:16we're heading out to the treacherous Seven Stones reef.
0:35:18 > 0:35:20We have to be very careful,
0:35:20 > 0:35:24as the rocks lying just beneath the waves could do us some serious damage,
0:35:24 > 0:35:26just as they did to the Torrey Canyon.
0:35:29 > 0:35:33So you can just see, out here, the tops of the Seven Stones.
0:35:33 > 0:35:37And here they are. It's a very complex little area.
0:35:37 > 0:35:43We can take our small orange boat, our inflatable, right inside the Seven Stones,
0:35:43 > 0:35:47and if we're careful, we can get right over the Torrey Canyon.
0:35:48 > 0:35:51'This is a dive loaded with difficulties.
0:35:51 > 0:35:55'Dive Supervisor Richard Bull has his concerns.'
0:35:55 > 0:35:58This is serious diving.
0:35:58 > 0:36:00We are a long way offshore.
0:36:00 > 0:36:03If we want help, it will be a long time getting here.
0:36:03 > 0:36:06What's it got on it? Bombs. Unexploded bombs.
0:36:06 > 0:36:10We're all school boys at heart, we all like things that go bang.
0:36:10 > 0:36:12But let's not make them go bang today. OK?
0:36:14 > 0:36:17Big swell, big wreck, bombs.
0:36:17 > 0:36:18How much more do you want?
0:36:21 > 0:36:25All around us, patches of white water are breaking over the rocks.
0:36:26 > 0:36:28Three, two, one, go!
0:36:30 > 0:36:31We've come at slack water,
0:36:31 > 0:36:35the calmest time of the day, but the sea's still quite choppy.
0:36:37 > 0:36:39Paul Rose, comms check. Over.
0:36:39 > 0:36:42'Loud and clear to me, over.'
0:36:42 > 0:36:44Enjoy your dive, guys!
0:36:56 > 0:36:59'I'm not quite sure what we'll see down here.
0:36:59 > 0:37:03'We believe the wreck is lying 30 metres beneath the surface.'
0:37:03 > 0:37:04Wow!
0:37:09 > 0:37:14Hard to tell what's rock and what's shipwreck.
0:37:14 > 0:37:16Cos it looks nothing like a ship.
0:37:19 > 0:37:24It's just so overtaken with this beautiful marine growth, it's hardly recognisable.
0:37:35 > 0:37:38Here's a patch of exposed Torrey Canyon.
0:37:40 > 0:37:42The rusty bit gives the game away.
0:37:43 > 0:37:45But for that clean patch,
0:37:45 > 0:37:49you could be excused for thinking it was just a load of seaweed-covered rock.
0:37:49 > 0:37:53This is quite obviously the shipwreck.
0:38:07 > 0:38:09It's worth coming underneath the wreck here,
0:38:09 > 0:38:13because you can see this is the bottom, these are all rocks.
0:38:13 > 0:38:18But above me is a great pile of the plates of the Torrey Canyon itself.
0:38:21 > 0:38:25'It looks like all that's left of the ship is giant sheets of mangled metal.'
0:38:26 > 0:38:28We've got to be very careful.
0:38:28 > 0:38:34Got myself tangled up on some bits of wreckage there.
0:38:34 > 0:38:37Quite a gloomy feeling in here.
0:38:39 > 0:38:41Hey, what the heck is this?
0:38:43 > 0:38:45Oh, it looks like a bomb.
0:38:45 > 0:38:47What did they say they've found?
0:38:47 > 0:38:49They've found a bomb.
0:38:50 > 0:38:53- 'That's a bomb!'- It's a bomb.
0:38:53 > 0:38:56I've found one. That's a bomb.
0:38:56 > 0:38:59Luckily, it's one that's already exploded.
0:39:01 > 0:39:04'This is just one of the many bombs
0:39:04 > 0:39:07'dropped by the RAF to sink the stricken vessel.
0:39:14 > 0:39:18'A few minutes later, we come across something I wasn't expecting to find.'
0:39:21 > 0:39:23This is the bridge!
0:39:23 > 0:39:26This is the main control centre of the ship.
0:39:26 > 0:39:30Have a look down there, through this hole. I'll have to be careful.
0:39:30 > 0:39:35But if you look down there, you get a sense that this really is a ship.
0:39:50 > 0:39:53Bloomin' great, this. Fantastic!
0:39:58 > 0:40:02Can you just imagine what it must have felt like to be on the bridge of the Torrey Canyon?
0:40:02 > 0:40:05Things were probably pretty calm.
0:40:05 > 0:40:10You're cruising along having a cup of coffee, talking to your mates,
0:40:10 > 0:40:15and then the unthinkable sound and feeling of "bang!" -
0:40:15 > 0:40:18this huge thing running aground.
0:40:31 > 0:40:36You come up from being underneath the wreck and you come into this burst of life.
0:40:36 > 0:40:39It's just teeming and thriving with life.
0:40:39 > 0:40:43The sea is finally taking over the Torrey Canyon, isn't it?
0:40:43 > 0:40:47There's no sign of the oil and the ship looks beautiful.
0:40:47 > 0:40:49Let's face it, the sea wins.
0:40:53 > 0:40:59'This may be Britain's biggest shipwreck and the site of our worst-ever oil spill,
0:40:59 > 0:41:04'but even after 40 years, I'm surprised how well the sea has healed itself.'
0:41:12 > 0:41:17The wreckage of the giant tanker might now be consumed by the sea,
0:41:17 > 0:41:22but 270km away on the Channel Island of Guernsey,
0:41:22 > 0:41:27Tooni went to see how the legacy of the Torrey Canyon disaster lives on.
0:41:27 > 0:41:3019 days after the Torrey Canyon ran aground,
0:41:30 > 0:41:33its huge oil slick hit the western coast of Guernsey.
0:41:33 > 0:41:37Then, as now, tourism was a major source of income for the island
0:41:37 > 0:41:42and the authorities knew they had to act quickly in order to save their beaches.
0:41:42 > 0:41:44They came up with a plan to gather the thick layer of oil
0:41:44 > 0:41:48from the surface of the sea and store it in a disused quarry.
0:41:48 > 0:41:52That was 43 years ago and, sadly, it's still here today.
0:42:05 > 0:42:11Tucked away in the far north-east of Guernsey, this quarry isn't on the tourist route.
0:42:11 > 0:42:14Yet here sits a piece of British maritime history.
0:42:18 > 0:42:21The quarry is a really weird, quite eerie place.
0:42:22 > 0:42:26And there is an all-pervading, overwhelming stench of oil
0:42:26 > 0:42:29that hits you literally as you just draw up.
0:42:31 > 0:42:35In the past 30 years, several attempts have been made to clear the oil.
0:42:35 > 0:42:39But modern technology may now provide the answer.
0:42:39 > 0:42:42Rob Roussel is in charge of the current clean-up operation.
0:42:44 > 0:42:47The line that's all around. The black line that's all around -
0:42:47 > 0:42:50- that was a previous level of where the oil was?- It is, yeah.
0:42:50 > 0:42:53In the 1980s, they pumped a lot of oil off the surface.
0:42:53 > 0:42:57We're probably talking about a metre thick of oil on the surface of the water,
0:42:57 > 0:42:59and it built up again, so we pumped it out.
0:42:59 > 0:43:04A lot of that oil was used locally in the power station, to generate electricity.
0:43:05 > 0:43:09Recently, Guernsey's government voted to try and completely remove
0:43:09 > 0:43:12this stain from its otherwise pristine landscape.
0:43:12 > 0:43:16But pumping out the remaining oil is no longer an option.
0:43:16 > 0:43:20Basically, a lot of the oil is tied up in the sediment at the bottom of the quarry.
0:43:20 > 0:43:23There's also unexploded ordnance from the Second World War in there.
0:43:23 > 0:43:25It's a fairly hazardous environment.
0:43:28 > 0:43:34In a final bid to rid the island of the last vestiges of the oil from the Torrey Canyon spill,
0:43:34 > 0:43:38Rob and his team are using a process called bioremediation.
0:43:38 > 0:43:43This is a biological approach using bacteria to literally munch their way through the oil.
0:43:44 > 0:43:50This is the first large-scale use of these micro-organisms anywhere in the British Isles.
0:43:50 > 0:43:53Technician Phil Ledger is on hand to supervise.
0:43:53 > 0:43:57In this jug, there is a million, trillion bacteria.
0:43:57 > 0:44:01And once we put the bacteria plus the nutrients into the water,
0:44:01 > 0:44:05that whole soup will create the solution to the oil in there.
0:44:07 > 0:44:13'The tank sits for 24 hours and then the bacteria are ready for action.'
0:44:13 > 0:44:17From their dehydrated state, they are now fully active and functional?
0:44:17 > 0:44:19Fully active,
0:44:19 > 0:44:24swimming around quite happily ready for their job, to eat the oil.
0:44:24 > 0:44:27Open the valve, you'll hear them going down the pipe.
0:44:31 > 0:44:34Looking down at the surface, you can see patches of oil
0:44:34 > 0:44:39simply disappearing into nothing as the bacteria munch away.
0:44:39 > 0:44:44The bio-remediation process has been working so well, the team hope to
0:44:44 > 0:44:48have the quarry pretty much cleared of oil in just a few short months.
0:44:50 > 0:44:53Some 40-odd years after our coastline suffered such a
0:44:53 > 0:45:00catastrophic ecological disaster, we've now found the solution to removing the remaining oil.
0:45:00 > 0:45:04Here on Guernsey, we might at last be able to write the final chapter
0:45:04 > 0:45:08in the disastrous story of the oil tanker Torrey Canyon.
0:45:13 > 0:45:18Oil tankers and container ships are still key to our survival as an island nation.
0:45:18 > 0:45:20And to make the ships more cost effective,
0:45:20 > 0:45:26they're being built even bigger, presenting challenges to our ports that are hundreds of years old.
0:45:26 > 0:45:30Frank went to Liverpool Docks, to see how our busiest port on the west coast
0:45:30 > 0:45:32deals with these man-made giants.
0:45:40 > 0:45:44The port of Liverpool handles over 40 million tonnes of imported cargo
0:45:44 > 0:45:49every year, from fruit and veg to recycled metal.
0:45:54 > 0:45:59But getting gigantic container ships safely into dock is quite a challenge.
0:45:59 > 0:46:06It's a job that begins way out west in North Wales, at the small harbour of Amlwch, in Anglesey.
0:46:12 > 0:46:17I'm being taken out to meet one of the biggest transatlantic container ships in the world.
0:46:21 > 0:46:28Making its monthly voyage from Nova Scotia in Canada, this is the 52,000-tonne Atlantic Companion.
0:46:33 > 0:46:39I want to see how this vast ship gets its precious cargo safely into Liverpool Docks.
0:46:44 > 0:46:47Captain Veeger has agreed to take me on a quick tour.
0:46:51 > 0:46:53We have a sports room in here.
0:46:53 > 0:46:55Oh, my Lord!
0:46:56 > 0:47:02Today, this ship is carrying everything from wine and cereal to beans and steel.
0:47:06 > 0:47:10Down below, they're also hauling some classic merchandise.
0:47:16 > 0:47:20Ships like this carry millions of pounds' worth of cargo.
0:47:20 > 0:47:23While we're all very aware of air travel, it's actually
0:47:23 > 0:47:27imports coming in by sea that our island really relies on.
0:47:27 > 0:47:31But getting a ship this size into Liverpool Docks is no easy matter.
0:47:31 > 0:47:34What you really need is an experienced and, above all,
0:47:34 > 0:47:35local pilot.
0:47:35 > 0:47:37Mersey, Companion.
0:47:37 > 0:47:42Just approaching south of the bar inbound, with no known defects and some hazardous cargo.
0:47:42 > 0:47:48Today, pilot David Boardman is the man who will take the helm for the final critical miles into port.
0:47:48 > 0:47:52You have to be trustworthy enough for the Captain to say, OK,
0:47:52 > 0:47:56take control of my enormous vessel and its priceless cargo.
0:47:56 > 0:47:59A lot of it is on trust and experience, and
0:47:59 > 0:48:03confidence as well in your own ability, but training as well.
0:48:03 > 0:48:07To become a first-class pilot in Liverpool is five and half years
0:48:07 > 0:48:09of experience and training.
0:48:09 > 0:48:11Do excuse me one moment.
0:48:12 > 0:48:14Mersey, Companion.
0:48:19 > 0:48:24David's job is to navigate the ship through the narrow Mersey Estuary.
0:48:24 > 0:48:26Each journey presents unique challenges.
0:48:28 > 0:48:32David's got to balance the effects of wind speed, tides and currents,
0:48:32 > 0:48:36plus the estuary itself has its own inherent hazards.
0:48:40 > 0:48:44Right now, we're in the middle of a specially dredged channel in the Mersey Estuary.
0:48:44 > 0:48:49But even that only gives a ship of this size about half a metre of bottom clearance.
0:48:49 > 0:48:52That makes navigation really, really tight and
0:48:52 > 0:48:56even if we make one tiny deviation, we could easily end up grounded.
0:48:58 > 0:49:02With only 50 centimetres between the bottom of the boat and the sea floor,
0:49:02 > 0:49:05this is a real test of skill and timing.
0:49:07 > 0:49:103.97. OK, thank you.
0:49:10 > 0:49:12So, at the moment, we're still pretty much short of water.
0:49:12 > 0:49:16We're looking for another metre of water.
0:49:16 > 0:49:18So what we don't want to do is be too early.
0:49:18 > 0:49:20Barbados, the Companion.
0:49:20 > 0:49:22Channel Six for me, please.
0:49:24 > 0:49:31David times his progress up the estuary to cross the shallowest point at the highest tide.
0:49:31 > 0:49:34He's fast approaching the point of no return,
0:49:34 > 0:49:38beyond which he can't turn back, and is committed to getting into dock.
0:49:40 > 0:49:44What we'd call the abort position now is the next buoy.
0:49:44 > 0:49:46Once I get past that buoy...
0:49:46 > 0:49:49- This buoy here? - Yes. ..I am committed then.
0:49:49 > 0:49:51Shouldn't you be sort of gripping the controls at this point?
0:49:51 > 0:49:54Not at all, not at all.
0:49:54 > 0:49:58I'll put it down, and hopefully, we'll see years of experience at doing this.
0:49:58 > 0:50:00I hope we don't catch the one time you mess it up.
0:50:00 > 0:50:02No, well, I hope that as well.
0:50:05 > 0:50:08Entry to the port is via a sea lock.
0:50:08 > 0:50:14To protect the lock from damage by tidal surges, it was built facing up-river.
0:50:14 > 0:50:17But that means David now has to make the maritime equivalent of
0:50:17 > 0:50:20a handbrake turn to be able to enter port.
0:50:24 > 0:50:29So what we're doing now is spinning round and trying to line ourselves up for the lock.
0:50:29 > 0:50:33We've only got a two-hour window to get in, at which point,
0:50:33 > 0:50:36they shut the doors and we've got enough water under our hull.
0:50:45 > 0:50:48It doesn't look like we are going to make it at all.
0:50:48 > 0:50:51But he's bargaining on the tide carrying us,
0:50:51 > 0:50:53so we get to line up with it.
0:50:53 > 0:50:56But at the moment, it doesn't even look close.
0:51:08 > 0:51:10Getting into the lock is a tight fit.
0:51:10 > 0:51:14There's just two metres spare on either side of the ship.
0:51:14 > 0:51:17West-side man, we've got the greens. OK, thank you.
0:51:17 > 0:51:20You can see the docking signals now, they've given us the green light.
0:51:20 > 0:51:23Tell me how you work out where you are?
0:51:23 > 0:51:26When I'm looking down the south side of these sheds
0:51:26 > 0:51:27and that quay wall there now,
0:51:27 > 0:51:31that tells me that our bow is 60 metres south of the entrance,
0:51:31 > 0:51:32so I pretty much know
0:51:32 > 0:51:36that I'm clear to drop in and slide past the entrance there.
0:51:38 > 0:51:40Slowly, we creep in.
0:51:44 > 0:51:47With the back gate shut, the lock is filled.
0:51:50 > 0:51:53The giant ship can then move into the dock itself.
0:52:15 > 0:52:18The ship's owners get charged by the hour for the time they
0:52:18 > 0:52:21spend at the dockside, so they really don't want to hang around.
0:52:21 > 0:52:25Nor do they want to miss their next exit window out to the ocean, which
0:52:25 > 0:52:28is the next high tide, so it's all a bit of a race against time.
0:52:35 > 0:52:42In just a few hours, around 15,000 tonnes of cargo will be offloaded from this one container ship.
0:52:42 > 0:52:45It then gets reloaded with British exports.
0:52:48 > 0:52:53I've been counting and I can see about 15 people on the dockside,
0:52:53 > 0:52:57and that's all that is required to offload this massive cargo.
0:53:01 > 0:53:03The innovation of containerisation has
0:53:03 > 0:53:07revolutionised the speed with which these giant ships can return to sea.
0:53:12 > 0:53:16As an island nation, we've always relied on our docks,
0:53:16 > 0:53:19and the port of Liverpool, and these vast container ships,
0:53:19 > 0:53:23will continue to play a key role in our future.
0:53:31 > 0:53:34Out in the Irish Sea, off the Isle of Man,
0:53:34 > 0:53:36we're coming to the end of our basking shark expedition.
0:53:38 > 0:53:40But there's one last secret to explore.
0:53:44 > 0:53:49Many of the basking sharks spotted off the Isle of Man seem to be quite young.
0:53:51 > 0:53:54Graham has spotted a shark, he thinks it's a very small one,
0:53:54 > 0:53:57so we're just going to creep closer and try and get some photographs
0:53:57 > 0:53:59and collect our data.
0:53:59 > 0:54:01It's quite a small shark, you can see its little nose...
0:54:01 > 0:54:05Could this area potentially be a breeding ground?
0:54:05 > 0:54:08Very little is known about basking shark reproduction.
0:54:08 > 0:54:13What is known is that when a female was caught in 1936, as she was towed
0:54:13 > 0:54:20into a Norwegian fjord, she gave birth to five live 1.5-metre pups.
0:54:20 > 0:54:23Marine Biologist Jackie Hall has evidence
0:54:23 > 0:54:28that the Isle of Man is a special place for these astonishing fish.
0:54:28 > 0:54:34We realised we were getting a lot of newborns, which is 1.5, 1.8 metres long,
0:54:34 > 0:54:37here on the Isle of Man.
0:54:37 > 0:54:44We have far more newborn sharks in this 40-kilometre stretch than in the whole of the rest of Britain.
0:54:44 > 0:54:48- So this could be a bit of a nursery? - If they're not being born here, they're being born very close by.
0:54:48 > 0:54:50Wow. Fantastic.
0:54:53 > 0:54:56So that would mean it would be a very important area for protection.
0:54:56 > 0:55:00Very. We know it's special for newborns, we know it's special
0:55:00 > 0:55:04for feeding, we know it's very special for courtship behaviour.
0:55:04 > 0:55:07For a small shark, that was a nice experience.
0:55:07 > 0:55:08He was beautiful!
0:55:08 > 0:55:11So not only do these giant fish come close into our
0:55:11 > 0:55:16western shores to feed, but it looks like they also come here to breed.
0:55:21 > 0:55:25With our expedition coming to a close, the day holds one last surprise.
0:55:27 > 0:55:32On the way back to port, we come across something I've never seen before.
0:55:32 > 0:55:34A giant swarm of jellyfish.
0:55:47 > 0:55:49So we're right in a swarm of moon jellies at the moment,
0:55:49 > 0:55:53which are these incredibly beautiful jellyfish.
0:55:53 > 0:55:55They've got sort of an iridescent top,
0:55:55 > 0:55:59which is basically their gonads, and it seems to vibrate with colour.
0:56:02 > 0:56:06These creatures are related to corals and sea anemones.
0:56:06 > 0:56:10Just like the basking sharks, they are here to eat the plankton.
0:56:11 > 0:56:14Jellyfish are predators, so they have stinging cells
0:56:14 > 0:56:17called nematocysts that hang down on their tentacles.
0:56:18 > 0:56:21If you swim through a swarm of moon jellies, you feel a sting,
0:56:21 > 0:56:23but it's very, very slight.
0:56:23 > 0:56:28So they're not these monstrous jellyfish that you sometimes find.
0:56:32 > 0:56:36The swarm is strung out, forming a line hugging the coast,
0:56:36 > 0:56:38stretching as far as the eye can see.
0:56:46 > 0:56:50Fantastic. There were so many jellyfish in there.
0:56:50 > 0:56:54Thousands and thousands of them, snacking on exactly the same food
0:56:54 > 0:56:57that our basking sharks will be after.
0:57:01 > 0:57:04With the sun going down, and no more sharks spotted,
0:57:04 > 0:57:09our voyage of discovery along Britain's west coast is over.
0:57:11 > 0:57:14We've found some astonishing giants,
0:57:14 > 0:57:18from the spider crabs of Wales and the wreck of the Torrey Canyon,
0:57:18 > 0:57:22to the container ships squeezing into Liverpool Docks.
0:57:24 > 0:57:29But for me, the basking sharks have been the highlight of the trip.
0:57:29 > 0:57:33I'm hopeful they have a bright future ahead.
0:57:35 > 0:57:39Interbreeding between transatlantic populations should be enough to
0:57:39 > 0:57:42maintain the genetic health of our basking sharks.
0:57:42 > 0:57:45But it does highlight the need for global
0:57:45 > 0:57:49rather than just national protection for these astonishing animals.
0:57:49 > 0:57:52And it has been a fabulous experience to swim
0:57:52 > 0:57:55with these gigantic creatures.
0:58:02 > 0:58:07Next time on Britain's Secret Seas, we uncover the wild North,
0:58:07 > 0:58:10revealing creatures that glow in the dark.
0:58:10 > 0:58:13Everything's fluorescing!
0:58:13 > 0:58:16Witness the success of the magnificent gannet.
0:58:16 > 0:58:18That is an incredible strength.
0:58:18 > 0:58:21And get hands on with our underwater bomb disposal.
0:58:21 > 0:58:243, 2, 1, now.