0:00:02 > 0:00:06It's said that half of all life in the British Isles
0:00:06 > 0:00:07belongs in the sea.
0:00:07 > 0:00:10It's all around our glorious landscape,
0:00:10 > 0:00:14a spectacular realm that's waiting to be explored.
0:00:15 > 0:00:22This is Waterworld, discovering life below the blue horizons.
0:01:10 > 0:01:14It's a quarter past four on a breathless summer morning.
0:01:19 > 0:01:24As dawn breaks on the Antrim coast, our team is already up and about
0:01:24 > 0:01:26at Glenarm marina.
0:01:33 > 0:01:36Hugh, Doug and Richard are preparing
0:01:36 > 0:01:40for what promises to be a dramatic day at sea.
0:01:40 > 0:01:44We're ready to search for the biggest fish in the Atlantic Ocean.
0:01:53 > 0:01:55The day is alive with possibility.
0:01:56 > 0:02:01We're all upbeat after weeks of weather watching,
0:02:01 > 0:02:03the prospects for success look bright.
0:02:09 > 0:02:12Filming basking sharks isn't nine to five,
0:02:12 > 0:02:17but I'm looking forward to what could be an unforgettable day
0:02:17 > 0:02:18at the office.
0:02:25 > 0:02:28It's just turned five o'clock in the morning,
0:02:28 > 0:02:30the sun has just come up
0:02:30 > 0:02:33and the moon is still there from the night before.
0:02:33 > 0:02:36This is kind of a defining moment for us on Waterworld
0:02:36 > 0:02:39because we've been monitoring whether the basking sharks
0:02:39 > 0:02:43that we want to film with have arrived here
0:02:43 > 0:02:46and we're told that there's a number of them
0:02:46 > 0:02:52off Malin Head in Donegal and well, the stars hold our fate.
0:02:52 > 0:02:55I just hope and pray that we'll get into the water with them today.
0:03:01 > 0:03:05Real life adventure is such a rare thing these days and yet, here I am,
0:03:05 > 0:03:12living the dream, entering the wide, blue yonder in search of Leviathans.
0:03:20 > 0:03:24It's a delicious prospect, but on a four-hour cruise,
0:03:24 > 0:03:28there's plenty of time to drift off,
0:03:28 > 0:03:32to sleep among gentle giants from another world.
0:03:36 > 0:03:42We're leaving the Antrim coast behind, and beyond Loch Foyle,
0:03:42 > 0:03:43the watch begins.
0:03:43 > 0:03:46Scanning the horizon for signs of life.
0:03:47 > 0:03:48Look, look!
0:03:48 > 0:03:51Oh, that's amazing.
0:03:51 > 0:03:53And then it happens.
0:03:53 > 0:03:56Suddenly, we're surrounded by huge sharks.
0:03:56 > 0:03:59Big, dorsal fins slice the surface.
0:04:04 > 0:04:09We count more than 20. Our decision to head north has paid off.
0:04:11 > 0:04:13We're actually seeing basking sharks.
0:04:13 > 0:04:15Portrush is just around the corner.
0:04:15 > 0:04:18We're just off the coast of Donegal.
0:04:18 > 0:04:20That is a majestic creature.
0:04:20 > 0:04:22I never actually believed, or dared to believe,
0:04:22 > 0:04:24that we could get among them.
0:04:24 > 0:04:28One here, one over there, one over there, there's two behind us.
0:04:28 > 0:04:33I really... My mouth has gone dry. I'm absolutely so nervous.
0:04:33 > 0:04:36I might actually get into the wetsuit now and go and see
0:04:36 > 0:04:39if I can swim with these things.
0:04:39 > 0:04:41Look at that.
0:04:41 > 0:04:43Just off the bow of the boat.
0:04:45 > 0:04:48These are probably the biggest fish in the Atlantic Ocean.
0:04:48 > 0:04:51The only thing that's bigger is the whale shark
0:04:51 > 0:04:53and you find them in the Pacifics.
0:04:56 > 0:04:59This is a once in a lifetime experience
0:04:59 > 0:05:03and our underwater cameraman, Doug Anderson, will keep me right.
0:05:03 > 0:05:05We want to be about 20 metres,
0:05:05 > 0:05:1150 feet in front...and just looking for a direction.
0:05:11 > 0:05:14- We just need to keep working on it.- OK.
0:05:14 > 0:05:19You've got a lot of experience of being in the water with big animals.
0:05:19 > 0:05:21What should I or shouldn't I do here?
0:05:21 > 0:05:24It's very difficult to tell you.
0:05:24 > 0:05:25Just get in there,
0:05:25 > 0:05:28get into a situation that you feel comfortable with,
0:05:28 > 0:05:31and if it's too scary, just close your eyes! That's what I do!
0:05:31 > 0:05:33- Really?!- Yeah.
0:05:33 > 0:05:38And the thing is, we have prayed for weather like this!
0:05:38 > 0:05:41You know, you couldn't look for a better day to do this
0:05:41 > 0:05:44and to be suddenly surrounded by basking sharks,
0:05:44 > 0:05:47it's beyond our dreams, isn't it?
0:05:47 > 0:05:51It's just ideal. We only get into these places...
0:05:51 > 0:05:52These are wild places.
0:05:52 > 0:05:54We only get in so many days of the year
0:05:54 > 0:05:56and this is just one of those days.
0:05:58 > 0:06:00Doug, Doug, Doug.
0:06:04 > 0:06:06Just cut it.
0:06:07 > 0:06:10I know this is bad form, but let's see what happens.
0:06:23 > 0:06:25I can't believe I'm doing this.
0:06:45 > 0:06:48The basking sharks swim up tide,
0:06:48 > 0:06:52extracting great mouthfuls of tiny plankton,
0:06:52 > 0:06:57sieving the equivalent of an Olympic size swimming pool every hour.
0:07:04 > 0:07:08I've always wanted to do this.
0:07:08 > 0:07:09To swim with fish as big as a bus
0:07:09 > 0:07:12and heavier than an African elephant.
0:07:14 > 0:07:15That was astonishing!
0:07:17 > 0:07:19Absolutely astonishing.
0:07:19 > 0:07:22- You saw four.- I had four sharks.
0:07:22 > 0:07:24Mouth closed. There's something else going on there.
0:07:24 > 0:07:27They weren't feeding, they were just together.
0:07:27 > 0:07:30Like, literally, two or three apart. Incredible.
0:07:30 > 0:07:32I've never seen anything like that.
0:07:32 > 0:07:35I really have never seen anything like that.
0:07:35 > 0:07:38I had a real Jaws moment because Doug pointed
0:07:38 > 0:07:43and I could see this enormous grey shape down there.
0:07:43 > 0:07:45Just astounding.
0:07:45 > 0:07:49The assumption was that was not feeding. That was an aggregation.
0:07:49 > 0:07:54We just get glimpses of their world and who knows what's going on there.
0:07:54 > 0:07:56'It's exceptional to encounter
0:07:56 > 0:07:59'so many of these colossal fish off our shores.
0:08:01 > 0:08:03'And then something even more exceptional.'
0:08:08 > 0:08:10A world exclusive.
0:08:10 > 0:08:14The first time a leaping basking shark has been filmed.
0:08:31 > 0:08:35Can't believe this. I'm quite seasick.
0:08:35 > 0:08:37It's the story of my life out here!
0:08:37 > 0:08:40Right in the silvery wilderness,
0:08:40 > 0:08:45surrounded by mega-sharks
0:08:45 > 0:08:47and I've been sick.
0:08:47 > 0:08:48But I'm absolutely determined.
0:08:48 > 0:08:52I don't care how long it takes and how sick I get.
0:08:52 > 0:08:54I'm going to get in there
0:08:54 > 0:08:57because I may never ever get the opportunity to do this again.
0:08:57 > 0:09:01It's kind of a dream that I've been living for quite a long time.
0:09:01 > 0:09:03I'm determined to get back in there.
0:11:00 > 0:11:03These prehistoric heavyweights are so big,
0:11:03 > 0:11:05yet we know so little about them.
0:11:12 > 0:11:15Basking sharks are symbols of the majesty
0:11:15 > 0:11:17and mystery of the world about us.
0:11:23 > 0:11:28What you can't get a sense of, when you see these creatures on TV,
0:11:28 > 0:11:31is the scale of them compared to yourself.
0:11:31 > 0:11:35I looked down and was able to watch them. These things have got
0:11:35 > 0:11:37a brain the size of a golf ball
0:11:37 > 0:11:40and a mouth the size of a jet engine.
0:11:40 > 0:11:44They just open it up like this huge canopy.
0:11:44 > 0:11:46All of that plankton is being poured in, poured in.
0:11:46 > 0:11:48And whenever they close their mouth,
0:11:48 > 0:11:50you'd actually see them working the food
0:11:50 > 0:11:53back down into their stomach. Phenomenal.
0:11:54 > 0:11:57You know the really nice thing about that encounter
0:11:57 > 0:11:58- was that it came to us.- Yeah.
0:11:58 > 0:12:04It just... He gave us two little passes and then, you know, away.
0:12:04 > 0:12:05No stress.
0:12:05 > 0:12:08- A very nice encounter.- Phenomenal.
0:12:08 > 0:12:10I'll remember this day for a while.
0:12:29 > 0:12:32Subtitles by Red Bee Media
0:12:32 > 0:12:35E-mail subtitling@bbc.co.uk