ALEX Mustard’s lungs were practically bursting after using all the air he had sucked in.

But with experience from his bulging CV of 3,500 dives, he’d spent hours carefully timing the exact second he would free dive into the Caribbean Sea off Mexico’s Yucatan Peninsula.

And now with the dark shadow of the world’s biggest fish – an imposing eight-metre whale shark, casting over his contorted face hidden only by his lens, there was simply no chance he’d let this moment pass him by.

“As serene as it looks in the photograph, it was pretty frantic. Taking the photo is the easy part,” Alex laughs.

“I’d waited for the shark to swim overhead and I was bursting for air. I wondered how much longer I could hold my breath for. The combination of excitement and awe didn’t help, or the fact I had five metres of water and a shark between me and the surface. But the result was definitely worth it.”

He’s not kidding.

The resulting photograph of the huge fish backlit with sunbeams spearing into the water along its flanks is now hanging in the Natural History Museum commended in the Wildlife Photographer of the Year awards.

A whale shark, Yucatan Peninsula image by Alexander Mustard

And it’s certainly not the first snap in his portfolio to have been marvelled by judges and the public.

Alex became hooked on marine life as a young boy.

He smiles as he recalls always returning from family holidays with his trademark tanned back and white belly from keeping his head in the water exploring the ocean.

He was just nine when he took his first underwater photo and says he was as determined as he is today to document and share his discoveries.

By 14 he had his scuba diving qualification and got a PhD from the University of Southampton’s National Oceanography Centre to become a marine scientist before turning to photography full-time in 2004.

Today, the fact it is nearly impossible to catch Alex when he’s on dry land is testament to the fact he is one of the world’s most renowned underwater photographers who has even presented his work to the Queen.

Rift Valley, Iceland image by Alexander Mustard

“I do spend a lot of time underwater,” the 39-yearold who last year completed 298 dives laughs.

“I’ve just got back from an untouched reef at Raj Ampat off Indonesia and next week I’m off to Norway.

“It’s hardly your average 9-5 job but I wouldn’t change it for the world.

“There is fascination absolutely everywhere you look,” he continues with his trademark enthusiasm.

“Underwater animals don’t have the same innate fear of man as animals do on land, so unlike a deer in the New Forest or a fox in your garden, they generally don’t see you as something to be wary of so we can get very close.

Mating Angelfish, Cayman Islands, image by Alexander Mustard 

“Imagine if a bird watcher could float out over the estuary to watch the birds above, or float up and see them nesting in trees. In water I can do that and it’s incredible.”

Once inside his mask, there is literally nothing that will stop Alex in his quest to document the world’s sealife.

He has braved water temperatures of minus one degree, depths of up to 200ft, raging seas, active volcanoes, earthquakes, even several hurricanes.

And even though he admits to being among the few people who encourage the world’s most feared creatures to swim towards him, all in the name of capturing their every detail in each eye-popping pixel, he has few fears.

“Sharks are generally really timid and in fact one of the main challenges is getting them to come towards you.

“Generally there isn’t much out in the ocean that’s out to get you.

“Personally I’m much more relaxed and braver under water than I am on land. Underwater I won’t think anything of working with creepy crawly crabs but get a spider in my bathroom at home and I get the Mrs to deal with it,” he jokes.

Though the jaws of sharks do not faze him, he does recall a rather terrifying incident involving an oversexed dolphin.

“It sounds funny, and it was at first, but we soon realised just how dangerous the situation was because we were not in control of it. Dolphins are typically very friendly but this wasn’t typical behaviour,” he says pausing to send me the link named ‘Dolphin Encounter.’

“The dolphin was a lone male and he was very amorous and kept trying to mate with me.

"But dolphins are extremely strong animals, they’re pure muscle, you only have to see how they jump out of the water to appreciate how powerful they are and we are completely at their mercy. Being pushed around like that was potentially very dangerous, anything could have happened.”

The dolphin biting Alex's fin, image by Alexander Mustard

The story is proof that anything can happen underwater, but for Alex that’s the joy of the job.

In fact he’s made many strange discoveries while exploring beneath the surface of the sea.

The list is endless from barnacle-encrusted shipwrecks to a British Second World War motorbike, a VW Beetle, even a swimming pig. Yes, really a swimming pig.

“I was in the Bahamas and I stuck my head out of the water and four little pink trotters were splashing about. It was very funny to see pigs in the sea.

A swimming pig, Bahamas, image by Alexander Mustard

“The clever pigs have worked out they can get food from the yachts so they plunge into the waves and swim in hope of a free meal.”

For someone whose life involves visiting the type of places most of us could only see on our computer screensavers, his choice of final destination if someone were to take his flippers away one last time frankly takes some registering.

“Yes you’ve heard right,” he says.

“It would without a doubt be to go out and experience the best of British. People just don’t realise what amazing things live just beyond their shore.

“People expect to look out across Ocean Village and it all looks brown and murky but some of the most exciting sealife is where people don’t expect to see it. I love to take photographs and amaze people by the wildlife that lives around them.”

Seahorse, Dorset, image by Alexander Mustard

It’s clear that engaging the public in the ocean’s beauty is a huge drive for producing his stunning images, especially at a time when marine life is under threat from overfishing and pollution.

“For all nature photographers it’s unavoidable to see the impact that mankind has on the natural world.

You can go to the most remote coral reefs on the pacific and see areas choked up with plastic. It’s hard to comprehend man’s impact and it’s almost impossible not to see everywhere.

“But though I see the trash on the seabed, the hooks in the fish’s mouths, I like to take celebratory pictures to make people appreciate just how wonderful the oceans are to show what’s at stake if we don’t change our habits.”

VW Beetle, UK, image by Alexander Mustard

For Alex, who owns a property off Winchester Road, in Southampton, it’s clear a lot is at stake, no matter how big or beautiful the animal is. I momentarily lose him while he is churning out facts and figures on sea slugs and shrimps.

“Whatever the subject, the challenge is to tell exciting stories of the ocean.

“I’m lucky I am among the small percentage of people who gets to see the wonders of the underwater world but I feel most proud I’m able to share that experience.

“No matter what it is, a shrimp or a great white, if you can reveal its beauty, reveal its life, its personality and through a photograph get people excited about what lies in the sea around them, then in my eyes that is job satisfaction.”