Fantastic voyages under the sea

He comes from a diving dynasty, the grandson of one of the greatest underwater explorers. Now Fabien Cousteau is making a name for himself, travelling the oceans to unlock the secrets of the beautiful marine world.

I started scuba diving when I was four years old - on my birthday. A family friend took me to the bottom of the pool to do body-breathing exercises and all the other skills people older than four usually learn. So that was my first dive. I just thought it was normal.

I've always loved swimming and going underwater, so the diving part was just a natural progression. Shortly after my fourth birthday I was given a custom-made set of gear that would fit my little body. And soon after that I experienced my first blue-sea (open-water) dive. I gradually progressed from shore dives to near-shore dives, and then more blue-sea dives.

At that time we were living in Los Angeles, diving off the coast of California. But the early diving that really stands out in my memory was when, aged seven, the family went on an expedition to Papua New Guinea. We were there for about five weeks and I recall a particularly wonderful set of dives.

I dived with my grandfather [Jacques Cousteau] many times. There would always be members of the family on the boat: my grandfather and grandmother, my father and mother, and in the early days my uncle would also come along. My grandfather was a wonderful person; he loved children and he would always pay us special attention. He had this huge desire to teach us about things in a fun and innovative way. He was a very philosophically minded human being and growing up with that was a precious gift.

One of the things that I inherited from my grandfather was the ability to think "outside the box", and try to see what's around the corner. This is what led to the creation of Troy, a shark-shaped submarine that was, in fact, a replica of a great white shark. The reason I chose great whites was because they're a flag-bearer for all the other 400 species of shark. They're very visual and very intelligent, with a large brain mass.

Another reason I embarked on this project was to realise a fantasy I'd had when I was kid. I'd read the Tintin book, Les Trésors de Rackham le Rouge. On its cover Tintin and his dog Snowy were pictured driving a shark-shaped submarine - I thought that was the neatest thing when I was seven years old. Years later I was considering how there had been a lot of research done on sharks and I thought, what if we applied more of a Dian Fossey, Jane Goodall approach, like they did with apes and chimps, going beyond that line and becoming one of them? I wanted to bring that kind of thinking to the underwater world.

Troy is a combination of technologies. It has a triple-layer double-lexan spine to give it flexibility. Its stainless-steel ribs give the submarine its form. And the fibreglass head, with reinforced aerospace-grade aluminium, contains all the electronics, camera housing, screens, dive computers, compass... The propulsion is a closed-circuit pneumatic system, which drives the tail in a natural sweeping motion. The shark itself is covered in a material called Skinflex, which is used in Hollywood for animatronics. My seat is right behind the dorsal fins, and I use a rebreather, so there are no telltale bubbles coming from inside the shark. Put all this together and you have a submarine that is physically identical to a 14ft-long female great white.

When we took it into the water off the Isla de Guadalupe in Baja California the great whites reacted to Troy with typical behaviour - rolling their eyes, puffing their gills - which was amazing. To get among these animals and observe them, I thought, "Wow! This opens the doors to all sorts of experimental possibilities."

The amount of diving I'll do depends on the project I'm involved in. For example, this year I filmed a television special for PBS with my dad called Underwater Treasures. It covered the 13 national marine sanctuaries of the United States. There are two in Hawaii now, one in Samoa, several on the west coast of California, one in the Caribbean, one off Florida.... We clocked up enough air miles to fly 20 times round the world. We did 342 dives for that film.

I'm very aware of the environmental impact of all the flying we do. There's not much of a solution in the short term unless we're able to figure out another way to travel in a relatively efficient way. As global explorers we're always on a tight budget and so we try to travel as efficiently as possible by default. We could get around by windpower - sailing - but that doesn't allow for the realities of producing TV programmes to a schedule.

Short of hiding out in a house with a candle, it's very difficult not to have a carbon footprint. What we can do is to continue to lobby for change.

My family is scattered all over the world. Most are in France, so I go back there as much as possible, especially to Paris where my mother lives. I also like to go down to the coast near Sanary, which is where my grandfather tried out the first ever scuba equipment.

Because we're scattered geographically, the best way for us to all meet up is on expeditions. At the moment, we're preparing to go to the Amazon. Sixteen of our crewmates are already there, including my sister. We're going to spend six weeks exploring the region, and then we'll return in March for another six weeks to compare the seasons, wet and dry.

We've got a hit list of 35

My top sport on the water

I love windsurfing. I like to go to a place called Cranberry Hole, which is at the end of Long Island in New York state. It's a fantastic spot for windsurfing in the summer. It's relatively shallow and there's a sandbar that separates the lagoon/inlet from the ocean, so the water is quite flat. Yet you get crosswinds from the ocean that sometimes gust up to 25 knots or more. If I get the chance, I like to go windsurfing in more exotic locations. I've always dreamed of windsurfing on Lake Arenal in Costa Rica but I haven't had the chance yet.

topics; it's a huge list to cover in 12 weeks. My guess is that we're probably not going to hit all of them. But the good news is that we have a basic comparison from the early 1980s, when my grandfather and other members of the family went on an expedition to the Amazon for 18 months.

I'm sure you can imagine that things were quite different then. I anticipate a lot of change in the areas we previously visited. We filmed a paper mill in one of the most remote areas there - it was the largest in the world. The last we heard they were experiencing quite a few problems, not only because of the location of the mill but also because of the way they decided to plant paper-making trees around it. And because, short-sightedly, they had planted two or three species of trees that had sapped the ground of the rich nutrients that made it fertile. So we're going to revisit to see what has happened since.

We'll also be looking at gold mining in the area, which presents a huge problem because they water-blast mountainsides and also use cyanide and heavy metals to bring the gold out of the earth. All that goes into the river system, devastating everything downstream.

Between these not so glamorous and not so positive topics, we'll also be exploring some of the most remote regions and meeting indigenous tribes. And we're going to film the pirarucu, a prehistoric lung fish that's traditionally caught by the Amazon people. They're enormous - up to 800lb - and live for up to 50 years. They're relatively easy to hunt because they come up for air, but until recently they were hunted only for food and only when needed by the local tribes. One of those fish could sustain a whole tribe for a week. We understand there's a market that exports these fish around the world that has tipped the balance of sustainability. One important reason why we go exploring is to be able to share what we see and experience. Not everyone can go and delve into these remote locations, certainly not for any length of time or with scientists on hand.

My most recent project has been working on a book titled Ocean, a lavish celebration of life on the water planet. I hate to use the word encyclopedia because the book is much more interesting than that word suggests, but it covers everything from the migration patterns of whales to the largest seaweed in the world. It gives a good overall view of the oceans - not only their bio-diversity but also the mechanics of how it all works, and what's happening in terms of global warming and other environmental issues. The book is incredibly detailed, with more than 1,300 images, profiles of some 450 species, and digestible snippets on the geology, geography, and ecology of the oceans. It has gorgeous pictures. I was amazed at how much they were able to put into it. It's taught me a lot.

'Ocean' is published by Dorling Kindersley (price £30). Nick Hanna is the author of 'The Art of Diving' (Ultimate Sports, £20). 'Ocean' is available for a special offer price of £25, including free p&p. To order, call the DK Bookshop (08700 707 717) and quote offer reference (INDEOCE) and the ISBN of the book (14053 12920). This offer is open until 12 January 2007, to UK residents only and is subject to availability. Allow up to 14 days for delivery.

The dive of my life

In the late 1980s I went diving with my father in Papua New Guinea to film a pair of orcas, or killer whales, in blue water (open ocean) some 1,300ft deep. We'd got within 50ft of the animals. I remember staring straight at the male orca - and it stared straight back at me. I felt unbelievably insignificant and alone and yet thrilled to be there.

The male suddenly dived into the blue and about a minute or so later came back up with a seven-foot shark in its mouth - still alive, thrashing around. The male and female orcas began playing cat and mouse with the shark. The male oriented the shark towards the female and let it go; the shark would start swimming off and the female would catch it, turn it around, and let it swim back towards the male.

They did this at least six times, then got bored so each of them took an end and they just shredded it to pieces in a matter of seconds. It was awesome to watch.