I have been travelling around working on a book, and meeting divers from, among other parts of the world, the USA, Germany, France, Israel and Sweden. I have talked to Russians and Moroccans, Pacific Islanders and Australian backpackers.
     From the Indian Ocean to the Atlantic, in the Bismarck Sea and Gulf of Mexico, I have watched them all sucking air. I'm interested in what makes divers tick, and what surprises me most is how few of them are interested in fish.
     In a vague sort of a way, they say they want to see fish under water, but most divers can accurately identify only a dozen or so species with confidence. When it comes to invertebrates and molluscs, corals and sponges, the success rate falls considerably. I think we need to do better.
     Divers dive for many reasons. Companionship, adventure and adrenalin rushes play their part. Some dive for spiritual communion with their inner self.
     Diving has its share of nerds, too. There are equipment bores, camera bores and yes, even fish bores, but in my experience this last category is surprisingly small.
     In Nassau I found a postcard with a picture of a grouper on it. Normally I try to avoid postcards which feature animals and speech bubbles but this one was irresistible. From the grouper's mouth came the phrase: "Eat more meat".
     I realise that sending the card to a friend who prides himself on not eating red meat or poultry but makes an exception of fish might seem a little cruel. But I did it anyway.
     The postcard was corny but it did set me thinking. Why, I wondered, do people continue to treat fish, or anything else that lives in water, with such disdain? Why do I continue to meet divers who will take a day off from scuba to go out on a fishing expedition?
     I would love to see a marlin under water. But what Jekyll & Hyde transformation comes over some divers, that they think it OK to sit on a boat, throw baited hooks into the sea and drag a large predatory game fish along until it is virtually dead from exhaustion, perhaps with a hook in its eye socket? Yet we get upset when we hear about the French and Italians catching sparrows in nets and eating them.
     We know that many species of fish are in severe decline. According to the WWF, many world fisheries are in crisis or at levels which are not biologically safe.
     The assault on our seas is visible all around us. Recently in central London I found myself in one of those fashionable home interior shops where you can buy anything from colonial-style rattan sofas to replica stone masks from the rainforests of Indonesia.
     In one corner were piles of seashells attractively packaged and framed in boxes for hanging on the wall - cowries and mitre shells, murex and spider shells.
     I rang the shop's head office on Monday morning and asked the marketing manager why they sold such items.
     "Our suppliers assure us that these shells are a by-product of the food trade," was the answer I received.
     Juvenile cowries? I don't think so.
     We know that sharks are being mercilessly exterminated for their fins. We know that grouper lips are a delicacy in the Far East. We know that over-development of the Red Sea coastline is damaging the reefs and that cyanide fishing and blasting is destroying coral all over the tropics.
     When divers get together, they tut-tut and shake their heads over the state of the reefs. Yet they are guilty of double-think. Why do we save up to go to the Caribbean and swim with sharks, marvel at the coral-encrusted reef walls and then in the evening happily gorge ourselves on conch fritters, the local delicacy?
     In many parts of the Caribbean the queen conch is in severe decline. It may be listed on CITES Appendix II, but when lightly grilled, sprayed with lemon juice and served on a bed of onions and fresh tomatoes, it is irresistible. Divers need to start thinking about these issues.
     And it's no good blaming the developing world. According to TRAFFIC, the wildlife trade monitoring group, the EU imported 2.5 million pieces of hard coral over a four-year period. It has a list of countries which continue to flout EU regulations on trade in endangered species, and even when trade is legal, it can have a bad effect on marine habitats.
     I am not an advocate of extreme animal rights. And I do eat fish, though I try to choose species which I know are caught in sustainable ways.
     On an individual level it's hard to know what to do about the issues which marine conservation raises. But divers talking to each other and to their non-diving friends about these things would be a start. Don't just go diving and then forget about what we see down there.
     Since mad cow disease came along, we have turned on to eating chicken. Let's face it, chickens don't stand a chance. They aren't pretty, they aren't clever and they survive just about anywhere.
     Eat more chicken, I say.