Subtitles section Play video Print subtitles In the north-east of the Indian Ocean, spanning a latitude of 6 to 16 degrees north of the Equator, lies the Andaman Sea. For the people of Thailand and Burma, also known as Myanmar, the two nations bordering the eastern edge of the Andaman, the sea has always been an integral part of life and the economy. The Andaman's warm waters support an enormity of marine life and they are relied upon for food as well as transport. Limestone formations such as those which make up the Phi Phi Islands contrast with granite outcrops like the Similan Islands. The warm, clear water and diversity of marine life make the Andaman an attractive dive destination and many divers visit each year to explore and enjoy the underwater world. And seldom is the marine landscape as diverse as it is here. Millions of years of decay have cut the limestone pinnacles of Burma's Mergui Archipelago into a terrain of underwater canyons and caves. Further south, the huge granite boulders of Thailand's Similan Islands continue beneath the waterline, creating dramatic caves and swim-throughs. Much of the submerged rock has been colonized by soft corals like this mushroom leather coral at Christmas Point or stony corals like this field of staghorn coral at Koh Bon or this Montipora coral at East of Eden. Elsewhere magnificent anemones have taken over. At shallow sites such as Richelieu Rock the ebb and flow of the tide brings the oxygen necessary for turtle weed, a type of green algae, to flourish. Dendronephthya soft corals adorn the valleys and slopes at Hin Muang, or "purple rock" in Thai. Elsewhere pretty crinoids, or "feather stars", take up prime positions for filtering plankton from the water. A feeding strategy shared by giant sea fans, whose sieve-like skeleton makes them highly efficient filter feeders. Here between the rocks and coral lie leopard sharks. These gentle creatures are quite the opposite of many people's impression of the fearsome shark. Rather than sharp teeth, their mouths contain ridged plates. Leopard sharks can be easily and safely approached but if divers get too close they will finally make their departure. Although "leopard shark" is the most commonly used name in the Andaman Sea, globally, these sharks are more commonly known as "zebra sharks", because the rarely seen juveniles have stripes, not spots. Bearing many similarities to leopard sharks, nurse sharks are also normally placid. Like leopard sharks they don't have sharp teeth. Nurse sharks should be treated with respect however. They have been known to bite divers when provoked, and if they bite they tend not to let go. During the day, tawny nurse sharks are normally found sleeping under ledges, often piled up in groups like here at Koh Bon Pinnacle. Although nurse sharks generally feed at night, here at the Burma Banks they are often on the prowl looking for food during the day time too. They have 2 barbels above the mouth which help them probe for food. When the shark senses prey such as small fishes or crustaceans it uses a strong sucking action to draw the food into the mouth. Bonds between nurse sharks appear to be closer than with many other shark species and they are often seen swimming in couples. At Thailand's Richelieu Rock, a whale shark makes a rare appearance. This is no whale but rather the world's largest fish. Whale sharks can grow up to 12 meters long, although unconfirmed reports circulate of giants up to 18 meters long. This female is about the average size of 8 meters. There is little to match the awe inspired by an encounter with a whale shark, and for many divers this is the pinnacle of their underwater experience. Their 3000 tiny teeth are rarely used. When feeding they hold their mouths open and feed on plankton, fish eggs and small marine creatures. Ridges down the whale shark's back are reminiscent of those on zebra sharks' backs and like the zebra shark, the whale shark poses little danger to humans. She has lost the top part of her tail, perhaps due to an attack by a predatory shark when she was a youngster, or possibly a collision with a boat's propeller. The shark's fins act like rudders, helping steer it gracefully through the water. For a long time whale sharks were thought to be oviparous, in other words hatching from eggs laid by the mother. However since 1995, females have been discovered containing hundreds of hatched pups, proving that the young complete their development inside the mother's body before birth. As is typical of large pelagic fishes, the back is darker than the belly. This countershading helps it blend in with its environment, and the abstract pattern of spots and stripes on the back enhances the camouflage from above. Some whale sharks attract shoals of fish around the head, such as these juvenile scad, protecting themselves from predators which may be intimidated by the shark. The shark itself does not prey on them, and they are careful enough to cruise in front of its cavernous mouth, without getting sucked in. This much younger whale shark approached boats near Western Rocky Island and stayed around for a long time. Although it might be tempting to touch or even hitch a ride on a whale shark, this practise is highly discouraged. It may modify the shark's natural behavior, or even cause infection. It can also be dangerous for the diver or snorkeler. Despite their usual graceful and stately motion, whale sharks can draw on great strength if they become agitated, and should be respected like any wild animal. Shark fin soup is seen as a delicacy and status symbol in many Asian markets. A single whale shark fin can fetch tens of thousands of dollars in some Chinese restaurants, and often a whale shark fin is not eaten but just used to advertise the availability of shark fin or shark fin soup. Whale sharks do not reach sexual maturity until they are 25 years old, and pregnancies are few and far between, so their survival is particularly at risk. Unless this culture changes, or legislation is introduced and enforced, whale sharks, like many other sharks, may soon disappear forever. From the shadows, and shoals of cardinalfish at Burma's Shark Cave, a grey reef shark emerges. This strong stocky shark feeds mainly at night, but may sometimes be seen cruising during the day. The canyon at Shark Cave provides an excellent viewing gallery. Although grey reef sharks can sometimes show aggression in their behaviour, this is extremely rare amongst those found in the Andaman. A visit to the Burma Banks will sometimes yield an interesting encounter with silvertip sharks. These juveniles are particularly curious of divers. As adults they will grow larger than grey reef sharks, up to 3 meters in fact, but they will also withdraw slightly and become more wary of close human contact. Already these young silvertips display the streamlined body and attractive coloration that make them a favorite amongst shark lovers. One of the most common sharks to be found across the Andaman Sea is the whitetip reef shark. Because of similar coloration of the dorsal and tail fins, the whitetip reef shark and silvertip shark are sometimes confused, but the whitetip has a wedge-shaped head, and it's cigar-shaped body is slimmer than the silvertip's. Black Rock, on the western edge of the Mergui Archipelago, is one of the area's best dive sites, and whitetip reef sharks are commonly encountered during the descent. The other main order of cartilaginous fishes to be found around the Andaman's reefs is the rays, and most common of these is the bluespotted stingray. This stingray's coloration and common name make it often confused with the more circular blue-spotted stingray found in the Gulf of Thailand, which belongs to a different genus. The bluespotted stingray is found on sandy bottoms at sites such as East of Eden in the Similans. The neutral color of the larger Jenkins whipray camouflages it well against the seabed. This ray has a pair of sharp and venomous spines near the base of its tail, and the name "whipray" comes from the ray's ability to whip it's long tail over fast and administer a nasty sting to a predator at any part of its circumference. The ray takes water in through its spiracle, a hole just behind the eye. This water can be blown out through the mouth to excavate food from the substrate. Another large stingray common to the area is the blotched fantail ray. This impressive species can grow nearly 2 meters in diameter and is often one of the highlights of dives in the Andaman. Blotched fantail rays are most impressive when they aggregate in shoals. Occasionally they can be witnessed in large numbers. I encountered this shoal of some 30 individuals at Black Rock. They had possibly gathered to mate. Another visitor to Black Rock and other deep-water sites is the spotted eagle ray. In some parts of the world eagle rays stay together in schools. In the Andaman Sea they are normally found alone. Just behind the short dorsal fin they have up to 6 venomous tail spines which can inflict serious damage on attackers. Between its wing-like fins it has a solid, heavy body and a deep head. The smoothtail mobula is a similar size to the eagle ray but can only usually be seen by divers in the northern Andaman at sites like Burma's Tower Rock, although they are occasionally seen in Thailand at sites such as Racha Noi. The mobula is a member of a group termed "devil rays", so named because of 2 protruding cephalic fins either side of it's mouth. These fins help to direct plankton and small marine creatures into the mouth for feeding. The mobula is a highly social fish and is often observed in large schools. The mobula is an impressive sight but shares our seas with a much larger devil ray: the king of all rays, the giant manta ray. Mantas are frequent visitors to sites such as Koh Bon. Giant mantas can grow to a width of over 6 meters and a weight of over 2 tonnes. These pelagic fish are always on the move and like mobulas, they feed by swimming open-mouthed and using the 2 cephalic fins to direct water into the mouth. The gills on its white underside contain rakers which filter out plankton and small organisms. The markings on the back and underside of mantas are highly variable and are useful in distinguishing individuals. Occasionally the cephalic fins are furled up into cylinders to improve streamlining. Mantas are one of the most intelligent fish, with the largest brain-to-body mass ratio of all elasmobranchs. They often seem to enjoy interaction with humans. A gentle approach by divers is often permitted, and mantas will sometimes approach divers, apparently out of curiosity. Mantas only give birth to an average of two pups every two years, and populations have long been in decline. The gill rakers of mantas and mobulas are used in a Chinese medicine that is thought to detoxify the blood. There is no scientific evidence that it works. Nevertheless the lucrative trade is on the increase. In November 2011 the International Union for Conservation of Nature declared giant manta rays as "vulnerable with an elevated risk of extinction". Down on the reef, a fish trap has caught a handful of bony fishes including a giant moray eel. This is the largest of all morays. Despite their fearsome appearance, morays are not as dangerous to humans as they look, although larger morays can attack if provoked and have been known to bite divers when being fed. The mouth contains sharp teeth for capturing and restraining prey. Once captured, a second set of jaws in the throat is launched forward to grab the prey and pull it down the moray's gullet. Anemone Reef is home to several specimens of yellow-edged moray. Like many morays they feed on small reef fishes. Khao Lak's Boonsung tin miner wreck has a particular concentration of honeycomb morays. This spotted moray at the Burma Banks is a close relative. Whitemouth morays are not at all common in the Andaman. This rare specimen was seen at Burma's Western Rocky Island. Another Myanmar speciality is the barredfin moray. When feeling threatened it adopts a very snake-like posture. Facial injuries are quite common amongst morays, and this palechin moray at High Rock bears the scars of past conflicts. The cartoon-like features of the greyface moray are much more common throughout the area and these eels are often found in pairs or small groups. This is a small and very energetic species and when it attacks it moves quickly. Greyface morays don't just live with each other; they often share their home with other species. In this case a fimbriated moray. And here we find a fimbriated moray with a snowflake moray. Whereas the previous species feed mainly on fishes, the snowflake moray feeds on shelled molluscs and crustaceans, so it's teeth are much more blunt. It's not difficult to see how the zebra moray got its name. This moray also feeds on crustaceans. Of all the marine creatures found in the Andaman Sea, possibly the tiger tail seahorse carries the most mystique. The seahorse finds a suitable holdfast, such as this black sun coral, and anchors itself to it using its striped tail.