Dive Atlas of the World. Jack Jackson

often ignore everything else. Whatever type of diving is preferred, most training agencies will offer a speciality course on how to enjoy it safely. Remember that deep dives, cold water and strong currents are physically demanding and conditions can change quickly, so always be prepared to abort a dive.

      We have chosen popular sites for each region, with a good range of underwater environments and geographical coverage. Our criteria included quality, quantity, beauty and uniqueness of marine life, accessibility and the requirement of only a reasonable degree of physical fitness. The selection offered here celebrates the underwater world while appealing to a broad spectrum of active and armchair divers.

      The book is organized according to oceans and regions within those oceans, beginning with the Atlantic and working west to east and north to south. Practical information is given in the directory appendix.

      There is considerable diversity among diving destinations. Most temperate and warm water species or seawater and freshwater species do not mix. Where regions become isolated, either permanently or temporarily such as when ice ages lowered sea levels and cut off the Red Sea, Gulf of Aden and the Arabian Gulf from the Indian Ocean, some species evolve in isolation and become endemic to those regions. Coral reefs harbour many colourful species. Nutrient-rich, cold waters offer abundant marine life that is often larger and longer-living than its tropical counterpart. Some regions have large tidal ranges. Under ice, over rock or coral and over deep water visibility can be exceptional, but where there is a large tidal flow, a sandy or muddy bottom or a plankton bloom, visibility can be awful.

      Most coral reef life evolved in what is now the region bordered by the Philippines, Malaysia and Papua New Guinea and then spread out to colonize other regions. The Atlantic Ocean formed late in geological time and, early in its development, was cut off from the Pacific by North and South America fusing together. The connecting ridges in the eastern Caribbean also prevent the interchange of deep water from the Atlantic into the Caribbean. Partly as a result of being cut off on west and east, the Caribbean has fewer marine species than the Indo-Pacific.

      Many Caribbean countries have sophisticated ambience, extensive facilities, maximum water clarity, habituated animal encounters and often current-free diving, a package that is particularly attractive to divers on vacation. The Indo-Pacific has the greatest species diversity, though the high level of plankton that feeds this profusion of life often degrades visibility. Some Pacific areas have strong currents and one tide each day much stronger than the other.

      SHORE DIVING

      Entering the water from a beach or jetty is relatively simple, but climbing over slippery rocks in full diving gear can be difficult. When entering from the rocks of a slope or wall, divers will require knowledge of the local tides because low water could result in a large drop into the water and a height too great for divers to be able to exit the water. There may be long swims across fringing reefs and photographers have extra problems with grit. Shore diving is cheaper than day-boat diving, but most of the accessible sites are not as good as those on offshore reefs.

      DAY-BOAT DIVING

      Day boats leave the shore for near-shore dive sites once or twice a day (few operators offer three per day). Night dives are optional. Frequently, equipment needs to be carried to and from the beach or jetty. As with any form of boat diving someone must be delegated to ensure that everyone who should be on board is on board when it departs and, most importantly, when it leaves the dive site.

      In the case of an inflatable or small tender, divers will embark already kitted-up, except for fins. On larger boats divers will kit up about 15 minutes from the dive site.

      Shore and day-boat diving are preferred by those who cannot sleep on a moving boat or are accompanied by non-diving partners or families and those with an interest in the local nightlife.

      LIVE-ABOARD BOAT DIVING

      With live-aboard diving there is less carrying of heavy equipment, no swimming over fringing reefs, biting insects are left behind when you leave port and sailing overnight maximizes the diving time on remote offshore sites. There are fewer restrictions on night dives and divers get three to five dives each day instead of heading back to shore after two dives. Photographers do not have to worry about sand damaging O-rings and have more time to sort out cameras between dives.

      On the minus side, narrow boats and those that are high in the water roll about with the slightest swell or chop, some people cannot sleep on a moving boat and rough seas can be frightening. Live-aboards appear expensive, but you get more dives for your money and all food is included. You need to pack warmer clothing for the cooler conditions at sea.

      While live-aboards may offer five dives per day, divers also have to think about tides, currents, personal nitrogen-loading, and the visibility on ebb tides can be poor. It is better to take fewer (quality) dives each day than five dives, of which some may be mediocre.

      Most divers do not like to have large numbers of people in the water at the same time. Larger live-aboard boats should either have two tenders serving two separate dive sites, or have a rota system whereby only half of their clients are in the water at any one time.

      There have been cases of live-aboard boats leaving divers in the water and sailing off without them, so make sure that the boat you use has a foolproof diver check-in and check-out system.

      REEF DIVING, DROP-OFFS AND WALLS

      Reefs may have several distinct profiles. The top of the reef is likely to be a coral garden with smaller species of fish and crustaceans. Slopes or drop-offs have larger gorgonias and larger fish in shoals. Walls combine the above and have larger pelagic species, especially when over deep water. A wall is near-vertical and may be overhanging or undercut, while drop-offs are steep slopes of 60–85°.

      Inshore fringing reefs tend to have poor visibility due to pollution from construction, domestic or industrial waste or mud carried down rivers, but they are good study areas as they harbour immature species.

      Where offshore reefs have lagoons, these are convenient for safe anchorage, muck diving and snorkelling, but many prefer the better diving outside the reef. Channels into lagoons are good places to dive when the current is running, because the nutrients it carries attract smaller fish, which in turn attract larger predators. Where one side of a reef is longer or more contorted than the other side, the current is slowed down more on that side. When the currents meet again at points on the lee end of the reef they are travelling at different speeds, producing whirlpools and upwellings full of nutrients that attract large shoals of fish. In turn these fish attract sharks and other predators. If you can find shelter from the current, these points are great places to dive.

       DIVING IN FRESHWATER

      The main difference between diving in seawater and diving in freshwater is that freshwater is less buoyant and there are few freshwater sites that are charted. Some freshwater sites will be at a high enough altitude to require the use of special dive tables and corrections to the measured depths. Heavy rain can reduce freshwater visibility to zero.

      In some areas lakes are fed by hot springs and can get very hot!

      Diving in lakes or flooded quarries is relatively easy, but diving in rivers can be difficult if they are fast flowing. In general the current will be slower near the riverbank due to the friction of the water against the bank, but you must always consider where you can exit the river before you enter it. Hooks can be used to pull yourself along the river bottom against the current.

      Freshwater and brackish-water sites, particularly lakes, quarries, dams, canals and slow-flowing rivers, often carry infections such as Weil’s disease (Leptospirosis) and, in countries where it is endemic, Bilharzia (Schistosomiasis).

      Some reefs are submerged and can only be found by a knowledgeable boat skipper or Global Positioning System. Divers have to descend quickly to the lee of the reef for shelter from the current before they get swept off. However, such reefs usually have top diving and pelagics.