Snorkeling.

Snorkeling. I INTRODUCTION Snorkeling, water activity in which swimmers hold their breath and use a diving mask, a snorkel, and fins to remain underwater for up to several minutes at a time. Because so little equipment is used in snorkeling, the activity is also called skin diving. Snorkeling is an easy way to observe the aquatic environment, and because it requires only a few simple skills, almost anyone who knows how to swim and feels comfortable in the water can learn how to snorkel safely. Snorkeling can be practiced in any body of water, but most people prefer to dive in oceans and seas, usually around shallow coral reefs, where marine life abounds. Many of the most popular snorkeling sites are found in the Caribbean Sea and in the South Pacific and Indian oceans. II BASIC SNORKELING Because snorkeling only requires basic equipment, most people find it easier to take up than scuba diving, which requires specialized equipment and training. The two differ in that snorkelers do not take air tanks underwater with them to enable them to breathe. Instead, snorkelers hold their breath while underwater and breathe only while at the surface. The primary swimming technique used by snorkelers is the free dive, also called a breath-hold dive. To make a free dive, snorkelers take a deep breath of air through the snorkel, bend their bodies down at the waist, and kick their feet up. This action forces their bodies underwater, and they can descend in a straight line. As snorkelers descend, they begin to feel a slight discomfort, or squeeze, in their ears and sinuses. This is caused by the pressure of the surrounding water. Snorkelers relieve this discomfort by holding their noses and blowing gently. This technique is called equalization, as it equalizes the pressure within the divers' bodies to that of the surrounding water pressure, allowing them to proceed safely. More experienced snorkelers can equalize their air passages simply by wiggling the jaw from side to side. Once the diver begins to run out of breath, he or she swims back up to the surface. By exhaling, or blowing strongly, the diver clears water that has entered the snorkel tube during the dive. The diver can then take another breath through the snorkel and resume floating at the surface without lifting the head above water. Without a snorkel, the diver would bob up and down on the surface and be hit by waves while struggling to breathe; in addition, the diver might lose sight of underwater objects of interest. By using a snorkel and remaining face down, the diver can easily float over the waves while continuing to breathe and maintaining focus on underwater objects. The length of time a person can remain underwater depends upon his or her physical condition, size, and comfort level in the water. Divers who are in good physical condition use oxygen more efficiently, so they can exert more energy or remain still for more time while underwater. Body size can be important. Thinner, more streamlined divers can glide through the water using less energy and less oxygen. Comfort level in the water also plays an important role. When a diver is at ease in the underwater environment, the body uses oxygen at a slower rate. The average person can go without taking a breath for about a minute. More experienced free divers train themselves to remain underwater for four or five minutes, and some can stay underwater for even longer. Snorkelers should always swim in pairs. As one diver descends, the other diver, called a buddy, remains on the surface and watches for potential problems. If an injury occurs, one diver is always ready to aid the other. Most people teach themselves to snorkel, but in many places, organizations offer courses and instruction on charter boats. Agencies that certify scuba divers also offer skin diving certification courses, but it is not necessary to become certified in order to snorkel. III EQUIPMENT All snorkelers wear a mask, snorkel, and fins. Depending on the dive location and activities, snorkelers may also choose to use exposure protection, such as a wet suit, and a weight belt. A diving mask allows the diver to see objects clearly while underwater. The mask completely encloses the nose and eyes, forming an air space between the diver's eyes and the water. The snorkel is a tube that enables the diver to breathe air from the surface while the head is slightly underwater. It fits in the diver's mouth and extends above the surface. Much like the flippers of a seal and the webbed feet of a duck, fins allow divers to propel themselves through the water with a smooth, energyefficient motion. All fins are composed of a secure foot pocket where a diver places the feet, and a large flipper-like sheet of flexible plastic, called a blade. In warm tropical water, most snorkelers wear only a bathing suit. In colder water, however, some sort of exposure suit, such as a lightweight neoprene-rubber wet suit, is preferred. An exposure suit enables snorkelers to remain warm while in the water for long periods of time. It also protects them from cuts and scrapes caused by coral, plants, and animals. Sometimes divers also wear a weight belt, which is made of neoprene with pieces of lead attached. A weight belt enables snorkelers to descend faster. A diver usually wears enough weight to become neutrally buoyant, a state of neither floating nor sinking. Snorkelers can also wear some form of flotation device, such as an inflation vest, to help them stay afloat should they become tired. These vests remain deflated until needed. They can be inflated manually by blowing through a valve or automatically by engaging a carbon dioxide cartridge that fills the vest in seconds. Snorkelers should always have a first aid kit readily accessible on the boat or on shore. They should also fly a diver-down flag (a red flag with a white diagonal slash) to alert boaters to their presence. IV HAZARDS The largest risk involved in snorkeling is a condition known as shallow-water blackout, in which a diver passes out because the diver does not realize that he or she is running out of breath. The condition occurs when the normal balance of carbon dioxide and oxygen in the body is upset. During a normal dive, carbon dioxide accumulates in the body as the snorkeler uses the air stored in the lungs. As the levels of carbon dioxide increase, the diver feels a natural urge to breathe. But shallow-water blackout can occur if a diver exhales too much (more than three or four breaths) right before a free dive and eliminates the natural levels of carbon dioxide in the body's respiratory and circulatory systems. During the dive, carbon dioxide does not accumulate fast enough to stimulate breathing before the body tissues consume all the oxygen. Without feeling the urgency to breathe, the diver remains underwater for too long and uses more oxygen than normal. This state causes hypoxia, or a depletion of oxygen in the diver's body, and the diver often passes out. Plants and animals can also pose a risk to snorkelers. The most common forms of injury are stings from jellyfish or jellyfish larvae, called sea lice. Some corals and poisonous fish can cause injury as well. On rare occasions, a shark may mistake a snorkeler on the surface for a seal, one of their natural prey. The best way to avoid injury from animals is to be aware of diving conditions at a site, to dive with a buddy, and to leave the water promptly should a problem occur. Boaters can also pose a serious threat to snorkelers. If not near a boat or a visible dive flag, snorkelers can be virtually invisible to boaters and can be run over. Another common danger in snorkeling is fatigue, which can lead to drowning. V WORKING UNDERWATER Most underwater work is accomplished by scuba divers because they can remain underwater at greater depths for longer periods of time. Free divers, however, accomplish some work, including food gathering and scientific research. In parts of the Caribbean where it is illegal to catch lobster using scuba equipment, free divers collect lobster, often making hundreds of dives in a single day. Spearfishing by snorkelers is also common in areas that prohibit catching fish while using scuba gear. Marine biologists sometimes snorkel to collect data in sensitive marine environments. They study aquatic animals in bodies of water of all types, from slow-moving rivers to the ocean. VI HISTORY People have practiced free diving for centuries to gather food and to salvage items from rivers, lakes, and oceans. One of the oldest free diving traditions is practiced in Japan and Korea. For more than a thousand years, young girls called ama have been trained to free dive to collect shellfish and seaweed. Some ama dive deeper than 50 ft (15 m). Another ancient tradition is found in the Mediterranean, where divers have collected sponges off the sea floor for centuries. In modern times, people continue to dive for food and valued objects, but competitive free diving has also become popular. It began in the early 1940s, when a group of athletes living in Mediterranean countries started to compete to dive deepest and stay underwater longest. Today, serious free divers practice regularly to descend below 400 ft (122 m). During the 1980s and 1990s, Cuban-born Francisco "Pipin" Ferreras became one of the most famous competitive free divers in the world. He broke the world record for the deepest free dive on several occasions and claims he can remain underwater for more than 14 minutes. Throughout the late 20th century, snorkeling's popularity grew, especially among travelers to warm vacation destinations. These divers and other enthusiasts snorkel as a way to explore the underwater environment and interact peacefully with aquatic life, without specialized training or equipment. Contributed By: Katie Schickel Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.