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Questions and Answers on
Physiology and Medical Aspects of Scuba Diving


Lawrence Martin, M.D. Copyright 1997


Buy the book
Scuba quiz
Myths & Misconceptions
Disclaimer & Invitation

Brief History of Diving
Recreational  Diving
The Respiratory System
Explanation of Pressure

Water & Physical Laws
Unequal Air Pressures
Decompression Sickness
Oxygen Therapy
Gas Pressure at Depth

Dive Tables & Computers
Stress & Diving
Non-air Gas Mixtures
Women & Diving
Medical Fitness for Diving
Asthma & Diving
The Great Debate

All About DAN
Scuba Training Agencies
Magazines & Newsletters
Books & Videos

Diving Odds N' Ends

Internet Links

Diving Odds N' Ends

Historical Diving Society

The U.S. Chapter of HDS is a non-profit educational corporation founded in 1992. HDS publishes a regular magazine (Historical Diver), sponsors tours, meetings, an annual conference, equipment rallies and opportunities to dive classic equipment. Individual membership is $30.00/year. Members receive an international register listing others with similar interests. Contact:

The Historical Diving Society USA
2022 Cliff Drive, #119, Santa Barbara, CA 93109
Phone: 805-963-6610
Fax: 805-962-3810

Scuba in Jules Verne's 20,000 Leagues under the Sea

A limited scuba apparatus was developed by Frenchmen Rouquayrol and Denayrouse in 1865 (see Figure 3). Verne was aware of this invention and incorporated it into his 1870 novel. Although the actual Rouquayrol-Denayrouse invention could only function as true scuba (i.e., untethered) for a few minutes at a time, Verne extended this to several hours in his nove. Inside the submarine Nautilus, just prior to a long underwater hike using the scuba apparatus, Captain Nem explains how it works to Professor Aronnax, a French naturalist (and the novel's narrator).

" You know as well as I do, Professor, that man can live under water, providing he carries with him a sufficient supply of breathable air. In submarine works, the workman, clad in an impervious dress, with his head in a metal helmet, receives aire from above by means of forcing pumps and regulators."

"That is a diving apparatus," said I.

Just so, but under these conditions the man is not at liberty; he is attached to the pump which sends him air through an india-rubber tube, and if we were obliged to be thus held to the Nautilus, we couldn not go far."

"And the means of getting free?"

"It is to use the Rouquayrol appartus, invented by two of your own countrymen, which I have brought to perfection for my own use, and which will allow you to risk yourself under these new physiological conditions, without any organ whatever suffering. It consists of a reservoir of think iron plates, in which I stor the air under preessure of fifty atmospheres. This reservoir is fixed on the back by means of braces like a soldier's knapsack. Its upper part forms a box in which the air is kept by means of a bellows, and therefore cannot escape unless at its normal tension. In the Rouquayrol apparatus such as we use, two india-rubber pipes leave this box and join a sort of tent which holds the nose and mouth; one is to introduce fresh air, the other to let out the foul, and the tongue closes one or the other according to the wants of the respirator. But I, in encountering great pressures at the bottom of the sea, was obliged to shut my head, like that of a diver, in a ball of copper and it is to this ball of copper that the two pipes, the inspirator and the expirator, open."

"Perfectly, Captain Nemo; but the air that you carry with you must soon be used; when it only contains fifteen per cent of oxygen, it is no longer fit to breathe."

"Right! but I told you, M. Aronnax, that the pumps of the Nautilus allow me to store the aire under considerable pressure and on these conditions the reservoir of the apparatus can furnish breathable aire for nine or ten hours."

"I have no further objections to make," I answered.

Seven Underwater Wonders of the World

According to Rick Sammon, who has published a book by that name, they are:

Belize Barrier Reef
Lake Baikal in Siberia
Norther Red Sea
Galapagos Archipelago
Austrailia's Great Barrier Reef
Deep Ocean Vents of the Mid-Ocean Ridge
Palau, a Pacific Archipelago

Sammon's book contains full color photographs of each of these underwater wonders. Interestingly, only one site, Belize, is convenient to North American divers. All the sites are accessible to scuba enthusiasts except, of course, the deep ocean vents, reachable only by submarine (and the only site not personally visited by the author). This ridge is a 40,000 mile long volcanic range and rift system that snakes across the bottom of the world's oceans "like the stitching on a baseball."

Do Fish Sleep?

For anyone who has ever done a night dive, the answer is apparent - many fish do sleep. During the day these fish keep their distance (unless we feed them), but at night some fish just over in water, seemingly oblivious to the diver. They appear to be in a state of suspended animation, i.e., asleep; you can even pet them, sometimes. Fish have no eyelids, so their eyes are always open even though they don't "see" while asleep.

Other sea creatures sleep during the day and come out only at night (some species of octopus, for example, although they are not fishes). Finally, some fishes, notably some species of shark, appear not to sleep at all.

How long do fish live?

The answer varies, of course, depending on the species, but it is extremely rare for a fish to live more than 25 years. Many large fish live for 15-20 years, including barracuda, tarpon and herring. Smaller fish live anywhere from one to five years - unless they are caught and eaten by bigger fish (or by people).

Whales, which are not fish but mammals, may live up to 60 years.

Great Lakes Shipwrecks

There are literally thousdands of shipwrecks along America's coasts and in the Great Lakes. No one knows exactly how many but, increasingly, scuba divers are helping to locate and explore them. For Gerald Metzler charting the Great Lakes wrecks, especially those of Lake Erie, has become a lifetime passion. A high school science teacher in Lakewood, just outside Cleveland, Mr. Metzler has located and dove dozens of wrecks himself, and maintains an extensive file on Lake Erie wrecks,a s well as detailed information on all 21000 ships ever built on the Great Lakes (Huechner 1994). As is well known among fresh water divers, cold temperatures and lack of wood worms favor preservation of Great Lakes wrecks. Metzler estimates there are 250-300 wrecks in Lake Erie, most of them known because of the Lake's shallow depth (av. about 60 ft., max. to about 200 ft.). the first Lake Erie wreck was a ship that went down in 1763.

Some Famous Wrecks

Apart from the Titanic (see Chapter 1), many other famous wrecks have been discovered or explored in recent years. Listed in alphabetical order are ten wrecks that continue to receive coverage in popular press and magazines. (fsw = feet sea water; figure shown is deepest depth of vessel).

Andrea Doria - 697-ft. Italian luxury liner, cruising from Genoa to New Your; hit by the Swedish passenger liner Stockholm on July 25, 1956; sank next morning in Atlantic Ocean, 50 miles south of Nantucket; 52 people died (Dorea has since claimed lives of many divers); 240 fsw.

Atocha - Spanish galleon carrying gold to Spain; sank in hurricane 1622, about 7 miles off southern tip of Florida; uncovered over period of 15 years (1970-1985) by Mel Fisher and his company, Treasure Salvors; is considered the world's richest discovered wreck; 132 fsw.

Bismark - German battleship, one of largest and most powerful of World War II; sunk by the British in the Denmark Strait between Greenland and Iceland, May 27, 1941; discovered June 1989 by Robert D. Ballard, using the same underwater camera vehicle his team used to discover Titanic; approx. 15700 fsw.

Central America - Side wheel steamer carrying gold from California to New York; sank in hurricane September 9, 1857, 160 miles off coast of Charleston, South Carolina; 8045 fsw.

Edmund Fitzgerald - Largest Great Lakes ship when built in 1958; over 700 feet long, 75 feet wide; sunk November 10, 1975 in Lake Superior, during a storm; later located broken in two, at depth of 530 feet.

Lusitania - 787-ft. luxury liner of British Cunard Line, largest and fastest liner at time of her launch in 1907; torpedoed by German submarine while sailing from U.S. to England, May 7, 19195; sunk 11 miles off coast of Ireland with loss of 1198 lives (out of 1959 crew and passengers); 320 fsw.

Monitor - Union ironclad warship, famous for its epic standoff with Confederate ironclad Virginia (originally named Merrimack) in March 1862; on December 31, 1862, while being towed, Monitor filled with wter and sank, 20 miles southeast of Cape Hatteras, North Carolina; 230 fsw.

Pandora - a British frigate carrying home prisoners who rebelled against Captain Bligh and were involved wiht the H.M.S. Bounty mutiny; Pandora struck a reef off coast of Australia in 1792; 110 fsw.

Rhone - British mail carrier traveling from England to St. Thomas, U.S. Virgin Islands; sank in hurricane 1859; off Slat Cay in British Virgin Islands; 90 fsw.

San Diego - World War I U.S. battleship; torpedoed by Germans July 18, 1918 off coast of Long Island, New Your, within sight of shore; now Long Island's "most dived wreck"; 75 fsw.

Selected Non-documentary Movies with Diving Themes/Scenes (of which there are a few, and most of them woefully hort on plot or acting, or both): listed in order of release:

Beneath the 12-mileReef: 1953. Entertaining film centered around sponge divers off the Florida coast.

20,000 Leagues Under the Sea; 1954. Disney version of the classic Jules Verne novel about Captain Nemo and his submarine Nautilus. this is the best of three movies with the same title; the other two appeared in 1916 (a silent film) and 1972.

The Silent Enemy; 1958. World War II adventure has frogmen fighting it out in Gilbralter Harbour. Movie highlights underwater photography (in black and white).

Thunderball; 1965. An early James Bond thriller starring Sean Connery; underwater scenes filmed off Nassau.

Around the world Under the Sea; 1966. Early underwater movie starring Lloyd Bridges of Sea Hunt fame in scuba gear.

The Deep; 1977. An action-adventure film about recovering treasure from a wreck off Bermuda. One of the better stories in films of this genre.

Airport 77; 1977. Typical Hollywood melodrama. Story about a Boeing 747 that crashes intact into the ocean, trapping its passengers. Film contains scene of Navy divers working to raise the plane. (Predictable outcome; excellent use of lift bags).

Raise the Titanic; 1980. About a plot to raise the world's most famous wreck in order to recover rare cargo of radioactive material.

For Your Eyes Only; 1981. A second James Bond thriller with under water scenes, this time starring Roger Moore as 007.

Never Say Never Again; 1983. Yet another James Bond movie with underwater action; a remake of popular Thunderball (1965).

The Big Blue; 1988. Loosely based on the life of world champion free diver Jacque Mayol.

The Abyss; 1988. the best of the underwater genre films, an engrossing story about aliens whose ship rests on the bottom of the ocean. Includes scenes on liquid breathing and the high pressure nervous syndrome.

Leviathan; 1988. A poor remake of Alien. Entire action except for last brief scene takes place three miles under water.

Deep Star Six; 1988. Drama centering on top-secret navy base on ocean floor; of 'B' or 'turkey' movie status.

Lords of the Deep; 1988. Another underwater thriller 'B' movie; this one at 10,000 fsw.

The Great White Shark

The great white share, Carcharodon carcharias, is the most feared fish in the sea. The 1975 movie Jaws, based on the Peter Benchly novel about a people-eating great white, actually caused a slump in the scuba industry. After seeing the great shark monster do its thing, many people simply would not go near salt water.

The great white is found in tropical and subtropical waters, but is especially numerous in Australian waters. Richard Ellis, who has written extensively on sharks, believes the great white has much more to fear from people than vice versa. His 1991 book, Great White Shark (co-authored with J.E. McCosker), includes a complete listing of great white attacks on humans from 1926 through 1990; several attacks are described in detail.

According to the U.S. Navy Manual, the shark can grow up to 25 feet long. Guinness Book of Records states that the largest great white accurately measured was 20 ft. 4 in. long and weighted 5000 lbs.; it was found in the Azores in 1978.

Earth's Most Venomous Creature

According to an 1994 article in National Geographic (Hamner WM), the distinction goes to Australia's box jellyfish, Chironex fleckeri. This species of jellyfish inhabits Australia's north coast from Queensland town of Rockhampton on the eastern shore all the way to the middle of Western Australia. it stays close to shore and affects swimmers in this huge coastal region. Fortunately the jellyfish is not found on the Great Barrier Reef.

At maturity the box jellyfish has a body as big as a basketball ( and is square or box like), with up to 60 tentacles each 15 feet long. Skin contact with the tentacles can kill a human in four minutes, and 65 people have died from its sting in this century. the Australians have developed a potent anti-venom to the box jellyfish which is credited with saving lives.

Top 10 Diving Destinations

According to polls in various magazines, the top 10 diving destinations for Americans are:

  • Florida Keys
  • Bahamas
  • Cozumel
  • Cayman Islands
  • Hawaii
  • U.S. Virgin Islands
  • East coast of Florida, off Broward and Dade Counties
  • British Virgin Islands
  • Bonaire
  • Turks & Caicos

Diving the Bikini Atoll

In 1946 the U.S. Military Governor of the Marshall Islands informed the 167 residents of Bikini - a tiny atoll in the Micronesian pacific halfway between Hawaii and Australia - that they would have to move. The U.S. had selected remote Bikini atoll as the site of post-war atom bomb testing. On July 1, 1946 a B-29 dropped the world's fourth atomic bomb over a fleet of 95 ships anchored in Bikini Lagoon, sinking them all. Declared uninhabitable until recently, Bikini may become the next dive mecca. Several travel companies are negotiating with native Bikinians (who have received millions of dollars from the U.S. government in compensation for their forced displacement) to allow diving over the wrecks of Bikini. (Davis, NYT, 1994)

The BIGGEST Animals in the Sea...

The biggest fish s the whale shark, scientific name Rhincodon typus. R. typus is pure shark but as big as a whale; adult whale sharks can grow up to 40 feet in length and weigh over 15 tons. Unlike most other sharks, the whale shark eats only plankton.

The biggest animal, of course, is a mammal - the whale. And the biggest of these is the blue or sulphur-bottom whale, Balaenoptera musculus. This animal can grow up to 110 feet in overall length and weigh over 200 tons. Some dinosaurs may have been as long but noe was as heavy. the blue whale is the largest animal that has ever lived on earth.

Lloyd Bridges

Bridges starred as Mike Nelson in the popular TV adventure series Sea Hunt, which aired weekly from 1957 through 1961. An avid diver himself, his show is generally credited with interesting many thousands of people in undersea life and diving.

Bridges also appeared in several undersea feature films, including 16 Fathoms Deep, Around the World Under the Sea, and Daring Game. His non-diving movies include Airplane, Airplane II, The Rainmaker and Hot Shots.

Less well know is that Bridges was co-author of an early dive training book, Mask and Flippers, published in 1960.

Why Don't Whales Get The Bends?

Whales can dive very deep and stay under water a long time before surfacing for air. How long? A bottlenose whale can stay submerged for up to two hours. Whales are able to stay under by efficient use of oxygen, plus the ability to carry a relatively large amount of oxygen on myoglobin (a muscle protien similar to hemoglobin).

How deep can they go? A pilot whale can dive to 1500 feet, a sperm whale to 3000 feet. According to Guiness Book of Records, the record belongs to the sperm whale, with a recorded depth of 8202 ft.

Whales don't get the bends from such deep dives because they don't breathe compressed air. Although they stay down far longer than any human breath-holder, the whale's relatively small lung volume (compared to body size) doesn't contain enough nitrogen to saturate much of its enormous body mass. Thus on ascent there is very little "extra" nitrogen to come out of the whale's tissues. (Humans have a much larger ratio of lung volume to body size, and some deep breath-hold divers have developed symptoms of the bends.)

Now if a whale dove with compressed air...

There Has To Be a Better Ending (The Big Blue)

Toward the end of the movie The Big Blue, Jacque Mayol's girlfriend is seen walking down a narrow street to his apartment. It is bright morning, and Mayol has had nightmares about his friend Enzo's death from free diving the previous day. His girlfriend enters the aprtment and gasps at the site: Mayol laying in bed, dazed, his nose and ears all blody. No explanation as to how he got that way. End of scene.

In the next frame Mayol is running out of the apartment, toward the dock and his free-diving apparatus (a sled that allows competitors to descend to record depths). His girlfriend gives chase, begging him not to dive. Mayol's bloody face is unchanged from the previous scene; girlfriend also looks the same. In fact everything is the same except...it is now night time. Clearly, in the context of the scene only a few minutes have elapsed since she entered Mayol's apartment. But the sun has long set and it is hours later! Minor editing glitch, you say. OK, OK, but the next (and last) scene makes Free Willy look like a sophisticated flic. Mayol's girlfriend, seeing that he is compelled to dive, has a change of heart and helps launch the sled. He goes deep, meets his friend the dolphin, then surfaces and cavorts with other dolphins. End of movie.

The Big Blue is muddled like this all the way through, but it is worth viewing for anyone addicted to diving lore. Just don't expect a true-to-life or true-to-the-facts film biography. Mayol himself has disavowed this film as a less than faithful biography.

Cousteau's Pneumothorax

According to Jacques Cousteau's biographers, the co-inventor of modern scuba gear suffered fractured ribs and a "punctured lung" (pneumothorax) in 1936, from an automobile accident. It took almost a year but he recovered fully. It was at that point that Cousteau began his hobby of spear fishing (with only a pair of Fernez goggles; scuba came much later, in the early 1940s).

Today, anyone with a history of traumatic pneumothorax would probably be advised not to take up scuba diving, because of the risk of another pneumothorax and possible air embolism. Fortunately Cousteau never got this advice (who knew?), and he wnet on to pioneer the sport.

Philipe and Jean-Michel Cousteau

Jacques and Simone Cousteau had two sons. Tragically Philipe, their youngher son, died June 18, 1979, in a seaplane accident. Age 39, he was landing his seaplane on the Tagus River near Lisbon, Portugal, when it flipped over after touching the water. Everyone else on the plane survived. Philipe's wife Jan, two months pregnant at the time of the accident, gave birth to Philipe Pierre Jacques-Yves Arnault Cousteau on january 20, 1980.

The older son, Jean-Michel, born 1938, remains very active in diving and ocean conversation, speaking all over the world. He now leads the Cousteau Society and is on the board of the Historical Diving Society. The next item quotes his feeling about a jubject of vital importance to all recreational divers, reef damage.

Are Divers Hurting Reefs?

Dozens of articles over the years have pointed out how careless divers harm the reefs, mainly by touching, grabbing, bumping and kicking them. However, Jean-Michel Cousteau was quoted in the Wall Street Journal (Sterba 1993) as saying that diver damage, while serious, is "insignificant" compared with other harmful factors such as soil runoff, chemical dumping, over fishing and boat anchoring.

Unfortunately many divers do hurt reefs. While this is both tragic and preventable, other human (and non-diving) activities hurt them far more.

There Has To Be A Better Ending (The Abyss)

At the end of The Abyss (my favorite of this genre), the characters are at a depth of 12,000 feet, but not in a submarine; they are in an alien space ship and have been there a while. Having arrived breathing some type of exotic gas mixture at the ambient pressure, their decompression time is probably measured in years. How are they gonna get back to the survace (and end this movie)? No problem. the friendly aliens bring them right up to the surface. In seconds. Wow.

Dive buffs are scratching thier heads. Don't those aliens know about the bends? Are they secretly trying to kill earthlings? The producers know they have a problem here. Hot to fix it so the scuba crowd doesn't belittle this film? On reaching the surface one character exclaims, "And we didn't even have to decompress!" Alien Magic? End of movie.

Homo Aquaticus Revisited

"The imperative need now is to place swimmers underwater for very long periods, to really learn about the sea. I think there will be a conscious evolution of Homo Aquaticus, spurred by human intelligence rather than the slow blind natural adaptation of species. We are now moving toward an alteration of human anatomy to give man almost unlimited freedom underwater."

Jacques Yves Cousteau, speaking at the World Congress on Underwater Activites, 1962 (as quoted in Madsen 1986).

Pacific Vortex, a novel by Clive Cussler (1982)

Aboard a ship in the north Pacific, Pitt (the novel's hero) and Boland (the captain) are looking for a missing U.S. Navy submarine, plus the solution to many other unexplained ship disappearances. A sonar man sees

"a school of fish about a hundred yards off the starboard beam...by rough count, over two hundred of them swimming at three fathoms."
"Size man. Size!" Boland snaps.
"Somewhere between five and seven feet in length."
Pitt's eyes shifted from the speaker to Boland.
"Those aren't fish. They're men."
The underwater pirates board the ship. They are humans who carry no breathing apparatus, only weapons of war...

...The only difference (Pitt's) eyes could detect, a difference he hadn't had time to notice before, was a small plastic box that seemed to be adhered to each man's chest under their armpits... It was now easy to see how these strange men from the sea, under concealment of the fog, had silently dispatched almost a hundred ships and thousands of their crewmen to the bottom of this godforsaken piece of the Pacific ocean.

Most Fequently Asked Question of Scuba Divers by People Who Have Never Dived (and Never Intend to):

"Aren't you afraid of sharks?"

Standard Answer: "Of all the things most scuba divers worry about, meeting a shark is not high on the list." The facts:

  1. More people are killed by lightning or bee stings each year than by sharks. Since 1965 the annual recorded number of shark attacks is about 40-100 worldwide; the number of shark-related deaths per year is 5-10. Very, very few diving related deaths appear to have anything to do with shark attack. Overall, considering the millions of people who enter the ocean for pleasure worldwide, shark attack is very rare.
  2. Only a few of the 360+ known species of shark pose any threat to humans. These include the great white, mako, tiger, white-tipped, hammer-head and lemon sharks.
  3. Through active hunting, and use of large fishing nets which trap sharks, people have posed a far greater threat to sharks than vice versa.
  4. On most recreational dives just seeing a shark is considered a thrill. Guided shark dives (no petting allowed) are growing in popularity and are offered in many sites around the world. In Australia you can even sign up for an underwater encounter with the great white shark; they put you in a "shark proof" cage and drop the cage in the water.

ama DIVERS of Japan and Korea

Professional breath-hold divers of Korea and Japan, known scientifically as "ama" divers, have been practicing their art for over 2000 years. They dive daily, usually to shallow depths, but have been known to go very deep. One study of working ama divers found that their total in-water time averaged about 180 minutes/day (Hong 1991). The average time per dive was about 30 seconds. Total bottom time per day was 27 minutes.

There Has To Be A Better Ending (Sphere)

In his 1985 novel The Sphere Michael Crichton conjures up an exciting story about discovery of a giant vessel found at the bottom of the sea. It has been there 300 years (based on coral encrustation), but is made of materials unknown on earth. Is it from the past? Or from the future? After some exciting hypothesizing and equally excitng underwater action scenes, the reader aches to see how all the unanswered questions will be resolved. Crichton probably ached also.

In the end he has the protagonists simply forget what they experienced. Literally. His characters give their reasons, and one can't fault a master writer for choosing a "mind game" ending. Nonetheless, the ending is un-satisfying because it seems so implausible. The reader can accept an alien intelligence at the bottom of the sea, but not that mere mortal humans can will themselves to forget all about it.

Sheck Exley and Jim Bowden

Sheck Exley, a pioneer of deep cave diving, died at age 45 on April 6, 1994. He failed to surface during a record-breaking attempt to 1000 feet/307 meters in the Zacaton sinkhole in northeast Mexico (located about 60 miles north of Tampico). He and partner Jim Bowden dove at the same time, using two separate descent lines, so they were relatively unaware of each other's position during the dive. (Each was trying to break Exley's previous open circuit scuba world depth records: 867 feet, 1989, Mante Mexico; and 863 feet, 1993, Bushmansgat, South Africa.) (Exley 1994, Hamilton 1994)

Bowden surfaced after reaching a new world record of 915 feet, as measured by one of two computers he carried; the other measured 924 feet (Taylor 1994). When Exley's body was finally pulled up his depth meter read 904 feet (Zumrick 1994).

Scuba Diving in Hawaii

For scuba divers perhaps the principal difference between Hawaii and most other popular warm water sites is...the absence of soft coral. Hawaii's lack of soft coral is attributed to both the islands north Pacific location (strong winter winds between September and May, with heavy surf conditions) and the fact that the sea bed near the islands is covered with volcanic lava. The result is much hard coral but no soft coral. Other differnces in the scuba experience have to do with the Hawaiian islands' remote location - the most gepgraphically remote islands on earth. Many fish species common elsewhere are not found in Hawaii (e.g., groupers, clown fishes), while an estimated 20% of the species in Hawaii are found nowhere else (e.g., the lemon butterfly fish, Chaetodon milaris; the Hawaiian sharpnosed puffer, Canthigaster jactator).

Cold Water Diving

Some of the best diving is in cold water, which I define as water colder than 75░F. I've seen no poll on this, but from numerous articles the following U.S. areas seem to be favorites for cold water diving:

  1. Central Florida springs (72░F year round)
  2. Southern California, including Catalina island
  3. Monterey Peninsula (central California)
  4. Wreck diving off the Atlantic Coast, from North Carolina to New Your
  5. Northwest U.S. (San Juan Islands)
  6. Wreck diving in Great Lakes region
  7. Bonne Terre Mine (near St. Louis)

Ocean Facts

  • The world's oceans are one vast interconnected body of water, commonly reffered to as the world ocean. The world ocean covers approximately 142,000,000 sq. miles, or 70.1% of the earth's surface, and has three main divisions: the Pacific Ocean (63,800,000 sq. miles); the Atlantic Ocean (33,420,000 sq. miles; and the Indian Ocean (28,350,500 sq. miles). Many geographiers consider the Arctic and Antarctic oceans extensions of the other three divisions.
  • The volume of the world ocean is approximately 326,000,000 cubic miles.
  • The salt content varies by location, and averages about 35 parts per thousand (ppt) by weight; the range is 33 to 36 ppt.
  • The deepest part of the ocean so far measured is a section of the Pacific's Mariana Trench, southwest of Guam; 36, 198 ft.). The bathyscape Trieste visited this trench in 1960, reaching a depth of 35, 820 ft.). (see Chapter 1). The deepest parts of the Atlantic and Indian Oceans are, respectively, the Puerto Rico Trench (28, 374 ft.) and the Java Trench (23, 376 ft.) Average depths of the three oceans are similar;: Pacific, 12, 925 ft.; Atlantic, 11, 730 ft.; Indian 12, 598 ft.
  • The continental shelf is the gently sloping floor of the ocean surrounding the continents, from sea level to a depth of about 600 feet. its width varies from almost nothing to 800 miles, with an average about 30 miles. Where the shelf leaves off the continental slope begins, reaching depths of 5000 to 11000 feet.
  • Scientists divide all living things in the ocean into three groups: the plankton, the nekton and the benthos. Plankton includes all plants and animals that drift about with the tides and currents; they are dubdivided into phytoplankton (microscopic plants such as diatoms) and larger zoo-plankton, which includes animals like the jellyfish and copepods.
  • The nekton comprises all the animals that can swim about, including fishes, squids and whales. An estimated 13,300 species of fish live in the sea, ranging in size from 40 feet (whale shark) to less than one inch long (gobies).
  • The benthos includes all bottom-dwelling life, both plans (kelp, sea grasses) and animals (starfish, corals, anemones).

The Compleat Goggler - Guy Gilpatric

Guy Gilpatric pioneered the modern sport of spear fishing when he discovered how easy it was to hunt for fish with watertight goggles (see Chapter 1). His book, The Compleat Goggler, published in 1938, was wide ly read at the time. Less well known is an article by the same name, published in the Saturday Evening Post October 6, 1934. Excerpts:

...The first thing you need, to be a successful goggle fisher, is a body of good clear water. Personally, I use the Mediterranean Sea, and there is still plenty of room in it; but parts of the Atlantic, most of the Pacific and all of the Mexican Gulf and the Caribbean will do just as well, and I know of many American lakes and streams which provide grand goggling. Next you need a pair of watertight goggles. I made my first pair myself from an old pair of flying goggles, plugging up the ventilating holes with putty and painting over it. The ones I now use were built for pearl diving...

...Here are some of the things we have learned: When you have to let out your breath to go down, go down feet first until you are completely under water; then, but not until then, lean forward and swim toward the fish. If you go down head first, you break the surface as you dive and drag with you air which raises in silver bubbles like sparks behind a rocket. All this frightens the fish. A feet-first descent doesn't cause a ripple for a bubble. Remember that through your lungs are empty and that you are therefore heavier than water, a couple of strokes with your free hand will shoot you up to the surface. Although you cannot remain under as long with empty lungs as with full, because you have no air to exhale as sort of last-gasp reserve, you save strength and avoid water disturbances because you have no buoyancy to struggle against. My useful limit under water is about fifty seconds; a goggler-fishing desciple of mine can stay two minutes, which I thought extraordinary until I heard of a Red Sea pearl diver's record of six minutes. This time seems incredible, but I have it on good authority... 

Highest-altitude Dives

In the 1993 Guiness Book of Records, teh record altitude dive was listed at 16, 200 ft. in the Himalayan lake Donag-Tsho (Nepal). The dive was accomplished by Frank B. Mee, Dr. John Leach adn Dr. Andy McLean on March 4, 1989, to a depth of 92 feet.

In the 1994 Guiness book, the record was changed to a dive made years earlier, by Richard Weihraunch of Germany. He is credited with diving ina a shallow crater lake inside the dormant Mexican volcano PopocatÚpetl, which is at an altitude of 16, 509 ft. This dive was made on November 20, 1983.

Coral Reef Facts

  • There are two main types of coral, hard and soft. Living coral reefs are made up of hard corals, which take calcium out of seawater and excrete skeletons of calcium carbonate (limestone). They are found only in warmer waters (>65░F or 18░F) because the polyps don't survive in colder temperatures. Coral reefs are also found only at shallow depths because of their need for sunlight to survive.
  • Soft corals, often found on our around hard coral reefs, don't excrete a limestone skeleton. Soft coral includes gorgonions (sea fans and sea whips), which have internal skeletons of a flexible, horny substance.
  • The individual coral polyp is a coelenterate, a large group of animals that includes jelly fishes and sea anemones. the coral polyp is typically less than one inch in diameter. it is the abiltity of coral polyps to form colonies that gives the fantastic shapes and colors visible on a coral reef.
  • Coral reefs occupy only 0.17% of the world ocean, or some 238,000 square miles. The three types of coral reefs are:
    • 1) fringing reefs, submerged platforms that extend from the shore into the sea;
    • 2) barrier reefs, which follow the shoreline but are separated from it by water; and
    • 3) tolls, ring-shaped coral islands in the open sea; an atoll is often the rim of an open volcano, and is most common inn the South Pacific.
  • The world's largest reef system is the Great Barier Reef which runs from about 1250 miles down the eastern coast of Australia; second in size is the Belize Barrier Reef.
  • One of the biggest natural predators of coral is the crown-of-thorns starfish, which has destroyed many coral formations. Other natural hazards include moring marine worms and storms.

Ciguatera & Scrombroid Poisoning

Two major types of fish poisoning are dcalled ciguatera and scrombroid. They are very different.

Ciguatera poisoning is the most frequently reported seafood related disease in the U.S. It occurs from toxins (ciguatoxin and others) supplied by dino-flagellates that are ingested by plant-eating fish. As these smaller fish are ingested by larger carnivorous fihs, the toxin increases in quantity, until the larger fish is caught and eaten by humans. This larger and older fish tend to be more toxic. Most commonly implicated fish: barracuda, snapper, jack and grouper.

The dino-flagellate is named Gambierdiscus toxicus. Common in the Caribbean and indo-Pacific islands, G. toxicus has been found in over 400 species of tropical reef fish. No known processing procedures, including cooking, are protective, so ciguatera poisoning is hard to prevent; presence of the toxins in fish does not affect their appearance, smell or taste.

Symptoms of ciguatera poisoning may begin minutes to hours after eating the fish, and include abdominal cramps, diarrhea, skin itching, skin tingling, headache, muscle aches, confusion, and facial pain. After initial recovery the victim may have sensory changes for months. Death can result from respiratory muscle paralysis. the average duration of illness is about 8 days.

Treatment is supportive, although some patients have marketly improved with intravenous mannitol, a drug used to treat brain edema (excess water on the brain). Improvement of confusion in the treated patients suggests they were suffering from brain edema.

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Scombroid poisoning resembles an acute allergic reaction. It comes from eating the breakdown products of certain types of fish which are improperly prepared for consumption.

Scrombroid poisoning can occur from eating fish of the Scombridae family (origin of its name), including mackerel, tuna and bonito; it can also occur from eating non-Scombridae fish such as mahi-mahi, bluefish and amberjack. Bacterial decomposition after the fish is caught produces high levels of histamine and oother toxic substances in the fish's flesh. Althugh at one time histamine was thought to be the sole culprit, other substances probably account for many of the symptoms.

The responsible toxin or toxins cause immediate reaction (within 30 minutes of eating), characterized by facial flushing, sweating and burning sensation of the mouth and throat. Other symptoms include nausea, vomiting, pain, large skin welts, blurred vision and asthma. Symptoms usually last anywhere from 4 to 24 hours, rarely longer.

Treatment is usually symptomatic. Antihistamines may be effective. At least one report has found intravenous cimetidine effective; this is a type of histamine blocker used to treat stomach ulcers.

Deepest Dives on Compressed Air

For many years the record for deepest dive on compressed air was the October 14, 1968 dive by John J. Gruener and R. Neal Watson, to 437 feet off Freeport, Grand Bahama Island. On February 14, 1990 Bret Gilliam dove 452 feet off the coast of Honduras (Roatan). He descended in 4 minutes 41 seconds and stayed at depth one minute 40 seconds. Then on March 18, 1994 Daniel J. Manion, M.D. dove to 510 feet on Clifton's Wall, Nassau, The Bahamas. the dives by Gilliam and Manion were solo dives and, as reported by the divers, went without a hitch. Both men made many dives prior to achieving their records. Both had decompression stops before surfacing.

Finally, both men acknowledge the extraordinary danger in diving to such depths on compressed air. Although the dives are necessarily short, death can occur as result of oxygen toxicity, nitrogen narcosis, air embolism or decompression sickeness. Many deep divers have never returned.

Eugiene Clark

Born in 1922, Eugiene Clark is perhaps the most famous of all women divers, and among the world's top oceanographers. With a Ph.D. in zoology, she pioneered research on sharks and has published several books on the subject. her personal memoir, Lady With a Spear, appeared in 1953 (now out of print).

Dr. Clark has dived in everything from scuba gear to helmet suits, from submarines to one atmosphere JIM suits. She is the jubject of numerous articles and books, including two written for children by Ann McGovern: Shark Lady: The Adventures of Eugiene Clark, and Shark Lady II: The Further Adventures of Euguiene Clark.

"Pipin" Ferreras and the Deepest Breath-hold Dive

On December 17, 1994, Francisco "Pipin" Ferreras, a Cuban-born immigrant to the U.S., dove to an incredible depth of 417 feet with a singele breath of air. He was under water for 2 minutes, 28 seconds. The dive, which took place near Pipin's home in Key Largo, Florida, bested his previous world breath-hold record of 413.3 feet.

Prior to December 1994, Pipin had already accomlished more than 500 breath-hold dives to greater than 350 feet, and has stated that his ultimate goal is 500 feet!

There are four main categories of breath-hold diving, and only the first three are recognized as a sport for world competition:

  1. totally unassisted;
  2. constant ballast, whereby the diver descends with the aid of a weight belt and ascends still carrying the belt.
  3. variable ballast, whereby the diver descends with a weight belt, then drops the belt and ascends under his own power; and
  4. "no-limit" breath-hold diving

To reach such fantastic depths (and come back alive), Pipin and other no-limit breath-hold divers descend with the aid of a heavily weighted sled, then ascent with the aid of a lift bag.

During these dives pipin is able to slow his heart rate from 60 to 8 beats/minute, decreasing his body's need for oxygen and allowing him to survive. Less understandable is how his lungs and chest cage are able to withstand the immense water pressure at 400+ feet.


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Last updated: 29/10/97