One day Capt. Gray took me out for lunch at a restaurant overlooking a popular bathing beach where hundreds of people were enjoying the warm, tropical waters. We sipped our drinks and philosophically discussed our mutual interests in collecting and observing marine animals. Capt. Gray mused, "it's a strange thing about tiger sharks and people. Look out there at the swimmers enjoying themselves. That's where we set our shark lines in the evening. Some of our best tiger sharks are caught there. Little do those swimmers realize that they are sharing an area with one of the world's most dangerous sharks."

"Where are the sharks now?" I asked. "Surely the swimmers and tiger sharks are not really sharing the same waters?"

"The sharks move out into deeper water, into the channels during the daylight, so they're not here now, but at night they move into very shallow water, right up where you see those children having fun."

That was a time when not much was known about keeping sharks alive in an aquarium and the big specimens in the donut channel suffered from various health problems so Capt. Gray was always busy catching new ones to replace the old.

A few years later I visited Sea World in San Diego with Dave Powell, the Curator of Fishes. He was trying to develop a suitable exhibit tank for the blue shark (Prionace glauca), a common pelagic shark off the coast of southern California. It is attractive and slender; dark above with bright blue sides and white belly. It reaches a length of perhaps 12 feet (3.8m), but typically is six or seven feet long. Like so many other open water species, it does not survive long after capture. It requires very careful lifting out of the water with good body support and immediate treatment with oxygenated water pumped through its gills. Every step in bringing the shark to its aquarium tank must be done with careful attention to the needs of the animal. In his new book, A Fascination for Fish, Adventures of an Underwater Pioneer, Dave explains how he towed a 50-pound burlap sack of ground mackerel slowly behind his boat leaving an odour trail that the sharks could follow. I was with him.

We went out a few miles chumming for sharks . Dave threw in a hand line and hauled a thrashing six-footer into a stretcher over the transom and put it into a water filled, coffin-shaped box. Turning the shark on its back, he then pumped oxygenated water over its gills through a mouthpiece and rushed back to Sea World.

Dave was experimenting with a saucer-shaped pool 50 feet in diameter. Although he developed the techniques for bringing them ashore in healthy condition and provided them with the correct California temperatures, he was never successful in maintaining the blue shark in good health forlong. Although they fed actively in captivity, their energy requirements maneuvering in the small pool seemed to deplete their livers and ultimately they could not maintain their buoyancy. Pelagic sharks depend upon their large livers filled with lightweight oil to keep them up in the water. Unlike bony fishes, they do not have swimbladders. Dave found that, over time, the blue sharks began to sink and did not do well in his experimental pool.

In 1971 I organized an expedition to the Florida Keys to collect live sharks, sawfish, and other Florida marinelife. We wanted to work with Gerrit Klay, a shark expert about whom I had heard many good things. When we arrived at Gerry's "Sharkquarium" at Grassy Key we examined the large net enclosure on the beach and saw that he had already caught a half dozen lemon sharks and several sawfish.

The lemon shark (Negaprion brevirostris) is a yellowish-brown, stout bodied, Caribbean shark with two large dorsal fins and a bad temper.

Although it tends to be shy in the wild and to avoid divers, it is known for its aggressiveness and may turn and attack if prodded or touched. It often swims into shallow seagrass areas, along the Florida coast where it reaches a length of about 11 feet (3.4m).

Gerry had built water carrying boxes with oxygenation, recirculating pumps and filters after those designed by Dave Powell. He explained that in transit the sharks became very stiff and cramped in close quarters and might die if not given good care. He said "sharks have weak circulatory systems and need to be regularly massaged during the flight."

"Massage the sharks!" I exclaimed, "You must be kidding".

Gerry explained that the circulatory system is weak, the heart is small and the movement of the body provides much of the force that circulates the blood. While sharks need to keep moving to keep water flowing over their gills, they also need to keep moving for blood circulatory reasons, too. If a large shark is transported in a box of water it may die because of inadequate blood circulation.

By "massage" Gerry meant moving the tail and body back and forth by hand. We massaged the lemon sharks across the continent to the Vancouver Aquarium.

Biologists at Sea World under Dave Powell and others greatly advanced our success in keeping sharks alive in good health. They developed large enclosures with rapidly recirculating sea water, carefully purified and maintained at exactly the right temperature for the particular species to be exhibited.

Never in my wildest dreams did I imagine that a whale shark (Rhincodon typus) would ever be exhibited alive in an aquarium. Now, however, whale sharks are being exhibited dramatically in both the Okinawa Expo Aquarium and the Rim of Fire Osaka Aquarium in Japan.

One of the most successful shark exhibits in the world is at the Okinawa Expo Aquarium in Japan where the director, Dr. Senzo Uchida has dedicated his life to studying giant sharks and developing giant tanks for them. He has not only been able to capture and keep many species of large sharks but he has been able to breed bull sharks and to raise the young. Over 20 years ago he began studying whale sharks in waters around Okinawa. These largest of all fish are plankton feeders reaching 45 feet (14m) in length. He built a floating tank that could be towed behind a boat and worked out a system where the shark could be transported, then lifted up into the aquarium and placed in a giant, acrylic surrounded tank. He knew that large sharks were easily damaged when moved in a canvas sling because the cartilaginous skeleton of the shark is not strong enough to support and protect its internal organs out of the water. He worked out the technique of moving and lifting them in water. Then the problem was how he would feed such a giant plankton feeder. He pumped masses of krill through a hose and discharged them in front of the shark as it slowly swam around its tank. Dr. Uchida has been so successful that when the Osaka Ring of Fire Aquarium was designed, a giant central tank was provided for whale sharks where they are now successfully exhibited.

There are about 350 species of sharks. They vary not only in size and shape, but also in behaviour and physiology. By observing them in aquariums we have learned a tremendous amount about them. Shark populations have been severely reduced by overfishing and many people have recognized the need for strong conservation measures if these interesting animals are going to survive worldwide.

Sharks have special abilities. The lack of a swim bladder allows them to come up swiftly out of the depths toward the surface with no gas expansion problems such as bony fishes have. Their negative buoyancy is compensated for by large livers filled with lightweight oil. Their well designed fins give them excellent control and their good eyesight, keen hearing and special sensory systems make them masters of the depths. Most sharks seem to be most active at dawn and dusk but that does not hold for all sharks at all times.

I guess we just take our chances­as do the sharks in this world. Of course, if we balance shark attacks against other dangers the numbers of attacks are insignificant. However, if we like to swim out over deep water in the evening and early morning we might just be changing the odds a bit.