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A Whale Shark.
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Photo: Iain Kerr |
September 20, 2002
Gentle Giants - Whale Sharks
Real Audio
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Log Transcript
This is Genevieve Johnson speaking to you from the Odyssey in the Indian Ocean.
There are some days on this expedition when we experience events so incredible that it is difficult for the crew to comprehend. Often it is only at the end of the day when we each have time to sit quietly in solitude and reflect, that the enormity of what has just transpired truly sinks in!
There is a species of shark in Seychelles waters that swims close to shore, can reach lengths in excess of 40 feet (13m), weighs over 10tons and has a mouth easily large enough to engulf a person whole. This shark can be found all around the globe in tropical and sub-tropical waters. Scientists recognize it as the largest fish in the sea.
Are these sharks survivors of the thought to be extinct species carcharadon megaladon, from the Pliocene, the giant, ferocious ancestor of the present day great white shark?
This morning we met these 'fierce monsters' of the deep in their own element, face to face. The Odyssey crew swam with whale sharks.
After experiencing miserable and even violent weather for the last two days that eventually culminated in an unusually strong tropical storm, the Odyssey crew took shelter inside Anse a la Mouche. Ronny Alcindor, our Seychelles observer from the Ministry of Environment, informed us that it is currently whale shark season here - the time of year when plankton blooms are most abundant in the area, which in turn attracts many whale sharks. Because these animals are known to feed along the exterior of the reef, it was an ideal opportunity to try and find them.
The crew piled into the dinghy early this morning in the hopes of encountering these illusive giants.
The weather was dreary, the wind, rain and seawater tore at our faces as we travelled headlong into the rolling 3-meter swell of the Indian Ocean. The hands of six brave souls gripped the handles along the sides of the dinghy. Our knuckles were white but the smiles on our faces were huge with the wild elements of the sea conditions only serving to fuel the thrill of the adventure. Then we spotted a flock of birds, something had captured their attention. Noddy's, terns and shearwaters skimmed the sea with their bills, snatching small fish from the surface that in turn fed on the plankton. Larger fish rose from below to feed on the smaller fish, a feeding frenzy was taking place right in front of us. We learned that where birds are feeding, whale sharks are often right below the surface.
The Odyssey crew are used to spotting whales by their large blow when they are at the surface. Because whales are mammals, they must surface to breathe through their blowhole. Whale sharks are fish and are more difficult to spot because they breathe through their gills underwater.
Suddenly Iain Kerr spotted a huge dorsal fin in the centre of the frenzied birds while the massive upper lobe of the tail sliced through the surface meters behind. The shark moved slowly, parallel to our dinghy about 10 meters away. The crew slid into the water, our faces below the surface and our eyes filled with anticipation at the thought of actually encountering this colossal animal.
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The Odyssey crew after the encounter with a whale shark.
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Photo: Chris Johnson |
Moving like a shadow, slowly distinguishing itself from the hazy deep blue background, the shark drifted toward us through its vast three-dimensional world. The crew stuck together in a tight group, the atmosphere below the surface was surprisingly calm and serene considering the calamitous world above. The shark turned in our direction and I could hardly believe what I was witnessing. The whale shark is the world's largest known fish, living or fossil, and in contrast to the ferocious great white shark, this enormous beast is docile, gentle and perhaps even curious. It swam toward us becoming larger and clearer with each stroke of its massive tail with no urgency in its movement. We hung motionless as it swept by us only a few feet away like a large grey school bus adorned with white spots and long, thick ridges. The shark appeared completely uninhibited by our presence.
We saw its small eyes far forward on the square head. They are situated on prominent bumps, allowing the shark to see in front of its mouth. With no membrane to protect the eyes, as in most other species, this shark rotates them and sucks them back into the head when threatened. As it swam past us we noticed a complex community of fishes surrounding the strongly flattened head, all hitching a ride in the hope of picking up some food while also seeking protection from predators.
Whale sharks together with the slightly smaller basking shark, the second largest fish in the sea, cruise the oceans feeding on concentrations of zooplankton, small fish and squid. The whale shark's 5-foot wide mouth contains 300 rows of tiny teeth, but ironically, they neither chew nor bite their food. Instead, the sharks use a fine mesh of rakers attached to their gills to strain food from the water. These rakers are functionally similar to the baleen plates possessed by many whales. When actively feeding, the gills flare out as the shark pumps large volumes of water through them, food is retained in the mesh of the gills and swallowed. Whale sharks are able to filter prey items that are only one millimeter in diameter. Because of their large size and the fact that they eat plankton, whale sharks are often confused with whales. However, they are among the most docile of sharks, their closest relatives being the nurse and wobbegong sharks.
It is believed that maturity is reached between twenty-five and thirty years of age. Such late maturation suggests that they may even live up to one hundred years of age. Whale sharks are viviparous animals, that is they are born live and do not hatch from eggs after they leave the uterus. In Taiwan a pregnant whale shark was harpooned, she contained 300 embryos. The pups that were freed from the yolk sac were up to 64cm(25 inches). (Environmental Biology of Fishes 46:219-223 1996). They are thought to be a highly migratory species, although, there is little information currently available on this aspect of their behaviour. Satellite tagging programs may soon help scientists understand more about their ecology.
Although an adult whale shark has little to fear in regard to predation, like all shark species, it is vulnerable to human pressures, including entanglement in fishing nets, boat strikes and a growing interest in the species for use in aquarium exhibits. It is estimated that over 100 million sharks of all species are captured annually, many of which are killed purely for their fins, which are used in shark fin soup. Whale sharks are becoming an increasingly valuable target for this wasteful trend. In Hong Kong a bowl of shark fin soup may be sold for US $100, while a single dorsal fin from a whale shark is worth a staggering US $14,000.
These sharks are the perfect ambassadors for an unfairly vilified species. Perhaps we can learn from the success of the world's whale watch industries and support tourism based on whale shark watching. Some countries such as Australia and the Seychelles have already begun to do so with great economic success, which at the same time has encouraged governments to recognize the ecological value of protecting these magnificent creatures. The growth of whale shark watching industries will help to ensure the long-term survival of these animals, while allowing people to experience an encounter with these unimaginably large gentle giants of the underwater world.
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Log by Genevieve & Chris Johnson
