World's Biggest Fish - the great whale shark in Western Australia

International Wildlife, Jan, 1999

That's where co-pepods come in, says Newbound. While our ship rides the swells, she describes how copepods, which resemble little horseshoe crabs, feed on the algae and bacteria growing on the whale shark's skin. The particular species she's studying cannot travel far unless they hitch a ride on their hosts. And since these copepods occur only on whale sharks, they serve as handy "biological tags." If DNA studies of copepods here on Ningaloo show that they are identical to copepods in Indonesia, then they must be riding on whale sharks. In this indirect way, studies of copepods may show whether Australia's whale sharks migrate.

Before I can ask her for more details, we are interrupted. The spotter has finally found the shark and is giving the signal. The captain yells, "Go, go, go," and we plunge over the side.

Entering the water, I look directly downward and see nothing. I start to raise my head and then notice what looks like a submarine looming towards me. The 20-foot-long whale shark is only a few yards away. It slowly glides to my lower left with 6-foot-wide jaws open, vacuuming up plankton. An armada of smaller fish swim underneath, coasting on its bow wave. As the whale shark passes beneath me, I notice white spots on its dark gray upper half. This coloration may act as camouflage; when seen from above, the shark's skin looks like the sun-dappled ocean floor.

I try to keep clear of the whale shark's tail, which is taller than a man. That slow-moving tail fin is deceptive: Enormous energy is required to move such a large object under water, and the back half of a shark is practically all muscle. An accidental wallop from a tail like that broke someone's ribs two weeks before. This latent power enables the shark to speed up easily. Nevertheless, we manage to keep it in sight until the leviathan tilts downward. The big fish submerges steadily, the blue of its body merging with the blue water until only its spots remain before fading into the background.

"That was amazing," says Newbound after we climb back aboard. "My hands are still shaking; my heart's still pounding." She tries to explain the whale shark's appeal, noting its differences from other sharks. Whale sharks aren't aggressive like tiger sharks, for example. Nor are they timid, like gray reef sharks, which are known to bluff their way out of trouble. To Newbound, the calm demeanor and massive size of whale sharks make them seem above all that: "The mystique is part of what draws people to them."

But what draws whale sharks to this isolated reef every year? At first the coral spawning was thought to be the key. For a short but intense period every year, coral produce hundreds of tons of protein-rich sperm and eggs. This food source attracts krill, crab larvae and mantis shrimp, which in turn attract bigger fish, including whale sharks--in theory.

The only problem is that the coral spawn is a very brief event that does not have time to work its way up the food chain, says Chris Simpson, the head of Western Australia's Department of Conservation and Land Management. In addition, tour-boat operators have reported seeing whale sharks arrive long before or after the spawn occurs. This year, few sharks appeared until well after the coral spawn.