Slack tide had killed the vis. The ripping ocean currents that normally clear the waters between Darwin Island and The Arch, a nearby rocky pinnacle, rested as the moon's pull prepared the Pacific to change from high to low tide. Despite that, there was no problem finding Galapagos and hammerhead sharks, which populated this site by the hundreds and frequently cruised within arm's length. But that was not my quest.Journeying to Galapagos, 600 miles off the Pacific coast of South America, was about finding the biggest shark in the ocean - the whale shark - and I needed it to happen here.I had been seeking these gentle giants for 15 years, and I didn't want to get shut out again. But after two days of travel and three days of diving, there were no sightings and the frustration was building. In my mind, this otherwise great diving experience would somehow feel hollow if I couldn't have just one encounter in this known hotbed of whale shark activity. Perhaps the other sharks swirling around had entranced me. Quite possibly I was fooled by the camouflage of white spots and vertical white lines. Maybe it was the poor visibility. Most likely it was all three, but somehow a 45-foot-long fish had sneaked up on me. However it happened, I was now engaged in one of the rarest and most sought-after animal encounters in all of scuba diving.Even with a hood on and exhaust bubbles filling the water, I could still hear the gleeful screams as my buddies caught sight of the whale shark. Despite the commotion, I was virtually catatonic. The regulator nearly fell from my slack jaw and the sensation jarred me from my immobility. I realized that the great fish was on the move. This would be the shortest whale shark encounter on record if I didn't do something.Finning for my life was just enough to keep me alongside the shark. But lactic acid began to build in my thighs. My pressure gauge needle dropped toward red. I rapidly began losing ground. The shark's tail, more than 12 feet tall, washed lazily to and fro, yet it moved the hulk with surprising speed. In 90 seconds, the whale shark was gone. The Known and UnknownEncounters with whale sharks are rare, an odd fact considering they inhabit oceans worldwide and spend the majority of their time filter feeding in the top 30 feet of the water column. But even at up to 60 feet long and weighing 20 tons, rhincodon typus is elusive.It is this cagey behavior, however, that has also helped put the whale shark at risk. Now, armed with mostly anecdotal evidence from scuba divers and just a few scientific facts, concerned environmental and animal-rights groups are working to head off what could be a wildlife management crisis rivaling those of manatees, sea turtles or any other known to date. The key to saving whale sharks, the groups believe, may rest in the hands of scuba divers.For sport divers, understanding the mysterious whale shark begins simply with understanding its name. Whale sharks are, biologically speaking, true sharks. They are not related to whales in any way. The whale moniker refers only to their size and filter-feeding pattern, both of which are similar to whales. But that is where the similarities end.Unlike whales, whale sharks are fish, not mammals. Whale sharks are, in fact, the largest living fish species. They are cold-blooded and breathe through five gills on each side flank. Their tails are vertical and use a side-to-side motion. (Whales' tails are horizontal and move up and down.)And while whales are known to live in social groups called pods, it is believed that whale sharks are largely solitary. They seem to gather only during certain peak feeding times and to mate. This isolation has slowed researching efforts.Until 1986, there were only 320 sighting reports in all of Western scientific literature, says Marie Levine, executive director of the Shark Research Institute (SRI). It was shortly thereafter that people discovered seasonal aggregations of whale sharks at Ningaloo Reef off western Australia. In the decade since then we have found similar seasonal groupings at other locations around the world, which has greatly helped expedite research efforts.More has come to light with recent research, but there are still few details known about the whale shark's existence.For example, no one has ever hazarded a guess at a total population. It is known that they inhabit the oceans worldwide, primarily in the tropics between 30 degrees north and south latitude. But there are loads of confirmed sightings outside that range, including at the oil rigs off the Texas coast and along the Gulf Coast of Florida. They've even been seen as far north as New Jersey.There are no specific details of their mating or birthing processes, except that they enter the water live from the mother after hatching from eggs within her - as many sharks are. There is a good estimate that they reach reproductive maturity at 20-30 years old.Using that number, researchers can project that whale sharks should live to 100-110 years old. (Biologists use a formula that says that sexual maturity occurs at about one-fifth of an animal's total life span.)Whale sharks are believed to be regional but not territorial. Todd Vickstrom, president of the Whale Shark Research Group and owner of the Soul Shine Resort in Belize, says that his team repeatedly identifies the same animals over periods of months. However, there is also a report confirmed by a satellite tag of a whale shark traveling from the Pacific coast of Mexico to Hawaii - about 3,000 miles - in just eight days. They are also known to travel continually. One tagged whale shark covered more than 14,000 miles during a 40-month period. Imprecise Means ImperiledThe lack of factual information about whale sharks is as massive as the animals themselves and is one of the key factors putting them at risk at the hands of their only true nemesis: human hunters. Without adequate information, it's nearly impossible to successfully lobby for legal protection.The human demand for whale shark products is rooted almost exclusively in the Far East. Demand really took off at the end of the 1980s with rising affluence across the region.The giant whale shark dorsal fin is being used for shark fin soup, which in some countries can cost more than $100 per serving.Whale shark meat is also growing in popularity at a staggering rate. Ironically, its popularity stems from the fact that it is almost totally tasteless. In Taiwan and other eastern countries, whale shark is called tofu shark because like real tofu, it tastes only like the seasonings that are added to it. This demand, along with large and rapid declines in the traditional shark fisheries, led fishermen - in places like India, Indonesia and Thailand - to seek out whale sharks. But figuring out the extent of the hunt and its impact on populations is again a problem because of the lack of definitive knowledge.In 2000, it was reported that 1,200 whale sharks were slaughtered during the six-week season in Gujarat, India, says Levine. But when I went to India in November 1999, I was told that the [reported] numbers referred to only a 12-mile section of the coast. I recently learned that some 6,000 animals were slaughtered there in 2000.Unfortunately, this kind of mis-reporting could be happening all over the world, which doesn't bode well for this slow-to-mature species. In fact, it's the same problem that put sea turtles, which also take about 25 years to mature, on the U.S. Endangered Species List.And as if the carnage isn't enough to merit protection, it's made more inconcevable given that Indian fishermen earn on average a measly 20 cents per pound for their catch. While the specifics are vague, the impact has become undeniable. David Rowat, director of Indian Ocean Explorer Cruises in the Seychelle Islands, says that in the mid-'90s, his scuba cruise patrons would see whale sharks by the dozens each week during peak season. In 1999 the number was down by about two-thirds.But providing the same protection sea turtles receive to whale sharks is currently impossible because there is no solid scientific baseline. With all of the unknowns, it is nearly impossible to legally stop the hunts. Despite this, there is some good legal news and the possibility of protection for this enigmatic species.