WHALE SHARKS

I first met Oscar, a young, four meter long whale shark at Hin Muang, a sea mount near Hin Daeng, just North of the Malay border. It is a beautiful, loaf-shaped reef covered with purple soft coral and green anemones sitting in forty meters of crystalline, blue water. I was loafing along at ten meters when schools of fish began dashing into the reef for shelter from a predator I couldn't see. I hung there, looking outward. Oscar swam leisurely into view, near the top of the reef. I had learned that the best way to enjoy time with these gentle giants is to hang quietly in the water. Oscar became curious; I let him explore me without touching him or swimming after him. Aggressive behavior may drive whale sharks away. He swam over to me, stopped, and looked me over with one big, brown eye. He casually swam along the reef, circling counterclockwise, until he was opposite me. I waved him, "Goodbye," but he surprised me by turning and swimming over to me again. After a while, he swam off.

I was astonished by this behavior-it was much more mammalian than fishy. Later, I was told that this is pretty typical. Frequently, whale sharks seem completely unafraid of divers, most unusual behavior for a fish, although not unusual for cetaceans such as dolphins.

Since this encounter, like many other divers, I have developed a passion for whale sharks. They are remarkable animals; we know little about them, but data are beginning to accumulate. The first reference to Rhincodon typus that I read was in Kon Tiki, by Thor Heyerdahl, written in the late 1940's when a giant whale shark crossed beneath the raft. By 1986, there had been only 320 reported sightings, world wide.

Whale sharks are the largest of the living fishes. One was caught in the Gulf of Thailand in 1925 estimated to be 18meters long. The largest one that has been accurately measured was caught off India in l983 and measured 12.2meters. When they are born they are 55 to 60 cm long. How long does it take to mature, and get so big?

These gentle giants eat tiny plankton, shrimp and small fish by straining enormous quantities through large gill rakers. They can open their mouths to form a perfect "O", the most efficient shape for taking in huge amounts of water. They appear almost toothless; they actually have thousands of rasp-like teeth that are imbedded in over 300 rows in their massive jaws. (The name of the genus, Rhincodon, means "rasp tooth".) In Thailand's seas, they appear to hang horizontally in the current for feeding. In other areas, including Belize, they have been observed hanging vertically, their heads above water, then sinking so that great quantities of water pour into their mouths, small and large animals included. Sometimes one may evert its stomach through its mouth, probably to get rid of something indigestible, such as a turtle shell.

Whale sharks have substantial economic value. They are a major value to Thailand as a tourist attraction. Many divers come here specifically to see them. Some dive operators mount liveaboard trips specifically to view them. Some even offer refunds if none are seen.

Whale Sharks, the largest fish in the sea, are among the most exciting animals to be seen in the waters off Thailand. It is astonishing that anything can grow that big eating plankton, krill and small fish. Only two other sharks are known to be filter feeders, the Basking Shark, Cetorhinus maximus, which grows to 9 meters, and the Megamouth Shark, Megachasma pelagios, only captured since 1976, which gets up to 5 meters. How long does it take a 55cm baby to reach 10 or 12 meters in length and tens of metric tons in weight? We still don't know how old a whale shark must be to breed, but it is currently thought that they wait until they are 20-30 years old, a typical age for other large, long-lived sharks. It is a considered possibility that whale sharks live to be 100 years old, or more.

Until two years ago, reproduction was the subject of debate. A nearly full term embryo had been recovered in Mexico in 1953, but it was unknown whether the fish deposited eggs in which the embryos developed (oviparous), or whether the eggs were retained within the female until they hatched, with the young born fully developed (ovoviviparous). In 1995, a Taiwanese fisherman speared a 10.5meter female which was found to contain 300 embryos, establishing it as ovoviviparous.

Whale sharks are found around the world in tropical and warm temperate oceans although they are notably absent from the Mediterranean. Until 1986 only 320 sightings had been recorded in scientific literature. We now see whale sharks every year in the Andaman Sea off Thailand. They appear to migrate North from the Malay border during December, January and February and to reach our northern border with Myanmar during February and March. They have been seen at Koh Phi Phi, Anemone Reef, and one spent a week in the harbor at Patong Beach, undeterred by the snorkelers who paddled out to swim with it. I saw six, consisting of two groups of three,during two consecutive dives at Richelieu Rock, a couple seasons ago. Each had particular scars or markings that distinguished it. They are observed in the Seychelles in August and November, Mozambique and the northern coast of South Africa from October to March, the West coast of Mexico from March to August, Belize in May and Queensland, Australia, in November and early December. This increase in sightings is probably due to more observers; could it be that there are more whale sharks? Whale sharks are being killed, either for food or accidentally, at a rate that scientists believe is faster than their reproduction rate, and may represent as much as a 2% annual decline.

This year there is concern over the effects that El Nino may have on Whale Sharks. El Nino results when the Trade winds, which normally blow strongly from East to West across the Pacific, slow down. The result is that the warmer waters of the Western Pacific which are normally kept at bay by the trades, sweep East, piling up against the West coast of South America, even raising tidal and ocean levels noticeably. This surge smothers the usual upwelling of cold water from the depths. This chilly upwelling contains enormous quantities of nutrients, primarily plankton and larval stages of many animals. Whether this blockage results in the death of the plankton and other tiny animals such as krill, or whether they emerge somewhere else is unknown. Krill, one of the most common and nourishing foods in the sea, mainly composed of tiny shrimp also appears to be declining, according to measurements being taken near Antarctica. In either event, the question is whether nutrients are there in the quantities needed to feed these huge fish. Whether El Nino will cause their more rapid decline is unknown.

Of more immediate concern is whether the changes in water temperature and nutrient content in the Andaman Sea will affect the migratory routes and patterns followed by Whale Sharks. Will they show up for the high tourist season here or will they be late, or skip Thailand altogether? Happily, there have been several sightings already. In November there were sightings at Hin Muang in the far South and Anemone Reef closer to Phuket. In December there were more sightings at Hin Muang and one at Koh Thachai. Two of the sightings claimed the sharks were six meters long. An auspicious beginning, and a hopeful sign, but this is only prologue, not the end of this chapter.

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