By Daniel Stolte
Somewhere in the Gulf of California, a dive boat slowly glides across the glassy sea. Tired from a morning of diving at a nearby island, some divers are napping on the deck, while others sit quietly in the galley, logging their dives or downloading pictures onto their laptops. Suddenly, excited shouting from the divemaster breaks the silence: “Whale shark!” – “whale shark!”
Startled, the divers congregate by the boat’s railing, squinting into the sun. The captain thrusts the engines in reverse and swiftly spins the wheel to swing the boat around. The divemaster points to a dark spot in the water, perhaps 30 feet from the boat’s starboard gunwale. A dark, diffuse shadow looms just a few feet below the surface. As the captain slowly brings the boat closer, a gaping mouth, four feet wide, breaks the surface, white flesh exposed, sucking in big gulps of seawater. Now merely inches below the surfaces, the mouth opens and closes in slow sequence, almost like a giant carp slurping duck weed from a pond’s surface. The image of an old man comes to mind, who forgot to put in his dentures.
This whale shark, basking on the surface, is at least 25 feet long. Through the clear water, the people on the boat can now see the outline of its massive body, resembling a submerged bus more than a living creature. The rays of the afternoon sun dance across the animal’s back and highlight its checkerboard pattern of bright spots.
The divers chatter excitedly while they hurry to zip up their wetsuits, strap on their masks and snorkels and slip into their fins. Within minutes of the discovery, people are back-rolling over the sides of the boat, splashing in and finning in the direction of the giant that hovers just below the surface, motionless except for the rhythmic opening and closing of its gaping mouth. An encounter with a whale shark is an experience no scuba diver will ever forget.
Mysterious giants
Named for their size and docile nature, which is more reminiscent of whales than their shark kin, whale sharks (scientific name Rhincodon typus) are not only the largest sharks, but also the largest fish in the world. Reaching lengths of up to 65 feet, they rival sperm whales in size. To put this size in perspective, picture this creature in the water, in its typical vertical feeding position with the head just below the surface, scooping in big gulps of plankton, and the massive body fading below into the blue, shimmering depths. Technically speaking, a curious new diver who wanted to take a look at the animal’s tail would have to obtain advanced open water certification first!
Despite their unique and impressive appearance, we still know very little about these gentle giants of the seas. Even though a large whale shark’s mouth is wide enough to swallow a diver whole, these fish are in fact filter feeders, unlike most of their kin, which includes some of the world’s most feared predators. Similar to buffalo roaming the Great Plains, whale sharks cruise the high seas like grazers. They eat plankton (microscopically small algae and animals), fish eggs and other minute marine creatures. When feeding, the whale shark typically assumes a near vertical position in the water and opens and closes its wide mouth, sucking in copious amounts of water in a rhythmic pumping motion. Specialized gill rakes trap any particle larger than a tenth of an inch or so before the animal expels the water through its enormous gill slits. In the course of a day a whale shark can process 1,500 gallons of sea water this way. Even though several thousand teeth line a whale shark’s jaws, they are tiny and serve no obvious function.
The life history of this relatively scarce but cosmopolitan species is poorly understood, but we do know that whale sharks migrate over vast distances. They inhabit a girdle of warm and temperate ocean that surrounds the globe and spans the equator between 30 degrees northern and 30 degrees southern latitude.
Surprisingly, the whale shark’s closest relative is the nurse shark (Ginglymostoma cirratum), a similarly docile, but much smaller shark that is a frequent and popular sight on shallow reef dives. In some cultures, especially of some ocean-going peoples, whale sharks occupy a mythical place in the local belief system. In Vietnam for example, the whale shark is known as “Ca Ong” or “Sir Fish,” and the fishermen erect shrines in the sand dunes along the coast in its honor. Despite their unique status, whale sharks are being hunted in many parts of the world, mainly for their fins. A single fin from a whale shark can fetch tens of thousands of dollars on the Chinese market. To satisfy the demand for shark fin soup, a highly prized delicacy in Asia, fishermen cut off a shark’s fins and throw the crippled animal overboard to die a slow and agonizing death. Each year, tens of millions of sharks are being killed and removed from their vital roles as top predators in marine ecosystems because of the cruel practice of shark finning.
So little is known about whale sharks that only fifteen years ago, nobody knew how whale sharks reproduce! Until then, it was thought that whale sharks lay eggs like most other fish, including the majority of sharks. This assumption was based on isolated finds of egg cases whose large size (over a foot in length) and the tell-tale dotted color pattern of the embryo inside gave them away as whale shark eggs. But in 1995, Taiwanese fishermen harpooned a 36-foot long female whale shark. Inside its two uteri, 300 fetuses were found, ranging from 1.5 to 2 feet in size. The discovery settled a long-standing debate: Whale sharks are ovoviviparous, meaning that the young develop inside an egg shell, but hatch in the mother and enter their watery world ready to swim and fend for themselves.
Space telescope software aids whale shark conservation
Nobody knows for sure how long whale sharks live. Some have estimated their life span to be 100 years or even longer. It is believed that by the time these animals can reproduce for the very first time, they are already at least 30 years old! Their slow maturation time renders them vulnerable to overfishing, as it takes a long time to replace individuals that have been taken. Add to that their large size and docile behavior, which makes them easy targets, and one can see why the International Union for Conservation of Nature (IUCN) has listed the whale shark as ‘vulnerable.’ There is indication that populations have been depleted by harpoon fisheries in several countries targeting localized concentrations of this huge, slow-moving and behaviorally-vulnerable species. Only very recently have several countries begun to take better care of their whale shark populations.
Similarly nebulous are estimates trying to pinpoint the worldwide population of whale sharks. In short, nobody really knows. To gain a better idea of whale shark numbers and behavior, Australian scientists conducted a study that involved large numbers of researchers and volunteer divers who photographed whale sharks over the course of 12 years in Ningaloo Bay on the northwest coast of Australia, one of the world’s most formidable gathering places for whale sharks. Using pattern-recognition software originally developed to keep track of stars and galaxies in images taken with the Hubble Space Telescope, the researchers were able to recognize individual animals based on their spot and stripe patterns, which are as unique as fingerprints. They found that, at least in Ningaloo Bay, whale shark numbers increased over time, a trend attributed to efforts in protecting the whale sharks in that area.
In recent years dive tourism has discovered the appeal of whale sharks in a number of locations around the world. More and more governments and agencies have started to realize that sharks are worth their weight in gold when they are left alive rather than killed for the market. As an attraction highly sought after by diving tourists from around the world, a single whale shark can bring in hundreds of thousands of tourism dollars. Accordingly, steps are being taken to protect these magnificent creatures.
Best whale shark diving spots
Any diver who is lucky enough to come face-to-face with a whale shark will likely never forget this breath-taking experience. Contrary to what you may see in some underwater movies or photographs, especially older ones, it is no longer cool to touch a whale shark, leave alone hitch a ride, tempting as it may seem. Even though the creatures don’t mind the contact in most cases, touching the animal damages the mucus layer covering the skin and renders it vulnerable to infections. When diving or swimming with a whale shark, we should remember that we are incredibly lucky to even come this close to a wild creature of such an enormous size – and take it in with our eyes and cameras only.
For scuba divers who want to observe whale sharks, the best places to visit are those where the otherwise pelagic animals congregate at certain times during the year. Popular destinations for whale shark diving and –watching include Gladden Spit in Belize; Ningaloo Reef in Western Australia; Útila in Honduras; Donsol, Pasacao and Batangas in the Philippines; off Isla Mujeres and Isla Holbox in Yucatan Mexico; Ujung Kulon National Park in Indonesia; Nosy Be in Madagascar and the Tanzanian islands of Mafia, Pemba and Zanzibar.
Want to see what it’s like to swim with a whale shark? Watch a video on the Florida Museum of Natural History website: http://www.flmnh.ufl.edu/fish/gallery/Descript/Whaleshark/whaleshark.html
