|Whale Shark FAQ|
by Shark Research Institute
How much do we know about whale sharks?
The whale shark (Rhincodon typus) is still relatively mysterious. It wasn’t fully described in scientific literature until 1829 and, by 1986, there were only 320 recorded sightings of this animal.
Because it is simply hard to find in its natural habitat, and because it does not fare well in captive environments, we’re still learning about it. We do know that the whale shark is a member of the elasmobranch family, which includes carilagenous fish with multiple gill slits—in other words, like other sharks that we are more familiar with. They are not teleosts, which are bony fish with swim bladders.
How large is the whale shark?
The whale shark is by far the world’s largest fish-like vertebrate. However, it is hard for us to know exactly what its maximum size is. Old “eyewitness” records, as well as recent tagging studies and whale shark fishers’ reports, suggest a maximum length of 17 to 18 meters, or perhaps as many as 21.4 meters. Specimens longer than 12 meters are uncommon. Thirty whale sharks reported from South Africa ranged from 4 to 11 meters long. A length of 13.7 meters is often given as the maximum size measured, with 12.1 meters as the most recently accurately measured.
In 1925 a whale shark estimated to be 60 feet in length [18 meters] was caught in the Gulf of Thailand, but the largest accurately measured whale shark was a 40-foot, 7-inch [12.2 meter] male caught in Bombay, India, in 1983. Its mouth was 4.5 feet wide [1.14 meters], and its pectoral fins were more than 6.5 feet long [1.98 meters].
The size at birth of the whale shark is between 55 and 64 centimeters. Males are considered immature at 299 centimeters or less, and considered adolescent at 390 to 540 centimeters. Females ranging from 340 to 760 centimeters are immature. Records also show a pregnant female at around 10.6 meters long and weighing 16 tons. Another adult female was about 12 meters long.
Researchers are still working to determine an agreed-upon number. One researcher assumes a maximum length of 14 meters and a weight of approximately 20 tons, while recent field records suggest even higher maximum lengths. For example, researchers tracked 12 whale sharks by satellite. Size estimates generally ranged between 3.0 and 7.1 meters, but two big females tagged in 1996 and tracked for four months were 15.0 and 18.0 meters long.
What is the purpose of their distinctive coloring patterns?
Like many species of sharks that hunt near the sea’s surface, whale sharks are countershaded. They have white bellies (which makes them hard to see if a potential predator is underwater and looking up at them) and dark backs (which makes them difficult to see if the predator is looking down on them). It has been suggested that the pale spots and lines on their backs are camouflage. And, to some, the pattern resembles a school of fish, while to others it suggests reflections of sunlight on a shallow reef.
What are the Ampullae of Lorenzini and how do they work?
The Ampullae of Lorenzini is composed of a complex network of small pits concentrated near a whale shark's snout but running from its head to its tail. The pits are filled with a jelly rich in charged ions; these pits detect electrical fields and signals like those discharged by moving fish.
Try this experiment to see how these pits work. Blow steadily on the palm of your hand. Can you feel the air movement? Now, wave a finger between your lips and your hand, and feel the interruptions in the movement of the air. Just as you feel the breaks in air pressure, so the ampullae can detect changes in water pressure. The shark uses this sense of “distant touch” to determine the speed, size and form of an object moving through the water.
How can you tell male and female whale sharks apart?
A quick look at the pelvic fin area will differentiate males and females. Males have large extensions, called “claspers,” on both pelvic fins, while females do not. And, like other sharks, females tend to grow much larger than males of a similar age.
Elasobranch - Lemon Shark
Teleost - Mutton Snapper
Whale Shark Mouth
Whale Shark Spot Pattern
Female - No Claspers
Male Whale Shark with Claspers
Close-Up of Claspers
What are the whale sharks feeding habits?
Whale sharks are planktivores, meaning that the feed primarily on plankton, which are microscopic creatures found in huge quantities throughout the oceans. They will also eat sardines, anchovies, mackerel and the occasional small tuna.
When a whale shark is feeding, it pumps large volumes of water over its gills and out its gill slits. The shark’s gills have very fine gill rakers which function as sieves and strain plankton from the water. This is known as “filter feeding.”
Even though the whale shark is a planktivore, it still has a mouthful of teeth—some 3000 teeth in 300 rows, as a matter of fact. That’s why the whale shark is known as Rhincodon, which means “rasp-tooth.” However, these teeth are very small (less than 1/12 of an inch), so they essentially serve no purpose.
How long do whale sharks live?
Scientists don’t know for certain how long whale sharks live. We do know that some species of sharks that live for 100 years are not able to breed until they are 20 years old. This means they must spend 1/5th (20%) of their lives evading capture until they can reproduce at all. It appears that male whale sharks are not able to breed until they are about 30 years old. If 30 years is 1/5th of a whale shark’s expected lifespan, it may then live for well over a century, possibly even 150 years or longer.
What about whale shark reproduction?
In 1953, a shark egg case containing a 14.5 inch [36.8 centimeter] whale shark embryo was found in a trawl net in the Gulf of Mexico. The find created a controversy that lasted 42 years; some scientists speculated that whale sharks are oviparous (egg laying), while others believed they were live-bearers and the egg resulted from a premature birth.
In 1995, the controversy ended when a team of scientists from National Taiwan Ocean University examined a 35-foot [10.6 meter] pregnant whale shark that had been harpooned by a Taiwanese fisherman. Her twin uteruses contained 300 embryos ranging in length from 16 to 25 inches [40 to 63 centimeters]. This was proof that whale shark embryos emerge from egg cases while still inside the mother’s body, and that whale sharks are therefore live-bearers. Of the 300 embryos, 15 were fully-developed and ready to be born.
Newborn whale sharks measuring 21 to 25 inches in length [55 to 63 centimeters] have been caught in the Pacific Ocean off the coast of Central America. In January 1996, there was an unconfirmed report that newborn whale sharks were found in the Marshall Islands. Newborn whale sharks have also been caught in the Gulf of Guinea, the Atlantic Ocean, and the Persian Gulf.
Nobody knows how frequently whale sharks reproduce, and the gestation period for the animal is also unknown. In fact, no one has ever witnessed a mating or birthing event.
Whale Shark Feeding
Whale Shark - Possibly Pregnant
: Range and Migration
Where is the whale shark found?
The whale shark can be found world-wide in tropical and temperate climates and in both coastal and non-coastal waters. They have been observed in many parts of the Indian Ocean, most notably at Ningaloo Reef, Western Australia, where there is now a large ecotourism industry devloped around them. Whale sharks have also been reported from India to the Maldives and the Seychelles, and along most of the coastline of eastern Africa.
Are whale sharks migratory?
Whale sharks are very migratory. Research projects have shown that some whale sharks have covered as much as 3700 kilometers in their travels. Much of this travel is likely due to following plankton blooms. Whale sharks have been seen to reach speeds of about two knots. They may occasionally gather in a group at particular locations, and will sometimes segregate themselves into smaller groups based on physical size.
Whale Shark Range
: Threats and Protection
What are the threats to whale sharks?
Young whale sharks have many predators, especially larger sharks. As they mature, their only natural predators are killer whales and white sharks.
On the other hand, human impacts on whale sharks are significant. While they are not actively fished by any Western nation, whale shark fins are highly valued in some places. Unfortunately, in much of the developing world, including Indonesia, whale sharks are slaughtered and their fins and flesh exported to Taiwan, Singapore and Korea.
How are whale sharks protected?
In Australia, Honduras, India, the Maldive Islands, the Philippines—and along the eastern coast of the United States—whale sharks are protected. All trade in whale shark products (fins, flesh and skin) is prohibited. South Africa is considering similar legislation.
On November 15, 2002, the whale shark and the basking shark were placed on Appendix II of the Convention on International Trade in Endangered Species (CITES), a United Nations Treaty Organization. The Appendix II listing requires the 160 member nations of CITES to monitor international trade in whale shark products and to ensure that trade does not threaten survival of the species.
The whale shark is also listed on Appendix II of the Convention on Migratory Species (also known as “CMS” or “The Bonn Convention”).