Whale Shark Facts

WHALE OF A TALE

Modern sharks began to appear between 100 million and 65 million years ago—their ancestry dating back to the Jurassic and Cretaceous periods. Yet there is no human record of the whale shark until 1828, when it was described and named by Andrew Smith, following the harpooning of a 15-foot-long specimen in Table Bay, South Africa. Since that time, stories of these massive creatures have found their place within history, as well as in fish lore.

In 1925, Hugh M. Smith published an article describing an enormous whale shark that had been caught off the coast of Thailand in 1919. Entangled in a bamboo fish trap, the massive shark was too heavy to drag ashore. Smith guessed that the shark must have weighed at least 37 tons and measured 56 feet in length, and there were even reports from 19th-century scientists such as E. Perceval Wright of sighting 69-feet-long whale sharks at sea. One piece of fish lore tells of the Maurguani, a vessel sailing the South Pacific in 1934, which rammed into a whale shark and splayed its 55-foot-long body across the prow of the ship. However, no reliable documentation exists of these claims. The largest whale shark ever recorded with certainty was near Baba Island, Pakistan, in 1947, weighing approximately 21.5 tons and reaching a length of 41.5 feet.

PHYSICAL CHARACTERISTICS

The distinctively marked whale shark is the world’s largest living fish and is the only surviving species in family Rhincodontidae. The average size of an adult whale shark is between 11 and 20 tons with a length of 20 to 40 feet. As with most shark species, female whale sharks are larger than males.

Its streamlined body and depressed, broad and flattened head distinguish it from other sharks. The mouth is transverse, extremely wide and toward the front of its blunt snout. It has five large pairs of gills that filter food and water. The whale shark’s two dorsal fins—a large dorsal followed by a small one—are set toward the back of the body, which ends with a caudal fin. This two-lobed tail is crescent-shaped in adults, while juveniles have a considerably longer upper fin.

The whale shark’s skin can be up to 4 inches thick, and it has a creamy white underbelly. Its coloration ranges from gray to brown with rows of white spots amid pale horizontal and vertical lines. These unique markings allow scientists to identify and track individual whale sharks in the wild. For the sharks, this pattern of lines and spots enables them to “blend” into their surroundings, making them less conspicuous in their oceanic environment. Also, these pigmented patterns may be connected to social behaviors, used for individual recognition and postural displays during courtship. Another possibility is that their coloration is an adaption to protect them from the sun’s ultraviolet radiation, since whale sharks frequently feed at the ocean surface.

The name “whale shark” is derived from the fish’s physiology—a shark as large as a whale that also shares similar filter feeder characteristics. As a filter feeder, the whale shark has a capacious mouth, which can measure up to 5 feet wide and contain 300 to 350 rows of tiny teeth, with a total of about 3,000 denticles or toothlike structures. However, the teeth appear to play no role in feeding and are, thus, of little use to the sharks.

DISTRIBUTION

Whale sharks have a wide distribution and are found in every warm-temperate and tropical sea except the Mediterranean. This species generally lives between latitudes 30°N and 35°S, in bodies of water with surface seawater temperatures between 69°F and 77°F. As a result, whale sharks occur throughout the Indian Ocean. They are found from California to Chile, off the coast of Hawaii and from Japan to Australia in the Pacific Ocean. In the Atlantic Ocean, they range from New York to Brazil and from Senegal to Gabon past the Gulf of Guinea.

Though primarily considered to be pelagic, whale sharks are found at several coastal feeding sites, including Australia’s Ningaloo Reef, Zanzibar and Pemba in Tanzania, Utila in Honduras and Donsol and Batangas provinces in the Philippines. Mexico seems to be one of the more reliable locations to find this species, and the Atlantic Mexican population is unique compared to other known populations because of its high concentration and variety in size of its members. Though mostly seen offshore, some whales travel closer to the coasts through coral reefs and lagoons, or close to the mouths of estuaries.

FEEDING HABITS

The whale shark is one of three plankton-eating shark species, along with the megamouth and the basking shark. This filter feeder ingests a diverse array of prey, including krill, copepods, schooling fish, fish eggs and periodically nektonic life such as small squids and mackerel. Whale sharks may also consume macro algae and phytoplankton.

Whale sharks feed in a vertical position, their head at or near the ocean’s surface. Their mouths open and jaws distended, they suck up seawater and prey, as they cast their head from side to side. Water is expelled from the gills, and plankton becomes caught in dermal denticles, which line the pharynx and gills. These toothlike, scaly serrations trap any prey more than 3 millimeters in length. Whale sharks have been observed coughing—a process that is thought to unlatch the plankton from these serrated structures in order to swallow.

Whale sharks have small eyes located toward the back of the head on either side. Due to these features, whale sharks are thought to have poor vision, relying on their sense of smell to detect prey. These creatures can sense the density of plankton with their nostrils, located above the upper jaw, and direct their heads accordingly while feeding at the surface.

BEHAVIOR

Whale sharks are the largest of the fish species, taking in oxygen through their gills. Although they are often observed swimming at the surface during seasonal aggregations, unlike air-breathing mammals such as whales and dolphins, whale sharks have no physiological requirements to do so. Evidence from tracking studies indicates they can dive to great depths of up to 2,300 feet and can remain away from the surface for long periods of time.

The whale shark is generally a solitary creature and is rarely found with other individuals unless hunting in areas with abundant prey. Unlike other sharks, which use their tail to propel themselves forward, whale sharks swim by moving their entire bodies from side to side. They are also slow swimmers, going no more than 3 miles per hour. Females have a smaller range than males.

MIGRATION

Whale sharks are migratory creatures, though their patterns are not fully understood. It appears that natural phenomena such as weather patterns and the geography of different regions can impact movements. Satellite tracking in U.S. waters and the South China Sea reveals that whale sharks can travel great distances of thousands of miles. However, these migrations may take years to complete, as again, whale sharks are slow swimmers. Short-term movements and behavior have also been successfully investigated using acoustic tracking.

REPRODUCTION

Little is known of whale shark reproduction. From a 1956 study of a single whale shark egg obtained off the coast of Mexico, it was thought to be oviparous, meaning that the female’s body expels egg cases from the uterus, which then hatch on the sea floor. However, in 1995, a 33-foot female was caught off the coast of Taiwan, and 300 pups were extracted from her two uteri. The pups, between 16 and 24 inches in length, proved that whale sharks are ovoviviparous, meaning that eggs hatch inside the mother’s body and live young are born. The smooth, amber-colored egg capsules found in the whale shark had respiratory openings on either side, and the ratio of male to female pups was 1:1.

Scientists believe that sexual maturity in both sexes may not occur until sharks reach over 25 feet in length and approximately 30 years of age. The location of whale shark breeding sites is unknown, and there are only a few scientific recordings of pregnant whale sharks. While it is not easy to distinguish males from females at first sight, males have claspers near the pelvic fin—organs that are absent in females.

IMPORTANCE TO HUMANS

Whale sharks are listed as a vulnerable species, and, until protections were enacted, hundreds were sold for their meat in India, the Philippines and Taiwan into the early 2000s. In 1997, a 10-ton whale shark would sell for about $70,000 in Taiwan. Today, meat continues to be sold by illegal fisheries, while demand for shark fins increases. Whale shark fins are known to have an ashy taste and are sought primarily for display in restaurants in China, Malaysia and Singapore. The liver oil has been used as a waterproof finish on wooden vessels, a shoe polish and as a treatment for skin conditions.

Another threat to whale sharks is when they become the product of bycatch, caught in fishers’ nets. They also risk being struck by vessels and boat propellers, especially when shipping lanes are placed close to their feeding sites. Pollution in whale shark hotspots, such as the 2010 BP oil spill in the Gulf of Mexico, is a further issue. More scientific studies are needed to better understand the population size, reproductive health and mortality of whale sharks so that we can recognize the protections this species requires.

THREAT TO HUMANS

Whale sharks are gentle giants, sometimes interacting with divers and posing no significant threat to humans. During public awareness initiatives, they are often used as an example to dissuade the perception of the “man-eating” shark. However, being a wild creature, they will inevitably react when physically confronted, and swimmers and vessels should avoid blocking their paths.

There have been a handful of instances where a whale shark has butted a fishing boat, possibly after being antagonized. But typically it is these sharks that become the victims, struck by ships while hunting or basking at the ocean’s surface.

WHALE SHARK CONSERVATION

Globally, whale sharks are listed as endangered on the IUCN Red List due to a decrease in numbers of more than 50 percent since the mid-20th century. This global population is split into two sub-populations: the Indo-Pacific and the Atlantic. An estimated 75 percent of the world’s whale sharks make the Indo-Pacific region their home, and the remaining 25 percent are found in the Atlantic. As you can imagine, it is difficult to get an accurate count of a shark that exists around the world and rarely comes to the surface, but the total population is estimated to be anywhere from 100,000 to 240,000.

The Atlantic subpopulation, which includes the whale sharks that feed near Isla Holbox, are faring better than the Indo-Pacific subpopulation and are listed as vulnerable. With aggregations of more than 1,000 whale sharks gathering during prime feeding times off the island, it can be hard to imagine that their numbers in the Atlantic have declined by more than 30 percent in the last 75 years.

The biggest threats to whale sharks today are commercial fishing with the sharks as the primary target, getting caught in nets intended for other fish species, and vessel strikes. Their large size, slow growth, late sexual maturation and extended longevity make it difficult for whale shark populations to recover from overexploitation. Because of this, regulations are now in place banning or limiting the number of whale sharks that can be caught by fishermen, and efforts are underway to educate ship captains about their migratory movements so that vessel strikes can be reduced.

The predictable occurrence of whale sharks in a few localities such as Isla Holbox has led to the development of an expanding tourism industry. In many of these areas, the whale shark is a protected species, and tourism is managed through a system of controls. The World Wildlife Fund and other organizations have developed sets of guidelines for tour operators and tour-boat captains to ensure whale sharks are not being negatively impacted by the presence of visitors.

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