International Whale Shark Day takes place annually on 30 August On the anniversary of Whale Sharks being added to International Union for Conservation of Nature (IUCN) Red List of Threatened Species.
The whale shark (Rhincodon typus) is a slow-moving, filter-feeding carpet shark and the largest known extant fish species. The largest confirmed individual had a length of 18.8 m (62 ft) The whale shark holds many records for size in the animal kingdom, most notably being by far the largest living nonmammalian vertebrate. It is the sole member of the genus Rhincodon and the only extant member of the family Rhincodontidae, which belongs to the subclass Elasmobranchii in the class Chondrichthyes. Before 1984 it was classified as Rhiniodon into Rhinodontidae.
The whale shark is found in open waters of the tropical oceans and is rarely found in water below 21 °C (70 °F). Modeling suggests a lifespan of about 70 years, and while measurements have proven difficult, estimates from field data suggest they may live as long as 130 years. Whale sharks have very large mouths and are filter feeders, which is a feeding mode that occurs in only two other sharks, the megamouth shark and the basking shark. They feed almost exclusively on plankton and small fishes, and pose no threat to humans.
The species was distinguished in April 1828 after the harpooning of a 4.6 m (15 ft) specimen in Table Bay, South Africa. Andrew Smith, a military doctor associated with British troops stationed in Cape Town, described it the following year. The name “whale shark” refers to the fish’s size, being as large as some species of whales, and also to its being a filter feeder like baleen whales. Whale sharks have a mouth that can be 1.5 m (4.9 ft) wide, containing 300 to 350 rows of tiny teeth and 20 filter pads which it uses to filter feed. Unlike many other sharks, whale sharks’ mouths are located at the front of the head rather than on the underside of the head. Whale sharks have five large pairs of gills. The head is wide and flat with two small eyes at the front corners. Whale sharks are dark grey with a white belly. Their skin is marked with pale grey or white spots and stripes which are unique to each individual. The whale shark has three prominent ridges along its sides, which start above and behind the head and end at the caudal peduncle. Its skin can be up to 15 cm thick and is very hard and rough to the touch. The shark has two dorsal fins set relatively far back on the body, a pair of pectoral fins, a pair of pelvic fins and a single medial anal fin. The tail has a larger upper lobe than the lower lobe (heterocercal). The whale shark’s spiracles are just behind its eyes. The whale shark is the largest non-cetacean animal in the world. The average size of adult whale sharks is estimated at 9.8 m (32 ft) and 9 t (20,000 lb). The largest total length the species can reach is uncertain due to a lack of information on how measurements were taken in many of the reported individuals. Several specimens over 18 m (59 ft) in length have been reported.
The whale shark inhabits all tropical and warm-temperate seas. The fish is primarily pelagic, living in the open sea but not in the greater depths of the ocean, although it is known to occasionally dive to depths of as much as 1,800 metres (5,900 ft). Seasonal feeding aggregations occur at several coastal sites such as the southern and eastern parts of South Africa; Saint Helena Island in the South Atlantic Ocean; Gulf of Tadjoura in Djibouti, Gladden Spit in Belize; Ningaloo Reef in Western Australia; Kerala, Lakshadweep, Gulf of Kutch and Saurashtra coast of Gujarat in India; Útila in Honduras; Southern Leyte; Donsol, Pasacao and Batangas in the Philippines; off Isla Mujeres and Isla Holbox in Yucatan and Bahía de los Ángeles in Baja California, México; Maamigili island, Maldives; Ujung Kulon National Park in Indonesia; Cenderawasih Bay National Park in Nabire, Papua, Indonesia; Flores Island, Indonesia; Nosy Be in Madagascar; off Tofo Beach near Inhambane in Mozambique; the Tanzanian islands of Mafia, Pemba, Zanzibar; Gulf of Tadjoura in Djibouti, the Ad Dimaniyat Islands in the Gulf of Oman and Al Hallaniyat islands in the Arabian Sea; and, very rarely, Eilat, Israel and Aqaba, Jordan. Although typically seen offshore, it has been found closer to land, entering lagoons or coral atolls, and near the mouths of estuaries and rivers. Its range is generally restricted to about 30° latitude or lower. It is capable of diving to depths of at least 1,286 m (4,219 ft), and is migratory. On 7 February 2012, a large whale shark was found floating 150 kilometres (93 mi) off the coast of Karachi, Pakistan. The length of the specimen was said to be between 11 and 12 m (36 and 39 ft), with a weight of around 15,000 kg (33,000 lb).
The whale shark is a filter feeder – one of only three known filter-feeding shark species (along with the basking shark and the megamouth shark). It feeds on plankton including copepods, krill, fish eggs, Christmas Island red crab larvae and small nektonic life, such as small squid or fish. It also feeds on clouds of eggs during mass spawning of fish and corals. Whale sharks are known to prey on a range of planktonic and small nektonic organisms that are spatiotemporally patchy. These include krill, crab larvae, jellyfish, sardines, anchovies, mackerels, small tunas, and squid. The many rows of vestigial teeth play no role in feeding. Feeding occurs either by ram filtration, in which the animal opens its mouth and swims forward, pushing water and food into the mouth, or by active suction feeding, in which the animal opens and closes its mouth, sucking in volumes of water that are then expelled through the gills.
There is currently no robust estimate of the global whale shark population. The species is considered endangered by the IUCN due to the impacts of fisheries, by-catch losses, and vessel strikes, combined with its long lifespan and late maturation In June 2018 the New Zealand Department of Conservation classified the whale shark as “Migrant” with the qualifier “Secure Overseas” under the New Zealand Threat Classification System. It is listed, along with six other species of sharks, under the CMS Memorandum of Understanding on the Conservation of Migratory Sharks in 1998, the Philippines banned all fishing, selling, importing, and exporting of whale sharks for commercial purposes,followed by India in May 2001, and Taiwan in May 2007.
In 2010, the Gulf of Mexico oil spill resulted in 4,900,000 barrels (780,000 m3) of oil flowing into an area south of the Mississippi River Delta, where one-third of all whale shark sightings in the northern part of the gulf have occurred in recent years. Sightings confirmed that the whale sharks were unable to avoid the oil slick, which was situated on the surface of the sea where the whale sharks feed for several hours at a time. No dead whale sharks were found. This species was also added to Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in 2003 to regulate the international trade of live specimens and its parts. Hundreds of whale sharks are illegally killed every year in China for their fins, skins, and oil.