As the largest fish in the sea, reaching lengths of 40 feet (12 meters) or more, whale sharks have an enormous menu from which to choose. Fortunately for most sea-dwellers—and us!—their favorite meal is plankton. They scoop these tiny plants and animals up, along with any small fish that happen to be around, with their colossal gaping mouths while swimming close to the water's surface.
Description
Whale sharks have a mouth that can be 1.5 m (4.9 ft) wide, containing 300 to 350 rows of tiny teeth and 10 filter pads which it uses to filter feed. Whale sharks have five large pairs of gills. The head is wide and flat with two small eyes at the front. Whale sharks are grey with a white belly. Their skin is marked with pale yellow spots and stripes which are unique to each individual. The whale shark has three prominent ridges along its sides. Its skin can be up to 10 cm (3.9 in) thick. The shark has a pair of dorsal fins and pectoral fins. Juveniles' tails have a larger upper fin than lower fin, while the adult tail becomes semilunate. 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 9.7 m (31.82 ft) and 9 t (20,000 lb). Several specimens over 18 m (59.05 ft) in length have been reported The largest verified specimen was caught on 11 November 1947, near Baba Island, in Karachi, Pakistan. It was 12.65 m (41.50 ft) long, weighed about 21.5 t (47,000 lb), and had a girth of 7 m (23.0 ft). Stories exist of vastly larger specimens – quoted lengths of 18 m (59 ft) and 45.5 t (100,000 lb) are common in the popular literature, but no scientific records support their existence. In 1868, the Irish natural scientist Edward Perceval Wright obtained several small whale shark specimens in the Seychelles, but claimed to have observed specimens in excess of 15 m (49.2 ft), and tells of shark specimens surpassing 21 m (68.9 ft).
In a 1925 publication, Hugh M. Smith described a huge animal caught in a bamboo fish trap in Thailand in 1919. The shark was too heavy to pull ashore, but Smith estimated the shark was at least 17 m (56 ft) long, and weighed around 37 t. These measurements have been exaggerated to 43 t (95,000 lb) and a more precise 17.98 m (59.0 ft) in recent years. A shark caught in 1994 off Tainan County, southern Taiwan, reportedly weighed 35.8 t (79,000 lb). There have even been unverified claims of whale sharks of up to 23 metres (75 ft) and 100 tonnes (220,000 lb). In 1934, a ship named the Maurguani came across a whale shark in the southern Pacific Ocean, rammed it, and the shark became stuck on the prow of the ship, supposedly with 4.6 m (15 ft) on one side and 12.2 m (40 ft) on the other. No reliable documentation exists for these claims and they remain "fish stories".
Diet and Feeding
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.
The whale shark, like the world's second largest fish, the basking shark, is a filter feeder. In order to eat, the beast juts out its formidably sized jaws and passively filters everything in its path. The mechanism is theorized to be a technique called “cross-flow filtration,” similar to some bony fish and baleen whales. The whale shark's flattened head sports a blunt snout above its mouth with short barbels protruding from its nostrils. Its back and sides are gray to brown with white spots among pale vertical and horizontal stripes, and its belly is white. Its two dorsal fins are set rearward on its body, which ends in a large dual-lobbed caudal fin (or tail).
Population
Preferring warm waters, whale sharks populate all tropical seas. They are known to migrate every spring to the continental shelf of the central west coast of Australia. The coral spawning of the area's Ningaloo Reef provides the whale shark with an abundant supply of plankton. Although massive, whale sharks are docile fish and sometimes allow swimmers to hitch a ride. They are currently listed as a vulnerable species; however, they continue to be hunted in parts of Asia, such as the Philippines.
Behavior Toward Divers
Despite its size, the whale shark does not pose significant danger to humans. Whale sharks are docile fish and sometimes allow swimmers to catch a ride, although this practice is discouraged by shark scientists and conservationists because of the disturbance to the sharks. Younger whale sharks are gentle and can play with divers. Underwater photographers such as Fiona Ayerst have photographed them swimming close to humans without any danger.
The shark is seen by divers in many places, including the Bay Islands in Honduras, Thailand, the Philippines, the Maldives close to Maamigili (South Ari Atoll), the Red Sea, Western Australia (Ningaloo Reef, Christmas Island), Taiwan, Panama (Coiba Island), Belize, Tofo Beach in Mozambique, Sodwana Bay (Greater St. Lucia Wetland Park) in South Africa, the Galapagos Islands, Saint Helena, Isla Mujeres (Caribbean Sea), La Paz, Baja California Sur and Bahía de los Ángeles in Mexico, the Seychelles, West Malaysia, islands off eastern peninsular Malaysia, India, Sri Lanka, Oman, Fujairah, Puerto Rico, and other parts of the Caribbean. Juveniles can be found near the shore in the Gulf of Tadjoura, near Djibouti, in the Horn of Africa.