Whale Shark (Rhincodon typus)

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The whale shark is the biggest shark and the biggest fish. It is NOT a whale. It has a huge mouth which can be up to 4 feet wide. Despite its huge size, they do not pose any significant danger to humans.

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[edit] Taxonomy

This distinctively-marked shark is the only member of its genus Rhincodon and its family, Rhincodontidae (called Rhinodontes before 1984), which is grouped into the subclass Elasmobranchii in the class Chondrichthyes.

Kingdom Animalia Phylum Chordata SubPhylum Vertebrata Class Chondrichthyes Subclass Elasmobranchii Order Orectolobiformes Family Rhincodontidae Genus Rhincodon Species Rhincodon typus (Smith, 1828)

[edit] Distribution

Whale sharks are found worldwide in the warm oceans from the equator to about ±30-40° latitude. They are not, however, found in the Mediterranean Sea. The whale shark inhabits the world's tropical and warm-temperate oceans. While thought to be primarily pelagic, seasonal feeding aggregations of the sharks occur at several coastal sites. It is found to a depth of 2,500 ft.

[edit] Physical Characteristics

They have a huge mouth which can be up to 1.4 m wide. Its mouth is at the very front of its head not on the underside of the head like in most sharks. It has a wide, flat head, a rounded snout, small eyes, 5 very large gill slits, 2 dorsal fins (on its back) and 2 pectoral fins on its sides. The spiracle, a vestigial first gill slit used for breathing when the shark is resting on the sea floor is located just behind the shark's eye. Its tail has a top fin much larger than the lower fin. The whale shark has distinctive light-yellow markings as a random stripes and dots on its very thick dark gray skin. Its skin is up to 4 inches thick. There are three prominent ridges running along each side of the shark's body.

[edit] Habitat

Whale sharks live in warm water near the equator both along the coast and in the open seas. They spend most of their time near the surface. Whale sharks are slow swimmers, going no more than 5 kph. They swim by moving their entire bodies from side to side not just their tails, like some other sharks do. Whale sharks are harmless to people and usually indifferent to divers. Whale sharks are solitary creatures. Groups of whale sharks have only rarely been seen.

[edit] Diet

The whale shark is a filter feeder that sieves small animals from the water. As it swims with its mouth open, it sucks masses of water filled with prey into its mouth and through spongy tissue between its 5 large gill arches. After closing its mouth, the shark uses gills rakers that filter the nourishment from the water. Anything that doesn't pass through the gills is eaten. Gill rakers are bristly structures (the thousands of bristles are about 4 inches or 10 cm long) in the shark's mouth that trap the small organisms which the shark then swallows. The water is expelled through the sharks 5 pairs of gill slits. The prey includes plankton, krill, small fish, and squid. The shark can process over 1500 gallons (6000 liters) of water each hour.

[edit] Behavior

Whale sharks are harmless to humans but are very curious when humans are in the water with them. During the night, the sharks generally remain in shallow water, feeding off plankton, and reserving deep dives for the heat of the day. Deep dives often end with a high-speed ascent, perhaps to deliver a burst of oxygen to their bodies after a period in deeper, less oxygenated water. Despite its huge size, it eats plankton rather than people, and its slow movements make it easy to catch by harpoon or net.

[edit] Breeding

Whale sharks are sexually mature at 30 years old. This is the age at which they are able to mate and reproduce. The Whale shark was long thought to be oviparous (an egg 14 inches (36 cm) long was found in the Gulf of Mexico in 1953; this would be the largest egg in the world. Recently, pregnant females have been found containing hundreds of pups, so, Whale sharks are vivparous, giving birth to live young. Newborns are over 2 feet (60 cm) long.

[edit] Threat

The Whale Shark is a protected species and is on the endangered list. Allegedly Whale Sharks are still hunted for their dorsal fins in the Far East but due to International awareness, this will hopefully be stopped or at least minimized as much as possible with effective policing. Although whale sharks are protected in some parts of the world, fishing still occurs. A majority of these sharks are caught before they reach maturity at over 20 years of age. Because of over fishing and their demand as a delicacy in countries like China, Taiwan and much of Southeast Asia, they are considered to be a vulnerable species. Unfortunately, their fins also have a very high value in Asian markets. Trade in whale sharks in now regulated by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

[edit] References

  • Rhincodon typus. 2006 IUCN Red List of Threatened Species. IUCN 2006
  • Rhincodon typus. FishBase
  • Species Fact Sheet, Rhincodon typus. Food and Agriculture Organization of the United Nations.
  • FAO catalogue, Sharks of the World

[edit] See Also