Butanding

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Whale shark
Whalesharkwithfish.jpg
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Order: Orectolobiformes
Family: Rhincodontidae
(Müller and Henle, 1839)
Genus: Rhincodon
Smith, 1829
Species: R. typus
Binomial name
Rhincodon typus
(Smith, 1828)


Butanding, or whale shark (Rhincodon typus), is a slow-moving filter-feeding animal that is considered as the largest fish in the sea, measuring 40 feet or more. This distinctively yellow-marked shark is the only member of its genus Rhincodon and its family, Rhincodontidae, which is grouped into the subclass Elasmobranchii in the class Chondrichthyes.

Believed to have originated about 60 million years ago, butanding can be found in the waters of Donsol, Sorsogon between the month of January and May.

Contents

Naming

The species was first identified in April 1828 following the harpooning of a 4.6 metres (15 ft) specimen in Table Bay, South Africa. It was described the following year by Andrew Smith, a military doctor associated with British troops stationed in Cape Town. He proceeded to publish a more detailed description of the species in 1849.

The name whale shark comes from the fish's physiology—that is, a shark as large as a whale that shares a similar filter feeder eating mode.

Different regions call the whale shark in different names:

  • Vietnam: Ca Ong (literally means "Sir Fish", believed to be a deity in the region)
  • Mexico and throughout Latin America: Pez dama, or domino (because for its patterns of spots)
  • Belize: Sapodilla Tom (due to the regularity of sightings near the Sapodilla Caves on the Belize Barrier Reef.)
  • Africa: Papa Shillingi in Kenya (the people believed that God threw shillings upon the shark which are now its spots), Marokinata in Madagascar (literally means "Many stars").
  • Indonesia (Java): geger lintang, meaning, "stars in the back"

Distribution and habitat

The whale sharks prefer to live in tropical and warm-temperate oceans, and thought to inhabit almost close to the bottom of the sea (the open sea). These sharks are often found passing by and feeding at several coastal sites such as Ningaloo Reef in Western Australia; Útila in Honduras; Donsol and Batangas in the Philippines; and Pemba and Zanzibar off the coast of Tanzania.

Often seen offshore, these creatures have also been found closer to shore, entering lagoons or coral atolls, and near the mouths of estuaries and rivers. Its range is restricted to about ±30 ° latitude, and found to a depth of 700 m.

The whale shark, however, is solitary and rarely seen in groups unless feeding at locations with an abundance of food.

Anatomy and appearance

A size comparison of a whale shark and a human.

As a filter feeder, the whale sharks have a capacious mouth of up to 4 to 5 feet wide and can contain almost 3,000 tiny teeth.

It has five large pairs of gills. The whale shark's flattened head sports a rounded blunt snout above its mouth with short barbels protruding from its nostrils, while its back and sides are gray to brown with white spots among pale vertical and horizontal stripes, and its belly is white. The mouth is found at the very front of its head (not on the underside of the head like in most sharks), and 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.

A juvenile whale shark's tail has a larger upper fin than lower fin, while the adult tail becomes semi-lunate (or crescent-shaped). Three prominent ridges run along each side of the animal and the skin is marked with a “checkerboard” of pale yellow spots and stripes, and each set of spots is unique to each whale shark—they can be used to identify each animal and hence make an accurate population count. Its skin can be up to 10 centimetres (about 4 in) thick. The shark, moreover, has two pairs each of dorsal fins and pectoral fins, and females are larger than males.

The whale sharks use their entire bodies for swimming, moving it from side to side, making them slow swimmers (which is unusual for sharks), having an average speed of only around 5 km/h.

Stories exist of vastly larger specimens - Quoted lengths of 18 m (59 ft) are not uncommon in the popular shark literature - but no scientific records exist to support their existence. The largest specimen regarded as accurately recorded was caught on November 11, 1947, near the island of Baba, not far from Karachi, Pakistan. It was 12.65 m (41.5 ft) long, weighed more than 21.5 tonnes (47,300 lb), and had a girth of 7 m (23 ft). In 1868 the Irish natural scientist E. Perceval Wright spent time in the Seychelles, during which he managed to obtain several small whale shark specimens, but claimed to have observed specimens in excess of 15 m (49 ft), and tells of reports of specimens surpassing 21 m (69 ft).

In a 1925 publication, Hugh M. Smith describes a huge whale shark caught in a bamboo fish trap in Thailand in 1919. The shark was too heavy to pull ashore, but Smith estimated that the shark was at least 17 m (55.7 ft) and weighed approximately 37 tonnes (81,500 lb), which have been exaggerated to an accurate measurement of 17.98 m and weight 43 tonnes in recent years.

There even had claims of whale sharks measuring up to 23 m (75 ft). In 1934 a ship named the "Maurguani" came across a whale shark in the Southern Pacific ocean, rammed it, and the shark consequently 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 of those claims and they remain little more than "fish-stories".

Diet

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 phytoplankton, macro-algae, plankton, krill and small nektonic life, such as small squid or vertebrates. The many rows of teeth play no role in feeding; in fact, they are reduced in size in the whale shark.

In order to feed, it juts out its formidably sized jaws and sucks in everything in the vicinity. It then shuts its mouth, forcing water to filter out of its gills. Everything that remains becomes the giant shark's dinner. During the slight delay between closing the mouth and opening the gill flaps, plankton is trapped against the dermal denticles which line its gill plates and pharynx. This fine sieve-like apparatus, which is a unique modification of the gill rakers, prevents the passage of anything but fluid out through the gills (anything above 2 to 3 mm in diameter is trapped). Any material caught in the filter between the gill bars is swallowed. Whale sharks have been observed "coughing" and it is presumed that this is a method of clearing a build up of food particles in the gill rakers. The shark can process over 1,500 gallons (6,000 liters) of water each hour.

Whale sharks congregate at reefs off the Belizean Caribbean coast, supplementing their ordinary diet by feeding on the roe of giant cubera snappers, which spawn in these waters between the full and quarter moons of May, June, and July.

The whale shark does not need to swim forward when feeding; it is often observed in a vertical position, 'bobbing' up and down swallowing water and actively filtering it for food. This is in contrast to the basking shark, which is a passive feeder and does not pump water; it relies on its swimming to force water over its gills.

Behaviour towards divers

This species, despite its enormous size, does not pose any significant danger to humans. It is a frequently cited example when educating the public about the popular misconceptions of all sharks as "man-eaters". They are actually quite gentle and can be playful with divers. Divers and snorkellers can swim with this giant fish without any risk apart from unintentionally being hit by the shark's large tail fin.

Butanding in the Philippines

The highest concentration of whale sharks is in the Philippines. From January to May they congregate in the shallow coastal waters of Donsol. Being migratory in nature, they travel across the oceans, usually close to the equator. Lucky divers have also come across whale sharks in the Seychelles and in Puerto Rico. Between December and September, they are well known to swim along the bay of La Paz in Mexico's Baja California. Sometimes, they are accompanied by smaller fish, in particular, the remora.

Reproduction

The reproductive habits of the whale shark are obscure. Based on the study of a single egg recovered off the coast of Mexico in 1956, it was believed to be [[oviparous (babies hatch from eggs), but the capture of a female in July 1996 which was pregnant with 300 pups indicates that they are ovoviviparous. The eggs remain in the body and the females give birth to live young which are 40 to 60 cm long. The offsprings reach sexual maturity at around 30 years and the life span has been estimated to be between 100 and 150 years.

Conservation status

The whale shark is targeted by artisanal and commercial fisheries in several areas where they seasonally aggregate. The population is unknown and the species is considered vulnerable by the IUCN. Whale sharks are known to frequent the waters off Donsol in the Sorsogon province of the Philippines.

Whale sharks in captivity

A whale shark is featured as the main attraction of Osaka Aquarium Kaiyukan and as of 2005, three whale sharks are being studied in captivity at the Okinawa Churaumi Aquarium in Japan. Three whale sharks, one male, Norton, and two females, Alice and Trixie, are held in the Georgia Aquarium, in Atlanta. A fourth whale shark, Ralph, died in captivity at the Georgia Aquarium on January 11, 2007.[1] The two females were added on June 3, 2006 in hopes that reproduction in whale sharks could be studied in captivity. All four whale sharks were imported from Taiwan, where whale sharks are dubbed as Tofu sharks because of the taste and texture of the flesh.

References

General references

External links

Citation

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