Everything about The Whale Shark totally explained
The
whale shark,
Rhincodon typus, is a slow
filter feeding shark that's the largest living
fish species. 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. The shark is found in
tropical and warm oceans and lives in the open sea. The species is believed to have originated about 60 million years ago.
Naming
The species was first identified in April 1828 following the harpooning of a 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. Known as a deity in a Vietnamese religion, the whale shark is called "Ca Ong", which literally translates as "Sir Fish"
Distribution and habitat
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 such as
Ningaloo Reef in
Western Australia;
Útila in
Honduras;
Donsol and
Batangas in the
Philippines; off
Isla Mujeres and
Isla Holbox in
Yucatan Mexico; and the
Tanzanian islands of
Pemba and
Zanzibar. Though it's often seen offshore, it has 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. It is found to a depth of . The whale shark is solitary and rarely seen in groups unless feeding at locations with an abundance of food. Males range over longer distances than females (which appear to favour specific locations).
Anatomy and appearance
As a
filter feeder, it has a capacious mouth which can be up to wide and can contain between 300 and 350 rows of tiny teeth. It has five large pairs of
gills. Two small eyes are located towards the front of the shark's wide, flat head. The body is mostly grey with a white belly; three prominent ridges run along each side of the animal and the skin is marked with a "checkerboard" of pale yellow spots and stripes. These spots are unique to each whale shark and because of this they can be used to identify each animal and hence make an accurate population count. Its skin can be up to thick. The shark has a pair each of
dorsal fins and
pectoral fins. A juvenile whale shark's tail has a larger upper fin than lower fin while the adult tail becomes semi-lunate (or crescent-shaped). The whale shark's
spiracles are just behind the eyes
The whale shark isn't an efficient swimmer since the entire body is used for swimming, which is unusual for fish and contributes to an average speed of only around . 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 long, weighed more than 21.5
tonnes (47,300
lb), and had a girth of . Stories exist of vastly larger specimens — quoted lengths of are not uncommon in the popular shark literature — but no scientific records exist to support their existence. In 1868 the Irish natural scientist
Edward 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, and tells of reports of specimens surpassing .
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 long, and weighed approximately 37 tonnes (81,500 lb), which have been exaggerated to a more precise measurement of and weight 43 tonnes in recent years. A shark caught in 1994 near
Tainan county in Southern
Taiwan is reported to have weighed 35.8 tonnes (78,887 lb). There have even been claims of whale sharks of up to . 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 on one side and 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're reduced in size in the whale shark. Instead, the shark sucks in a mouthful of water, closes its mouth and expels the water through its gills. 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's presumed that this is a method of clearing a build up of food particles in the gill rakers.
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 is an active feeder and targets concentrations of plankton or fish by
olfactory cues. Rather than simply "vacuuming" constantly, it's able to pump water over its gills. The shark can circulate water at a rate up to 1.7 L/s (3.5 U.S. pint/s). The whale shark doesn't need to swim forward when feeding; it's 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 doesn't pump water; it relies on its swimming to force water over its gills. The eggs remain in the body and the females give birth to live young which are to long. It is believed that they reach sexual maturity at around 30 years and the life span has been estimated to be over 100 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., followed by Taiwan in May 2007 .
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. Four whale sharks, two males, Taroko, and Yushan, and two females, Alice and Trixie, are held in the
Georgia Aquarium, in
Atlanta. Two male whale sharks, Ralph and Norton, died in captivity at the Georgia Aquarium on January 11, 2007 and June 13, 2007 respectively. The two males were added on
June 3,
2006 in hopes that reproduction in whale sharks could be studied in captivity. All six whale sharks were imported from
Taiwan, where whale sharks are dubbed
tofu sharks because of the taste and texture of the flesh.
Further Information
Get more info on 'Whale Shark'.
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