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Whale Shark Facts & Figures

See also - Whale Shark in UtilaResearch, Controversy, Encounters

Whale Shark Mouth - Click to enlarge
Whale Shark feeding - Photo by Werner Mischler

Whale Shark Facts - provided by Steve Fox of Deep Blue Divers

The whale shark - latin name: rhincodon typus - is the largest fish in the sea, averaging 9 meters in length. The smallest whale shark seen by Deep Blue Divers in the waters of Utila was approximately 3 meters, the largest approximately 12 meters in length. The whale shark is believed to be highly migratory and the deep waters of the north side of the island of Utila is on their migratory path. They cruise at only 2-3 knots filtering thousands of tons of water containing very small particles of food every hour. Its jaws are lined with 300 rows of tiny teeth, approximately 2mm in size. It is suggested that whale sharks do not reach maturity until they are over 30 years of age and a size of 9 meters. They are can live to be over 100 years old.

Nomenclature

Latin Name: Rhincodon typus
German: Walhai
French: Requin baleine
Spanish: Tiburon ballena

The whale shark was first described and named in 1828, based on a specimen harpooned in Table Bay, South Africa. Historically, there have been many synonyms (alternative scientific names) for family, genus and species names. However, in 1984 the International Commission on Zoological Nomenclature suppressed previous generic variations in favor of genus name Rhincodon, and the family name Rhincodontidae. Others generic names formerly used include Rhiniodon and Rhineodon and the family names Rhiodontidae and Rhineodontidae. Systematically, Rhincodontidae is placed in the order Orectolobiformes, which also includes families such as Ginglymostomatidae (nurse sharks) and Orectolobidae (wobbegongs). The interrelationships between these families are based on anatomical and morphological similarities.

Synonyms for the whale shark in past scientific literature include Rhinodon typicus (Müller & Henle 1839), Rhinodon typicus (Smith 1845), Micristodus punctatus (Gill 1865), and Rhinodon pentalineatus (Kishinouye 1901). The genus of the currently valid name Rhincodon typus, is derived from the Greek words "rhyngchos" = snout and "odous" = teeth. The species name, typus, translates as type.

Distribution

Unlike most other sharks in this order (Orectolobiformes), which are bethnic, (live on or near the bottom) the Whale Shark is Pelagic, an open ocean dweller. It is found in most tropical, temperate seas across the world and seems to prefer warmer waters ranging in temperature from 21C to 28C (70F to 82F). Whale Sharks around the world, Utila included, do come close to shore at times; sometimes less than 1 mile and will occasionally enter lagoons and coral atolls.

The Whale Shark is thought to be highly migratory, but without proof, that is until Scott Eckert and Brent Stewart working with Hubbs Sea World Research Institute used radio telemetry to track Whale Sharks they had tagged between 1994 and 1996 one migrated to the Western North Pacific covering over 13,000 kilometers (more than 8,000 miles) in 37 months and in Australia a Whale Shark was tracked using satellite tracking technology for 3,000 kilometers (nearly 2,000 miles) from Ningaloo north west across the Indian ocean. Therefore we, at Deep Blue Divers, believe that this warrants much further investigation, though Photo ID and satellite tracking.

Biology

Size - Whale Sharks are reputed to have been seen up to 18m (60ft) long but the official world record size, which is listed in the Guinness Book of World Records, is 12.65m (41ft 6in), we believe that there are larger ones, but in general the most common size seen in Utila is between 6m and 10m (20ft and 33ft). [weigh about 20 tons] Here in Utila there is the story about Old Tom a Whale Shark said to be at least 18m (60ft) in length seen by fishermen.

Age - nobody knows but it is thought that Whale Sharks could possibly live up to 150 yrs old.

Shape - The shape of the Whale Shark is very distinctive; unlike most other sharks it does not have its mouth on the underside of its broad flat head. On Its body there is a pattern of light spots and stripes set on a dark background graduating to a light color on its underside, which helps with camouflage. The base color of a Whale Shark varies from brown to bluish/grey. It has two dorsal fins the front being much larger that the rear, its caudal fin (tail) has a much larger top lobe, much more noticeable in juveniles.

Teeth - The teeth are very small about 6mm (1/4 in) long and have about 3,000 teeth set in 300 rows in each jaw, these teeth are not used for feeding.

Skin - The skin is comprised of what are called Dermal Denticals, basically the skin is made up of small teeth like structures.

Feeding - Whale Sharks are filter feeders, and their main food is plankton. Plankton is a microscopic organism that floats freely with oceanic currents and in other bodies of water. Plankton is made up of tiny plants (called phytoplankton) and tiny animals (called zooplankton). The word plankton comes from the Greek word "planktos" which means, "drifting."

The whale shark feeds actively by opening its mouth, distending the jaws and sucking, then it closes its mouth and the water flows out its gills. During the slight delay between closing the mouth and opening the gill flaps, plankton may be trapped against the dermal denticles lining the gill plates and pharynx. The fine sieve-like apparatus, a unique modification of the gill rakers, forms an obstruction to the passage of anything but fluid, retaining all organisms above 2 to 3mm in diameter. Practically nothing but water goes through this sieve. Individuals have also been observed coughing, a mechanism that is thought to be employed to clear or flush the gill rakers of accumulated food particles. Whale sharks move their heads from side to side, vacuuming in seawater rich in plankton, or aggressively cut swathes through schools of prey.

Groups of individuals have been observed feeding at dusk or after dark. The density of plankton probably is sensed by the well-developed nostrils, located on either side of the upper jaw, on the leading edge of the terminal mouth. The frequent turns may keep the whale sharks in the denser parts of the plankton patches, searching and scanning when an olfactory cue weakens on one side or the other. The whale shark's small eyes are located back on the sides of the head. Because of this, vision may play a much smaller role than olfaction in directing the head turns during surface feeding. One live whale shark pup removed from its dead mother was maintained in captivity in Japan. It did not eat for the first 17 days, even though it swam constantly. This suggests that the pup had substantial stores of endogenous (stored) energy.

Reproduction - It is believed that Whale Sharks do not become sexually mature until they are about 25 to 30 years old and about 9m (30ft) in length. There has been a lot of confusion about how Whale Sharks gave birth. There are 3 forms of reproduction in sharks ovoviviparity, oviparity and viviparity;

In 1995, an 11-meter female whale shark was harpooned off the eastern coast of Taiwan and 300 fetal specimens, ranging in length from 42 to 63cm, were taken from the two uteri. This discovery proved that the species is a livebearer, with an ovoviviparous mode of development. Whale Sharks have never been seen mating or giving birth. Males have Claspers, which are inserted into the female.

Predators - Humans are the main predators of Whale Sharks, also the remains of young have been found in the stomachs of Blue Sharks and Marlins. It is also believed that Orcas, (Killer Whales) may attack Whale Sharks.

Whale Shark Conservation

See also - Whale Shark in Utila, Research, Controversy, Encounters


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