Last Update : Tuesday 7 August, 2001 2:55 AM

Shark
Giant Shark Nurse Shark Leopard Shark Silvertip Shark Whaleshark

WHALE SHARK...OGRE OF THE OCEAN

          The name whale shark is well known among divers, one of the most sought after creatures under the sea. Some people even go diving abroad, just to ensure the probability to capture the sight of them. In Thailand, whale shark is one factor that has made the name Richeliu Rock famous among divers around the world. How many people would know that, whale shark is being threatened? Why had not any one met whale shark in the Andaman Sea during the past season? You might find the answer after you have finished reading this story.

          “Before doing anything, we have to know it.” This is our principle. So, when we decided to study the whale shark, we had to research the information from various sources, so that this presentation can also be used as reference.

 

Taxonomic Order

• Phylum               Vertebrata
  
• Class                 Chordata
  
• Order                 Orectolobiformes
  
• Family                Rhincodontidae
  
• Genus                Rhincodon
  
• Sciencetific name Rhincodon typus
  
• ชื่อไทย                 ฉลามวาฬ หัวบุ้งกี๋
  
• Common name      Whale shark
  

 

Knowing whale shark

          Whale shark (Rhincodon typus)  is a cold blood animal in the cartilaginous fish group, the same as other sharks. It is the only fish belonging to Rhincodontidae Family, but shares the Orectolobiformes Order with leopard shark and nurse shark.

          Whale shark uses gill in respiration system. It has 5 gill slits, 2 pelvic fins, 2 pectoral fins, 2 anal fins and 1 caudal fin(tail). The whale shark’s tail is in the right angle position with the body and moves in a horizontal direction. This is different from warm blood animals in the sea whose tail is in the parallel position and move in a vertical direction, such as whale, dolphin, dugong etc.

          Whale shark is the largest fish and cold blood animal in the world. This fish eats plankton like manta ray (Manta brevirostris). But he has a different eating method. It would swim toward the group of plankton, take a large gulp of water in its mouth and use the gill raker to filter the plankton; whereas, manta ray would open its mouth all the time to let the water flow through.

          The appearance that distinguishes whale shark from other type of sharks is the large head comparing to body size and mouth that is in front instead of underneath. Eating characteristic is not the factor that scientist used to separate whale shark from other sharks because there are two more types of plankton-eating shark in a different Order with whale shark.

 

Life cycle

          Life cycle of whale shark is still mysterious. As far as we know, whale shark has a long life span. Report from Australia shows that whale shark starts to propagate at the age of 30 years old. Comparing to the propagating age of other sharks in the same Order, it is expected that whale shark’s life span could be 100 years. No one has seen whale sharks mating in the water. It is expected to happen in the deep sea. Moreover, we do not know exactly if whale shark spawn or give birth to a baby.

          In 1953 a fishing boat caught whale shark ovum size 35 centimeters in a net, from the depth of 55 meters with the embryo of whale shark inside. But we are not sure that whale shark is oviparous because no one has ever seen whale shark ovum since.

          Many scientists believe that whale shark is ovo-viviparous. It is presumed that whale shark has more than 100 ova in the ovary. However, this presumption is still not confirmed.

          Some people might like to know why could we not refer to other sharks in the same Order. The answer is that sharks in the same Order could either be oviparous (nurse shark) or viviparous (leopard shark). An interesting fact is that almost all whale sharks found is larger than 3.5 meters, with the exception of three i.e. 60 cm, 1.3 and 3 meters consecutively.

 

Dispersion

          Whale sharks are found in tropical seas around the world except Mediterranean Sea. They usually live in the area where water temperature is 21-26 degrees Celsius. Dispersion relates to warm water current in some areas. They are often found where warm and cold water streams meet and the upwelling with plenty of plankton. (Upwelling is a place where underwater current makes an impact with rocks, then food substance is flown to the upward water mass.)

          Moreover, many believe that whale sharks migrate. But migration course has not been established yet. In Thailand, whale sharks are mainly spotted around underwater rock piles in the open sea at the depth of 30 meters up like Richeliu, Hin Muang, Hin Daeng, Southwest Pinnacle (Kong Tung-gu), Losin etc. The point where whale sharks are most often spotted is Richeliu Rock . There is a possibility of whale shark migration for hundreds of kilometers. For example, it has been found that there was a whale shark migration from Papua-New Guinea Island to the east of the Great Barrier Reef.

 

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