Friday, January 1, 2010

Diving with Kindness Giant - Whale Shark

The whale shark is a slow moving filter feeding shark, the largest living fish species. The largest confirmed individual had a length of 41.50 ft and a weight of more than 21.5 tonnes, but unconfirmed claims report considerably larger whale sharks. This distinctively-marked fish is the only member of its genus Rhincodon and its family, which belongs to the subclass Elasmobranchii in the class Chondrichthyes. The shark is found in tropical and warm oceans, lives in the open sea with a lifespan of about 70 years.

Whale Shark
Photo: whale-shark.org

The species originated about 60 million years ago. Although whale sharks have very large mouths, they feed mainly, though not exclusively, on plankton, microscopic plants and animals, although the BBC program Planet Earth filmed a whale shark feeding on a school of small fish. The whale shark is a filter feeder one of only three known filter feeding shark species. It feeds on macro-algae, plankton, krill, Christmas Island red crab larvae, 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. 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, trapping anything above 2 to 3 millimeters in diameter. 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. Whale sharks migrate to feed and possibly to breed. The best dives in the world for swimming with whale sharks have been visited by Dive The World and you could go there too. While some people are intimidated by its size, the whale shark is actually a gentle giant keen to avoid confrontations and generally trusting of humans.

Diving with Whale Shark
Photo:cancuncd.com

Considered the biggest fish in the world, the whale shark is a cold blooded cartilaginous fish like any other shark. It breathes through gills. Its tail is vertical and moves from one side to another when it swims, unlike other warm-blood animals which have parallel tails and breathe through lungs like the whale, dolphin and dugong. Whale sharks can weigh over 9 tons and grow up to 12 metres in length, although there are questionable, unconfirmed sightings of specimens up to 18 metres in length.

They can generally be found in the entire Indian Ocean in depths of up to 130 metres. The whale shark is easily recognised by its immense size and a 2-tone pattern of light spots and lines on a dark brown dorsal surface. Unlike that of most other sharks its enormous mouth is terminal in position and can be opened wide to filter large amounts of water for small fish, squid, crustaceans, and other plankton organisms.

Sources: dive-the-world.com, wikipedia.org

Post a Comment