Friday 6 December 2013

Whale Sharks in the Andaman Sea









The largest living fish species is the whale shark, Rhincodon typus. Whale sharks grow up to 12.2 m and can weigh up to 13.6 tonnes. The species is believed to have first appeared about 60 million years ago and is now the last surviving species of this group of giant sharks.



The shark is found in tropical and subtropical temperatures mostly in the open sea. It will enter lagoons and coral atolls, bays, and rarely estuaries if the water is rich with plankton (microscopic marine plants and animals). It is migratory and probably returns to the same areas to feed each year.

 
 Whale sharks grow up to 12.2 m and can weigh up to 13.6 tonnes

Little is known about this ocean giant. Scientists believe that they live for about 70-100+ years. The whale shark is generally solitary. They reach sexual maturity at around 30 years, when the female can become pregnant with up to 300 pups. These are born alive after the eggs hatch inside her (they are ovoviviparous). The pups are about 40-60 centimetres long at birth.

 
The whale shark is no threat to the diver


Although whale sharks have very large mouths, they feed solely on plankton and other small animals by filter feeding. To catch their meal they pass water through their five pairs of gills which are covered in fine, bristle-like structures that strain and hold the food (anything above 2 to 3 mm in diameter is trapped). Studies show that their diet consists of plankton and larger algae, zooplankton, krill and slow swimming animals like small squid and juvenile fish.


 


About 60 million years ago whale shark evolution solved the problem of finding enough dolphins and small whales to eat. They switched their diet to the tons of plankton that could not escape their huge mouths (which can be up to 1.5 metres wide). Evidence of their once predatory nature is still provided by 300 -350 rows of tiny teeth. These teeth are no longer used in feeding and have become very small in size.



When feeding in low concentrations of plankton, the whale shark simply cruises along at an average speed of about 5 km per hour with its mouth open. When it encounters schools of krill or small fish it slows and begins gulping and filtering water at hundreds of liters per minute.

 
 Many thanks to my friend Ellen for this great whale shark feeding photo


Two small eyes are located towards the front of their head and their vision is probably poor. A whale shark’s 10 centimeter thick skin protects them from the bite of smaller sharks. It is believed that adults have few predators.



The largest specimen recorded was caught near Karachi, Pakistan. It was 12.65 metres long, weighed more than 21.5 tonnes, and had a girth of 7 metres. There are stories of much larger specimens (quoted lengths of 18 metres) in the popular shark literature but no scientific records support their existence.


 

These gentle giants are not a danger to humans. They are actually quite gentle and will play with divers. Divers and snorkelers can swim with whale sharks without risk other than being struck by the shark's large tail as it swims past.

Sadly, these wonderful animals, the largest fish in the sea, are killed just for their fins. The fins are used to make soup for fancy dinners.




Check out some other really cool creatures in some of the other posts on this blog site.
















Wednesday 25 September 2013

INCREDIBLE GIANT SQUID











Giant squid can grow to an awesome size with their bodies reaching 2 metres in length and a weight of 275 kg. When you add the eight shorter arms used for holding and the two long tentacles used for grabbing prey, giant squid can be up to 13 metres long. The giant squid is the second largest mollusc loosing first place to the colossal squid.




 


The first photos of a live giant squid in its natural habitat were taken during September, 2004 by researchers from the National Science Museum of Japan and the Ogasawara Whale Watching Association using special underwater cameras.


 



The image is used here strictly for educational purposes. Original copyright for this image: "Copyright (C) Kyoto Prefecture





Marine biologists have discovered that giant squid feed on deep-sea fish and smaller squid. They catch their prey using the two muscular tentacles which are armed with sharp-edged suckers on the ends. The food is brought back toward the mouth where a powerful beak (like a parrot beak) tears it to pieces. The pieces are then shredded with the radula (a tongue with small teeth) and swallowed.



While suckers are found only on the ends of a squids two tentacles, they are also found along the full length of the inside of the eight arms. Suckers on the arms are smaller (2-5cm) but there are hundreds of them.



It is thought that the only things powerful enough to eat a grown giant squid are sperm whales and the huge Pacific sleeper sharks found in freezing depths. Scientists often find circular scars left by the sharp suckers on the head of sperm whales. Who usually wins the gigantic battles thousands of metres below the surface is unknown.






Giant squid have three hearts: one for each of the two gills and one for the body. They have a very advanced brain able to deal with all the muscles and sensory nerves. They also have the largest eyes of any living creature (except for the colossal squid) — at more than 30 centimetres.





Giant squid are found in all of the world's oceans. They are usually found near continental and island slopes that drop into the depths of the abyss. They like cold, deep water and are seldom found in tropical and polar latitudes.



 

In 2005, the Melbourne Aquarium in Australia paid AUD$100,000 for a giant squid, frozen in a huge block of ice. It was caught by fishermen off the coast of New Zealand.

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