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