The whale shark, Rhincodon typus,
is a slow moving filter feeding shark that is the largest living fish
species. It can grow up to 12.2 m. (40 ft.) in length and can weigh up
to 13.6 tonnes (15 short tons). . The shark is found in tropical
and warm oceans and lives in the open sea and can live for about 70
years. The species is believed to have originated about 60 million years
ago.
This distinctively-marked shark is the only member of its genus Rhincodon and its family, Rhincodontidae (called Rhinodontes before 1984), which is grouped into the subclass Elasmobranchii in the class Chondrichthyes.
The
species was first identified in April 1828 following the harpooning of a
4.6-metre (15.1 ft) specimen in Table Bay, South Africa. It was
described the following year by Andrew Smith, a military doctor
associated with British troops stationed in Cape Town. He proceeded to
publish a more detailed description of the species in 1849. The name
"whale shark" comes from the fish's physiology; that is, a shark as
large as a whale that shares a similar filter feeder eating mode. Known
as a deity in a Vietnamese religion, the whale shark is called "Ca Ong",
which literally translates as "Sir Fish".
In Mexico, and throughout much of Latin America, the whale shark is
known as "pez dama" or "domino" for its patterns of spots. Whales sharks
go by the name of "Sapodilla Tom" in Belize due to the regularity of
sightings near the Sapodilla Cayes on the Belize Barrier Reef. In
Africa, the names for the whale shark are very evocative: "Papa
Shillingi" in Kenya came about as it is believed that God threw
shillings upon the shark which are now its spots, and in Madagascar
whale sharks are known locally as "Marokintana" which means "Many
stars". In Indonesia, Javanese also called this species referring to
star as "geger lintang" which has meaning "stars in the back".
The
whale shark is a filter feeder — one of only three known filter feeding
shark species (along with the basking shark and the megamouth shark).
It feeds on phytoplankton, macro-algae, plankton, krill 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 (anything above 2 to 3 mm in diameter is
trapped). Any 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 congregate at reefs off the Belizean Caribbean coast,
supplementing their ordinary diet by feeding on the spawn of giant
cubera snappers, which spawn in these waters between the full and new
moons of March through September.
|
No comments:
Post a Comment