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Introduction
The
first scientific report of the whale shark was made by Andrew Smith,
with an animal harpooned at
Table Bay
,
South Africa
(Smith1828, 1829 and
1849 in
Overwhelm, 1997), nameing the species as Rhincodon
typus, according to Colman (1997ª) and Chang, et al (1997). In the
1984 International Commission on Zoological Nomenclature accepted the
genus Rhincodon (Smith 1829).
Probably
due to its pelagic habitat, and its unpredictable and sporadic
occurrences, the whale shark has been poorly studied, leaving several
aspects of its ecology unknown. It is the only representative of the
Rhincodontidae Family, within the Order Orectolobiformes. The whale
shark is the only pelagic species within the order, and the only member
that feds on plancton (Fowler, 2000).
Biology:
 The
whale shark is the biggest fish in the world. It has a massive, fusiform
body that can reach sizes of even
14 meters
(
Taylor
1999) or between 15 and
18 m
(Kukuyev, 1996).
Its
coloration is gray or dark blue on its back, with circular spots and
light colored horizontal and vertical lines (white or yellowish) and a
white belly. These patterns give the whale shark its local name:
"domino." In other areas, its appearance makes it known as
“checkerboard”. Each individual displays a unique pattern which
allows its identification, since it does not change with growth. It is
possible that these markigs are the result of a phylogenic connectioncconnectio
with other sharks of the Orectoibiformes order, like the nurse shark
(Ginglymostomatidae) and leopard shark (Stegostomatidae). These sharks
are bottom dwellers, where the dorsal marks act as camouflage (Compagno,
1984; Last & Stevens,
1994 in
Colman, 1997). Sharks display a high level of visual development and the
distinguishing marks on pelagic species can be socialy important, for
example in demonstrations of position and recognition processes
(Myrberg,
1991 in
Colman, 1997). Another possibility is that these patterns of
pigmentación can be an adaptation to protect itself from the radiation,
which is important for those species that remain a significant part of
the time on the water surface.
 It
has ridges all along the back of its body that become deeper along its
sides. (
Taylor
1997). Unlike other sharks, its mouth is on the front end of its wide
head and occupies the entire width of its body (Taylor 1997),
facilitating plancton feeding. Its eyes are very small and are located
on the lateral end of the head (
Taylor
1997).
Its
pectoral fins are very powerful, the pelvic ones are small, over which
the first dorsal fin is located, ending with the large, powerful,
semiciruclar cudal fin that is used for propultion.
Feeding
 The
whale shark moves slolwly near the water surface, since it filters great
amounts of water to retain an ample variety of plancton and necton,
including small crustaceans like krill, crab larva and copeados, small
fish like sardines, anchovetas, mackerel and ocasionaly prey of greater
size like small tunas and squid (Compagno, 1984; Last & Stevens,
1994, in
Colman, 1997). Phytoplankton and seaweeds could also be a componentary
part of its diet. When analyzing the stomach contents of an individual
captured of the coasts of India in
1961, a
variety of food was found, including "... great amounts of
zooplancton, partially digested fish, crustaceans, moluscs and small
amounts of seaweed, doubtlessly suggesting a omnivorous diet
"(Silas & Rajagopalan,
1963 in
Colman, 1997).
Individuals
have been observed passively feeding, by swimming with an open mouth, as
well as actively feeding, by sucking water rich in prey (Clark
&Nelson,
1997 in
Colman 1997). The shark does not depend on its movement to operate the
filtration mechanism; instead it displays a versatile method of suction
that allowing the introduction of water at an elevated speed. Devoid of
developed teeth, it counts on highly developed internal filters, located
on its gills, to retain its small prey within its great mouth. This
mechanism can impel the water through the mouth while swimming, working
not only as a filter but also as a water pump sending a great amount of
concentrated plankton to its mouth (
Taylor
1997). Whale sharks have also been observed caughing which is considered
a gill rinsing mechanism to wash out accumulated food.
This
allows it to capture larger amounts and more active nektonic prey, like
zooplancton aggregations. However, it does not concentrate diffuse
plancton efficiently limiting its feeding areas to those with high
plancton concentrations.
Their
migrations and aggregations are associated to ocean currents of high
primary production and nutrient upwellings. Specific feeding sites are
also known, for reproductive aggregations of fish in
Belize
and massive coral spawning in
Australia
.
Reproduction,
Development and Growth
Males
have a pair of copulation organs that extend from each ventral fin
called claspers which they use to internally fertilize females. Once
fertilized, there is no sturdy umbilical fixation of the embryo towards
the mother. Instead the embryo developes in an egg within the female’s
body, leaving by the cloaca of the female shortly after hatching (Joung et
al., 1996; Taylor
1997 in
Rodriguez Dowdell et
al., 2003). This defines the whale shark as ovoviviparous.
 In
spite of the large size adult whale sharks reach, yearlying are small,
between the 40 and
50 cm
(Rodriguez Dowdell et
al., 2003). Other authors report a pregnant female with hundreds of
young of around
60 centimeters
of length (
Taylor
1997). In 1995, an
11 m
female was harpooned near
Taiwan
, with 300 embryos of around 55cm of length in its uterus (Joung et
al. 1996). Possibly the life cycle of R.
typus is similar to that of the nurse shark (locally also known as
cat shark) Ginglystoma
cirratum, that after a short gestation period, produces a great
amount of small but fast growing young (Castro,
2000 in
Fowler, 2000).
 The
little information available supposes that the whale shark reaches
sexual maturity at 30 years of age and that the longevity the whale
shark is more than 100 years. External observations of males and
internal observations of captured females indicate that the size of
sexual maturity is
9 m
(Colman, 1997). The information on the male to female ratio is also very
scarce. It is interesting to emphasize that the 300 embryos found within
the female whale shark in 1996 presented a 1:1 male to female ratio. The
east Australian population presents a majority of immature male sharks
(Taylor,
1994 in
Colman, 1997). Nor is there information on its growth rate and
morphometric studies have been made.
 
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