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What To Look For:
A gigantic shark with a broad flat head and checkerboard pattern of spots
and stripes on its back.
Color:
Dark grey, bronze or greenish grey above with white to cream spots and
transverse stripes; white to cream below.
Size:
This is the largest fish in the world; most individuals encountered by
divers range between 18 and 35 ft (5.5 to 10.6m) total length. The largest
accurately measured individual was a 39.9 ft (12.19m) male caught off
Bombay, India, in 1983. Maximum total length is uncertain, possibly to 60
ft (18m).
Teeth:
Minute; the shark strains prey through internal filter screens on its
gills.
Habitat:
An epipelagic oceanic and coastal shark of tropical and warm temperate
seas. The shark appears to prefer areas where the surface temperature is
between 70" and 77"F (21" and 25"C). The shark is
usually encountered near upwellings of cold water 62"F (17"C);
conditions which bring to the surface the plankton and small nektonic
organisms on which it feeds. Whale sharks are often seen far offshore, but
they also come close inshore and sometimes strand. Divers generally
encounter whale sharks at or near the surface.
Distribution:
Circumglobal in tropical and warm-temperate seas.
Biology:
• Food Types:
The whale shark is a versatile suction-feeder that feeds on a wide variety
of planktonic and nektonic organisms: masses of krill are regularly
consumed, along with squid, and small fish: sardines, anchovies and
mackerel.
• Reproduction:
This has been a subject of controversy among shark scientists. In 1953 a
very large egg-case containing a 14.5-inch (36 cm) whale shark embryo was
brought up in a trawl net in the Gulf of Mexico, which led to speculation
that whale sharks are oviparous. It is now thought that the Gulf of Mexico
egg-case was an abortion, and whale sharks are ovoviviparous; that is, the
sharks hatch from eggs while still inside their mother's uterus, and are
born some time later. Newborn whale sharks (so determined by the presence
of `umbilical' scars) measuring 21 to 25 inches in length (55 to 63 cm)
have been caught in the Pacific Ocean off the coast of Central America, and
in January 1996 there was an unconfirmed report that newborn whale sharks
washed ashore in the Marshall Islands Newborn whale sharks have also been
found in the Gulf of Guinea in the Atlantic Ocean. and in the Persian
Gulf.
• Lifespan:
Some species of sharks which live for 100 years, are not able to breed until
they are 20 years old and spend 1/5th of their lives evading capture until
they can reproduce. Recent studies suggest that male whale sharks are not
able to breed until they are about 30 years old. If 30 years is 1/5th of a
whale shark is expected life span, it may normally live for well over a
century, possibly even 150 years or longer.
Behaviour:
• Activity Patterns:
Solitary sharks have been observed in many areas, but large congregations
occur in only a few spots in the world. In the Eastern Pacific many sharks
are seen off Mexico from Cabo San Lucas to Acapulco from March to August,
and in the Western Pacific there are frequent sightings of the sharks off
the Queensland coast in January and February. In the Indian Ocean. whale
sharks mass at Ningaloo Reef, northwestern Australia, in March and April
when the coral spawn The sharks congregate in Seychelles in August and
November but the greatest aggregations appear to occur along the coast of
East Africa (South Africa and Mozambique) from October through April.
• Feeding:
The whale shark is often observed feeding near the surface. Sometimes the
shark assumes a vertical posture with its mouth uppermost, then bobs up and
down in 15- to 20-second cycles, pausing at the surface to let food-laden
water rush into its mouth and strain through its gill plates. There are
numerous reports of pelagic gamefish (particularly skipjack, albacore and
cobia) swimming with whale sharks; it is thought that the gamefish may prey
on smaller fishes that, like the whale shark, are feeding on the
plankton.
Disposition:
Whale sharks may be wary of divers and difficult to approach, indifferent,
or exhibit curiosity and approach divers closely, apparently to examine
them.
• Danger To Humans:
Unaggressive to divers but occasionally bumps a boat that is reeling in a
gamefish. Not considered dangerous despite its great size.
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