Whale Shark Ecology
Kevin Carey
The whale shark, Rhiniodon typus, is the largest fish and often comes across as one of
the oddest in physical appearance. With little information known about this marine species we
can only speculate how exactly its environment and other species are affecting its behavior,
morphology, and ecology. Millions of years of natural selection and environmental pressures
have led this creature to adapt perfectly to its surroundings and habitats. First described in
1828, the whale shark is known for its flat head, extremely large terminal mouth, massive gill
slits, and distinct spots and stripes on its dark body. Most likely acting as camouflage, this
coloring helps the whale shark blend into its surrounding and better enable it to hide from
potential prey or it may serve as a form of recognition between other whale sharks. Another
very interesting theory is that the coloration in species that spend much time near the surface
could serve as protection from radiation. The flat head and suction-like mouth enable it to act
as a filter feeding on a mix of planktonic, small schooling fish, small tuna, squid, and large
amounts of zooplankton. Their large mouth is perfect for feeding on dense schools of fish
perhaps making up for its less efficient filteringapparatus.
Very little is known about the whale sharks migratory movements although it is
speculated that they are probably related to food availability such as plankton blooms and
spawning events. Whale sharks may respond to each particular habitat in its own unique way
and so movements may be sporadic and localized. Mainly found in tropical ,equator waters
there are a few known large aggregations such as the one in the Indian Ocean near Christmas
Island which may coincide with the mass spawning of red crabs. A study done near the Belize
Barrier Reef done between 1998 and 1999 confirmed that the seasonal aggregation of whale
sharks was likely due to the spawning of reef snappers. With their mouths open, the whale
sharks swim through the spawning clouds perfectly adapted to gulp up its prey while filtering
out water and other particles through its large gills. Their body shape also helps them to turn
around rapidly and swim back through the cloud feeding on more prey, a method known as
ram ventilation feeding. Often sighted with pelagic fish, whale sharks may be following other
species that feed on the same prey. Whale sharks have been sighted with large schools of
hammerheads, tiger sharks, and manta rays.
The whale shark is also affected by human interations as well to some degree. Although,
the whale shark is not seen in high demand by humans, most interactions is caused by boat
collisions, bycatch, and entanglement in fish nets. Their fins are also used in shark fin soup on
some Asian countries. Figures and exact numbers of abundance are still very unclear although
there is a defined need for on-going studies with clear objectives in the future to help conserve
this wonderful species.
Citations:
Heymn, William D., Graham, Rachel D., Kajerive, Kjorn, Johannes, Robert E. 2001. Whale sharks
Rhincodon typus aggregate to feed on fish spawn in Belize. Marine ecology Progress Series. 215: 275282.
Colman, J.G. 1997. A review of the biology and ecology of the whale shark. Journal of Fish Biology. 51:
1219-1234.