Whale Sharks
I saw a news articles on Yahoo News about a Georgia aquarium that keeps whale
sharks. Well, actually, the article was about how they failed to keep whale
sharks… They’ve had two die in the last few months. You can read the link
here: http://news.yahoo.com/s/ap/20070613/ap_on_sc/whale_shark_dies;_ylt=AvwkMwHazr_wOWMp7Hh_pjXMWM0F
After I read this, I was wondering: Just what is a whale shark, and why are
they so hard to keep in captivity?
As the fish’s name suggests, whale sharks are the shark equivalent of baleen
whales. They are big (growing up to 40 feet long), and they are plankton-eating
filter feeders. They are found in tropical seas, worldwide, usually near the
surface. They are harmless to humans.
Like all filter feeders, whale sharks have an enormous mouth for their body
size; their mouths can be over 4 feet wide. Unusually for sharks, their mouths
are also at the very front of the head, instead of on the underside; this allows
the shark to simply open its mouth while swimming to suck in the huge volume of
water they need in order to filter out enough food. Remember, these are 15 ton
animals, which eat some of the very smallest prey available.
Whale sharks have an ingenious adaptation for filter feeding. Like all fish,
they have gills. The external features of gills are obvious to humans: the
slits along the sides of the animal, just behind the head. Internally, however,
gills have a very complex, comb-like structure, designed to get the maximum
water flow over tiny blood vessels, so that the animal can extract oxygen from
that water. This structure is a good pre-adaptation for filter feeding. (I may
talk about pre-adaptation in a future post; it is a fascinating subject in
evolutionary biology.) The whale shark will eat anything which the internal
gill structure traps in the mouth.
While I was looking up information about whale sharks, I came across several
references to Thor Heyerdahl’s famous Kon Tiki expedition, when he sailed a
primitive raft across the South Pacific, and proved that human colonization of
the Polynesian islands was technically feasible for Stone-Age people. During
the trip, he had an encounter with a whale shark, which he described as the
biggest and ugliest face any of us had ever seen in the whole of our
lives.
Whale sharks might not be pretty, but they are fascinating.
Powered by ScribeFire.
