There are lots of fishes in the sea, but there are none bigger than the Whale Shark (Rhincodon typus). These huge sharks live in tropical waters around the globe, and we have had encounters with them in many locations. Seeing these magnificent animals always is a thrill. Their size -- up to about 40 feet (12 meters) in length -- is impressive, and their grace is almost magical.
Unlike most sharks, Whale Sharks are filter feeders. They feed on krill, algae, plankton, and other small organisms suspended in the water. They take in large gulps of sea water, and sieve out the food as it passes over the denticles that cover their pharynx and gill plates. The water is expelled through the gills, while the filtered-out food remains and is swallowed.
No one knows for sure how long Whale Sharks live, but estimates of the creatures' natural lifespan range from 70 to about 100 years. Whale Sharks do not reach sexual maturity until they are about 30 years old. They are ovoviparous: that is, their eggs hatch inside the mother, develop without a placenta, and then emerge as live young.
Whale Sharks are curious and often approach divers and snorkelers to have a look, and will sometimes swim alongside them, but these sharks are not known to be aggressive. Encounters with these enormous but docile creatures are a joy for divers.
Here is a video, shot at Christmas Island in the Indian Ocean, that perfectly illustrates the excitement of divers who encounter Whale Sharks in the open water:
If the video does not play or display properly above, click here to view it on YouTube.
If you are interested to learn more about Whale Sharks, we recommend you have a look at this Whale Shark (Rhincodon typus) Issues Paper, from the Australian Dept. of the Environment, Water, Heeritage and the Arts; and the Whale Shark page on the National Geographic Web site.