Whale shark closeup
Largest Fish is Mainly a Mystery
Contrary to its name, the whale shark is not a whale; it is, rather, the world’s largest fish, growing as long as 60 feet. It is widely distributed, found worldwide in tropical and warm temperate seas, except the Mediterranean. As it swims, it sucks water through its gargantuan mouth, as wide as 5 feet, then filters out plankton and other microscopic organisms through its gills. It is an extremely patient feeder. Individuals have been observed waiting as long as 14 hours for fish to spawn on reefs in order to eat the eggs. Whale sharks migrate long distances according to food availability and water temperature. One specimen was tracked 8,000 miles across the Pacific.
Thought to have evolved 200 million years ago, one might think that humans would have had ample time to study the species, but its life history remains poorly understood, partially because it is both rare and migratory. Jacques Cousteau is reported to have observed only two whale sharks in his life. Scientists do know that the species gives birth to live young, unlike most fish, the eggs hatching in the mother’s body. Litters number up to 300 pups, but survival rates are thought to be low. If they do survive, they may live as long as 100-150 years, reaching sexual maturity around 25 years.
The whale shark is listed as Vulnerable by the IUCN. Because of its size, slowness, long development time, and high value on international markets, the species is inherently vulnerable to intentional fishing. Incidental entanglement is also a threat. In recent years, some locales have begun to feature whale sharks in ecotourism. Docile and slow, the gentle fish is an alluring target for recreational divers.