Compared to its marine cousins, the whale shark, the largest fish on Earth, is a relative newcomer to the ocean ecosystems of our planet. While ancestral sharks and boney fish appeared in the Devonian Period, some 375 million years ago (MYA) and modern sharks arose in the Jurassic (160 MYA), current fossil evidence suggests that whale sharks did not evolve until the early Tertiary Period, about 60 MYA; ironically, this was the same time that their unrelated namesake, the mammalian whales, where returning to the sea.
Solitary for much of the year and known for their long migrations, whale sharks favor tropical and subtropical seas where they filter-feed near the surface, scooping in plankton, krill, small squid and small fish with their wide mouths. They do congregate at certain feeding grounds during specific times of the year, drawn by the seasonal spawning of coral or by plankton blooms; perhaps the most famous whale shark rendevous is at the Ningaloo Reef, off the west coast of Austalia.
Often exceeding 40 feet in length and weighing over 20 tons, whale sharks live for 70 years or more (perhaps as much as 120 years). Females give birth to hundreds of live young, each about 2 feet long; those that survive predation by other sharks and large fish will be sexually mature by the age of thirty. Despite bans, adult whale sharks are hunted by various human cultures, especially in Southeast Asia. Since they move slowly and feed near the surface, they are also prone to injury from motorized boats and, like many other marine species, have become the target of eco-tourism.