Size - The largest confirmed individual had a length of 12.65m (41.5ft) and a weight of about 21.5t (47,000lb). The whale shark holds many records for size in the animal kingdom, most notably being by far the largest living nonmammalian vertebrate. The smallest on record is a 38cm (15in) long whale shark found in the Philippines on March 7, 2009.
The whale shark is found in open waters of the tropical oceans and is rarely found in water below 21°C (70°F). The most reliable sites tend to be the feeding and mating areas, as the sharks actually stick around long enough to see, rather than just passing through. The West end of the Caribbean Sea holds some of the best spots to experience a whale shark dive.
Isla Holbox, Mexico - One of the most popular spots on the planet to dive with whale sharks is just off the shores of Cancun, Mexico from mid-June to mid-September. Peak season is mid-July to mid-August. There are numerous companies running pickups from Cancun, Playa Del Carmen, and Holbox. Although Holbox is the closest town, it is quiet and off the beaten path from substantial tourism. Cancun is also relatively close, and numerous tours launch from there, but tourism is heavy, so expect a more cattle-like treatment. It should also be noted that Mexican whale shark tours are limited by law to having only 2 divers in the water at a time with the dive guide, so swim time is often very limited. This applies whether the divers are snorkeling or scuba diving, which causes more of these dives to be snorkeling instead of scuba diving.
Philippines - There are numerous places to see whale sharks in the Philippines. Oslob is the most reliable for year round sightings but also the most controversial because they use extensive man-made feeding practices to make sure the sharks stick around year round that can potentially cause the sharks to become dependent on humans. Other sites, like Panglao and Southern Leyte have aggressively tried to keep their whale shark tourism as natural as possible, reducing the reliability of sightings outside peak season (November through May). You can also try Donsol which continues to stray away from man-made feeding practices for most dive operators, but doesn't have as developed of a search process as the prior areas leaving the best peak times in only February, March, and April.
Gladden Spit, Belize - Whale sharks frequent the Gladden Spit and Silk Cayes Marine Reserve for the fish spawning season of March through June, peaking in April and May. It's located about 40km off the southeastern peninsular town of Placencia. In season, Placencia's Sea Horse Dive Shop offers both scuba and snorkeling tours to the area.
Utila, Honduras - Off the Northern Caribbean coast of Hondruas lies the small island of Utila. Although whale sharks can be found here year round, the peak season is March and April, and slowest season in September through December. As an island with prime scuba conditions, there are numerous dive resorts in the immediate area, although whale shark sighting tend to be on the north end of the island.
Ningaloo Reef, Australia (West Coast) - Coral spawning season brings in the whale sharks mid-March through July. Most tours depart from Exmouth with local pickup. Because the reef is over 300km long, it's easy to miss the whale sharks. To handle this, dive operators at Ningaloo Whaleshark Swim have their own spotter plane they use to scout with, drastically increasing your chances of swimming with whale sharks.
Feeding - Whale sharks have very large mouths and are filter feeders, which is a feeding mode that occurs in only two other sharks, the megamouth shark and the basking shark. They feed almost exclusively on plankton and small fishes, and pose no threat to humans. Even if a human was to get trapped in their mouth, there's still little danger. Although they can have over 3000 teeth, those teeth are about the size of a match head. And even though their mouth is more than large enough to fit a full grown human, their throat is tiny -- around the size of a baseball.
Swimming Speed - Whale sharks are very fast swimmers, deceptively so because of their size. Their long bodies and tails generate extremely high amounts of thrust with very little effort. As a result, they're difficult to keep up with when swimming alongside them. Divers should stay at least 2m away from their heads and at least 4m away from their tails.
Don't Touch - As with all fish, whale sharks have a protective slime layer on their outer surfaces that helps them resist infection. Divers should not touch any type of shark, including whale sharks, as it can remove this protective layer, increasing the shark's chances of infection. In some places, including Mexico, the law prohibits touching whale sharks.
Phylum: Chordata
Class: Chondrichthyes
Order: Orectolobiformes
Family: Rhincodontidae
Genus: Rhincodon
Species: R. typus