6 November 1998

Whale sharks are huge, filter-feeding members of the family Rhicondontidae and are actually sharks. They are the largest fish in the world, even though they may seem more "whale-like" because of their size and the way they eat. The whale shark (Rhiniodon typus) strains small crustaceans and fishes out of the water with sieves on its large gills. Some whales use similar straining methods and are considered filter-feeders as well.

Divers consider it a special treat to encounter a whale shark in the open ocean.

Whales, however, are mammals, not fish. Whales have skin and hair, lungs and need to surface to breath air. They are warm-blooded. Whale sharks have the tough skin typical of other types of sharks, five gill slits and are cold-blooded.

Even though it catches its food by straining water through its gills, the whale shark does have teeth -- several thousand in about a dozen rows in its jaws. Each tooth is only 1/12th of an inch long. When feeding, whale sharks sometimes stop swimming and appear to be standing on their tails so that they are vertical in the water. When they open their mouths in this position, they gulp down krill and small fish.

The whale shark is gray-brown to reddish or greenish. It is distinguished by a unique checkered color pattern made up of whitish spots and bars. Its shape is somewhat different from other shark species in that its head is wider than other sharks and it has a humped back and a large lunate or crescent-shaped tail. The whale shark probably gets its name from its size. In 1919, a whale shark estimated at 60 feet was caught in the Gulf of Thailand. It was so large, fishermen were unable to haul it ashore, and no measurements were taken. The largest accurately measured whale shark was a 40-foot, 7-inch male caught in Bombay, India, in 1983. Its mouth was 4-feet, 6-inches wide and its pectoral fins were more than 6 feet, 6 inches long. By contrast, the blue whale, (Balaenoptera musculus), the largest living whale and mammal, grows to 98 feet in length.

Rhiniodon typus lives in the open sea and can be found world wide; in the Atlantic it ranges from as far north as New York to as far south as Brazil. It prefers temperate or tropical waters.

The basking shark (Cetorhinus maximus) is similar in size, but lacks the unusual color pattern. It is member of a different family of sharks, the Cetorhinidae. Generally, both the whale and basking sharks are considered harmless. In fact, divers often refer to whale sharks as the "gentle giants".

Related Links

Shark Research Institute