Is a Whale Shark a Whale or a Shark? The Name Explained

Why is it called a whale shark?

The whale shark was first described for science in 1828, from a 4.6 m (15 ft) shark caught in Table Bay, South Africa, and named by the Scottish army surgeon and zoologist Andrew Smith. Its scientific name, Rhincodon typus, refers to its tiny, rasp-like teeth rather than to whales.

The common name simply reflects how whale-like it is in size and lifestyle. Adults are commonly 8–12 m (26–39 ft) long, larger than many whales, and the biggest reliably recorded was about 18.8 m (62 ft). It cruises slowly near the surface with its huge mouth open, much as baleen whales do. Other languages use different images: in Japan it is jinbei-zame, after a patterned summer garment, and in Madagascar marokintana, “many stars”, after its spots.

What makes the whale shark a shark?

Everything about the whale shark’s body says shark. Its skeleton is made of cartilage, the flexible material in your nose and ears, rather than bone, a feature it shares with all sharks and rays; see Do sharks have bones? Its skin is covered with tiny tooth-like scales called dermal denticles, and five pairs of gill slits run down each side of its head.

Its tail is upright and sweeps from side to side, like the tail of other sharks. It also has no swim bladder; instead, a large, oily liver helps it control its buoyancy. Within the shark family tree, it belongs to the carpet sharks (order Orectolobiformes). Its closest living relatives are the zebra shark, the nurse sharks and the wobbegongs, most of which are small and live on the seabed.

Whales, by contrast, are mammals. Their skeletons are made of bone, their skin is smooth and lined with blubber, and their tail flukes lie flat and beat up and down. Their nearest living relatives on land are hippos. The last common ancestor of whale sharks and whales lived more than 400 million years ago, long before either group existed, which is why scientists see the two as entirely separate kinds of animal.

Gills vs blowholes: how they breathe

The clearest difference is how each animal gets oxygen. A whale shark takes in water through its mouth and pushes it out over its gills, where blood picks up the oxygen dissolved in the water. Small openings behind the eyes, called spiracles, can also take in water. The shark never needs to surface to breathe and can stay in deep water for days.

A whale breathes air with lungs, like you. It must rise to the surface and breathe through a blowhole on top of its head; baleen whales have two blowholes and toothed whales have one. The visible “spout” is the whale’s warm breath condensing in the air. A whale that cannot reach the surface will drown, while a whale shark taken out of water suffocates. The details are in How do whales breathe?

Babies, milk and body heat

Whale sharks and whales also raise their young in completely different ways. A female whale shark carries eggs that hatch inside her body, and she gives birth to live pups about 40–60 cm (16–24 in) long. One female caught off Taiwan in the 1990s carried about 300 embryos. The pups get no care or milk and must fend for themselves from birth.

A whale gives birth to a single calf after a pregnancy of about a year. The mother feeds it rich milk for months and keeps it close while it learns to dive and find food. A blue whale calf is already 6–7 m (20–23 ft) long at birth.

Body temperature differs too. Whales are warm-blooded and keep their bodies at about 36–37 °C (97–99 °F), insulated by thick blubber. A whale shark’s body stays close to the temperature of the water around it, although its sheer bulk means it cools down and warms up slowly. Tracking suggests that it returns to warm surface waters after deep, cold dives.

Filter feeding: the whale-like habit

The habit that most reminds people of whales is filter feeding. A whale shark swims with its mouth open or sucks in water, and spongy filter pads in its throat, probably modified gill rakers, trap plankton, fish eggs and small fish. Baleen whales, such as the blue whale and humpback whale, do the same job with baleen, comb-like plates of keratin that hang from the upper jaw.

The two groups evolved filter feeding separately, a classic example of convergent evolution, in which unrelated animals arrive at similar solutions to the same problem. Huge filter feeders can grow so large because plankton is plentiful and low in the food chain. Learn how the baleen system works in What are baleen whales?, or see the two giants side by side in whale shark vs blue whale.

Other animals with misleading names

The whale shark is far from the only animal with a confusing name. Animal names were often given long before scientists understood how species are related, and many are based on looks alone:

• Killer whale (orca): a member of the dolphin family, as explained in Is an orca a whale or a dolphin?
• Starfish and jellyfish: invertebrates, not fish at all.
• Seahorse: a true fish, despite its horse-like head.
• Whales and dolphins: often called “fish” in the past, but mammals.

So the best short answer is that the whale shark is a giant, gentle shark with a whale-sized body and a whale-like way of eating, but nothing else in common with whales.