Head to head
Whale vs Shark
Whales and sharks are both large, streamlined ocean animals with fins, and the very largest of each patrol the open sea straining tiny prey from the water. But one is a mammal and the other a fish, and almost everything below the surface of that shape is different.
| Whale | Shark | |
|---|---|---|
| Animal group | Mammal (Cetacea) | Fish (cartilaginous) |
| Skeleton | Bone | Cartilage |
| Breathing | Air, through a blowhole, must surface | Extracts oxygen from water through gills |
| Body temperature | Warm-blooded | Cold-blooded (a few are partly warm) |
| Tail and swimming stroke | Horizontal flukes, up-and-down | Vertical fin, side-to-side |
| Young | Live birth, nursed on milk | Eggs or live young, no milk |
| Largest species | Blue whale, ~30 m, ~180 t | Whale shark, ~18 m |
| Skin | Smooth, hairless | Rough, covered in denticles |
Whale vs Shark: common questions
Is a whale shark a whale or a shark?
A whale shark is a shark, and a fish. The name refers only to its enormous, whale-like size, since at up to around 18 metres it is the largest fish in the world. In every anatomical respect it is a shark: a cartilage skeleton, gill slits, denticle-covered skin, and a vertical tail fin that beats side to side. Like the baleen whales, though, it makes its living by filter feeding, cruising slowly with its huge mouth open and straining plankton, fish eggs, and small fish from the water, which is another case of a shark and a whale converging on the same lifestyle from different starting points.
Which is more dangerous to people, a whale or a shark?
Neither is a major danger, and the risk from both is often exaggerated. Sharks cause on average fewer than ten human deaths worldwide per year, and the vast majority of the roughly 500 shark species have never harmed a person; a small number of large predatory species account for almost all serious incidents, usually cases of mistaken identity. Whales essentially never attack people. Injuries involving whales are rare accidents, such as a boat strike, a breaching whale landing on a small vessel, or a captive orca incident, rather than predation. Wild killer whales, the ocean's top predator, have no confirmed record of killing a human.
Did whales evolve from fish?
Not directly. Whales are mammals, and their ancestors were fish only in the sense that all four-limbed land vertebrates trace back to fish that crawled onto land around 375 million years ago. From there the whale lineage spent hundreds of millions of years as land animals, and the immediate ancestors of whales, around 50 million years ago, were small deer-like hoofed mammals living near water. Those animals gradually returned to the sea, evolving flippers from legs, a blowhole from nostrils, and flukes from a tail, but keeping the mammalian traits of warm blood, air breathing, live birth, and milk. So a whale is a mammal that went back to the water, not a fish that stayed.