Mammals
Whale
Cetacea · also called whales, cetaceans
A whale is a mammal that went back to the sea and stayed. Fifty million years ago its ancestors were small hoofed animals on land; today a whale cannot come ashore without its own weight crushing it. It still breathes air, nurses its young on milk, and is warm-blooded — all now done in the open ocean, by animals that include the largest creature ever to have existed.
Overview
Whales are the order Cetacea, around 90 species, in every ocean and up several large rivers. They split into the baleen whales — blue, fin, humpback, right, and grey whales — which strain small prey through fringed plates, and the toothed whales — sperm whales, beaked whales, and all the dolphins and porpoises — which hunt fish and squid. Their closest living relative on land is the hippopotamus.
The blue whale
The blue whale reaches about 30 m and 180 tonnes, heavier than any dinosaur. Its heart is the size of a small car, and its tongue alone can weigh as much as an elephant.
Living in water, breathing air
A whale decides to breathe, surfacing to use the blowhole on top of its head, so it can never be fully unconscious — it sleeps one brain hemisphere at a time. Toothed whales echolocate, reading the echoes of their own clicks; male humpbacks sing long songs that change year to year and spread between populations. Bowhead whales have been aged at over 200 years, likely the longest-lived mammals.
Death that feeds the deep
A dead whale that sinks becomes a whale fall, supporting scavengers, then bone-eating worms and bacteria, for decades — an oasis on the bare deep-sea floor.
Status
Whales as a group are Not Evaluated. Industrial whaling killed around three million whales in the 20th century, cutting the great whales by over 90 per cent, before a 1986 moratorium. Humpback and southern right whales have recovered strongly, but the North Atlantic right whale is down to ~350 and the vaquita porpoise to around 10, from net entanglement, ship strikes, noise, and prey loss.
Whale: common questions
What is the difference between a whale, a dolphin, and a porpoise?
They are all cetaceans, and dolphins and porpoises are simply small toothed whales, so every dolphin and porpoise is a whale in the broad sense. In common usage, whale is kept for the larger species, dolphin for the sleek, beaked, highly social small toothed whales such as the bottlenose, and porpoise for a group of smaller, chunkier animals with rounded heads and spade-shaped teeth. The killer whale, or orca, is the largest dolphin. The blue whale, humpback, and right whales are baleen whales, a separate branch with no teeth, and are not closely related to dolphins at all beyond both being cetaceans.
How do whales sleep if they have to breathe consciously?
They sleep with half the brain at a time. In a whale or dolphin, breathing is a voluntary act, not an automatic reflex as it is in humans, so an animal that lost consciousness completely would drown. Instead cetaceans use unihemispheric slow-wave sleep, shutting down one half of the brain and closing the opposite eye while the other half stays awake enough to control surfacing and breathing and to watch for danger. After a couple of hours the halves swap. Some whales rest by hanging vertically or lying still just below the surface, and calves and mothers may go days with very little sleep after a birth.
Why did whaling drive some whales close to extinction?
Whales were hunted for oil, used for lighting, lubrication, and later margarine, and for baleen and meat, and industrial whaling in the 19th and especially the 20th century, with factory ships and explosive harpoons, killed an estimated three million whales in the 1900s alone. The largest and most valuable species were taken first, and blue, fin, right, and humpback whales were reduced by well over 90 per cent. Because whales breed slowly, producing one calf every two to four years, populations could not keep pace. A global moratorium on commercial whaling took effect in 1986, and most species have been recovering since, though a few started too low or face new threats.
Are whales still in danger today?
Some are, from causes other than hunting. The main modern threats are entanglement in fishing nets and lines, which drowns or slowly kills large whales and is the leading cause of death for the North Atlantic right whale; collisions with ships along busy coasts and shipping lanes; underwater noise from vessels, sonar, and seismic surveys, which disrupts communication and feeding; chemical and plastic pollution; and the loss of prey to fishing and to climate-driven changes in the ocean. The vaquita, a small porpoise in the Gulf of California, is down to around ten individuals because of gillnets and is likely to be the next cetacean lost.