Porpoises are the small, shy members of the whale family. Most people have seen far more dolphins than porpoises, and many have never knowingly seen a porpoise at all. That is partly because porpoises are quiet: they rarely leap, rarely ride bow waves (with one big exception), and tend to surface with a brief, rolling glimpse of back and fin before disappearing. In Florida, you will often hear boat captains call bottlenose dolphins “porpoises,” an old regional habit that adds to the confusion. Biologically, though, porpoises are their own family with only seven species, and several of them are among the least-known mammals on Earth.

This page is our hub for porpoises: what makes a porpoise a porpoise, a guide to all seven species, and links to the deeper pages on each one.

What makes a porpoise different from a dolphin?

Porpoises have spade-shaped teeth, short rounded heads with no beak, and usually a small triangular dorsal fin. Dolphins have cone-shaped teeth, usually a beak and a curved, hooked fin.

Porpoises and dolphins are both toothed whales (odontocetes), but they belong to separate families that split millions of years ago. Their closest relatives are not each other in the way people assume: porpoises are more closely related to the beluga and narwhal family than you might expect from appearance. Porpoises are generally smaller and stockier than dolphins, which helps them hold heat in the cold water many species prefer. They also tend to live in small groups rather than the big, noisy pods typical of many dolphins. Our full comparison is at dolphin vs porpoise.

Porpoises are also acoustically distinctive. They produce narrow-band, high-frequency clicks, well above the range of human hearing and above the hearing of killer whales, their main predator. Many researchers think this “acoustic crypsis” helps porpoises echolocate without being overheard. It is also why acoustic detectors are used to count porpoises, including the near-invisible vaquita.

Harbour porpoise

The harbour porpoise (Phocoena phocoena), called the harbor porpoise in North America, is the porpoise most people mean. It lives in cool coastal waters of the North Atlantic and North Pacific, including the North Sea, the Baltic, the Gulf of Maine, the Pacific Northwest and the Black Sea, and is often seen in bays, estuaries and harbours, hence its name. It is small, dark grey above and paler below, with a low triangular fin, and usually travels alone or in small groups. Its biggest threat is accidental capture in gillnets; some isolated populations, such as the Baltic Proper harbour porpoise, number only a few hundred.

Vaquita

The vaquita (Phocoena sinus) lives only in the far northern Gulf of California, Mexico, and has the smallest range of any marine mammal. It was described scientifically only in 1958. It has dark rings around its eyes and dark lips, and is the smallest porpoise. Drowning in gillnets, especially those set illegally for the totoaba fish, whose swim bladder is trafficked to Asia, has driven it to the edge: recent surveys have estimated only around ten animals. It is the rarest marine mammal in the world; see the rarest sea animals for context.

Burmeister’s porpoise

Burmeister’s porpoise (Phocoena spinipinnis) lives along the coasts of South America, from northern Peru around Cape Horn to southern Brazil. It is dark grey to almost black and has an unusual dorsal fin set well back on the body and angled backwards, with small bumps called tubercles on its leading edge. It is rarely seen alive at sea because it surfaces discreetly in often rough water, and much of what is known comes from animals caught in fishing nets, which remains its main threat.

Spectacled porpoise

The spectacled porpoise (Phocoena dioptrica) is one of the least-known cetaceans. It lives in the cold waters of the Southern Ocean, recorded off southern South America, the Falklands, South Georgia, Tasmania, New Zealand’s sub-Antarctic islands and other remote islands. It is sharply two-toned, black above and brilliant white below, with a dark ring around the eye outlined in white, like a pair of spectacles. Adult males carry a large, rounded dorsal fin. Most records come from stranded animals; living spectacled porpoises have been seen and photographed only a handful of times.

Dall’s porpoise

Dall’s porpoise (Phocoenoides dalli) is the largest and fastest porpoise and the exception to the shy rule. It lives across the cold North Pacific from Japan and Russia to Alaska and California. Stocky and black with big white flank patches, it is sometimes mistaken for a baby killer whale. Dall’s porpoises are energetic and often ride bow waves, throwing up a characteristic V-shaped plume of spray called a “rooster tail” as they swim fast at the surface. It is the porpoise you are most likely to see from a ferry or whale-watching boat in Alaska or British Columbia.

Finless porpoises

The two finless porpoises have no dorsal fin at all, just a low ridge along the back covered in tiny bumps. The Indo-Pacific finless porpoise (Neophocaena phocaenoides) lives in shallow coastal waters from the Persian Gulf through India and Southeast Asia to southern China. The narrow-ridged finless porpoise (Neophocaena asiaeorientalis) lives in the waters of China, Korea and Japan, and includes the famous Yangtze finless porpoise, the only porpoise that lives in fresh water, in China’s Yangtze River and its lakes. The Yangtze population is treated as Critically Endangered; some scientists argue it is a separate species. Following the extinction of the Yangtze river dolphin, the baiji, China banned fishing on the Yangtze for ten years from 2020, and recent surveys suggest finless porpoise numbers there have begun to stabilise.

How porpoises live: diet, breeding and lifespan

Porpoises live fast by whale standards. Most species eat small schooling fish, squid and crustaceans, and because they are small animals in cool water, they need to eat often; studies of harbour porpoises suggest they forage almost constantly, catching hundreds of small fish an hour, and cannot go long without food. Females of many species mature at around three to five years old and can give birth almost every year, after a pregnancy of roughly ten to eleven months. Calves are born tail first and stay with their mothers for several months. Lifespans are short for cetaceans: harbour porpoises rarely live past about 12 years in the wild, and few porpoises of any species are known to exceed about 20–24 years.

That fast pace means porpoise populations can recover relatively quickly when threats are removed, at least compared with long-lived, slow-breeding whales and dugongs. It also means they feel food shortages and disturbance quickly. A porpoise that is repeatedly driven off its feeding grounds by noise or boat traffic can lose condition in days rather than months.

What threatens porpoises?

Bycatch, accidental drowning in fishing nets, is the biggest threat to almost every porpoise species. Porpoises live close to shore, where gillnets are common, and their echolocation does not always detect thin nylon mesh. Other threats include noise from shipping, seismic surveys and pile driving for offshore construction, pollution, and declines in the fish they eat. In some places, acoustic deterrent “pingers” on nets and seasonal fishing closures have cut porpoise bycatch. Where those measures are enforced, populations such as the harbour porpoise in parts of the North Sea are doing reasonably well. Where they are not, as the vaquita shows, the outcome can be catastrophic.

From my years in the reef hobby I have learned that the animals that struggle most are often the ones with the narrowest needs: a coral that only thrives in one flow pattern, a fish that only eats one food. The vaquita’s tiny range is the ocean-scale version of that lesson. When an animal only lives in one small corner of the sea, every threat in that corner counts.

Porpoise guides on TheSea.Org

More pages on porpoises and their relatives: