Dolphin vs Porpoise: Differences and How to Tell Them Apart

Key differences at a glance

Dolphins and porpoises are both toothed whales, and people often use the two names as if they meant the same thing. Biologists place them in separate families. The oceanic dolphin family, Delphinidae, has more than 35 species, from the small Hector’s dolphin to the orca and the pilot whales. The porpoise family, Phocoenidae, has only seven or eight species, depending on how the finless porpoises of Asia are split: the harbor porpoise, the vaquita, Dall’s porpoise, Burmeister’s porpoise, the spectacled porpoise and the finless porpoises.

Despite their dolphin-like shape, porpoises are more closely related to belugas and narwhals than to dolphins. The confusion is partly historical: for centuries English-speaking sailors called many small toothed whales porpoises. The word itself comes, through Old French, from Latin words meaning “pig fish”, and the bottlenose dolphin was often called a porpoise in the US.

Head, beak and teeth

Most dolphins, such as the common bottlenose dolphin, have a clear beak, a snout that sticks out in front of the rounded forehead. Porpoises have a short, blunt head with hardly any beak, which gives them a stubby, rounded profile. There are exceptions: a few dolphins, including Risso’s dolphin, the pilot whales and Hector’s dolphin, also lack an obvious beak.

The most reliable difference is inside the mouth. Dolphins have pointed, cone-shaped teeth, around 18–28 on each side of each jaw in the bottlenose dolphin. Porpoises have flattened, spade-shaped teeth. Scientists use the teeth to identify stranded animals when other features are unclear.

Dorsal fin and body shape

A bottlenose dolphin’s dorsal fin is tall and curves backward like a hook, a shape biologists call falcate. The harbor porpoise has a small, low, triangular fin set in the middle of its back, and the finless porpoises of Asia have no dorsal fin at all, only a low ridge.

Porpoises also look chunkier. The harbor porpoise is stocky, thickest just in front of its fin, while dolphins tend to be longer and more slender. Inside, porpoise neck bones are fused for stability, while the bottlenose dolphin has a more flexible neck and can turn its head slightly.

Which is bigger?

Dolphins are usually bigger. The common bottlenose dolphin measures 2–4 m (6.6–13 ft) and weighs 150–650 kg (330–1,430 lb). The harbor porpoise is one of the smallest whales of all, at 1.4–1.9 m (4.6–6.2 ft); males weigh up to about 61 kg (134 lb) and females up to about 76 kg (168 lb). Unlike many dolphins, female porpoises are usually larger than males.

There is some overlap at the extremes. Dall’s porpoise, the largest porpoise, reaches about 2.3 m (7.5 ft) and 130–220 kg (290–490 lb), while Hector’s dolphin of New Zealand, one of the smallest dolphins, is only 1.2–1.6 m (3.9–5.2 ft) long and weighs 40–60 kg (88–132 lb). At the other end, the orca, the largest dolphin, can grow to about 8–9.8 m (26–32 ft).

Behavior, sounds and life history

Behavior at sea is often the best clue from a distance. Bottlenose and common dolphins are frequently seen leaping and riding the bow waves of boats. Harbor porpoises are shy: they rarely approach boats, and they surface quietly in a smooth roll, often with a short puffing breath that earned them the nickname “puffing pig” in parts of Atlantic Canada. Dall’s porpoise of the North Pacific is the exception, racing alongside boats and throwing up a spray called a rooster tail.

Dolphins are very social and usually travel in groups of a few to about 15, sometimes in hundreds. Harbor porpoises are mostly seen alone or in twos and threes, although loose gatherings of up to 200 have been reported.

Their sounds differ too. Dolphins whistle, squawk and click, and bottlenose dolphins use signature whistles like names; see How do dolphins communicate? Porpoises never whistle. They use narrow-band clicks at around 130 kHz, well above human hearing and above the best hearing range of orcas, which may help them avoid these predators.

The two groups also live at different speeds. A harbor porpoise female can breed at 3–4 years old, carries her calf for 10–11 months and may give birth every year, while usually living only 8–13 years. A bottlenose dolphin starts breeding at 5–15 years, is pregnant for about 12 months, raises a calf for 3–6 years and often lives 40–60 years.

Where to see dolphins and porpoises in Europe and North America

The harbor porpoise is the most common cetacean in the North Sea, where surveys in 2022 estimated roughly 339,000 animals. It lives in cool coastal waters of the North Atlantic, from West Africa and the Bay of Biscay to Norway and Iceland, and in the Black Sea, where it is a separate subspecies. In North America, it is found from West Greenland to North Carolina and on the Pacific coast from central California to Alaska. Only about 500 survive in the central Baltic Sea; read more in Where do harbor porpoises live?

Bottlenose dolphins live in warmer and more varied waters. In Europe, the best-known groups are in the Moray Firth in Scotland, Cardigan Bay in Wales and the Shannon Estuary in Ireland. In North America they range from Massachusetts to Florida, through the Gulf of Mexico and along the Pacific coast of California. Both species can be seen from shore in places such as the Moray Firth, ideally on calm days when fins are easy to spot.

The most endangered porpoise, the vaquita, lives only in the northern Gulf of California, Mexico, where gillnets have reduced it to fewer than a dozen animals; see Why is the vaquita almost extinct?

Do dolphins and porpoises get along?

Not always. In Scotland’s Moray Firth, researchers found that bottlenose dolphins attack and kill harbor porpoises, usually without eating them. Similar attacks have been recorded off Virginia and filmed in Cardigan Bay, Wales, in 2014. Scientists have suggested competition for food, practice for killing young dolphins, which has also been seen in some populations, or simple aggression, but the cause is still debated.

There are no confirmed hybrids between dolphins and porpoises. Hybrids do occur within each family: harbor porpoises and Dall’s porpoises have interbred in the North Pacific, and bottlenose dolphins have produced hybrids with several other dolphins, including the false killer whale. For a different kind of comparison, see dolphin vs shark.