Harbor Porpoise (Phocoena phocoena): Facts and Habitat

What does a harbor porpoise look like?

A harbor porpoise has a stocky, rounded body that is thickest just in front of the dorsal fin. The head is small and blunt, with no obvious beak, and the low, triangular dorsal fin sits in the middle of the back. The flippers are short and dark, and the tail flukes are small.

The back is dark gray, the sides are a paler, slightly speckled gray and the belly is white. Most individuals have a dark stripe running from the corner of the mouth toward the flipper. Inside the mouth are a few dozen small teeth shaped like spades, a key difference from the cone-shaped teeth of dolphins. For a full side-by-side guide, see dolphin vs porpoise.

At sea you rarely see more than a dark back and fin. A porpoise surfaces with a quick, smooth roll, like a slowly turning wheel, and then disappears. In calm weather you may hear the short puff of its breath, which gave it the nickname “puffing pig” in Atlantic Canada.

How big is a harbor porpoise?

The harbor porpoise is one of the smallest whales, dolphins and porpoises in the world; only a few species, such as its relative the vaquita, are smaller. Females are slightly longer and heavier than males.

Being small in cold water is costly. A porpoise loses heat quickly, so it relies on a layer of insulating blubber and a fast metabolism. That means it needs to eat almost constantly, a fact that shapes much of its behavior.

Where do harbor porpoises live?

Harbor porpoises live in cool, shallow seas on both sides of the North Atlantic and North Pacific. In the Atlantic they range from West Greenland to North Carolina, and from the Barents Sea along the coasts of Norway, Britain, Ireland, France and Iberia to northwest Africa. In the Pacific they are found from Japan and the Bering Sea to Alaska, British Columbia and central California. A separate subspecies lives in the Black Sea.

Most stay over the continental shelf in water less than 200 m (650 ft) deep, in bays, estuaries, fjords and harbors, which is how they got their name. They do not live in the Southern Hemisphere, and they are almost absent from the Mediterranean. Populations are split into many regional groups that rarely mix. Read more in where do harbor porpoises live?

What do harbor porpoises eat?

Harbor porpoises are carnivores that eat mainly small fish. Common prey includes herring, sprat, sandeels, capelin, cod, whiting, hake, gobies and other fish that live in schools or near the seabed. They also take squid and shrimp in some areas. Most hunting happens close to the bottom in shallow water.

A 2016 study by Danish researchers, who fitted wild porpoises with sound-recording tags, showed just how hard they work. The animals hunted almost around the clock, making up to about 200 catch attempts an hour by day and up to 550 an hour at night. They caught around 90 percent of the fish they chased, and almost all of them were tiny, only 3–10 cm (1–4 in) long.

This nonstop feeding leaves little room for disturbance. If noise or boats keep a porpoise from hunting for a few hours, it can quickly run short of energy. Most dives last about a minute, but porpoises have been recorded diving to about 220 m (720 ft) and staying down for around five minutes.

Behavior and echolocation

Harbor porpoises are usually seen alone, in pairs or in small groups of up to about 10, often a mother and calf. Larger, loose gatherings sometimes form where food is plentiful. Unlike many dolphins, they rarely leap, do not ride the bow waves of boats and tend to move away from engines.

Porpoises find their prey with echolocation, sending out clicks and listening for the echoes. Their clicks are unusually high-pitched, at around 130 kHz, far above the upper limit of human hearing at about 20 kHz. They do not whistle like dolphins. One leading idea is that these very high, narrow clicks help porpoises avoid orcas, which hear poorly at such frequencies.

Because porpoises click almost all the time, scientists can track them by sound. Underwater recorders called click detectors, moored on the seabed, log every porpoise that passes, day and night and in any weather. This method was used across the Baltic Sea in the early 2010s to estimate how few porpoises remain there and to find their main breeding area, on offshore banks south of the Swedish island of Gotland.

Most harbor porpoises do not make long migrations. Instead they shift inshore and offshore with the seasons, following their prey or avoiding ice. In the western Atlantic, porpoises that spend the summer in the Bay of Fundy and the Gulf of Maine spread south in winter, some as far as North Carolina.

Reproduction and life cycle

Harbor porpoises mature early and breed fast for a cetacean. Females usually have their first calf at about 3–5 years old. Mating takes place mainly in summer, and males have very large testes for their size, a sign that females mate with several males and that sperm compete inside the female.

Pregnancy lasts about 10–11 months, and most calves are born between May and August. A newborn is 67–85 cm (26–33 in) long. Calves nurse for about 8–12 months. Many females become pregnant again while still nursing, so they can produce a calf every year for several years in a row, something few whales or dolphins do.

How long do harbor porpoises live?

Harbor porpoises have short lives for a cetacean. Scientists count growth layers in the teeth to estimate age, and most wild porpoises live about 8–13 years. In a study of 239 dead porpoises from the Gulf of Maine and Bay of Fundy, the vast majority were younger than 12 and the oldest was 17. NOAA Fisheries gives a maximum of about 24 years.

By comparison, a bottlenose dolphin often lives 40 years or more. The porpoise’s fast pace of life, with early breeding and frequent calves, makes up for its short lifespan.

Predators and threats

Natural predators include orcas and large sharks, especially great white sharks. In Scotland’s Moray Firth, Wales and other areas, bottlenose dolphins have been seen attacking and killing harbor porpoises without eating them; the reason is still debated. Since the 2010s, scientists in the North Sea have also documented gray seals attacking and feeding on porpoises.

People are the bigger threat. The main danger is bycatch: porpoises become tangled in gillnets set on the seabed and drown. Several thousand die this way each year across the North Atlantic, the Baltic and the Black Sea. Acoustic alarms called pingers, attached to nets, have been shown to reduce entanglements.

Noise is a growing concern. Busy shipping lanes, seismic surveys and the pile driving used to build offshore wind farms can drive porpoises away, in the case of pile driving sometimes more than 20 km (12 mi) from the site. Pollutants such as PCBs build up in their blubber, and overfishing or climate shifts can reduce the small fish they depend on.

Conservation status

The IUCN Red List classifies the harbor porpoise as Least Concern (assessed in 2020, amended in 2023), with a global population of at least 700,000. A large 2016 survey of European Atlantic waters, from Gibraltar to northern Norway, estimated about 467,000 harbor porpoises, making it one of the most common cetaceans in Europe, and that population appears stable.

Some groups are much less secure. Only about 500 porpoises remain in the central Baltic Sea, an isolated population listed as Critically Endangered, and the Black Sea subspecies is listed as Endangered. In Europe the species is strictly protected under the EU Habitats Directive and a regional agreement called ASCOBANS. In the US it is protected by the Marine Mammal Protection Act, and a take reduction plan uses seasonal net closures and pingers to cut bycatch.

Its tiny cousin in Mexico shows what can happen when bycatch is not controlled: see why is the vaquita almost extinct?

Harbor porpoises and people

People have hunted harbor porpoises for centuries for meat and for blubber used as lamp oil. In Denmark’s Little Belt strait, thousands were caught each year in a drive hunt until it was banned in 1899. Today legal hunting continues mainly in Greenland, as part of traditional Inuit hunting.

Porpoise watching is now popular from headlands and ferries in Wales, Scotland, Cornwall, Denmark, the Netherlands, the Gulf of Maine and the Pacific Northwest. A few porpoises live in human care, such as at the Fjord & Bælt center in Kerteminde, Denmark, where they help scientists study porpoise hearing and the effects of noise.

Myth: porpoises are baby dolphins. They are a separate family of fully grown animals, not young dolphins.

Myth: harbor porpoises are rare. They are among the most numerous cetaceans in European waters, even though few people notice them.

Fact: they can travel up rivers. Porpoises sometimes swim far into estuaries and large rivers, although they are marine animals and always return to the sea.