Harbor porpoise

Harbor porpoises live in cool seas in the north of the world.

They swim near the coast, in bays and harbors. That is how they got their name!

Harbor porpoises live in cool northern seas: the North Atlantic, the North Pacific and the Black Sea. They like shallow water near the coast, such as bays, river mouths, harbors and fjords, usually less than about 200 meters deep.

They are found from the United States and Canada to Greenland, Iceland and Norway, around Britain and Europe and down to West Africa, and from Japan and Russia to Alaska and California. The harbor porpoise is the only whale or dolphin that regularly lives in the Baltic Sea.

The IUCN describes a range in cold temperate to subpolar Northern Hemisphere waters, mostly over the continental shelf. In the North Pacific it runs from central California and northern Honshu to the southern Beaufort and Chukchi seas; in the North Atlantic from the southeastern United States to southern Baffin Island, and from Senegal to Novaya Zemlya, including Greenland, Iceland and the Faroes. It is the only cetacean that currently occurs regularly in the Baltic Sea, and it lives in the Black Sea, Sea of Marmara and Sea of Azov but not, regularly, in the Mediterranean.

Porpoises typically use bays, estuaries and tidal channels less than about 200 meters deep, though tagged animals off Greenland range beyond the 300-meter contour and have dived to at least 400 meters.

Harbor porpoises eat fish.

They like fish that swim in big groups, like herring. Sometimes they eat squid and octopus too.

Harbor porpoises eat mainly fish, especially fish that swim in schools, such as herring and mackerel. Now and then they catch squid and octopus.

They also hunt fish near the seabed, and what they eat changes from place to place. When one kind of fish becomes scarce, porpoises switch to another.

Harbor porpoises take a wide variety of fishes and cephalopods, and the main prey varies by region (IUCN). Small schooling fish such as herring are important, but feeding near the seabed is typical in many areas; in much of the North Atlantic the diet is dominated by a few prey species from six fish families, including cod relatives, herrings and sand eels, while small gobies become more important when prey are counted by number.

The IUCN notes that porpoises shift their diet when important prey declines, and that the original prey does not always return to the diet when stocks recover. NOAA lists herring and mackerel as main prey, with occasional squid and octopus.

Harbor porpoises are shy.

They swim alone or with one or two friends. They do not play next to boats like some dolphins do.

Harbor porpoises are shy animals. They are usually seen alone, in pairs or in small groups of up to about 10, although groups of up to 200 have been reported.

Unlike many dolphins, they do not ride the waves in front of boats. They often avoid coming up near boats at all. Many move between the coast and deeper water with the seasons, following their food or staying where the water is free of ice.

Harbor porpoises usually occur singly, in pairs or in groups of up to 10, with occasional aggregations of up to 200 (NOAA). They do not bow-ride and often avoid surfacing near vessels, which makes them harder to study than more conspicuous dolphins.

Most seasonal movements appear to be between inshore and offshore waters and may follow prey or ice-free water. Their coastal habits keep them close to busy human waters, which exposes them to fishing gear, pollution and underwater noise.

There are many harbor porpoises.

But some get caught in fishing nets by accident. Noise and dirty water can also cause problems. People are working to keep porpoises safe.

Harbor porpoises are listed as Least Concern: there are well over a million of them. But because they live near the coast, they often get caught by accident in fishing nets, especially gillnets, which are walls of net that hang in the water.

Some groups are in serious trouble. The porpoises of the Baltic Sea are critically endangered, with only a few hundred left, and the Black Sea porpoises are endangered. Underwater noise, pollution and overfishing of their food add to the problems.

The IUCN's 2023 global assessment (assessed 2020) lists the species as Least Concern with an unknown trend: estimates total well over a million. Bycatch, especially in gillnets, occurs throughout the range, and porpoises are hunted directly in some areas, especially Greenland. Contaminants, noise and prey depletion also affect their health.

The Baltic Sea subpopulation is Critically Endangered; acoustic monitoring in 2011 to 2013 estimated about 497 animals. The Black Sea subspecies is Endangered, and the small Afro-Iberian population may need its own assessment. In the United States, harbor porpoises are protected under the Marine Mammal Protection Act, and NOAA monitors fisheries to reduce bycatch.