Photograph by Bill Curtsinger, Nat Geo Image Collection
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Harbor porpoises will dive as deep as 656 feet, but they usually stay near the surface, coming up frequently to breathe.

Photograph by Bill Curtsinger, Nat Geo Image Collection

Harbor Porpoise

Harbor porpoises are shy, elusive sea mammals whose numbers are declining primarily because they are frequently caught by accident in commercial fishing nets. Specific numbers are unknown, but some scientists think their enormous range may mean that despite the declines, sizable populations could remain.

Habitat and Diet

Harbor porpoises are found throughout the temperate coastal waters of the Northern Hemisphere. As their name suggests, they prefer the shallows, less than 500 feet deep, and are commonly seen in harbors and bays. They are also known to frequent inland waters, including rivers, estuaries, and tidal channels.

Harbor porpoises survive primarily on fish and are among the smallest of the cetaceans, reaching an average size of about 5 feet and 121 pounds. They can dive deep, more than 655 feet, but usually stay near the surface, coming up about every 25 seconds to breathe with a distinctive puffing noise that resembles a sneeze.

Differences With Other Dolphins

Unlike their dolphin relatives, they have a blunt, rounded head rather than a prominent forehead and snout. Their mouths are short with black, inward-curving lips and spatulate, or spade-shaped, teeth. Their necks, short and immobile, are virtually undistinguishable from their grayish bodies, which taper to a tail with small, curved flukes and a middle notch.


Because of their retiring nature, scientists know little about the behavior of these creatures in the wild, and much species research is focused on specimens rescued or killed as bycatch in fishing nets. In the Gulf of Maine region in the early 1990s, for example, as many as 3,000 were annually drowned in commercial fishing gear like gill nets. Populations are also harmed by chemical and noise pollution.