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New Jersey Endangered and Threatened Species Field Guide

Image of This is often the best view of a harbor porpoise most people get because they are a small and shy marine mammal.Zoom+ This is often the best view of a harbor porpoise most people get because they are a small and shy marine mammal. Image courtesy of Flickr user Sean McCann.

Harbor porpoise

Phocoena phocoena

Species Group: Mammal

Conservation Status

State: Special Concern



The harbor porpoise is New Jersey’s smallest species of whale at a length of 5 to 5 ½ feet. Females are slightly larger than males. They have a very short beak and a small triangular dorsal fin halfway down their body. Overall coloration is darker along their back and lighter on their belly. They also have a dark chin and eye patch.

This is a very difficult species to observe and identify. They are small (for a marine mammal) and spend little time at the surface when they come up to breathe. In choppy seas especially, their small dorsal fin is easy to miss.

Image of Range of the harbor porpoise in New Jersey.Zoom+ Range of the harbor porpoise in New Jersey.


The harbor porpoise can be found within temperate coastal waters within the North Atlantic and North Pacific Oceans, as well as within the Black Sea. Within the western North Atlantic Ocean, they can be found as far south as North Carolina and as far north as Greenland.

In New Jersey waters, they can be found within the Atlantic Ocean as well as bays, estuaries, and harbors. This is a coastal species, never ranging too far from land and generally found over the continental shelf. They are typically found in New Jersey waters only during the winter, but may occasionally be observed during other seasons as well.


The harbor porpoise feeds on schooling fish usually less than 16 inches in size. Typical prey includes herring and capelin. They will also feed on squid.


This is generally a solitary animal. They usually travel alone or in groups of 2-5 individuals. Little is known about their social behavior as they are difficult to observe due to their small size. They are also difficult to approach because they are very shy and are less likely than dolphins to approach a boat.

The harbor porpoise gives birth to its young between May and August. Mothers give birth to only one young and a gestation period of 10-11 months. The calf will nurse for 6-10 months and may remain with its mother for a longer period of time. Males appear to play no role in raising the calf.

Some harbor porpoise populations, including those in New Jersey waters, migrate throughout the year. The porpoises found in New Jersey waters during the winter may move as far north as Greenland eastern Canada during the summer.

They may live to an age of 25 years, but only a small percentage of them survive past the age of 12 years. Harbor porpoises have a number of predators due to their small size. Large sharks or killer whales will prey on them. Adult bottlenose dolphins have also been observed killing harbor porpoises, but they do not feed on them. The reason for this behavior is unknown.


There may be hundreds of thousands of harbor porpoises around the world. Some of the individual populations, however, are very small and their ranges are cut-off from other populations. Some populations are substantially reduced from historic levels because of that isolation.

Negative impacts to whale habitat may take the form of offshore development, pollution, noise, overfishing, and climate change. Offshore energy development may destroy whale habitat or displace whales which would normally use the area. Oil spills and other chemical pollutants are also a threat to whales and the prey which they feed on.

Another form of pollution is noise pollution. Porpoises’ primary means of communication, navigation, locating food, locating mates, and avoiding predators and other threats is through their sense of hearing, which is much more highly developed than that of humans. Noise pollution created by ship traffic or offshore construction may negatively impact whales by disrupting otherwise normal behaviors associated with migration, feeding, alluding predators, rest, breeding, etc. Any changes to these behaviors may decrease survival, simply by increasing efforts directed at avoidance of the noise and the perceived threat.

Active sonar, such as that used by the Navy, also threatens marine mammals by disrupting navigation, foraging and communication abilities. There have been instances of stranding and death caused by acoustic trauma. This may be due to a fatal injury within the structure of the ear, or may result from the distressed animal surfacing too rapidly and developing nitrogen bubbles within their blood (decompression sickness). In addition to the direct threat posed by active sonar, it may indirectly harm marine species by causing changes in behavior.

Overfishing of the fish and squid which harbor porpoises feed upon is another potential cause for concern as well as the potential impacts of global climate change. This issue may be the greatest long-term threat to the marine habitat and its species. Climate change may significantly alter the chemical balance of the seas, off-shore currents, and plankton distribution and abundance, thereby affecting migration routes of marine species and impacting the entire food web.

The greatest immediate threat to harbor porpoises is entanglement in fishing gear. Individuals may become wrapped-up in nets and/or fishing line around their tail, mouth, or other body part. Discarded nets and lines may float at sea for decades or become snagged on rocks or debris at the ocean bottom. Once entangled in fishing gear, the porpoise may eventually drown since they require air to breathe.

The harbor porpoise, like all marine mammals has been provided with protection with the Marine Mammal Protection Act of 1972. Although they are not considered endangered or threatened within the United States, it is illegal to harm them in any way. A status review completed in 2009 by the New Jersey Endangered and Nongame Species Program found that the harbor porpoise should be listed as a species of special concern. This listing is due to the high numbers of porpoises dying as bycatch in some fisheries. Further survey effort targeted at this species will be necessary in order to determine distribution and abundance within New Jersey waters.

Text written by Michael J. Davenport in 2011.

Scientific Classification

Kingdom: Animalia
    Phylum: Chordata
       Class: Mammalia
          Order: Cetacea
             Family: Phocoenidae
                Genus: Phocoena
                   Species: P. phocoena

Find Related Info: Special concern, Mammals

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