Porpoises are the smallest toothed whales, divided into three genera, and 6 species. The best known is the harbour porpoise (Phocoena phocoena). Four subspecies are known of the harbour porpoises: P. p. phocoena in the North Atlantic, P. p. vomerina in the eastern North Pacific, P. p. relicta in the Black sea and one more unamed subspecies in the western North Pacific. The other five species are vaquita (P. sinus), spectacled porpoise (P. dioptrica), Burmeister's porpoise (P. spinipinnis), finless porpoises (Neophocaena phocaeniodes) and two subspecies of Dall's porpoises - Dall's porpoise (Phocoenoides dalli dalli) and True's porpoise (P. d. truei). The largest porpoise is the Dall's porpoise reaching a length of 2,3 meters and can weight as much as 220 kg, the other species are smaller with the shortest being the vaquita reaching 1,5 meters and the lightest being the finless porpoise weighting between 30 - 45 kg. Porpoises are known to live around 8-10 years but might live as long as 20 years (harbour porpoises are known to live for 23 years).
Porpoises are different from dolphins, porpoises are smaller and don't have the long beak as most dolphin species have, they also have spade-shaped teeth unlike dolphins conical teeth and there are also differences in the brain and vocalization. Like the dolphins and other toothed whales they use echolocation to find their food, and they feed mainly on small schooling fish, cephalopods and crustaceans.
The behaviour is different from dolphins too, porpoises are more timid animals, swims slow and are not very active on the surface. They live alone or in small pods, and the most common social group is mother and calf. Harbour porpoises can dive as long as 6 mins. Dall's porpoises are more active then other porpoises and they are one of the fastest cetaceans in the world reaching speeds up to 55 km/h, just like one of their threats: the orca or killer whale.
By-catch is the main threat to the porpoises. Gill nets are a big threat to the harbour porpoises, the smallest cetacean in the North Atlantic. Habitat destruction (especially no calm bays for the females to nurse their young due to boat traffic), pollution and lack of food are also big threats, to porpoises as well as many other cetaceans. The harbour and finless porpoises are two species that also face the threat of being captured for captivity. The Dall's and True's porpoises are hunted by the thousands outside of Japan every year (some years as many as 40 000). Spectacled porpoises are taken intentionally off of Southern Chile for use as crab bait, also the Burmeister's porpoise is taken off the coats of Chile and Peru for its meat for human consumption and as crab and shark bait.
In the Azores there's only been one recording of a harbour porpoise, that was found stranded in 2004.
Status for the only porpoise in the North Atlantic, the harbour porpoise: Least Concern, population in the Black sea is Endangered and in the Baltic sea Critically Endangered.
The vaquita is on the brick of extinction, with only about 100 to 500 in the world.