| Harbour porpoise
Porpoise refers to a group of dolphin-like mammals of the family Phocoenidae, consisting of three genera and eight living species found primarily in coastal waters world-wide.
The name itself has its origins in the Middle English porpoys (ca. 1275–1325), which itself came from the Medieval Latin porcopiscis, a combination of two Latin words (porcus + piscis) which, quite insultingly, gave the animal the name "pig-fish", and is today reflected in the scientific family and genera names. In the modern sense, however, the term "porpoise" has come to mean a "leap" or "plunge", in reference to the animals habits of leaping from the water at speed.
In immediate appearance porpoises are hardly indistinguishable from dolphins, so much so that even the names for both animals are used interchangeably. They are small, with the largest species (Phocoenoides dalli) reaching a length of up to 7.5 feet and weighing 370 to 490 pounds, while the smallest species (Phocoena sinus) comes in at 4.9 feet and up to 120 pounds - the smallest completely-marine mammal - barely larger than the sea otter (Enhydra lutris), which is the smallest marine mammal of any kind.
The primary differences from dolphins are in the structure of the teeth, which are spade-shaped and flattened; dolphin teeth are conical. Porpoises also have a more dense, stocky build. The heads are small, blunted, and lack a beak (the extinct porpoise Semirostrum ceruttii had a well-developed beak with a strongly protruding lower jaw). The dorsal fin is triangular rather than hooked, and the front fins are rather short and shifted towards the head. Body coloration is contrasting, with black, white and gray areas, or monochromatic, with the occasional albino. And unlike dolphins, females are slightly larger than males.
Porpoises of the genera Phocoena and Neophocaena prefer to stay in bays, coves, fjords, estuaries and lower rivers. They are comparatively slow, and travel in small groups of 6 to 20 individuals. Dall's and spectacled porpoises live in the open sea, in pods of several hundred to thousands; they are fast and agile swimmers, reaching speeds of up to 35 mph. They are capable of echolocation, using a variety of clicks and whistles for communication with each other as well as for hunting. The diet of porpoises consists mainly of fish, as well as cephalopods and lamellar molluscs and crustaceans. In search of food, they dive to a depth of just over 200 feet and for a period of no more than 6 minutes. They give birth to one, rarely two calves, and usually in the summer months.
- Genus Neophocaena
- Genus Phocoena
- Genus Phocoenoides
- Dall's porpoise, Phocoenoides dalli
Bycatch deaths in fishing nets are their greatest threat, with the vaquita in the Gulf of California classified as critically endangered by the ICUN; its wild numbers have dwindled to 18 mature individuals as a result. In some countries, they are hunted for food or to use their meat as bait. Porpoises are rarely kept in zoos or dolphins, as they are unable to adapt well to life in captivity and are not as easy to train as dolphins.