| Porpoise Temporal range: Miocene to Recent
| |
|---|---|
| |
| The harbor porpoise (Phocoena phocoena) | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Superfamily: | Delphinoidea |
| Family: | Phocoenidae Gray, 1825 |
| Type genus | |
| Phocoena Cuvier, 1816
| |
| Genera | |
Porpoises (/ˈpɔːrpəsɪz/) are small dolphin-like cetaceans classified under the family Phocoenidae. Although similar in appearance to dolphins, they are more closely related to narwhals and belugas than to the true dolphins.[1] There are eight extant species of porpoise, all among the smallest of the toothed whales. Porpoises are distinguished from dolphins by their flattened, spade-shaped teeth distinct from the conical teeth of dolphins, and lack of a pronounced beak, although some dolphins (e.g. Hector's dolphin) also lack a pronounced beak. Porpoises, and other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates.
Porpoises range in size from the vaquita, at 1.4 metres (4 feet 7 inches) in length and 54 kilograms (119 pounds) in weight, to the Dall's porpoise, at 2.3 m (7 ft 7 in) and 220 kg (490 lb). Several species exhibit sexual dimorphism in that the females are larger than males. They have streamlined bodies and two limbs that are modified into flippers. Porpoises use echolocation as their primary sensory system. Some species are well adapted for diving to great depths. As all cetaceans, they have a layer of fat, or blubber, under the skin to keep them warm in cold water.
Porpoises are abundant and found in a multitude of environments, including rivers (finless porpoise), coastal and shelf waters (harbour porpoise, vaquita) and open ocean (Dall's porpoise and spectacled porpoise), covering all water temperatures from tropical (Sea of Cortez, vaquita) to polar (Greenland, harbour porpoise). Porpoises feed largely on fish and squid, much like the rest of the odontocetes. Little is known about reproductive behaviour. Females may have one calf every year under favourable conditions.[2][3] Calves are typically born in the spring and summer months and remain dependent on the female until the following spring. Porpoises produce ultrasonic clicks, which are used for both navigation (echolocation) and social communication. In contrast to many dolphin species, porpoises do not form large social groups.
Porpoises were, and still are, hunted by some countries by means of drive hunting. Larger threats to porpoises include extensive bycatch in gill nets, competition for food from fisheries, and marine pollution, in particular heavy metals and organochlorides. The vaquita is nearly extinct due to bycatch in gill nets, with a predicted population of fewer than a dozen individuals. Since the extinction of the baiji, the vaquita is considered the most endangered cetacean. Some species of porpoises have been and are kept in captivity and trained for research, education and public display.
- ^ McGowen, M.R.; Tsagkogeorga, G.; Alvarez-Carretero, G.; et al. (2020). "Phylogenomic Resolution of the Cetacean Tree of Life Using Target Sequence Capture". Syst Biol. 69 (3): 479–501. doi:10.1093/sysbio/syz068. PMC 7164366. PMID 31633766.
- ^ Read, A.J.; Hohn, A.A. (1995). "Life in the fast lane: the life history of harbour porpoises from the Gulf of Maine". Marine Mammal Science. 11 (4): 423–440. Bibcode:1995MMamS..11..423R. doi:10.1111/j.1748-7692.1995.tb00667.x.
- ^ Sørensen, T.B.; Kinze, C.C. (1994). "Reproduction and reproductive seasonality in Danish harbour porpoises, Phocoena phocoena". Ophelia. 39 (3): 159–176. doi:10.1080/00785326.1994.10429541.