| Harbor Porpoise[1] | |
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| Size comparison against an average human | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Cetacea |
| Suborder: | Odontoceti |
| Family: | Phocoenidae |
| Genus: | Phocoena |
| Species: | P. phocoena |
| Binomial name | |
| Phocoena phocoena Linnaeus, 1758 |
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| Harbour Porpoise range | |
The Harbor Porpoise (Phocoena phocoena) is one of six species of porpoise. It is one of the smallest ocean mammals. As its name implies, it stays close to coastal areas or river estuaries and as such is the most familiar porpoise to whale watchers. This porpoise often ventures up rivers and has been seen hundreds of miles from the sea.
Phocoena phocoena may be polytypic with populations representing distinct races: P. p. phocoena in the North Atlantic and West Africa, P. p. relicta in the Black Sea and Sea of Azov, an unnamed population in the North West Pacific and P. p. vomerina in the North East Pacific..[3]
The species is sometimes known as the Common Porpoise in texts originating in the United Kingdom, though this usage appears to be dying out.[citation needed]
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Physical description
The Harbor Porpoise is a little smaller than the other porpoises. It is about 67-85 cm (26-33 in) long at birth. Both sexes grow up to be 1.4 m to 1.9 m (4.6-6.2 ft). The females are heavier, with a maximum weight of around 76 kg (167 pounds) compared with the males' 61 kg (134 pounds). The body is robust and the animal is at its maximum girth just in front of its triangular dorsal fin. The beak is poorly demarcated. The flippers, dorsal fin, tail fin and back are a dark grey. The sides are a slightly speckled lighter grey. The underside is much whiter, though there are usually grey stripes running along the throat from the underside of their body.
Population and distribution
The species is widespread in cooler coastal waters in the Northern Hemisphere, largely in areas with a mean temperature of about 15°C. In the Atlantic, Harbour Porpoises may be present in a concave band of water running from the coast of western Africa round to the eastern seaboard of the United States, including the coasts of Spain, France, the United Kingdom, Isle of Man, Ireland, Norway, Iceland, Greenland and Newfoundland. In prehistoric times this animal was hunted by the Alby People of the east coast of Oland, Sweden. There is a similarly-shaped band in the Pacific Ocean running from Sea of Japan, Vladivostok, the Bering Strait, Alaska and down to Seattle and Vancouver. There are diminishing populations in the Black and Baltic Seas.
Prey and predators
Harbour Porpoises feed mostly on small fish, particularly herring, capelin, and sprat. The deepest dive recorded was 224 m (735 ft) deep. Young porpoises need to consume about 7% to 8% of their body weight each day in order to survive.
Significant predators of Harbor Porpoises include white sharks and orcas. Researchers at the University of Aberdeen in Scotland have also discovered that the local Bottlenose Dolphins attack and kill Harbour Porpoises without eating them due to competition for a decreasing food supply.[4]
Conservation
Harbor Porpoises were traditionally hunted for food and especially fat used for lighting purposes in Denmark, especially in the Little Belt strait. Currently, however, this species is not subject to commercial whaling.
Currently, the total population is in the hundreds of thousands and the Harbor Porpoise is not under threat of extinction. There are, however, a number of threats that impact population distribution and numbers:
Interactions with fisheries
The main threat for porpoises is formed by static fishing techniques such as gill and tangle nets. Static fishing bycatch is considered as the main anthropogenic mortality factor for harbour porpoises worldwide. Bycatch from static fishing is reported from the Black and Baltic Seas and the North Sea. Anchored to the sea floor and up to 12,5 miles (20 kilometer) in length, different types of static net are used to target specific species of fish. Porpoises may not be able to detect these nets using echolocation). Entanglements cause various types of wounds that many porpoises die from, directly or indirectly. Dead porpoises stranded on the beach are used for necropsy. Porpoise-scaring devices called pingers have been developed to keep the cetaceans at distance from nets, but these devices are quite expensive and there are a number of issues with their deployment.
Mortality resulting from trawling bycatch seems to be less of an issue, probably because porpoises are not inclined to approach motor vessels.
Climate change
An increase in the temperature of the sea water is likely to affect the distribution of porpoises and their prey. Reduced stocks of sandeel along the east coast of Scotland seems to have been the main reason for the malnutrition in porpoises in the area.
Overfishing
Overfishing may reduce preferred prey availability for porpoises. Overfishing resulting in the collapse of herring in the North Sea caused porpoises to hunt for other prey species. Reduction of prey may result from climate change or overfishing, or both.
Noise pollution
Noise from ship traffic and oil platforms is thought to impact on the distribution of toothed whales, like the Harbour Porpoise, that use echolocation for communication and prey detection. The construction of thousands of offshore windmills is being planned in different areas of North Sea. The effect of noise generated by windmills on porpoises is not known. Construction and maintenance of these windmill parks will further increase noise levels in the sea.
Pollution
Marine top predators like porpoises and seals accumulate pollutants such as heavy metals, PCBs and pesticides in their fat tissue. Porpoises have a coastal distribution which potentially brings them close to sources of pollution. Porpoises may not experience any toxic effects until they draw on their fat reserves, such as in periods of food shortage, during migration or reproduction.
References
- ^ Mead, James G. and Robert L. Brownell, Jr (November 16, 2005). Wilson, D. E., and Reeder, D. M. (eds). ed. Mammal Species of the World (3rd edition ed.). Johns Hopkins University Press. pp. 723–743. ISBN 0-801-88221-4. http://www.bucknell.edu/msw3/browse.asp?id=14300116.
- ^ Hammond, P.S., Bearzi, G., Bjørge, A., Forney, K., Karczmarski, L., Kasuya, T., Perrin, W.F., Scott, M.D., Wang, J.Y., Wells, R.S. & Wilson, B. (2008). Phocoena phocoena. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 7 October 2008.
- ^ Shirihai, Hadoram and Jarrett, Brett (2006). Whales, Dolphins and Seals - A Field Guide to the Marine Mammals of the World. A&C Black Publishers. ISBN 0-7136-7037-1.
- ^ Read, Andrew (1999). Porpoises. Stillwater, MN, USA: Voyageur Press. ISBN 0-89658-420-8.
Bibliography
- Phocoena phocoena (TSN 180473). Integrated Taxonomic Information System. Retrieved on 18 March 2006.
External links
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Wikimedia Commons has media related to: Phocoena phocoena |
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Wikispecies has information related to: Phocoena phocoena |
- ARKive - images and movies of the harbour porpoise (Phocoena phocoena)
- Whale & Dolphin Conservation Society (WDCS)
- The harbour porpoise in the southern North Sea: Abundance, threats and research- & management proposals by Jan Haelters & Kees C.J. Camphuysen for IFAW.
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