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Finless Porpoise
At Miyajima Public Aquarium, Japan
Size comparison against an average human
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Eutheria
Order: Cetacea
Suborder: Odontoceti
Family: Phocoenidae
Genus: Neophocaena
Species: N. phocaenoides
Binomial name
Neophocaena phocaenoides
(G. Cuvier, 1829)
Finless Porpoise range

The Finless Porpoise (Neophocaena phocaenoides) is one of six porpoise species. In the waters around Japan, at the northern end of its range, it is known as the sunameri. A freshwater population found in the Yangtze River in China is known locally as the jiangzhu or "river pig".

Contents

Distribution

The Finless Porpoise lives in the coastal waters of Asia, especially around India, China, Indonesia, Bangladesh and Japan. A unique fresh water population is found in the Yangtze River. At the western end, their range includes the length of the western coast of India and continues up into the Persian Gulf. Throughout their range, the porpoises stay in shallow waters (up to 50 m [160 ft]), close to the shore, in waters with soft or sandy seabeds. In exceptional cases they have been encountered as far as 160 kilometres (100 miles) off-shore in the East China and Yellow Seas, albeit still in shallow water.

Physical description

The Finless Porpoise almost completely lacks a dorsal fin. Instead there is a low ridge covered in thick denticulated skin. This demonstrates that the body shape that has evolved to be the optimum for sharks, dolphins and porpoises is not the only possible body shape for a marine animal.

Adult Finless Porpoises are a uniform light grey colour. Newborn calves are mostly black with grey around the dorsal ridge area, becoming fully grey after 4–6 months. Adults grow more than 1.55 m (5 ft) in length and up to 30–45 kg (65–100 lb) in weight. Males become sexually mature at around 4–6 years of age, and females at around 6–9 years of age.

Diet

The Finless Porpoise, subspecies Neomeris kurrachiensis, in the vicinity of Karachi, British India, now Pakistan, as drawn by R. A. Sterndale, in the Journal of the Bombay Natural History Society, volume 1, number 1, 1886.

Finless Porpoises are reported to eat fish and shrimp in the Yangtze River, and fish, shrimp and squid in the Yellow Sea/Bohai area and off Pakistan. In Japanese waters they are known to eat fish, shrimp, squid, cuttle fish and octopuses. Finless Porpoises are opportunistic feeders utilising various kinds of available food items available in their habitat. Seasonal changes in their diets have not been studied. They also apparently ingest some plant material when living in estuaries, mangroves, and rivers including leaves, rice, and eggs deposited on vegetation.

Schooling

Finless Porpoises are generally found as singles, pairs, or in groups of up to 12, although aggregations of up to about 50 have been reported. Recent data suggests, that the basic unit of a Finless Porpoise pod is a mother/calf pair or two adults, and that schools of three or more individuals are aggregations of these units or of solitary individuals. Social structure seems to be underdeveloped in the species, and the mother/calf pair is probably the only stable social unit.

Behaviour and reproduction

Like other porpoises, their behaviour tends to be not as energetic and showy as that of dolphins. They do not ride bow waves, and in some areas appear to be shy of boats. In the Yangtze River, Finless Porpoises are known to leap from the water and perform "tail stands". Breeding occurs in late spring and early summer, after a gestation period of 10–11 months. Calves cling to the denticulated area of skin on their mother's back and are carried by her as she swims. Calves are weaned at 6–15 months.

Swimming style

Although they show no acrobatics in the water, Finless Porpoises are believed to be very active swimmers. They typically swim just beneath the surface of the water and roll to one side when surfacing to breathe. This rolling movement disturbs very little water on the surface, so they are often overlooked when rising to breathe. Surfacing generally lasts for one minute, as they take 3 to 4 quick successive breaths, then quickly submerge into the water. The Finless Porpoise often surfaces a great distance from the point where it dives beneath the water's surface.

Conservation

There are not enough data to place Finless Porpoises on the endangered species list, except in China, where they are endangered. Since this species is the most coastal of all porpoises, it has the most interaction with humans. This interaction often puts the Finless Porpoise at risk. Like other porpoises, large members of this species are killed by entanglement in gill nets. Except for being briefly hunted after World War II due to the lack of seaworthy fishing boats, Finless Porposes have never been widely hunted in Japan. It is a species protected since 1930 at the area around Awajima Island, Takehara and this coverage had since been extended to all Japanese coastal waters. The primary danger to the species is the environmental degradation. In addition, unlike other members of this family, Finless porpoises have lived under captivity for over 15 years.

There are no well established estimates of the animals' abundance. However, a comparison of two surveys, one from the late 1970s and the other from 1999–2000 shows a decline in population and distribution. Scientists believe that this decline has been ongoing for decades and that the current population is just a fraction of its historic levels. A 2006 expedition estimated that fewer than 400 of animals survived in the Yangtze River.[2]

At the end of 2006 it was estimated that there are about 1400 porpoises left living in China, with between 700 and 900 in the Yangtze, with about another 500 in Poyang and Dongting Lakes.

2007 population levels are less than half the 1997 levels, and the population is dropping at a rate of 7.3 per cent per year. Current conservation efforts were undertaken alongside those for the recently functionally extinct Baiji. In 1990 5 individuals were relocated to the Tian-e-Zhou Oxbow Nature Reserve and now a population of 28 currently habituate the lake.[3]

Sand dredging has become a mainstay of local economic development in the last few years, and it is an important source of revenue in the region that borders Poyang Lake. But at the same time, high-density dredging projects have been the principal cause of the death of the local wildlife population.

Dredging makes the waters of the lake muddier, and the porpoises cannot see as far as they once could, and have to rely on their highly-developed sonar systems to avoid obstacles and look for food. Large ships enter and leave the lake at the rate of two a minute and such a high density of shipping means the porpoises have difficulty hearing their food, and also cannot swim freely from one bank to the other.[4]

References

  1. ^ Reeves, R.R., Collins, T., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K. (2008). Neophocaena phocaenoides. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 24 March 2009. Database entry includes a brief justification of why this species is of vulnerable.
  2. ^ http://www.cnn.com/2006/TECH/science/12/13/china.dolphin.ap/index.html
  3. ^ "Scientists Join Hands to Seek the Last Yangtze River Dolphin". WWF China. http://www.wwfchina.org/english/loca.php?loca=412. Retrieved 2007-08-19.  
  4. ^ Poyang Lake: saving the finless porpoise

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