The finless porpoise (Neophocaena phocaenoides) is one of six porpoise species. A freshwater population found in the Yangtze River in China is known locally as the jiangtun (江豚) or "river porpoise". In the waters around Japan, at the northern end of its range, it is known as the sunameri (砂滑). There is a degree of taxonomic uncertainty surrounding the species, with the N. p. phocaenoides subspecies perhaps representing a different species from N. p. sunameri and N. p. asiaeorientalis.
The finless porpoise lives in the coastal waters of Asia, especially around Korea, India, China, Indonesia, Bangladesh and Japan. A unique fresh water population (N. p. asiaeorientalis) 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 (99 mi) off-shore in the East China and Yellow Seas, albeit still in shallow water. N. p. phocaenoides has wide ridge on its back and ranges from Pakistan to the Taiwan straits. N. p. sunameri has a narrower ridge, and is found from Taiwan, north to the Sea of Japan. The population in coastal waters around Japan is geographically isolated by the deep waters between Japan and continental Asia. 
The finless porpoise almost completely lacks a dorsal fin. Instead there is a low ridge covered in thick denticulated skin.
Adults are a uniform, light grey colour. Newborn calves are mostly black with grey around the dorsal ridge area, becoming fully grey after four to six 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 four to six years of age, and females at around six to nine years of age.
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. They are opportunistic feeders using 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.
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 suggest the basic unit of a finless porpoise pod is a mother/calf pair or two adults, and 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. The calf clings to the denticulated area of skin on their mother's back and is carried by her as she swims. Calves are weaned at 6–15 months.
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 three to four quick successive breaths, then quickly submerge into the water. They often surface a great distance from the point where they dive beneath the water's surface.
On the IUCN "red list" database of endangered species, the finless porpoise is listed as "vulnerable" due to apparent declines in the best studied populations in the Sea of Japan, and the Yangtze river basin. The fresh water subspecies in the Yangtze river is characterized as endangered. Since this species remains in coastal waters, it has a high degree of interaction with humans, which often puts the finless porpoise at risk. Like other porpoises, large numbers 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 porpoises 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 in 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 this decline has been ongoing for decades, and the current population is just a fraction of its historical levels. A 2006 expedition estimated fewer than 400 animals survived in the Yangtze River.
At the end of 2006, an estimated 1400 porpoises were left living in China, with between 700 and 900 in the Yangtze and another 500 in Poyang and Dongting Lakes. The 2007 population levels were less than half the 1997 levels, and the population was dropping at a rate of 7.3% per year. A 2012 survey indicated the rate of decline had accelerated to 13.7% per year.
Current conservation efforts were undertaken alongside those for the recently functionally extinct baiji. In 1990, five individuals were relocated to the Tian-e-Zhou Oxbow Nature Reserve, and now a population of 28 currently inhabit the lake.
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. At the same time, though, 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.
The Finless porpoise is listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix II as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.
- Wang, J. Y. & Reeves, R. (2011). "Neophocaena phocaenoides". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 18 January 2012. Database entry includes a brief justification of why this species is of vulnerable.
- Cetacean Specialist Group (1996). Neophocaena phocaenoides ssp. asiaeorientalis. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 9 September 2010.
- "China's white dolphin called extinct after 20 million years". Associated Press (CNN). 13 December 2006. Archived from the original on 10 January 2007.
- "Rare porpoise halved in six years, endangered". China Daily. 29 March 2013.
- "Yangtze River expedition points to decline of endangered finless porpoise". World Wildlife Fund. 20 November 2012.
- "Scientists Join Hands to Seek the Last Yangtze River Dolphin". WWF China. Archived from the original on 12 November 2007.
- Zhang, Kejia (9 March 2007). "Poyang Lake: saving the finless porpoise". China Dialogue. Archived from the original on 18 July 2011.
- "Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS)". Conference of the Parties. cms.int. 5 March 2009.