The Finless porpoise (scientific name: Neophocaena phocaenoides) is one of six species of cetacean in the family Phocoenidae. The other five are the Spectacled porpoise, the Harbour porpoise, the Gulf of California harbor porpoise, Burmeister's porpoise, and Dall's porpoise.
|Finless porpoise. Source: Alessio Marrucci/ConserveNature.org|
|Size comparison of an average human against the Finless porpoise. Source: Chris Huh|
Common Names:Black finless porpoise
As its name suggests, this small marine mammal is the only porpoise that lacks a dorsal fin, and instead has a ridge that runs down the middle of the back.
The Finless porpoise can also be distinguished by its rounded head, lacking an apparent beak, and relatively slender body, which is dark to pale grey and lighter on the underside. A scattering of horny tubercles (small, raised bumps) are found on the ridge; this is thought to create an anti-slip surface when mothers carry their calves on their back or, more likely, used as sensory organs, as numerous nerve endings are found in the tubercles.
Three subspecies of the Finless porpoise are recognized:
- Neophocaena phocaenoides phocaenoides is found in coastal marine waters, as well as some river mouths and estuaries, from the Persian Gulf eastwards around the rim of the Indian Ocean to the Taiwan Strait area.
- Neophocaena phocaenoides asiaorientalis (Yangtze finless porpoise) is a freshwater subspecies found in from the estuary to 1600 km upstream including lakes Poyang and Dongting and their tributaries. this subspecies in endangered
- Neophocaena phocaenoides sunameri is found in coastal waters from the Taiwan Strait, including the western coast of Taiwan, through the East China Sea north to the Bohai/Yellow Sea in China and the waters of Korea and Japan.
Neophocaena phocaenoides asiaorientalis (Yangtze finless porpoise) and Neophocaena phocaenoides sunameri both have narrow and prominent ridges, while the ridge of N. phocaenoides phocaenoides is wider, and almost flat towards the head. N. p. phocaenoides is also a lighter colour when born, and darkens with age, resulting in almost black adults.
Finless porpoises are rather shy and elusive animals, which do not form large schools and are most often seen in pairs consisting of a mother and calf or an adult pair. They generally swim quietly, rarely leaping, splashing, or riding the bow waves of boats like other small cetaceans. They are opportunistic feeders, consuming a variety of schooling fishes, squids, octopuses, shrimps and prawns. The Finless porpoise itself is known to be preyed on by the great white shark. Knowledge of reproduction in the finless porpoise currently comes only from individuals in Japanese and Chinese waters. Females are thought to calve every two years, with the peak calving season varying with location. For example, on the Pacific coast of Japan calving takes place in May and June, while it occurs in April and May in the Yangtze River. It is estimated that the gestation period in this species is around eleven months and that the mother feeds her calve for approximately seven months. Finless porpoises are known to reach sexual maturity at four to nine years of age and live for up to 25 years.
Neophocaena phocaenoides is sometimes called the Black finless porpoise because of the common misconception that its skin is black. In reality, the upper portions of Neophocaena phocaenoides are gray with touches of blue on the back and sides. The ventral parts are paler. Pale spots do however decrease with age, and the skin turns black immediately after death. Further, the skin coloring differs from pale in oceanic and brackish waters, to almost black in rivers.
Neophocaena phocaenoides has no dorsal fin but has instead has a midline dorsal ridge. This ridge contains horny papillae. N. phocaenoides is the smallest cetacean and grows to only 150-190 centimetres.
The Finless porpoise has a distinct eel-like shape due to its lack of dorsal fin and round, beakless head. The jaw of Neophocaena phocaenoides contains 15 to 21 spade shaped teeth on each side of the upper and lower jaw. (Ganslosser 1988, Herman 1980, Nowak 1991)
Mass: 30 to 45 kg; avg. 37.5 kg (66 to 99 lbs; avg. 82.5 lbs)
Other Physical Features: Endothermic; Bilateral symmetry
Neophocaena phocaenoides is a relatively slow swimming marine mammal. It rolls to the surface to breath and is rarely observed jumping out of the water. Maximum dives last up to 11-15 seconds. It forms mostly small schools and is rarely seen in groups of more than four. More often, Neophocaena phocaenoides is solitary or in mother-offspring groups. Some of the groups of N. phocaenoides (mainly the Japanese groups) are migratory. They frequent the Inland Sea during the spring and migrate to the Pacific coast from late summer to midwinter. (Gaskin 1982, Ganslosser 1988, Nowak 1991)
Key Behaviors: natatorial; motile; migratory; solitary; social
Maximum longevity: 33 years (captivity) Observations: Normally, these animals do not live more than 20 years. In Chinese waters, however, they reach sexual maturity at later ages (four to ten years) and also live longer (Ronald Nowak 2003). One captive specimen lived for 28.8 years (Richard Weigl 2005).
Neophocaena phocaenoides can reach sexual maturity by the age of two. Reproductive cycles differ among geographic groups such as those located near Japan and those near China. The breeding cycle is one to two years and gestation lasts between 10 and 11 months. Births occur between February and August and there is usually 1 young per birth. Newborns are around 25 kilograms and are weaned between September and June. Neophocaena phocaenoides has been found to live up to 23 years. (Bryden & Harrison 1986, Nowak 1991).
Mothers carry their offspring on a patch of skin on the dorsal surface which is covered with horny papillae. This acts like a saddle on which the young can attach and be carried. Although obviously for carrying young, the horny papillae contain nerve endings and may be a means of auxillary orientation. This "extra" means of orientation could be very beneficial to the Finless porpoise since it often lives in murky waters.
Key Reproductive Features: Iteroparous; Seasonal breeding; Gonochoric/gonochoristic/dioecious (sexes separate); Sexual; Viviparous
Distribution and Movements
Neophocaena phocaenoides is found in the coastal waters and rivers of Southeast Asia. It is concentrated in the eastern IndoPacific region. N. phocaenoides can be found from Pakistan to Korea, Japan, Borneo and Java. (Gaskin 1982, Nowak 1991)
The IUCN Red List provides additional details:
In general, the species occurs in a narrow strip of shallow (usually less than 50 metres deep) coastal water around the northern rim of the Indian and western Pacific oceans from the Arabian (Persian) Gulf in the west to the Indo-Malay region in the east and to Java, Indonesia (but apparently not the Philippines, apart from Palawan), northern China, Korea and northern Honshu, Japan. The distribution also includes a few estuaries and rivers (e.g., the N. p. asiaeorientalis subspecies appears to be found exclusively in the Yangtze River system) (Gao 1991, Gao and Zhou 1995). Human coastal development and other activities already may have substantially reduced and fragmented the distribution of this species (Reeves et al. 1997).
N. p. phocaenoides – Coastal marine waters, as well as some river mouths and estuaries, from the Persian Gulf eastwards around the rim of the Indian Ocean to the Taiwan Strait area (Gao 1991, Gao and Zhou 1995). It is the most tropical and wide-ranging of the three subspecies.
N. p. sunameri – Coastal waters from the Taiwan Strait, including the western coast of Taiwan, through the East China Sea north to the Bohai/Yellow Sea in China and the waters of Korea and Japan (Gao 1991, Gao and Zhou 1995). Korean and Japanese populations are geographically separate (Shirakihara et al. 1992, Yoshida 2002).
N. p. asiaeorientalis – Middle and lower reaches of the Yangtze River (= Chang Jiang), where it ranges (or did until recently) to 1,600 km upstream, i.e. to the gorges above Yichang (200 m above sea level). The range includes Poyang and Dongting lakes and their tributaries, the Gan Jiang and the Xiang Jiang (Gao 1991, Gao and Zhou 1995). The subspecies is thought to be restricted to fresh water.
The Finless porpoise inhabits tropical and warm temperate coastal waters, preferring areas over sandy or soft bottoms, including shallow bays, mangroves and estuaries, but it can also be found in some large rivers. The Yangtze finless porpoise is the only subspecies that occurs wholly in freshwater, and can be found up to 1,600 kilometres from the sea.
Neophocaena phocaenoides lives in both fresh and salt water habitats. It is found in shallow coastal waters such as the Sea of Japan as well as fresh water rivers like the Yangtze river in China. N. phocaenoides is occasionaly found in inland lakes which have been cut off from the ocean but are still salt water. Neophocaena phocaenoides seems to prefer rocky promonotories and strong currents (Ganslosser 1988).
Neophocaena phocaenoides feeds mainly in the euphotic zone. It consumes benthic invertebrates, mollusks, crustaceans, cephalopods such as squid, and small demersal fish. N. phocaenoides is an aggresive hunter, and fish have been observed leaping out of the water when chased by it (Bryden & Harrison 1986). (Gaskin 1982)
Economic Importance for Humans
Neophocaena phocaenoides is hunted by humans for its meat, skin and oil (Nowak 1991); however, the total quantities taken provide only a minute quantity of human goods, whereas the human actions are risking extinction of this entire species.
Threats and Conservation Status
The IUNCN Red List notes:
Although there is no population estimate for Finless porpoises throughout their range, they are widespread and regularly sighted in some areas. However, their range appears to be discontinuous in some regions. Given the size of their range and the likely total numbers of individuals throughout that range, Finless porpoises do not meet criteria B, C or D for any threatened category. Also, available data are far from sufficient to support a quantitative analysis of the probability of extinction, thus ruling out criterion E. Therefore, the only criterion to consider is A, the decline criterion.
Obtaining conclusive quantitative evidence of population trend for this species throughout its range is next to impossible. The only area with clear evidence of trend is the Inland Sea of Japan, where a decline of nearly 70% was estimated over a period of 22 years, from 1976-1978 to 1999-2000. Another area with some evidence of a rapid decline in recent decades is the Yangtze River and adjoining lake systems of China. Given that the factors responsible for these declines (mainly incidental mortality in fisheries, but also habitat degradation and loss) have not been addressed and are pervasive, and likely increasing, an overall decline of at least 30% over the last three generations (about 50 years; see Taylor et al. 2007) is suspected. Thus, the species qualifies for Vulnerable A2c,d,e, considering that the causes of decline – bycatch (interpreted here as “exploitation”), decline in habitat quality, and possibly pollution – have not ceased and are not all well understood.
Although Neophocaena phocaenoides is not classified as endangered, there are many threats to its survival as individuals if not as a species. Neophocaena phocaenoides is effected by pollution as well as bottom dredging. It is also killed by motor boat collisions, hunters, fish and shrimp nets, and its natural predator, the shark. (Bryden & Harrison 1986, Nowak 1991)
The finless porpoise's preference for coastal and riverine habitats makes it highly vulnerable to the impacts of human activities that take place in these regions. Although the finless porpoise is not directly targeted by fishermen, large numbers die when they become entangled in fishing nets, particularly gillnets. Electric fishing also threatens the finless porpoise in the Yangtze River; despite being illegal, this destructive fishing method has become widespread in the river system during the last decade, not only killing some porpoises outright but also depleting their prey. Furthermore, high levels of toxic pollutants have been reported from Japanese finless porpoises, and while finless porpoises tend to avoid boats, mortalities caused by collisions with vessels may be a problem in busy shipping areas, such as Hong Kong. The deforestation of mangrove areas, rampant harbour expansion and the development of shrimp farms is taking place throughout Asia, degrading the spedies coastal habitat. The Yangtze River finless porpoise is particularly vulnerable to habitat degradation, with the river not only being impacted by fishing and water pollution, but also by the numerous dams that dot the Yangtze River basin. The impact that these threats may have on the Yangtze finless porpoise is illustrated only too well by the recent tragic demise of the baiji (Lipotes vexillifer - Chinese river dolphin), which was believed to have gone extinct from the Yangtze River in 2006.
Currently, conservation measures appear to only exist for the Yangtze finless porpoise. Since the 1980s, conservation measures have been proposed and implemented for this endangered subspecies. Preserving its natural habitat within the river has been the principal concern and so by 2008, six natural reserves had been created in areas of the river that contain high numbers of the porpoise. In these reserves, the use of harmful fishing gear has been banned and these parts of the river are patrolled. However, these reserves are unable to eliminate all threats to the finless porpoise and thus ex-situ conservation has also been undertaken.
The Baiji Dolphinarium was established in China in 1992, creating the opportunity to study endangered river animals in captivity. Yangtze finless porpoise have been reared here for several years, with one giving birth in 2005; the first freshwater cetacean to have ever been born in captivity. Another calf was born in 2008. Another small group inhabit a 'semi-natural reserve', which was initially created for the baiji, comprising an oxbow lake and an 89 kilometre long section of river section. While such efforts should be commended, not all have had particularly promising outcomes and the future of the Yangtze finless porpoise remains uncertain. Hopefully the fate of the baiji will act as a poignant warning and lesson for the Yangtze finless porpoise, and that research is promptly undertaken on the other finless porpoise subspecies, to determine whether they may also be in need of rapid and intensive conservation efforts.
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