Finless porpoise  (Neophocaena phocaenoides)

As its name suggests, this small marine mammal is the only porpoise that lacks a dorsal fin (4), and instead has a ridge that runs down the middle of the back (2). The finless porpoise can also be distinguished by its rounded head, lacking an apparent beak (2), and relatively slender body (4), which is dark to pale grey and lighter on the underside (2). A scattering of horny tubercles (small, raised bumps) are found on the ridge; this is thought to create a 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 (2). Three subspecies of the finless porpoise are recognised. Neophocaena phocaenoides asiaorientalis (Yangtze finless porpoise) and Neophocaena phocaenoides sunameri both have narrow and prominent ridges, while the ridge of Neophocaena 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 (2).

The finless porpoise occurs along the coasts of southern and eastern Asia, from the Persian Gulf, east to Japan and south to Java, Indonesia (5). N. p. phocaenoides occurs in the Indian Ocean and the South China Sea, N. p. sunameri occurs in the East China Sea, Yellow Sea and off the coast of Korea and Japan, and N. p. asiaorientalis is found only in the middle and lower reaches of the Yangtze River and adjoining lake systems (2) (5).

The finless porpoise inhabits tropical and warm temperate coastal waters (4), preferring areas over sandy or soft bottoms, including shallow bays, mangroves and estuaries, but it can also be found in some large rivers (2). The Yangtze finless porpoise is the only subspecies that occurs wholly in freshwater (4), and can be found up to 1,600 kilometres from the sea (2).

Finless porpoises are rather shy and elusive animals (4), which do not form large schools and are most often seen in pairs consisting of a mother and calf or an adult pair (2). They generally swim quietly, rarely leaping, splashing, or riding the bow waves of boats like other small cetaceans (2). 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 (2).

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 (2). 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 (2).

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 (2). Although the finless porpoise is not directly targeted by fishermen, large numbers die when they become entangled in fishing nets, particularly gillnets (2) (5). 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 (5).

Furthermore, high levels of toxic pollutants have been reported from Japanese finless porpoises, and while finless porpoises tend to avoid boats (2), mortalities caused by collisions with vessels may be a problem in busy shipping areas, such as Hong Kong (5).

The deforestation of mangrove areas, rampant harbour expansion and the development of shrimp farms is taking place throughout Asia, degrading the porpoises' coastal habitat (2) (5). The Yangtze River finless porpoise is particularly vulnerable to habitat degradation, with the river not only being impacted by fishing and pollution, but also by the numerous dams that dot the Yangtze River basin (5). 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), which was believed to have gone extinct from the Yangtze River in 2006 (6).

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 (7). 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 (7) (8). 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 (7).

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 (7). Another calf was born in 2008 (9). Another small group inhabit a ‘semi-natural reserve', which was initially created for the baiji (10), comprising an oxbow lake and an 89 kilometre long section of river section (8). While such efforts should be commended, not all have had particularly promising outcomes and the future of the Yangtze finless porpoise remains uncertain (10). Hopefully the fate of the baiji will act as a poignant warning and lesson for the Yangtze finless porpoise (10), and that research is promptly undertaken on the other finless porpoise subspecies (2), to determine whether they may also be in need of rapid and intensive conservation efforts.

For further information on the finless porpoise see:

• Baiji.org:
  www.baiji.org
• Reeves, R.R., Smith, B.D. and Kasuya, T. (2000) Biology and Conservation of Freshwater Cetaceans in Asia. IUCN, Gland, Switzerland and Cambridge, UK. Available at:
  http://cms.iucn.org/resources/publications/publications_search/index.cfm

Authenticated (01/09/08) by Catharina Clausen, baiji.org Foundation and Dr. Hao Yu Jiang, Institute of Hydrobiology.