Narrow-ridged finless porpoise

Neophocaena asiaeorientalis
Other names: 
  • Yangtze finless porpoise
  • Finless porpoise
  • Black finless porpoise
  • Black porpoise
Maximum length: 
  • Male: 2m
  • Female: 2m
  • Calf: 0.75m
Maximum weight: 
  • Male: 55kg
  • Female: 60kg
  • Calf: Unknown
Diet: 
  • Fish
  • Squid
  • Crustaceans
Estimated population: 
500
IUCN Listing: 
VU (Yangtze River sub-species listed as CR)
CITES Appendix: 
I
CMS Appendix: 
II
Classification: 

Historically, the genus Neophocaena contained only one recognised species, the finless porpoise N. phocaenoides. It has very recently been split into two species: the Indo-Pacific finless porpoise N. phocaenoides and the narrow-ridged finless porpoise N. asiaeorientalis, formerly recognized as the subspecies N. phocaenoides asiaeorientalis. Two subspecies are retained within N. asiaeorientalis; the Yangtze finless porpoise N. a. asiaeorientalis (the world’s only freshwater porpoise) and the East Asian finless porpoise or sunameri, N. a. sunameri. Where this species has been studied fairly well, there is evidence to suggest subpopulation structure. 

 

Appearance: 

The two species of finless porpoise are the only members of the porpoise family without a dorsal fin and are easily recognisable at sea. The low profile makes it nearly invisible if the seas are rough. Both species of finless porpoise have a dorsal ridge along the back that runs from above the flippers to the beginning of the tail stock. This ridge is covered in circular wart-like tubercles or bumps, and in the narrow-ridged finless porpoise, as the name would suggest, the tubercules cover a narrow area. Both species are one of the smallest cetaceans and the only member of the porpoise family to have a bulbous melon - there is no prominent beak. The mouth is small and curves slightly upwards and there is a slight depression behind the blowhole. Both species of finless porpoise have a small, streamlined body which is pale grey-blue in colour with a lighter belly and white chin. Adults usually grow to between 1.2 and 2metres in length.

 

Behaviour: 

Both species of finless porpoises are active animals, usually swimming in small groups or alone. They swim just below the surface of the water with sudden, darting movements. Little disturbance is caused when they break the surface and they tend to roll onto their sides when doing so. They have been known to spyhop, but are rarely seen breaching. They are generally shy, apart from some individuals living in the Yangtze River, China, which have become accustomed to heavy boat traffic. Calves have been sighted riding on the mother's back, gripping the dorsal ridge, and coming out of the water when the mother breathes.

 

Distribution: 

The narrow-ridged finless porpoise is a temperate-water species occurring in coastal waters (rarely seen more than 5 km from the coast) from Korea and Japan south to the southern East China Sea and in the Yangtze River. The major threat to finless porpoises is entanglement in fishing nets, especially gillnets. Other threats include hunting, live capture for display, human disturbance, habitat degradation, boat strikes and chemical and noise pollution. The population of narrow-ridged finless porpoises is unknown and the species is listed as Vulnerable by IUCN (2008), although the Yangtze subspecies has recently been listed as Critically Endangered. The change in threat status for the Yangtze finless porpoise (it was previously classified as EN) is based on analysis of data for 279 stranded porpoises collected from the middle and lower reaches of the Yangtze River from 1978 onwards, which reveal that the porpoise population is experiencing an accelerating decline, and a further population decline of >80% is predicted within three generations. Recent survey results from late 2012 suggest that the population in the main Yangtze channel has halved since the previous survey in 2006, with initial estimates suggesting that there are now only around 500 individuals left in the mainstem compared to over 1,100 six years earlier.