The finless porpoise lives in the coastal waters of Asia, especially around Japan, Korea,
China, Indonesia, India, and Bangladesh.
The finless porpoise (Neophocaena phocaenoides) is one of six porpoise species. Most of the population has been found around the Korean peninsula in the Yellow and East China Seas, although a freshwater population is found around Jiuduansha near Shanghai at the mouth of China's Yangtze River. Genetic studies indicate that the finless porpoise is the most basal living member of the porpoise family.
The finless porpoise is the only porpoise to lack a true dorsal fin. Instead there is a low ridge covered in thick skin bearing several lines of tiny tubercles. In addition, the forehead is unusually steep compared with those of other porpoises. With fifteen to twenty-one teeth in each jaw, they also have, on average, fewer teeth than other porpoises, although there is some overlap, and this is a not a reliable means of distinguishing them.
Finless porpoises can grow to as much as 2.27 m
(7 ft 5 in) in length, and can weight up to 72 kg
(159 lb), although most are rather smaller. The flippers are moderately large, reaching up to 20% of the total body length. Adults grow more than 1.55 m (5 ft) in length and up to 30–45 kg (65–100 lb) in weight.
Finless porpoises are opportunistic feeders using various kinds of available food items available in their habitat, including fish, crustaceans, and cephalopods. 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.
Breeding occurs in late spring and early summer. The young are born in in spring, summer, or winter, depending on the geographic locality, after a gestation period of ten to eleven months. Newborn finless porpoises are reported to 72 to 84 cm (28 to 33 in) in length. Males reach sexual maturity at four to six years of age, and females at six to nine years. Finless porpoises have lived up to 33 years. It has been claimed that young calves cling to the denticulated area of skin on their mother's back and are carried by her as she swims, but there is no clear evidence of this happening. Calves are weaned at 6–15 months.
In Chinese coastal waters and the Yangtze River, finless porpoises are generally found in groups of three to six, although aggregations of up to about fifty have been reported. In Japanese waters, groups appear to be smaller, with pairs being typical, and even rare aggregations being no larger than thirteen individuals. 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.