STUDIES ON THE AGE DETERMINATION, GROWTH AND REPRODUCTION OF FINLESS PORPOISE NEOPHOCAEN A PHOC AENOIDES

Based upon 68 specimens collected from the northeast China coastal waters, the middle and lower Changjiang (Yangtze) River and its estuary, this work attempted to study age determination method for finless porpoise, Neophoc ena phocaenoides. Problems of age, growth and reproduction of the finless porpoise were analysed. The relationship between age and body length, in a certain phase, follows the model of power function. Y=axb A rapid growth of body length, in both sexes, appears at the ages younger than 4-5 years and reduces gradually later on. Males attain sexual maturity at about 4.5 years and females at 4 years, with the corresponding body length of 140cm and 133cm espectively. According ro the data of 16 fetuses,it was backdated with logarithmic cutting that mating period may be long and there are two,possible peaks of mating around the year. Parti ition peaks during February and April. Weaning age is about half a year. Rough estimate of annual reproductive rate is 20％. There are different characteristics in body shapes and population structures of the finless porpoises collected from the River and from the northeast China coastal waters. Age composition indicates that the immature group (0-4 years) constitutes a large proportion.