A QUANTITATIVE ASSESSMENT OF DOMINANCE RELATIONS AMONG THE CAPTIVE YANGTZE FINLESS PORPOISES (NEOPHOCAENA PHOCAENOIDES ASIAEORIENTALIS)

This study was designed to investigate whether dominance relations exist among captive Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis)and how the relations establish, as well as how porpoises maintain the relations stable.The studied captive porpoise group was kept in Baiji Dolphinarium of Institute of Hydrobiology of the Chinese Academy of Sciences, and consisted of three females (two adults and one calf)and three males (two adults and one subadult).Successively, the porpoises were randomly put into eight small groups with different compositions during the study, and were kept in three indoor pools with different dimensions.Three types of interactions, approach-flee, approach-contact and approach-tail flap occurred within each of the small groups were observed using focal sampling method from January to April 2000 and from April 2000 to April 2002, respectively.In all, 1, 685 dyadic interactions were recorded during 8, 162min of observation during 27-month study.The three types of interactions were used as identifications of dominance relations between pairs of individuals, and either opponent of each pair was assigned different dominant scores in different interactions.Dominance relationships between individuals were analyzed quantitatively using a method of dominant score matrix.Results indicated that dominance relationships among males or females were influenced by the age and captive duration of participants.Old porpoises were dominant to young ones;short-term captive individuals were dominant to long-term captive ones.In contrast, dominance relationships between adult males and females were changeable.