Observation on Some Sexual Behavior of the Yangtze Finless Porpoise (Neophocaena phocaenoides asiaeorientalis) in Captivity

The finless porpoise (Neophocaena phocaenoides) is a small-toothed cetacean species, and distributes in a narrow band along the coast of tropical and temperate Asia. The population inhabited in the Yangtze River is a unique freshwater subspecies, and is known as the Yangtze finless porpoise (N.p.asiaeorientalis). Its population size has been decreasing remarkably in recently years.In order to breed the animals in captivity for the purpose of conservation, 3 Yangtze finless porpoises have been kept in our aquarium for 3 to 6 years. The rearing hall is a round building that is 30 m across, with a main kidney shaped pool that is 20 m×7 m×3.5 m, an auxiliary round pool that is 10 m across and a medical pool that is 7 m across. The main pool has 7 under water viewing windows that are 2 m×1.5 m in size, where that animals was kept and observation was carried out. The window in the middle of the pool was chosen to be the observation site. A pre-designed sheet was used to record behaviors and other environment information. Data recorded included record date, record time, weather, air and water temperature, air pressure, pH, clarity, penis erected behavior, water layers (up, middle and low) in which it happened, the time length it maintained, which female it chased when penis was erected, and responded behavior of the females, and so on. A 35 mm camera with 80-300 mm lens and a digital video camera were used to take pictures. A digital voice recorder pencil was used to record comments by the recorder, a digital recorder was used to measure water and air temperatures and pH values, a air pressure metre was used to measure air pressure, and Secchi disc was used to measure clarity of the water. In total, 120 stationary observations were carried out from December 2001 to November 2002. The total observation time is 4 800 min. In this period, 105 times behaviors of penis erected were observed. Statistical analyses of the data indicated that the male animal stretched penis out of its body every month, the duration was from 1 to 6 s with the average of 2.8 s (±SD 0.3). This kind of behavior had 2 peaks during April to May and September to October. The behavior could happen in different water layers, and there was no significant differences between them. The pattern that the male stretched penis out of body included sidestroke erection; bend erection; up erection; down erection and perpendicular eretion.This may indicate the diversity of the animals'mating patterns.The male chased adult female more often than juvenile one.We conclude that mix group is better for normal breeding behavior development of this animal.During the observation period,the range of air pressure was 1 000-1 025 hpa,clarity was 3-3.5 m,pH value was 7.1-7.53,and the pool was lighted naturally.The sexual behavior was not affected by these environmental factors.During peak seasons of penis erected behavior, water and air temperatures were 17-23℃,the difference between them was 0-4℃. These results provide a base for reproducing the Yangtze finless porpoises in captivity.