Aggregation and spatio-temporal distribution of the Yangtze finless porpoise Neophocaena phocaenoides asiaeorientalis in Tian-E-Zhou National Baiji Reserve

The finless porpoise( Neophocaena phocaenoides) is a small-toothed cetacean species. The population inhabited in the Yangtze River is a unique freshwater subspecies and is known as the Yangtze finless porpoise( N. p. asiaeorientalis). The population size has been decreasing remarkably and it suffers from many of the same impacts that affect the baiji (Lipotes vexillifer) in the Yangtze River. Tian-E-Zhou oxbow is located in Shishou City of Hubei province, which is a 21 km long old course of the Yangtze,with width 1-2km. Several groups of the Yangtze finless porpoise had been introduced into the area since 1990 to establish a breeding population for the purpose of conservation of the porpoise. For assessing their habitat use, grouping behavior, and spatio-temporal distribution in the reserve, land based and boat based surveys were conducted from May 2001 through April 2002. During boat surveys, two small fishing boats,with 4.5hp power engine, were used to move along with both shores at a speed of 7-8km/h. Handheld VHF transreceivers were used for communication between the two boats. A 35mm camera with 80-300mm lens and a digital video camera were used to take pictures when animals were found. Using grid chart to cover the whole reserve, the reserve was separated into ten different sections, about 2km in length each, which were orderly named Section A, B, C, D, E, F, G, H, M, and N from the upper end down to the lower end of the reserve. The daytime,from 6am to 18pm,was divided into 48 time zones, which means that an quarter equals to I time zone. Environmental types in the reserve were also coded as Type I, II, III, and IV, which represent stony and steep slope area, muddy slope area, muddy and shallow area, and central area respectively. Other parameters, such as visibility, platform height, start and end time of the sighting, air and water temperature, animal behavior, human activities, etc., were also recorded on a pre-designed sheet. The surveys were conducted once or twice a week,with each lasted 5-12 hours. The whole survey time was 720 hours in total. 588 aggregations of the porpoises, consisting of individuals varied from 2 to 20, were sighted in the reserve during the time. Most of the aggregations were composed of 2-11 individuals, which accounted for 82.6% of the total aggregations. There were two relatively independent schools in the reserve, each consisted of 9-11 individuals. The two schools occupied relatively independent two different section in the reserve. Each school was usually consisted of a few smaller core groups. The core groups usually had 2-3 animals, among which, groups with 3 animals were observed most frequently. Seasonal aggregation models were very similar in spring, autumn, and winter, while slightly different in summer, which was probably because of the high water level in flood season. On the other hand, the daily aggregation model showed that there were three aggregation peaks during the daytime, which occurred on 9:00-11:30am, 12:30-16:15pm, and 17:15-18:00pm respectively. Grouping of the porpoises was in relatively low level during noon. The porpoises aggregated mainly in Section D, E, F, G, and H, where most of the aggregations, counted for about 70%, were observed, and schools were rarely found in both ends of the reserve. From the above assessment and observation, some management measures for protecting the porpoises in the reserve are proposed. Any human activities should not be allowed in the Section C, D, E, F, G, and H, where are considered as core areas of the reserve. Stationary observation from bank is recommended as the first choice when observing the porpoises in the reserve. Some further studies on monitoring movement and grouping of the porpoise in the reserve are suggested here as well.