Abstract:

Balijiang section is one of the most important habitats for Yangtze finless porpoise in the Yangtze River.The abundance and distribution of porpoises in this area was investigated by 10 line transect surveys between July,2005 and May,2008.Survey length amounts to 1 460.2 km with 374 sightings in total.Based on our findings,the mean densities over 10 surveys were 0.67 porpoises/km2 (range:0.10~1.28 porpoises/km2,〖WTBX〗s〖WTBZ〗=0.41) and 1.75 porpoises/km2 (range:0.62~3.0 porpoises/km2,〖WTBX〗s〖WTBZ〗=0.72),respectively in the upper and lower stratifications,and their corresponding mean abundances were 37 porpoises (range:5~71 porpoise,〖WTBX〗s〖WTBZ〗=23) and 52 porpoises (range:22~78 porpoises,〖WTBX〗s 〖WTBZ〗=17).Overall,the mean abundance in Balijiang section was approximately 90 porpoises and seasonal estimates might fluctuate around this number (range:44~121 porpoises,〖WTBX〗s 〖WTBZ〗=24).This population is still declining by comparing with the historical survey results,however,the current study failed to detect the trends of this population statistically over 3years study period.According to the variations and occurrence times of the fluctuations,we presume that this porpoise population may be subject to an emigration (~40 porpoises) from the middle to the end of the flood season.The population status of Yangtze finless porpoise is deteriorating due to a combination of dredging,illegal fishing,transportation,pollution and water constructions etc.,consequently,we strongly recommend to establish a natural reserve in Balijiang section immediately.