Predation Rhythm Of Yangtze Finless Porpoise In The Confluence Water Of Wanhe Estuary

The confluent waters are the confluence of tributaries with the main stream of Yangtze River,with diverse geomorphological features and complex hydrodynamic conditions.It is an important channel for the transfer of materials and biological communities in adjacent river sections,and an important predation water for Yangtze finless porpoise.Yangtze finless porpoise(Neophocaena asiaeorientalis)is a critically endangered freshwater cetacean species in China,eight nature reserves have been established on the main stem of the Yangtze River and the study of habitat selection mechanism based on predation rhythm become a core issue in the conservation biology of endangered animals.In the confluence waters,one of the important habitats of Yangtze finless porpoise,this study conducted a preliminary investigation on the predation rhythm of Yangtze finless porpoise.The purpose of the study is to strengthen the scientific management of in situ conservation.In the branching river section,the porpoises mainly move around the river core.According to the statistical analysis of the fieldwork data of previous years,the results of the flow analysis show that the sightings and cluster scale of the Yangtze finless porpoise has no significant difference in the branching channel(p>0.05);The sightings in the bifurcation upon bar were significantly lower in the low discharge than in the high discharge(p<0.05);On the contrary,the sightings and cluster scale in the estuary confluence area were significantly higher in the low discharge than in the high discharge(p<0.05).For the study of Yangtze finless porpoise on habitat flow selection,statistical analysis was conducted through the data of previous years’ fieldwork,so this paper selected the confluence waters of Wan-river estuarine confluence and used passive acoustic recorders(Soundtrap300HF)and arranged them at the mouth of Wan-river and its upstream and downstream 600 m respectively.The high-frequency acoustic signals of porpoises were recorded continuously for one month in 2021 during the low,medium and high discharge,respectively.According to the earth’s rotation pattern,each day is divided into six periods: the second half of the night,dawn,morning,afternoon,dusk and the first half of the night.The number and duration of highfrequency bursts of Yangtze finless porpoise in the confluent waters of the Wan-river in different seasons and time periods were statistically analyzed using spss20.0.This result suggests that porpoises have obvious seasonal rhythms and significant differences in estuarine confluence waters.The predation frequency and cluster size of porpoise in the estuarine stagnation zone and upstream deflection zone are higher than those in the downstream separation zone in the low discharge(p<0.05);Predation frequency and cluster size were significantly higher at night than during the day in the low discharge(p<0.05);The diel rhythm of predation frequency of porpoise is not obvious in the high discharge(p>0.05).The results of the study suggest that protection measures for estuarine confluence waters should be strengthened during the low discharge.This study is the first preliminary study on the diel predation rhythms of Yangtze finless porpoise in the field,based on the existing studies of our disciplinary group.It enriches the knowledge of freshwater dolphin ecology and provides guidance for in situ management.However,the higher frequency of Yangtze finless porpoise predation at night during the low discharge may be related to the diel migration of fish or human activities during the day,which needs further study.