Study On The Activity Rules And Influencing Factors Of Yangtze Finless Porpoise In Wanhe Estuary

This paper takes the wanhe estuary as the center,and the upper and lower reaches of the Yangtze river trunk stream as the study waters within 5km,taking the Yangtze river finless porpoise in this region as the study object,Focusing animal sampling method and continuous sampling method were used to systematically observe the distribution characteristics of the Yangtze finless porpoise.Based on the investigation results of water environment and aquatic biology in this area,the main factors affecting the activity and distribution of finless porpoises in the Yangtze river estuary of wanhe estuary were analyzed.The main result of study is as follows:1.According to the environmental investigation results,the surrounding area of wanhe estuary is in good condition,with no obvious pollution sources such as factories and enterprises.In some regions,there are many docks,but no obvious impact has been caused.Human activities are the only factors affecting water quality.The results of annual water quality monitoring and carlson’s nutrition index show that the water in wanhe estuary is poor in nutrition and the water quality is excellent throughout the year.Meanwhile,it is rich in fish resources.By using the plankton method to calculate the fish productivity,it is known that this water area can provide food for 49 adult Yangtze finless porpoises for one year.2.The cumulative value of the maximum number of observation heads of the Yangtze river finless porpoise was found to be 324(including the number of repeated heads)through fixed point observation,and the total number of water outings of the Yangtze river finless porpoise was recorded to be 3,455 times,with the activity duration of 5,8186 seconds.Group activity over 2 heads accounted for 73.3%,nearshore activity(<500m)accounted for 89.2%.Moreover,the finless porpoise of the Yangtze river only appeared in the north bank,and the water frequency,the maximum number of observation head and the activity duration were significantly different in different regions,with region B and region C being the most significant.There were significant differences in different seasons,with winter as the most important,autumn as the second,and no discovery in spring or summer.3.During the study period,65 species of fish were collected using floating gill nets,submerged gill nets and ground cages,with a total of 13,651 fish(255.5kg).It belongs to 8 orders,16 families and 54 genera.It is mainly composed of bottom fish and freshwater sedentary fish.Hemiculter bleekeri、Coilia nasus、Pseudobrama simoni and Siniperca chuatsi are the absolute dominant species,with 13 important species.There was a significant difference in the number of fish species collected by the three nets,with 61 species of multi-eyed net,57 species of multi-eyed net and 45 species of ground cage.The tail and weight of catches are consistent in many ways: In terms of time: the total catches and floating net catches were the most in summer,while the upper-middle catches were the most in winter.In terms of Spatial,the catches on the north bank of anhui estuary were significantly higher than those on the south bank,and the catches were the highest at points 2 and 3.In terms of time,the total catches of small fish were the most in summer,the catches of middle and upper layers were the most in winter,and in terms of space,the most in the north coast and mainly at points 2 and 3.The Yangtze river finless porpoise likes fish most in summer,most on the north bank of the space,and mainly 2,3 points as the most.In the period of time,midday time frame is the most in all respects.There was no significant difference in fish community diversity between seasons and points.4.The following conclusions can be drawn by combining the activity rules of finless porpoises in the Yangtze river with the status quo of aquatic biological resources,(1)The activity pattern of Yangtze finless porpoises in the wanhe estuary is closely related to the distribution of fishes,especially the distribution of small fishes in the upper and middle layers.The Yangtze finless porpoises in the wanhe estuary will choose areas with high density of fish resources to hunt and play for a long time.The Yangtze finless porpoises in other regions mainly pass through and converge to the wanhe estuary.The number of finless porpoises in the Yangtze river,the accumulation of the maximum number of observation heads and the duration of activities were negatively correlated with the index of fish community richness and the floating net catch.There were significant positive correlations with total catch,bottom catch,upper middle catch and upper middle small catch.(2)The activity of Yangtze finless porpoises is also closely related to the water level,which only occurs in autumn and winter when the water level is low,but not in spring and summer when the water level is high.(3)The Yangtze river finless porpoise has the highest probability of appearing on the natural shoreline,accounting for 93.4%.The density is 797.3 times/km measured by the number of times of water discharge,and the density of the artificial shoreline is 35.4 times/km.