Relationship Between Spatial And Temporal Distribution Characteristics Of Fishes And Environmental Factors In Caojie Reservoir Area Of Jialing River And Its Tributaries In Chongqing

The lower reaches of the Jialing river are rich in fish resources due to the favorable natural environment.However,in recent years,after the construction of Caojie avionics hub project,the basin above Caojie hydropower station has been transformed into a reservoir area,which has caused a significant impact on the water ecological environment(especially the spatial distribution of fish)of the lower reaches of the Jialing river and its tributaries.In this study,Simrad EY60 echo detector was used in April(spring)and December(autumn)2019 to investigate the hydroacoustic detection of the whole Jialing river and its tributaries in Caojie reservoir area of Chongqing,including the lower reaches of the Jialing river area,the Hechuan section of Qu river and the Hechuan section of Fu river.The environmental indexes of the main distribution points of fish were collected and determined.The spatial and temporal distribution of fishes in this basin was analyzed and the relationship between spatial distribution of fishes and environmental factors was studied by means of canonical correspondence analysis.The main research results are as follows:(1)Fish density distribution in the lower reaches of the Jialing river is uneven in spring and autumn.The average density of fish increases from spring to autumn.Spawning ground or feeding ground has:Xiaonantuo,Dongjintuo,Moershi,Bagongfen,Shuibi yard,Yunmen town,Yanjiaba and Lizechang a total of 9.In autumn,the larger density of fish points has:Juliangtuo,Diaoyucheng,Xiaonantuo,Yunmen town,Shentiangou,Qianniufangzi a total of 6 place.The vertical distribution of fish in both seasons showed obvious stratification,and the density of fish in the middle and lower strata was obviously higher than that in the upper strata.Spearman correlation analysis of fish horizontal density distribution and water depth found that only in spring river fish density had significant positive correlation with the two depth factors of average and maximum water depth(P<0.05).The average body weight of fish in spring is 14.147g,the body length range of fish is 3.94-49.55cm,the average body length is 13.96cm,the fish with the largest proportion is only 7.85cm.The average weight of fish in autumn is 19.628 grams.The body length ranged from 4.41 to 55.59cm,with an average body length of 15.67cm.The fish with the largest proportion only had a body length of 8.81cm.Fish resources are few and far between.(2)The horizontal distribution of fish density in Hechuan section of Qu river is not uniform.From spring to autumn,fish density decreases in most directions.In spring,there are seven places with high density of fish:Quhezui,Gongjiawan,Tianrentang,Bosiwuji,Huabanzhu,Shuanghuai town and Miaoliangzi,which are spawning grounds or feeding grounds.In autumn,the larger density of fish points are Quhezui,Gongjiawan,Tianrentang,Bosiwuji a total of four.On the vertical distribution,the density relation in spring is:the lower layer>the middle layer>and the upper layer.In autumn,the density relation is:middle layer>lower layer>upper layer.It was found that the density of fish in the river was negatively correlated with the maximum water depth(P<0.05).The density of fish in the left,middle and right rivers had little correlation with the average and maximum water depth.The body length of fish in spring ranged from 3.94 to 62.37cm,with an average body length of 15.67cm.The fish with the largest proportion had a body length of 3.94cm,while the fish with the largest proportion had a body length of 8.81cm,11.09cm and 13.96cm.In autumn,the body length also ranged from 3.94 to 62.37cm,with an average body length of 15.67cm.However,the body length of the fish with the largest proportion was 5.56cm and6.99cm,and that of the fish with the highest proportion was 9.89cm.The average weight of the fish was only 20.01g,and the maximum weight in the spring was 0.318g,while the most common weights were 3.556g,7.092g and 14.147g.In autumn,the most weight was 0.894g and 1.776g,and the most weight was 5.03g.The fish biomass is less,and only four river sections such as Bosiwuji base are rich in resources.(3)Fish density distribution is not uniform in the horizontal direction of Hechuan section of Fu river.In terms of time,the average density of fish in left river increased from 6.36 ind/km~3 in spring to 11.65ind/km~3 in autumn,the average density of fish in the center of river increased from 5.87ind/km~3 in spring to 6.4 ind/km~3 in autumn,and the average density of fish in right river decreased from 8.37ind/km~3 in spring to6.17ind/km3 in autumn.There was no significant difference in average fish density between spring and autumn(P>0.05).The area with more fish in spring has Xiaoanxi estuary,Tanmucun,Baishapu and Weituo hydropower station four,for spawning or feeding ground.In autumn,the fish density in Hechuan section of Fu river is larger.There are three sections,namely Baita street community mouth,Xiaoanxi estuary and Weituo hydropower station.In vertical distribution,the average density of pelagic fish increased from 4.69ind/km~3 to 11.5ind/km~3.The middle level increased from 6.1ind/km~3to 12.9ind/km~3,and the lower level increased from 10.39ind/km~3 to 16.16ind/km~3.It shows that different water layers have little effect on fish distribution in Fu river.There is little difference between horizontal distribution and vertical distribution in Hechuan section of Fu river.But fish stocks are severely inadequate.The body length range of fish in spring is 3.94～62.37cm,with an average body length of 15.67cm,and the fish with the largest proportion are 15.67cm and 17.58cm.The body length range of fish in autumn is also 3.94～55.59cm,with an average body length of 13.96cm,but the fish with the largest proportion are 3.94cm,8.81cm and 9.88cm.The average body length of fish changed little from spring to autumn,decreasing from 15.67cm to 13.96cm.However,compared with spring,the body length of fish with the largest proportion decreased significantly in autumn.Compared with the previous two rivers,the fish resources in Fu river are the least,and the middle layer with the highest amount of resources in autumn is only 234.89g/1000m~3,facing the most serious"no fish"situation.(4)The collection of water environmental factors include:water temperature(WT),p H,dissolved oxygen(DO),total phosphorus(TP),total nitrogen(TN),ammonia(NH3-N),electrical conductivity(EC),total solid solubility(TDS),transparency(SD),chemical oxygen demand(COD),density(Pd),phytoplankton biomass of phytoplankton(Pb),the density of zooplankton(Zd),zooplankton biomass(Zb),a total of 14indexes.When analyzing the corresponding correlation between the spatial distribution of fish and the model of environmental factors,it was found that most of the environmental factors(p H,COD,TP,TN,NH3-N,EC,TDS,etc.)were positively correlated with the density of fish in the middle side of the spatial distribution of fish.Only SD and DO were positively correlated with fish distribution on the left and right sides of the river section.