Temporal And Spatial Distribution Characteristics Of Fish In The National Aquatic Germplasm Resources Conservation Area Of The Four Major Fishes In The Chongqing Section Of The Yangtze River

The four major areas of national-level fish germplasm resources conservation(hereinafter referred to as protected areas)in the Chongqing section of the Yangtze River starts from Guangyang Town in the Nan'an District to Nantuo Town in Fuling District.According to the catch results obtained by traditional fishing techniques in previous years,there are abundant fish resources in the protected area,but the status of fish resources in protected areas is still unclear,and traditional fishing techniques have high cost,long time,and uneven distribution of sampling points.Inadequacies.The emergence of hydroacoustic technology can solve most of the problems faced by traditional fishing technology.In this paper,the Simrad EY60 echo detector was used to detect the spring and winter hydrophones in the Fuling River section and the Nan'an to the Changshou section of the reserve from 2017 to 2019.The relationship between fish distribution and environmental characteristics and seasons in different seasons was discussed.At the same time,the results of recent catches and hydroacoustic data are compared and analyzed.In order to provide a basis for the protection and management of fish resources in protected areas.The main findings are as follows:(1)According to the analysis of Amplitude Detection(AMP),The results show that the protected section of the river section presents different characteristics in the spring and winter seasons.In the Nan'an to Changshou River section,the average density of the entire water layer in spring is 1.53 in./1000 m~3,and the maximum density is located at the confluence of the tributary of the Changshou Bridge and the main stream of the Yangtze River,which is 36.5 ind./1000 m~3.In winter,the average density of the entire water layer It is 25.51ind./1000m~3,and the maximum density is located in the river section near the safflower,which is 293.3ind./1000m~3.In the section of the Yangtze River tributary and main stream junction,the density of fish detected in spring and winter is relatively large.In the Fuling River section,most fish in spring are distributed in curved river sections and tiller-type river sections.The average density of the whole water layer is 15.35ind./1000m~3,and the maximum density is located in the section near the Fuling Yangtze River Bridge,which is as high as 70.4ind./1000m~3.In winter,fish are mostly distributed in the river sections with wider surface,slower flow and deeper water depth.The average density of the whole water layer is 26.40ind./1000m~3,and the maximum density is located in the river section near Piaoertan,up to 116.9 ind./1000m~3.(2)In the vertical direction of the water body,the water from the South Bank to the Changshou District is relatively flat,and the average water depth detected in April is 6.50m.The average water depth obtained was 14.05 m.The water bottom structure of the Fuling District is complex and diverse.The average water depth from the April survey is 10.43m,and the average water depth from January is 22.47m.The water layer in the AMP was divided into an upper layer(0 to 33%),a middle layer(33 to66%),and a bottom layer(66 to 100%)for analysis.In the Nan'an to Changshou River section,the density of fish in the upper,middle and lower layers of spring was 5.88,1.64 and 0.44 ind./1000m~3 respectively.The density of fish in the upper,middle and lower layers of winter was 66.97,14.71 and 45.86 ind./1000m~3 respectively.In the Fuling River section,the density of fish in the upper,middle and lower layers of spring was 21.47,4.47 and 2.31 ind./1000m~3 respectively;the density of fish in the upper,middle and lower layers in winter was 172.19,21.6 and 43.31 ind./1000m~3respectively.(3)According to Foote's TS-TL empirical formula,the fish body length data is obtained in spring and winter.The TS of spring fish from the Nan'an to the Changshou River section ranges from-60 to-39 dB,and the average TS is-49.5 dB.The TS with the highest proportion is-59,-58dB.According to the TS-TL formula,the body length range is 3.94~44.16cm,the average body length is 13.18cm,and the body length is4.42 and 4.95cm.The winter fish TS ranges from-60 to-38 dB,and the average TS is-49 dB.The most probable TS are-60,-55,-53,-51 dB.According to the TS-TL formula,the fish body length is known.The range is 3.94~49.55cm,the average body length is 13.96cm,and the body length is 3.94,7.00,8.81,and 11.09cm.The TS of spring fish in the Fuling section is-60~-40dB.According to the TS-TL formula,the body length range of fish is 3.94~39.36cm,and the most TS is-58dB,and the average TS is-50dB.It means that the fish with the longest body length is about 4.95cm,and the average body length is 12.45cm.Winter fish has a TS range of-60 to-39 dB.The same range of fish body length is 3.94~44.16cm according to the formula.The highest TS is-54dB,and the average TS is-49.5dB.The fish with the longest body length was7.85 cm and the average body length was 13.18 cm.It can be seen from the results that the body length of winter fish is slightly larger than that of spring.(4)According to the statistics of the target signals in the AMP,there are three major types of fish accumulation in the spring in the protected area.First,the fish are distributed in the upper layer of the water,away from the shore,and close to the deep upper fish.Second,the fish is distributed in the middle layer of the water,the middle layer fish from the water surface and the bottom of the water;the third is the bottom layer of fish distributed in the lower layer of the water,close to the shore,away from the deep concave,close to the bottom of the river.There are 18 upper fishes,35 middle fishes and 3 bottom fishes in Fuling River.There are 35 middle-layer fish and 3bottom-layer fish in the section from Nan'an to Changshou River.Comparing the location of the fish density in the protected area with the maximum water depth and average water depth at the location,the results show that the distribution of fish in winter is greatly affected by the water depth.(5)The rivers with higher density in spring include Luxiqi,Shangqiantan,Mopanshi,Guanyintan,Huangcaoxia,Jincaibei,Goujiatuo,Wayaotuo,Pingxiba main stream and the upper and lower reaches of the Fuling Yangtze River Bridge.The rivers with higher density in winter include Yaotangqi,Dajiantan,Nanpingba,Guanyintan,Changshou Yangtze River Bridge,Shiniulan,Jinchuanqi,Scissor Beam,Piaoertan,Suimiqi,Sanduizi.