Method for counting key factors influencing spawning space-time distribution of domestic fish at downstream of reservoir

Abstract

The invention discloses a method for counting key factors influencing spawning space-time distribution of domestic fish at the downstream of a reservoir. The method mainly comprises the steps of fish early-stage resource monitoring, hydrological element monitoring, numerical simulation of waterpower conditions of a river channel, result analysis and the like. The fish early-stage resource monitoring mainly comprises surface layer and middle bottom layer sampling, on-site sample sorting and counting, live sample culture, observation and identification, long-term storage after dead sample identification, section coefficient checking, sample accuracy statistics and the like. Hydrological element monitoring mainly relates to water level monitoring, water temperature testing, flow velocity distribution testing, flow testing, large section measurement and the like. A two-dimensional hydrodynamic mathematical model is adopted to calculate the hydrodynamic conditions of the spawning site reach in the numerical simulation of the waterdynamic conditions of the river channel; according to result analysis, hydrodynamic conditions in a computational domain, actually measured hydrological elements and the spawning amount of the domestic fish are associated, so that key factors influencing spawning space-time distribution of the domestic fish at the downstream of the reservoir are defined. The method has the advantages that the key factors influencing the spawning space-time distribution of the reservoir downstream domestic fish are found out through statistical analysis of the multi-source data, and the method is an effective way for accurately counting the key factors influencing the spawning space-time distribution of the reservoir downstream domestic fish.

Description

Technical Field

[0001] The invention relates to the field of reservoir ecological regulation, and in particular to a method for statistically analyzing key factors affecting the temporal and spatial distribution of spawning of domestic fish downstream of a reservoir. Background Art

[0002] The four major carps are typical species of the river and lake complex ecosystem in the middle and lower reaches of the Yangtze River, and their resource quantity can represent the health status of the water ecosystem. In the 1950s, during the research and demonstration stage of the Gezhouba Project, the issue of the possible impact of dam construction on the reproduction of the four major carps was raised. Subsequently, during the demonstration and construction stages of the Gezhouba Project and the Three Gorges Project, the scale and distribution changes of the spawning grounds of the four major carps became the focus of attention and research. Investigations and studies have shown that the spawning grounds in the Yichang section of the middle reaches of the Yangtze River are relatively stable and large spawning grounds over the years. After the Three Gorges Reservoir was impounded, more attention was paid to the impact of the hydrological rhythm changes caused by the Three Gorges Reservoir regulation on the reproduction of the four major carps, and the early resource changes of the four major carps after impoundment and their response analysis to the hydrological process were studied. In particular, since the Three Gorges Group implemented the ecological regulation experiment for the natural reproduction of the four major carps in 2011, relevant units have analyzed and studied the impact of ecological regulation on the spawning of the four major carps, and believed that the implementation of ecological regulation has played a significant role in promoting the spawning of domestic fish. However, most of the current research is still mainly focused on the early resources of the four major carps and the large-scale distribution changes of spawning river sections. There is a relative lack of research on the spatiotemporal variation characteristics of specific spawning of domestic fish and their influencing factors. Summary of the invention

[0003] This patent provides a method for statistically analyzing the key factors affecting the temporal and spatial distribution of spawning of domestic fish downstream of a reservoir, which can solve the problem of the shortcomings of existing research methods and achieve more comprehensive and accurate statistics of the key factors affecting the temporal and spatial distribution of spawning of domestic fish downstream.

[0004] The technical solution to achieve the purpose of the present invention is a method for statistically analyzing the key factors affecting the temporal and spatial distribution of spawning of domestic fish downstream of a reservoir, including early fish resource monitoring, hydrological element monitoring, numerical simulation of river hydraulic conditions, and result analysis; The early fish resource monitoring is carried out at a location 20-30 km downstream of the spawning grounds. The monitoring method includes collecting samples from the surface and middle and bottom layers using a fishing net and a cone net, checking the cross-sectional coefficient, and performing sample accuracy statistics. The hydrological element monitoring includes water level monitoring, water temperature testing, flow velocity distribution testing, flow testing, and large-section measurement; The water level monitoring is to conduct manual water level observation on a water gauge that is set up in advance and measures the zero point elevation during flow measurement, and use the GNSS-RTK method to calibrate the water level; The water temperature test uses a sound velocity profiler to measure the layered water temperature along the water depth direction at the middle position of the monitoring section within a fixed period of time; The velocity distribution test adopts ADCP test and extracts vertical velocity distribution data. The velocity measurement vertical lines of each section are generally evenly arranged, and the velocity measurement vertical lines are densely arranged in the main channel of the deep trough, and the vertical line spacing is not greater than 1 / 10 of the river width; The flow test adopts ADCP flow measurement, which is synchronized with the flow velocity test, and is measured at least 3 times a day; The large-section measurement is carried out using underwater measurement software Hypack, Trimble 852GPS section measurement, DGPS plane positioning and HY1601 echo sounder, and the section spacing is not more than 1km; The numerical simulation of the hydraulic conditions of the river channel adopts a two-dimensional hydrodynamic mathematical model to simulate and calculate the study section of the river: The result analysis associates the numerical simulation area of ​​the river hydrodynamic conditions with the corresponding water level, water temperature, flow velocity distribution, flow rate, and large-section values, and conducts a correlation analysis with the spawning amount of domestic fish in the area, thereby statistically analyzing the key factors affecting the temporal and spatial distribution of domestic fish spawning downstream of the reservoir.

[0005] Furthermore, the method also includes early fish resource monitoring, and the early fish resource monitoring also includes collecting samples from the surface and middle and bottom layers using a fishing net and a cone net.

[0006] Furthermore, in the step of numerically simulating the hydraulic conditions of the spawning ground river channel, a number of computational grids are arranged in the simulated river channel area, wherein the average grid length along the water flow direction is 15 to 25 m; the average grid width along the river width direction is about 15 to 20 m; Furthermore, in the flow test step, at least three measurements are performed every day.

[0007] Furthermore, in the water temperature testing step, two tests are performed every day, in the morning and afternoon.

[0008] Furthermore, in the velocity distribution test step, in order to ensure the accuracy of the cross-sectional velocity distribution, the vertical line spacing is not greater than 1 / 10 of the river width.

[0009] The advantages of the present invention are that, based on the two-dimensional mathematical model and the analysis of the boundary conditions of the river section of the spawning ground, the distribution location and range of the spawning ground are clarified, and based on the hydraulic characteristics of the river channel of the spawning ground combined with the measured hydrological elements during the ecological regulation of the reservoir and the early resource changes of domestic fish, accurate statistics of the key factors affecting the spawning of domestic fish are achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. 1 Schematic diagram of the spawning grounds of the four major carps and early resource monitoring locations in the YC section of the river; Fig. 2. Cumulative proportion of typical spawning ground flow velocity at different flow levels; Figure 3 Statistics of annual changes in spawning volume of the four major carps after the impoundment of Reservoir A; Fig. 4 Annual distribution of spawning quantity of four major carps after the impoundment of reservoir A; Fig. 5 Correlation diagram between daily egg production of domestic fish and daily water temperature; Fig. 6 Variation of total egg quantity of domestic fish with water temperature gradient; Fig. 7 Correlation diagram between daily egg production of domestic fish and daily average flow rate; Fig. 8 Variation of total egg production of domestic fish with flow level; Figure 9 The 7-day cumulative spawning process of domestic fish in 2020. DETAILED DESCRIPTION

[0011] According to the results of early fish resource monitoring and environmental DNA monitoring, it is clear that the YC section of the middle reaches of the Yangtze River is the largest known spawning ground for the four major carps. The spawning ground in the YC section is 10.2 km long, about 50 km from the upstream reservoir A, and the YD section of the downstream fish early resource monitoring point is about 25 km away from the spawning ground (Figure 1). The method proposed in this patent includes early fish resource monitoring, hydrological element monitoring, numerical simulation of river hydraulic conditions, and result analysis to statistically analyze the key factors affecting the temporal and spatial distribution of spawning of domestic fish downstream of the reservoir.

[0012] The early resource monitoring of fish: the surface and middle and bottom layers are sampled with a net and a cone net respectively. The collected fish egg and fry samples are sorted on site, and the live samples are cultured, observed and identified to verify the accuracy of the identification of the eggs and fry of the four major carps, and the dead samples are identified and stored for a long time. Sampling is carried out 2-3 times a day, 30-60 minutes each time, and the section coefficient is checked according to the amount of eggs and fry. When checking the section coefficient, 5 sampling vertical lines are arranged on the left, left middle, middle, right middle and right of the conventional sampling section. Each vertical line takes the upper, middle and lower 3 sampling points for section sampling, and the distribution of eggs and fry in the section is counted. A large number of live samples collected are cultured indoors for a long time to verify the accuracy of the identification results of domestic fish. Early fish eggs are cultured separately in temporary containers, and species identification is carried out after 7-10 days of culture. The identified samples are concentrated in temporary boxes for long-term culture, and the accuracy of the identification samples is counted later.

[0013] The hydrological element monitoring mentioned above: focus on monitoring the hydrological and hydraulic elements of the main spawning areas of the YC River section (a total of 12 monitoring sections, namely STDD1~STDD12), including water temperature, flow process, flow velocity distribution, section geometric parameters, etc. The monitoring of each hydrological element is as follows: Water level monitoring: When measuring flow, manual water level observation is carried out on the water gauge that has been set up in advance and measures the zero point elevation, and the water level is calibrated using the GNSS-RTK method.

[0014] Water temperature test: Every morning and afternoon, the stratified water temperature is measured along the water depth direction at the center of the monitoring section.

[0015] Velocity distribution test: Adopt ADCP test. The velocity measurement vertical lines of each section are generally evenly distributed, and the velocity measurement vertical lines are denser in the main channel of the deep trough. The vertical line spacing is generally not more than 100m, and the section vertical lines are not less than 10 lines.

[0016] Flow test: Adopt cruise ADCP flow measurement, synchronized with flow velocity test, and conduct three tests per day.

[0017] Large-section measurement: The underwater measurement software Hypack, Trimble 852GPS section measurement, DGPS plane positioning and HY1601 echo sounder were used to conduct large-section measurement of 12 sections.

[0018] By performing correlation analysis on the above data, we can analyze whether there is a certain dependence relationship between random variables, and explore the correlation direction and degree of correlation of specific dependent random variables. Spawning of domestic fish is a biological characteristic of fish, and external environmental factors (including hydrology, water temperature, hydraulic elements, etc.) are closely related to the spawning behavior of domestic fish. Combined with historical monitoring data, the correlation analysis was carried out between the water temperature, hydrological conditions and hydraulic elements of the river section and the spawning amount of the four major carps, and the correlation degree between each factor and the spawning amount was studied to clarify the adaptive hydrological and hydraulic indicators of the spawning of the four major carps.

[0019] Numerical simulation of river hydraulic conditions: A two-dimensional hydrodynamic mathematical model was used to simulate the spawning ground river section. The total length of the calculation domain was about 10.2 km. A total of 500×85 calculation grids were arranged in the simulated river area, of which 500 grids were arranged along the direction of water flow, with an average grid length of 15 to 25 m; 85 grids were arranged along the river width, with an average grid width of about 15 to 20 m. The model was verified using multiple sets of measured data from 2013 to 2015.

[0020] The numerical simulation area of ​​the hydraulic conditions of the river is associated with the corresponding water level, water temperature, velocity distribution, flow rate, and large cross-section values. If there is no correlation after analysis, it is not associated. The number of spawning of domestic fish in a certain area is measured, and a relationship diagram between water level, water temperature, velocity distribution, flow rate, large cross-section values ​​and the number of spawning of domestic fish is established. That is, the number of spawning of domestic fish can be calculated through water level, water temperature, velocity distribution, flow rate, and large cross-section values. The important analysis content is temperature. Domestic fish spawning requires suitable water temperature conditions, suitable water rise process and specific spawning grounds. The water temperature should be the reproductive restriction condition for the four major domestic fishes and other fishes that lay drifting eggs. Fish can only start breeding activities when a certain water temperature is reached; the water rise process and specific spawning grounds are important environmental conditions that stimulate fish reproduction and promote breeding activities.

[0021] Monitoring of hydrological process changes: The flow rate of the spawning ground downstream of Reservoir A gradually increased during the monitoring period, with a flow rate change of 10,000~25,000m 3 / s; the vertical flow velocity of each section is mainly in the range of 0.6~2.5m / s, the flow velocity in the center of each section is greater than the flow velocity on both sides, and the change process of the flow velocity is basically consistent with the change process of the flow rate in each section; there is basically no stratification in the water temperature of each section, and the water temperature is mainly concentrated in 21~23℃.

[0022] Hydraulic condition simulation: The model calculates the velocity distribution of the river section at different flow levels, the change of velocity with flow direction, and the proportion of velocity in the river section at different flow levels (see Figure 2 ). The calculation results show that the flow velocity in the main channel of the river changes with the flow more obviously than near the shore. When the flow rate in the spawning ground is between 10,000 and 20,000 m³ / s, the flow velocity and flow direction change most obviously with the increase of flow rate. When the flow rate changes between 10,000 and 20,000 m³ / s, the flow direction changes in the spawning ground section are more complicated. When the flow rate is 10,000 m³ / s, the largest flow velocity is 1.0 m / s to 1.5 m / s, accounting for 62%; when the flow rate is 15,000 m³ / s, the largest flow velocity is 1.0 m / s to 1.5 m / s, accounting for 50%; when the flow rate is 20,000 m³ / s, the largest flow velocity is 1.5 m / s to 2.0 m / s, accounting for 61%; when the flow rate is 25,000 m³ / s, the largest flow velocity is 1.5 m / s to 2.0 m / s, accounting for 60%. See Table 1 for the statistical table of the proportion of flow velocities within the river channel at different flow levels.

[0023] Table 1 Statistics of the proportion of flow velocity in the river at different flow levels

[0024] Result analysis: 1) Interannual variation characteristics The interannual variation of domestic fish spawning can be generally divided into three stages (see Figure 3 ): The first stage was from 2011 to 2014, with a small scale of spawning, not exceeding 200 million eggs, and the spawning volume was relatively stable each year, with a total spawning volume of 460 million eggs; the second stage was from 2015 to 2018, with a significant increase in spawning volume compared with the previous stage, but with annual fluctuations and a small range of variation, with a total spawning volume of 6.6 billion eggs; the third stage was from 2019 to 2021, with a significant increase in spawning volume, with a slight decrease in 2020 compared with 2019, and an explosive growth in 2021, with a total spawning volume of 29.4 billion eggs.

[0025] Overall, the scale of domestic fish has shown an upward trend, which may be related to the comprehensive protection measures such as strengthening fishing bans, releasing domestic fish parents and implementing ecological scheduling in recent years. From the perspective of ecological scheduling, the main reasons for the changes in the spawning volume of domestic fish in these three stages are: in the first stage, the overall spawning volume did not change much, and the inter-annual variation was not obvious. The main reason was that the hydrological and hydraulic indicators for ecological scheduling were not clear, and various indicators were still in the test, analysis and research stage; the obvious increase in spawning volume in the second stage showed that the preliminary exploration and research of ecological scheduling, such as the starting flow, flow increase, and suitable water temperature, had achieved significant results; the main reason for the decrease in spawning volume in 2020 in the third stage was that in the early stage of scheduling, the water temperature reached 18°C ​​10 days later than in 2019, resulting in a small number of broodstock arriving at the spawning grounds during the monitoring period. At the same time, the average water temperature during the scheduling period in 2020 was 19.86℃, 0.5℃ lower than in 2019; the spawning volume increased explosively in 2021. On the one hand, the implementation of ecological scheduling promoted the large-scale spawning of the four major carps. At the same time, starting from January 1, 2021, the Yangtze River implemented a "ten-year fishing ban" in key waters of the Yangtze River Basin, further protecting the breeding populations of the four major carps.

[0026] 2) Distribution characteristics within the year Daily egg production of the four major carps From mid-May to early July, domestic fish generally have 1 to 3 large-scale spawning processes, mainly concentrated in late May to late June, and the spawning volume accounts for about 87% of the total egg production during the monitoring period. The largest large-scale spawning is from early June to mid-June, accounting for 39% of the large-scale spawning volume ( Figure 4 ).

[0027] 3) Main influencing factors The natural reproduction of the four major carps is closely related to water temperature conditions, and reservoir dams are considered to be the most important factors that significantly change river water temperature, especially the large difference between the discharge temperature of large reservoirs and the natural water temperature. The minimum water temperature for domestic fish reproduction is 18°C, and the water temperature during the peak spawning period is 20°C to 24°C. The higher the water temperature within the suitable temperature range, the higher the hatching rate; and water temperatures below 18°C ​​or above 30°C will cause embryonic development to stagnate or cause deformities and death. When hatching within a certain temperature range, the speed of embryonic development also accelerates with the increase of water temperature. Since the spawning and reproduction period of the four major carps is relatively long, the water temperature range is also relatively large.

[0028] According to the analysis of the daily water temperature and daily spawning of domestic fish in the YC River section from 2011 to 2020, there is a close correlation between the number of domestic fish eggs and the water temperature ( Figure 5 ): The daily spawning amount and daily spawning peak of domestic fish are mainly concentrated in the water temperature of 20°C ~ 24°C, which is consistent with the existing research results. The relationship between the total egg amount of domestic fish and water temperature under different gradient water temperature conditions is statistically analyzed ( Figure 6) It can be seen that: in the range of 18°C ​​~ 25°C, the total number of eggs of domestic fish gradually increases with the increase of water temperature, and gradually decreases with the increase of water temperature after reaching 22°C; under the water temperature conditions of 21°C ~ 23°C, the total number of eggs of domestic fish maintains a peak value, and the number of eggs of domestic fish under this water temperature condition accounts for about 63% of the total, indicating that the most suitable water temperature for domestic fish spawning is 21°C ~ 23°C.

[0029] Based on the above analysis, a statistical method for the key factors affecting the spatiotemporal distribution of spawning of domestic fish downstream of the reservoir can be further refined.

[0030] Spatial distribution characteristics of spawning of four major carps and their influencing factors The large-scale spawning behavior of the four major carps is closely related to the hydraulic elements of the river. The hydraulic characteristics of fish habitats mainly include water depth, flow velocity, flow velocity gradient, Reynolds number, Froude number, vorticity, and curl, which divide the four major carps' preference for water flow into four levels: ① slow flow, that is, flow velocity less than 0.7m / s; ② flat flow, that is, flow velocity in the range of 0.7~1.3m / s, which is the suitable flow velocity for domestic fish to spawn; ③ rapid flow, that is, flow velocity in the range of 1.3~2.0m / s, which is the flow velocity that domestic fish find difficult to overcome; ④ torrent, that is, flow velocity greater than 2.0m / s, which is the flow velocity that domestic fish cannot overcome and is difficult to swim upstream.

[0031] According to the results of hydraulic model simulation: In this example, the flow rate and flow direction of the key monitored river channel change significantly with the increase of flow rate when the flow rate is 10000m³ / s~15000m³ / s, and the proportion of rivers with flow rates in the range of 0.5m / s~1.5m / s reaches 64%~90%. Among them, at 10000m³ / s, the proportion of rivers with flow rates of 0.5m / s~1.5m / s is 90%; at 15000m³ / s, the proportion of rivers with flow rates of 0.5m / s~1.5m / s is 64%. It can be seen that this river section is mainly slow flow and horizontal flow at 10000m³ / s~15000m³ / s, which is more suitable for spawning of the four major carps.

[0032] According to the river topographic characteristics of this river section, there are obvious shoals in the middle of this river section (STDD8~STDD11), and the shoals are located near the middle of the river section. The river topography is relatively complex, which can make the water flow roll up and down and communicate vertically, and the flow velocity and direction change greatly, that is, it is easier to produce "bubble vortex water" suitable for domestic fish spawning, so that the eggs of domestic fish will not sink, ensuring the fertilization and normal hatching of fish eggs, which is conducive to domestic fish spawning. According to the results of the spawning site survey conducted by environmental DNA technology in the YC river section in 2017, extremely high values ​​of environmental DNA concentration appeared in the cross-section of this river section, and this range is basically consistent with the range of hydraulic element analysis. In summary, it can be considered that the large-scale spawning sites of the spawning river section are mainly concentrated in the middle of this river section; from the perspective of cross-sectional distribution, they are mainly close to the middle of the river section, that is, near the river shoals.

[0033] Correlation between spawning of four major carps and hydrological elements 1) Traffic The correlation analysis of the daily egg production of domestic fish and the corresponding daily average flow data during the monitoring period from 2011 to 2020 was conducted: the results show that the reproduction of the four major carps is more obvious during the flow of 10000m³ / s~30000m³ / s in the YC section of the river, and the daily egg production of more than 500 million grains is mainly concentrated in the flow range of 10000m³ / s~20000m³ / s. Among them, the total egg production of domestic fish is the largest in the flow range of 10000m³ / s~15000m³ / s, followed by the range of 15000m³ / s~20000m³ / s. Overall, the total egg production of domestic fish under the flow conditions of 10000m³ / s~20000m³ / s accounts for about 65% of the total egg production during the entire monitoring period, indicating that this flow level is a suitable flow range for domestic fish spawning.

[0034] 2) Increased traffic A correlation analysis was conducted on the spawning volume of domestic fish during the concentrated spawning period from 2012 to 2020 and the rising flow rate of the corresponding flood process: the results showed that the large-scale spawning of domestic fish was mainly concentrated in the rising flow rate range of 10,000m³ / s~20,000m³ / s, but under the conditions of rising flow rate below 10,000m³ / s or greater than 25,000m³ / s, the spawning volume of domestic fish was still considerable, which shows that the size of the rising flow rate is only a necessary but not sufficient condition for the large-scale spawning of domestic fish.

[0035] 3) Daily increase in traffic A correlation analysis was conducted on the amount of eggs laid by domestic fish during the concentrated spawning period from 2012 to 2020 and the average daily increase in flow during the corresponding flood process: it was preliminarily believed that the large-scale spawning of domestic fish was relatively insensitive to the increase in flood processes. According to statistical results, large-scale spawning processes occurred under conditions where the average daily flow increase was 500m³ / s~3500m³ / s.

[0036] 4) Duration of water rise A correlation analysis was conducted on the amount of eggs laid during the concentrated spawning period of domestic fish from 2012 to 2020 and the number of days of continuous rising water in the corresponding flood process: the results show that the continuous rising water process for large-scale spawning of domestic fish generally takes 3 to 8 days, and the spawning effect of 4 to 7 days is more obvious. The longer the period lasts, the greater the total amount of eggs laid.

[0037] 5) Flooding process Since the spawning of domestic fish has a clustering effect and the spawning process takes some time. The results of fish egg monitoring show that domestic fish spawn on a large scale 2 to 3 days after the start of the flood, and after the flow reaches the peak, the spawning of domestic fish will also peak or delay the peak by 1 to 2 days. According to the results of fish egg monitoring from 2011 to 2021, the spawning runoff was accumulated and counted daily at 3d, 5d, and 7d. The results show that: from May to July, domestic fish generally have 1 to 3 concentrated spawning processes, and the rule of 7 days as a spawning period is more obvious; the time of the first concentrated reproduction each year is relatively stable, from late May to early June; the peak of each spawning period basically corresponds to the peak flow during that period.

[0038] Conclusion Analysis After the impoundment of Reservoir A, the hydrological rhythm of the YC section of the Yangtze River changed significantly. The changes in water temperature, hydrological processes and river hydraulic conditions in the downstream section caused by the impoundment of the reservoir had a certain impact on the temporal and spatial distribution of spawning of the four major carps.

[0039] (1) Temporal distribution characteristics. From mid-May to early July, the four major carps will have 1 to 3 large-scale spawning processes, among which the largest-scale spawning is mainly concentrated in early to mid-June. The main reason is that after the reservoir is filled with water, the water temperature in the YC section of the river generally reaches the peak spawning period of domestic fish (20°C to 24°C) from late May to early July; and according to the correlation between the daily spawning amount of domestic fish and the daily water temperature of the river section, the amount of domestic fish eggs reaches a peak when the water temperature is 21°C to 23°C, which corresponds to the end of May to early to mid-June.

[0040] (2) Spatial distribution characteristics. When the flow rate of the YC section is 10,000 m³ / s~15,000 m³ / s, the proportion of slow flow and horizontal flow suitable for spawning of domestic fish is about 64%~90%. Large-scale spawning grounds suitable for spawning of domestic fish are concentrated in sections of the river that are prone to "bubble vortex water" and are close to areas with large terrain changes near the beach.

[0041] (3) Correlation between spawning and hydrological elements. Under the stimulation of continuous water rise, the four major carps begin to spawn in large numbers after 2 to 3 days. There are generally 1 to 3 concentrated spawning processes, and the regular pattern of 7 days as a spawning period is more obvious; the peak of each spawning period corresponds to the peak flow rate during that period. The spawning amount increases with the duration of water rise, indicating that continuous water rise may be able to fully stimulate spawning, allowing them to spawn fully at one time under suitable conditions.

[0042] The above-mentioned embodiments only express the implementation methods of the present invention. Although the description is relatively specific and detailed, it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be based on the attached claims.

Claims

1. A method for statistically analyzing the key factors affecting the temporal and spatial distribution of spawning of domestic fish in the downstream of a reservoir, characterized by: The methods described include early fish resource monitoring, hydrological element monitoring, numerical simulation of river hydraulic conditions, and result analysis; The early fish resource monitoring includes collecting samples from the surface and the middle and bottom layers using a net and a cone net, the early fish resource monitoring site is located 20-30 km downstream of the spawning ground, the collected egg and fry samples of the four major carps are sorted and counted on site, the live samples are cultured, observed and identified, and the dead samples are stored for a long time after identification, the samples are sampled 2-3 times a day, each time for 30-60 minutes, and the section coefficient is checked at an appropriate time according to the amount of eggs and fry; When checking the section coefficient, five sampling vertical lines are laid out on the conventional sampling section, namely left, left middle, middle, right middle and right. Three sampling points, upper, middle and lower, are selected for section sampling on each vertical line to count the spatial distribution of eggs and fry in the section. A large number of live samples collected are cultured indoors for a long time, and the accuracy of the identification results is verified by microscopic observation. The fish eggs are cultured separately in temporary containers, and the domestic fish species are rechecked after 7-10 days of culture. The identified samples are concentrated in temporary boxes for long-term culture, and the accuracy of the identification samples is counted later. The hydrological element monitoring includes water level monitoring, water temperature testing, flow velocity distribution testing, flow testing, and large-section measurement; The water level monitoring is to conduct manual water level observation on a water gauge that is set up in advance and measures the zero point elevation during flow measurement, and use the GNSS-RTK method to calibrate the water level; The water temperature test uses a sound velocity profiler to measure the layered water temperature along the water depth direction at the middle position of the monitoring section within a fixed period of time; The velocity distribution test adopts ADCP test and extracts vertical velocity distribution data. The velocity measurement vertical lines of each section are generally evenly arranged, and the velocity measurement vertical lines are densely arranged in the main channel of the deep trough, and the vertical line spacing is not greater than 1 / 10 of the river width; The flow test adopts ADCP flow measurement, which is synchronized with the flow velocity test, and is measured at least 3 times a day; The large-section measurement is carried out using underwater measurement software Hypack, Trimble 852GPS section measurement, DGPS plane positioning and HY1601 echo sounder, and the section spacing is not more than 1km; The numerical simulation of the hydraulic conditions of the river channel uses a two-dimensional hydrodynamic mathematical model to simulate and calculate the study river section: The result analysis associates the numerical simulation results of the river's hydrodynamic conditions with the measured water level, water temperature, flow velocity distribution, flow rate, and large-section values, and conducts a correlation analysis based on the number of spawning fish in the area, thereby statistically analyzing the key factors affecting the temporal and spatial distribution of spawning fish downstream of the reservoir.

2. The method for establishing a temporal and spatial distribution system for spawning of domestic fish in the downstream of a reservoir according to claim 1, characterized in that: In the numerical simulation step of the river hydraulic conditions, a number of computational grids are arranged in the simulated river area, wherein the average grid length along the water flow direction is 15 to 25 m; and the average grid width along the river width direction is about 15 to 20 m.

3. The method for establishing a temporal and spatial distribution system for spawning of domestic fish in the downstream of a reservoir according to claim 1, characterized in that: In the flow test procedure, three measurements are performed every day: morning, noon and evening.

4. The method for establishing a temporal and spatial distribution system for spawning of domestic fish in the downstream of a reservoir according to claim 1, characterized in that: In the water temperature test procedure, the test is conducted twice a day, in the morning and in the afternoon.

5. The method for establishing a temporal and spatial distribution system for spawning of domestic fish in the downstream of a reservoir according to claim 1, characterized in that: In the velocity distribution test step, in order to ensure the accuracy of the cross-sectional velocity distribution, the vertical line spacing is not greater than 1 / 10 of the river width.

Images