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

Abstract

A method for statistically analyzing key factors affecting the spatiotemporal distribution of spawning of domesticated fish downstream of a reservoir mainly includes early fish resource monitoring, hydrological element monitoring, numerical simulation of river hydraulic conditions, and result analysis. Early fish resource monitoring mainly includes surface and mid-bottom layer sampling, on-site sample sorting and counting, culture and observation of live samples, long-term storage of dead samples after identification, cross-sectional coefficient verification, and sample accuracy statistics. Hydrological element monitoring mainly involves water level monitoring, water temperature measurement, flow velocity distribution measurement, flow measurement, and large-section measurement. The numerical simulation of river hydraulic conditions uses a two-dimensional hydrodynamic mathematical model to calculate the hydrodynamic conditions of the spawning ground river section. The result analysis correlates the hydrodynamic conditions within the calculation domain, the measured hydrological elements, and the spawning amount of domesticated fish, thereby clarifying the key factors affecting the spatiotemporal distribution of spawning of domesticated fish downstream of the reservoir. The advantage of the present invention is that, by statistically analyzing multi-source data, the key factors affecting the spatiotemporal distribution of spawning of domesticated fish downstream of the reservoir are identified, which is an effective way to accurately analyze the key factors affecting the spatiotemporal distribution of spawning of domesticated fish downstream of the reservoir.

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 complex ecosystems of rivers and lakes in the middle and lower reaches of the Yangtze River, and their abundance is a proxy for the health of this aquatic ecosystem. During the research and demonstration phase of the Gezhouba Dam project in the 1950s, the question of the potential impact of dam construction on the reproduction of the four major carps was raised. Subsequently, during the demonstration and construction phases of the Gezhouba Dam project and the Three Gorges Project, the size and distribution of their spawning grounds became a 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 have been relatively stable and large over the years. Since the impoundment of the Three Gorges Reservoir, increased attention has been paid to the impact of hydrological rhythm changes caused by reservoir operations on the reproduction of the four major carps. Studies have examined early changes in the four major carp populations after impoundment and their response to hydrological processes. In particular, since the Three Gorges Corporation implemented an ecological operation experiment for the natural reproduction of the four major carps in 2011, relevant institutions have analyzed and studied the impact of ecological operation on the spawning of the four major carps, concluding that the implementation of ecological operation has significantly promoted spawning. However, most current research still focuses 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 insufficient 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;

[0005] The early fish resource monitoring is carried out at a location 20-30 km downstream of the spawning grounds. The monitoring method includes sampling the surface and mid-bottom layers using a net and a cone net, verifying the cross-sectional coefficient, and performing sample accuracy statistics.

[0006] The hydrological element monitoring includes water level monitoring, water temperature testing, flow velocity distribution testing, flow testing, and large-section measurement;

[0007] The water level monitoring is to conduct manual water level observation on a water gauge that has been set up and measured at the zero point elevation during flow measurement, and to use the GNSS-RTK method to perform water level verification;

[0008] The water temperature test uses a sound velocity profiler to measure the stratified water temperature along the water depth direction at the middle position of the monitoring section within a fixed period of time;

[0009] The velocity distribution test uses a cruise-type ADCP test and extracts vertical velocity distribution data. The velocity vertical lines for each section are generally evenly distributed, and the velocity vertical lines are densely distributed in the main channel of the deep trough. The vertical line spacing is no more than 1 / 10 of the river width.

[0010] The flow test adopts a cruise ADCP flow measurement, which is synchronized with the flow velocity test, and is measured at least 3 times a day;

[0011] The large-section measurement is carried out using underwater measurement software Hypack, Trimble 852GPS cross-section measurement, DGPS plane positioning and HY1601 echo sounder, with the cross-section spacing not exceeding 1 km;

[0012] The numerical simulation of the hydraulic conditions of the river channel uses a two-dimensional hydrodynamic mathematical model to simulate the study section:

[0013] The results 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.

[0014] Furthermore, the method also includes early fish resource monitoring, and the early fish resource monitoring also includes collecting samples using a net and a cone net to collect surface and middle and bottom samples respectively.

[0015] Furthermore, in the numerical simulation step of 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 meters; the average grid width along the river width direction is about 15 to 20 meters;

[0016] Furthermore, in the flow test step, at least three measurements are performed every day.

[0017] Furthermore, in the water temperature test step, two tests are conducted every day, in the morning and afternoon.

[0018] 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.

[0019] The advantage of the present invention is 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

[0020] Figure 1. Schematic diagram of the spawning grounds and early resource monitoring locations of the four major carps in the YC section of the river;

[0021] Figure 2. Cumulative proportion of river channels with typical spawning ground flow velocities at different flow levels;

[0022] Figure 3. Statistics of annual changes in spawning volume of the four major carps after the impoundment of Reservoir A.

[0023] Figure 4. Distribution of spawning quantity of the four major carps within a year after the impoundment of Reservoir A;

[0024] Figure 5. Correlation between daily egg production of domestic fish and daily water temperature;

[0025] Figure 6: Variation of total egg production of domestic fish with water temperature gradient;

[0026] Figure 7. Correlation between daily egg production of domestic fish and daily average flow rate;

[0027] Fig. 8 Variation of total egg production of domestic fish with flow level;

[0028] Figure 9 The 7-day cumulative spawning process of domestic fish in 2020. DETAILED DESCRIPTION

[0029] Based on the results of early fish resource monitoring and environmental DNA monitoring, the YC section of the middle Yangtze River has been identified as the largest known spawning ground for the four major carps. The spawning ground in the YC section is 10.2 km long and approximately 50 km from the upstream reservoir A. The downstream early fish resource monitoring point, section YD, is approximately 25 km from the spawning ground (Figure 1). The method proposed in this patent, which includes early fish resource monitoring, hydrological element monitoring, numerical simulation of river hydraulic conditions, and analysis of the results, statistically analyzes the key factors influencing the spatiotemporal distribution of domestic carp spawning downstream of the reservoir.

[0030] Early fish resource monitoring involves sampling the surface and mid-bottom layers using both nets and cone nets. Collected fish eggs and fry samples are sorted on-site, and live samples are cultured, observed, and identified to verify the accuracy of egg and fry identification for the four major carps. Dead samples are then stored for long-term storage after identification. Sampling is conducted 2-3 times daily, each lasting 30-60 minutes. Section coefficient verification is performed based on the number of eggs and fry. To verify the section coefficient, five sampling vertical lines are laid out along the regular sampling section: left, left center, center, right center, and right. Cross-sectional sampling is performed at the top, center, and bottom of each vertical line, and the distribution of eggs and fry along the section is statistically analyzed. A large number of live samples collected undergo long-term indoor culture to verify the accuracy of the fish identification results. Early-stage fish eggs are cultured individually in temporary holding containers. After 7-10 days of culture, species identification is performed. Identified samples are then concentrated in temporary holding tanks for long-term culture, and the accuracy of the identified samples is later statistically analyzed.

[0031] The hydrological element monitoring mentioned above focuses on monitoring the hydrological and hydraulic elements of the main spawning grounds in the YC River section (a total of 12 monitoring sections, namely STDD1 to STDD12), including water temperature, flow process, flow velocity distribution, cross-section geometric parameters, etc. The hydrological elements monitored are as follows:

[0032] 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 the zero point elevation is measured, and the water level is calibrated using the GNSS-RTK method.

[0033] Water temperature test: Every morning and afternoon, the layered water temperature is measured along the water depth direction at the center of the monitoring section.

[0034] Velocity distribution test: Adopting the ADCP test. Velocity measurement vertical lines are generally evenly distributed in each section. Velocity measurement vertical lines are densely distributed in the main channel of deep trough. The vertical line spacing is generally no more than 100m, and there are no less than 10 vertical lines in each section.

[0035] Flow test: Use cruise ADCP to measure flow, synchronized with flow velocity test, and conduct 3 tests per day.

[0036] Large-section measurement: The underwater measurement software Hypack, Trimble 852GPS cross-section measurement, DGPS plane positioning and HY1601 echo sounder were used to conduct large-section measurement of 12 sections.

[0037] Correlation analysis of the above data can be used to determine whether there are dependencies between random variables and to explore the direction and degree of correlation for specific dependent random variables. Spawning is a biological characteristic of domestic fish, and external environmental factors (including hydrology, water temperature, and hydraulic elements) are closely linked to their spawning behavior. Combining historical monitoring data, correlation analysis was conducted between river section water temperature, hydrological conditions, and hydraulic elements and the spawning yield of the four major carps. The degree of correlation between each factor and spawning yield was studied to identify the adaptive hydrological and hydraulic indicators for the spawning of the four major carps.

[0038] Numerical simulation of river hydraulic conditions: A two-dimensional hydrodynamic mathematical model was used to simulate the spawning grounds. The computational domain was approximately 10.2 km long. A total of 500 × 85 computational grids were arranged within the simulated river channel. 500 grids were arranged along the flow direction, with an average grid length of 15 to 25 meters; and 85 grids were arranged along the river width, with an average grid width of approximately 15 to 20 meters. The model was validated using multiple sets of field data from 2013 to 2015.

[0039] The numerical simulation of river hydraulic conditions is correlated with corresponding water level, water temperature, velocity distribution, flow rate, and large cross-sectional values. If no correlation is found after analysis, the correlation is removed. Furthermore, a relationship diagram is established between the measured number of spawning fish within a specific area and the water level, water temperature, velocity distribution, flow rate, and large cross-sectional values. This allows the number of spawning fish to be estimated based on these values. A key analysis factor is temperature. Spawning fish require appropriate water temperatures, a suitable flooding process, and specific spawning grounds. Water temperature is considered a limiting factor for the reproduction of drifting spawning fish, such as the four major carps. Reaching a certain water temperature is crucial for the initiation of reproduction. The flooding process and specific spawning grounds are crucial environmental conditions that stimulate and promote fish reproduction.

[0040] Monitoring of hydrological process changes: The flow rate of the river section downstream of Reservoir A during the monitoring period gradually increased, with the flow rate changing from 10,000 to 25,000 m 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 flow velocity is basically consistent with the change process of 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℃.

[0041] Hydraulic condition simulation: The model calculates the velocity distribution of the river section under different flow levels, the change of velocity with flow direction, and calculates the proportion of velocity in the river section under different flow levels (see Figure 2Calculation results show that the flow velocity in the main channel changes more significantly with flow than near the shore. The most pronounced changes in flow velocity and direction with increasing flow are observed when the flow rate in the spawning grounds is between 10,000 and 20,000 m³ / s. When the flow rate varies between 10,000 and 20,000 m³ / s, the flow direction in the spawning grounds becomes more complex. When the flow rate is 10,000 m³ / s, the flow velocity with the largest proportion is 1.0 m / s to 1.5 m / s, accounting for 62%; when the flow rate is 15,000 m³ / s, the flow velocity with the largest proportion is 1.0 m / s to 1.5 m / s, accounting for 50%; when the flow rate is 20,000 m³ / s, the flow velocity with the largest proportion is 1.5 m / s to 2.0 m / s, accounting for 61%; when the flow rate is 25,000 m³ / s, the flow velocity with the largest proportion 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.

[0042] Table 1 Statistics of the proportion of flow velocity in the river at different flow levels

[0043]

[0044] Result analysis:

[0045] 1) Interannual variation characteristics

[0046] 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 in 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 the interannual fluctuations were not large, 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.

[0047] Overall, the scale of domesticated fish production has shown an upward trend, likely due to comprehensive conservation measures implemented in recent years, including strengthened fishing bans, the release of broodstock, and the implementation of ecological regulation. From an ecological regulation perspective, the main reasons for the changes in spawning production during these three phases are as follows: In the first phase, spawning production remained largely unchanged, with minimal interannual variation. This was primarily due to the lack of clarity regarding the hydrological and hydraulic indicators for ecological regulation, which were still undergoing testing and analysis. The significant increase in spawning production during the second phase suggests that the initial exploratory research on hydrological regulation parameters, such as starting flow, flow rate increase, and suitable water temperature, has yielded significant results. The decrease in spawning production during the third phase, in 2020, was primarily due to the fact that water temperatures reached 18°C ​​10 days later than in 2019 during the early stages of regulation, resulting in fewer 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, the Yangtze River implemented a "ten-year fishing ban" in key waters of the Yangtze River Basin from January 1, 2021, further protecting the breeding populations of the four major carps.

[0048] 2) Distribution characteristics within the year

[0049] 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 occurs in early June to mid-June, accounting for 39% of the large-scale spawning volume ( Figure 4 ).

[0050] 3) Main influencing factors

[0051] The natural reproduction of the four major carps is closely linked to water temperature conditions, and reservoir dams are considered the most significant factors in significantly altering river water temperatures. Discharge temperatures from large reservoirs, in particular, can differ significantly from natural water temperatures. The minimum water temperature for carp reproduction is 18°C, with peak spawning temperatures ranging from 20°C to 24°C. Within the optimal temperature range, higher water temperatures increase the hatching rate; however, temperatures below 18°C ​​or above 30°C can cause embryonic development to stagnate or lead to deformities and death. Within a certain temperature range, embryonic development accelerates as water temperature rises. Because the four major carps have a long spawning and reproduction period, they operate within a relatively wide water temperature range.

[0052] 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 spawning volume of domestic fish and the water temperature ( Figure 5 ): The daily egg production and peak production of domestic fish are mainly concentrated in water temperatures of 20°C to 24°C, which is consistent with existing research results. The relationship between the total egg production of domestic fish and water temperature under different gradient water temperature conditions was statistically analyzed ( Figure 6 ) It can be seen that: in the range of 18°C ​​to 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 water temperature conditions of 21°C to 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 to 23°C.

[0053] Based on the above analysis, a statistical method can be further refined to analyze the key factors affecting the spatiotemporal distribution of spawning of domestic fish downstream of the reservoir.

[0054] Spatial distribution characteristics of spawning of four major carps and its influencing factors

[0055] The large-scale spawning behavior of the four major carps is closely related to river hydraulics. The hydraulic characteristics of fish habitats, including water depth, flow velocity, flow gradient, Reynolds number, Froude number, vorticity, and swirl, categorize the preferences of the four major carps for flow speed into four levels: ① Slow flow, defined as less than 0.7 m / s; ② Flat flow, defined as 0.7-1.3 m / s, which is suitable for spawning; ③ Rapid flow, defined as 1.3-2.0 m / s, which is difficult for carps to overcome; and ④ Torrent flow, defined as greater than 2.0 m / s, which is difficult for carps to overcome and therefore difficult to swim upstream.

[0056] According to hydraulic model simulation results, in the river section monitored in this example, flow velocity and direction change significantly with increasing flow at flow rates between 10,000 and 15,000 m³ / s. Flow rates within the 0.5 to 1.5 m / s range account for 64% to 90% of the river. At 10,000 m³ / s, 90% of the river has a flow rate between 0.5 and 1.5 m / s; at 15,000 m³ / s, 64% of the river has a flow rate between 0.5 and 1.5 m / s. This indicates that this river section, with flow rates between 10,000 and 15,000 m³ / s, primarily experiences slow and advection flow, making it suitable for the spawning of the four major carps.

[0057] The topographic characteristics of this river section reveal a prominent shoal in the central section (STDD8-STDD11), located near the middle of the channel. The complex topography in this area causes the water to tumble and circulate vertically, resulting in significant variations in flow velocity and direction. This creates a favorable environment for spawning fish, known as "bubbling vortexes," which prevent eggs from sinking, ensuring fertilization and proper hatching, and thus facilitating spawning. Furthermore, a 2017 spawning ground survey using environmental DNA technology in the YC section of the river revealed extremely high environmental DNA concentrations across this section, a range that is generally consistent with the range analyzed using hydraulic elements. Therefore, it is believed that the large-scale spawning grounds in this section are primarily concentrated in the central section of the river; judging by cross-sectional distribution, they are primarily located near the central section, near the shoal.

[0058] Correlation between spawning of four major carps and hydrological factors

[0059] 1) Traffic

[0060] A correlation analysis was conducted between daily egg production and corresponding daily average flow data during the monitoring period from 2011 to 2020. The results showed that the four major carps exhibited significant reproduction during flows between 10,000 and 30,000 m³ / s in the YC section of the river. Daily egg production exceeding 500 million eggs was primarily concentrated in flows between 10,000 and 20,000 m³ / s. The highest egg production occurred in flows between 10,000 and 15,000 m³ / s, followed by flows between 15,000 and 20,000 m³ / s. Overall, egg production during flows between 10,000 and 20,000 m³ / s accounted for approximately 65% ​​of the total egg production during the entire monitoring period, indicating that this flow range is suitable for spawning.

[0061] 2) Increasing traffic

[0062] 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 of the corresponding flood process: the results showed that large-scale spawning of domestic fish was mainly concentrated in the rising flow range of 10,000 m³ / s to 20,000 m³ / s, but under the conditions of rising flow below 10,000 m³ / s or greater than 25,000 m³ / s, the spawning volume of domestic fish was still considerable, which shows that the size of the rising flow is only a necessary but not sufficient condition for large-scale spawning of domestic fish.

[0063] 3) Daily traffic growth

[0064] 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 large-scale spawning of domestic fish was relatively insensitive to the increase in flow during the flood process. According to statistical results, large-scale spawning processes occurred when the average daily flow increase was 500m³ / s~3500m³ / s.

[0065] 4) Duration of water rise

[0066] 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 showed 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.

[0067] 5) Rising water process

[0068] Because domestic fish spawn in clusters and the spawning process takes time, egg monitoring results indicate that large-scale spawning occurs 2-3 days after the start of flooding, and the spawning peaks immediately after or 1-2 days after the flow peaks. Based on three years of egg monitoring from 2011 to 2021, cumulative spawning runoff was calculated daily, at 3, 5, and 7 days. The results show that domestic fish generally have one to three spawning clusters from May to July, with a clear pattern of 7-day spawning periods. The first spawning cluster occurs consistently each year, from late May to early June. The peak of each spawning period generally corresponds to the peak flow rate during that period.

[0069] Conclusion Analysis

[0070] After the impoundment of Reservoir A, the hydrological rhythm of the YC section of the Yangtze River underwent significant changes. The changes in water temperature, hydrological processes, and river hydraulics in the downstream reaches caused by the reservoir impoundment had a certain impact on the spatiotemporal distribution of spawning of the four major carps.

[0071] (1) Temporal distribution characteristics. From mid-May to early July, the four major carps will undergo one to three large-scale spawning events, with the largest spawning occurring in early to mid-June. This is mainly because after the reservoir is filled, the water temperature in the YC section of the river generally reaches the peak spawning period for domestic carps (20°C to 24°C) from late May to early July. Based on the correlation between the daily spawning volume of domestic carps and the daily water temperature in the river section, the peak spawning volume of domestic carps occurs when the water temperature is between 21°C and 23°C, corresponding to the end of May to early to mid-June.

[0072] (2) Spatial distribution characteristics. Under the condition of a flow rate of 10,000 m³ / s to 15,000 m³ / s in the YC section, the proportion of slow flow and horizontal flow suitable for spawning domestic fish is approximately 64% to 90%. Large-scale spawning grounds suitable for spawning domestic fish are concentrated in sections prone to "bubbling vortex water" and near areas with large terrain changes near shoals.

[0073] (3) Correlation between spawning and hydrological factors. 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 a spawning period of 7 days is more obvious. The peak of each spawning period corresponds to the peak flow rate during that period. The spawning volume increases with the duration of water rise, indicating that continuous water rise may be more effective in stimulating spawning, allowing them to spawn fully at one time under suitable conditions.

[0074] The above-described embodiments merely illustrate the implementation of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for statistically analyzing key factors affecting the temporal and spatial distribution of spawning of domestic fish downstream of a reservoir, characterized by: The methods described include early fish resource monitoring, hydrological element monitoring, numerical simulation of river hydraulic conditions, and analysis of results; The early fish resource monitoring includes collecting samples from the surface and 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 living samples are cultured, observed and identified. 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. The cross-sectional coefficient is checked at an appropriate time according to the amount of eggs and fry. When verifying the cross-sectional coefficient, five sampling vertical lines (left, left center, center, right center, and right) are laid out on the conventional sampling cross-section. Cross-sectional sampling is conducted at three sampling points (upper, middle, and lower) along each vertical line, and the spatial distribution of eggs and fry in the cross-sectional area is statistically analyzed. A large number of live samples collected are cultured indoors for a long period of time, and the accuracy of the identification results is verified by microscopic observation. Fish eggs are cultured individually in temporary holding containers, and after 7-10 days of culture, the fish species are re-verified. The identified samples are then concentrated in temporary holding tanks for long-term culture, and the accuracy of the identified samples is later statistically analyzed. 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 has been set up and measured at the zero point elevation during flow measurement, and to use the GNSS-RTK method to perform water level verification; The water temperature test uses a sound velocity profiler to measure the stratified 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 the underway ADCP test and extracts the vertical velocity distribution data; the velocity vertical lines of each section are evenly distributed, and the velocity vertical lines of the deep trough main channel are densely packed, and the vertical line spacing is no more than 1 / 10 of the river width; The flow test adopts a cruise 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 cross-section measurement, DGPS plane positioning and HY1601 echo sounder, with the cross-section spacing not exceeding 1 km; The numerical simulation of the hydraulic conditions of the river channel was carried out by using a two-dimensional hydrodynamic mathematical model to simulate the study section of the river: The results analysis correlates 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 statistically analyzing the key factors affecting the temporal and spatial distribution of spawning of domestic fish in the downstream of a reservoir according to claim 1 is characterized by: In the numerical simulation step of the river hydraulic conditions, a number of calculation grids are arranged in the simulated river area, wherein the average grid length along the water flow direction is 15 to 25 meters; and the average grid width along the river width direction is 15 to 20 meters.

3. The method for calculating the key factors affecting the temporal and spatial distribution of 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 determining the key factors affecting the temporal and spatial distribution of spawning of domestic fish in the downstream of a reservoir according to claim 1, wherein: In the water temperature test step, two tests are conducted every day, in the morning and in the afternoon.

5. The method for statistically analyzing the key factors affecting the temporal and spatial distribution of spawning of domestic fish in the downstream of a reservoir according to claim 1 is characterized by: 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.

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