Fish spawning site establishing method suitable for spawning and juvenile breeding

Abstract

The invention mainly relates to the technical field of ecological restoration, in order to improve the restoration effect of a fish spawning site and improve the fish living environment, the invention provides a fish spawning site establishment method suitable for spawning and juvenile rearing, and the core is as follows: spawning site bottom roughness test is performed for a first spawning area and a second spawning area respectively, and the riverbed roughness is determined; constructing a hydrodynamic model according to the riverbed roughness, determining the water depth, the flow velocity and the substrate index of the corresponding oviposition area, and respectively determining the current substrate index suitable index, the flow velocity suitable index and the water depth suitable index of the corresponding oviposition area according to the substrate index, the flow velocity and the water depth of the corresponding oviposition area in combination with the obtained suitability index curve; weight available areas of the first spawning area and the second spawning area are calculated, the substrate, the water depth and the flow of the corresponding spawning area are adjusted, the survival requirement and the spawning requirement of the juvenile fish are met at the same time, and the operation effect of the spawning site is improved.

Description

Technical Field

[0001] This invention mainly relates to the field of ecological restoration technology, and in particular to a method for establishing fish spawning grounds suitable for spawning and raising young. Background Technology

[0002] The construction of artificial spawning grounds for fish is one of the important measures to mitigate the impact of hydropower development on aquatic ecosystems. Domestic and international research on spawning ground restoration primarily employs methods such as hydrological modification, river channel dredging, and topographic reshaping. In my country, the restoration of artificial spawning grounds began in 1983 with the restoration of the natural spawning ground of the scaly gudgeon, which mainly involved altering hydrological conditions. In recent years, with the deepening of aquatic ecological protection, more and more research has begun to focus on fish spawning ground restoration.

[0003] (1) The application of ecological groynes to the restoration of spawning grounds of the schizothorax bream. Ecological groynes are one of the hydraulic habitat restoration measures for fish spawning grounds, but there is very little research on them both domestically and internationally. After the construction of ecological groynes or groups of ecological groynes, the local flow regime in the vicinity changes, and water flow phenomena such as separated flow, rotating flow, curved shear layer, and high turbulence intensity are generated, thereby creating new spawning grounds or restoring the hydraulic conditions of damaged spawning grounds.

[0004] (2) In response to the current problems of large-scale water conservancy projects and tidal flat reclamation in the Yangtze River estuary, which have led to the degradation of fish habitats and the destruction of fish spawning grounds, "floating artificial wetlands" are constructed to restore fish spawning grounds and give full play to their functions. While conducting research on the restoration of fish spawning grounds, corresponding technical research and development has also been carried out, resulting in some technical solutions, such as "Site Selection and Construction Methods for Muddy Artificial Spawning Grounds for Schizothorax acutus in Plateau Rivers". For Schizothorax acutus in plateau rivers, muddy substrate is used to cover suitable river sections to reshape the terrain to meet the burrowing behavior of Schizothorax acutus during spawning; or wooden frames and simulated habitats are used to form spawning grounds to provide suitable habitats and development space for fish that prefer flowing water; or baffles are set up to mitigate the adverse effects of clear water discharge on the downstream river topography and avoid the disappearance of spawning grounds caused by human activities.

[0005] Currently, several hydropower stations in China have constructed varying numbers of artificial spawning grounds for fish. The main measures for creating these artificial spawning grounds include constructing spawning substrates (pebble beaches) and planting riparian vegetation. The primary purpose is to create diverse habitats and provide richer environments for fish spawning. However, based on the monitoring and evaluation results of various tiers of artificial spawning grounds after their construction, most artificial spawning grounds have failed to collect fertilized fish eggs, only fish distribution data, reflecting a problem with the design effectiveness of these artificial spawning grounds. The reasons for this are threefold: First, fish are relatively primitive organisms, and their ecological habits are developed over a long period; adapting to a new spawning ground is not a short-term process. Second, the spawning grounds lack adaptability and are severely affected by rising water levels and floods, often failing to maintain their original function after the flood season. Third, the operation and maintenance costs are high. Because existing artificial spawning grounds have weak resistance to floods and flood season impacts, floods easily cause substrate siltation and facility damage, greatly increasing the difficulty and cost of operation and maintenance. Fourth, the spawning function is not adequately considered. Most spawning grounds are designed with a single spawning function in mind, and do not adequately consider the survival needs of fry. For example, the lack of aquatic plant buffer zones, gravel crevices and other hiding places makes fry vulnerable to predators. The simple bottom structure makes food organisms scarce and affects growth. In contrast, the artificial fish nests in Chaohu Lake have created a composite environment that combines spawning and fry rearing, which significantly improves the survival rate of fry. This highlights the limitations of single-function spawning grounds in terms of population replenishment. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: a method for establishing spawning grounds for fish that is suitable for spawning and raising young, with the aim of improving the restoration effect of fish spawning grounds and improving the living environment of fish.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] A method for establishing spawning grounds for fish, suitable for spawning and juvenile rearing, the method comprising:

[0009] Step S1: Conduct bottom roughness tests on the first and second spawning areas respectively to determine the riverbed roughness; the first spawning area is used for fish larval rearing and to provide refuge during the dry season, and the second spawning area is used for spawning of schizothorax fish;

[0010] Step S2: Construct a hydrodynamic model based on the riverbed roughness, determine the water depth and flow velocity of the first and second spawning zones, and determine the sediment index based on the sediment composition of the corresponding spawning zones;

[0011] Step S3: Obtain the substrate index suitability curve, current velocity suitability curve, and water depth suitability curve for the target fish in the first and second spawning areas;

[0012] Step S4: Based on the bottom sediment index, current velocity, and water depth of the first and second spawning areas, and combined with the suitability index curves obtained in Step S3, determine the current bottom sediment index suitability index, current velocity suitability index, and water depth suitability index of the first and second spawning areas, respectively.

[0013] Step S5: Calculate the weighted available area of ​​the first and second spawning areas based on the current substrate suitability index, flow velocity suitability index, and water depth suitability index, and adjust the substrate, water depth, and flow rate of the corresponding spawning areas according to the weighted available area.

[0014] Furthermore, step S1 includes:

[0015] Substrate materials were laid in the flume according to the riverbed conditions of the first and second spawning zones, respectively. Different flow rates were set up, and after the flow stabilized, the water levels at the upstream and downstream sections of the flume were measured under different flow rates. The corresponding water depth, cross-sectional area, and hydraulic gradient of the flume were calculated, and the overall roughness of the flume was also calculated. , in, For traffic, For the water flow area, The hydraulic radius of the cross section, For wet period, For hydraulic gradient;

[0016] Based on the comprehensive roughness of the water tank Calculate the roughness of the riverbed sediment: ,in, For the roughness of the water tank, The total wetted perimeter of the cross-section. The wetted perimeter occupied by the side wall water tank, The wetted perimeter is the area occupied by the substrate material.

[0017] Furthermore, in step S1, hydrodynamic models of the first and second spawning zones are constructed based on River2D to simulate the flow velocity and water depth of the corresponding spawning zones under different flow rates.

[0018] Furthermore, the hydrodynamic model is as follows:

[0019] ;

[0020] In the formula, , , , H is the water depth. Let g be the density of water, g be the acceleration due to gravity, and U and V be the average flow velocities in the x and y directions, respectively. and These represent the riverbed slopes in the x and y directions, respectively. and These represent the frictional resistance in the x and y directions, respectively. , , , , , The x-axis represents the horizontal turbulent shear stress component, with the x-axis being the downstream direction and the y-axis being the cross-flow direction.

[0021] Furthermore, step S4, adjusting the flow rate, water depth, water temperature, and substrate of the spawning area, includes:

[0022] A cross-flow assembly and an L-shaped permeable weir are installed upstream of the first spawning area, with the cross-flow assembly located upstream of the L-shaped permeable weir.

[0023] The L-shaped permeable weir includes a first weir body arranged laterally along the river channel and a second weir body connected upstream or at a set angle to the shoreline, with the first and second weir bodies rigidly connected; the bottom layer of the cross-flow regulating component is an integral continuous piece formed by single gabion mesh, and the upper layer is single gabion mesh arranged at intervals.

[0024] Furthermore, the L-shaped permeable weir is a reinforced gabion mesh structure.

[0025] The beneficial effects of this invention are:

[0026] (1) Based on the requirements of fish juveniles and refuge during the dry season and spawning season for the suitability of water flow and bottom sediment in the spawning ground, calculate the available area of ​​habitat weight for the corresponding period, construct artificial beach / sandbar-deep pool in the form of fusion of spawning and juvenile sites, meet the survival needs of juvenile fish and spawning needs at the same time, and improve the operation effect of spawning ground;

[0027] (2) By setting up cross-flow regulating components and L-shaped permeable weirs, artificial spawning grounds are controlled and guided to prevent siltation in deep pools, improve the adaptability of spawning grounds to different upstream flow rates, alleviate the annual maintenance pressure of spawning grounds, and reduce operating costs. Attached Figure Description

[0028] Figure 1 To meet the flow velocity requirements of schizothorax fish during their spawning period;

[0029] Figure 2 To determine the appropriate water depth for schizothorax fish during their spawning period;

[0030] Figure 3 The substrate suitability requirements of schizothorax fish during their spawning period;

[0031] Figure 4 This is a schematic diagram of the spawning ground structure.

[0032] Figure 5 This is a top view of the flow control component structure;

[0033] Figure 6 This is a cross-sectional view of the flow control component structure;

[0034] Figure 7 This is a schematic diagram of an L-shaped permeable weir. Detailed Implementation

[0035] The core of this invention's technical solution to the aforementioned technical problems is as follows: Based on the requirements of fish larval rearing, dry season refuge, and spawning season for the suitability of water flow and bottom sediment in the spawning grounds, the available area of ​​habitat weights for the corresponding periods is calculated to create an artificial beach-deep pool spawning ground. The first spawning area is constructed with a deep pool to provide refuge for fish larval rearing and during dry seasons, while the second spawning area is constructed with an artificial beach to serve the spawning of schizothorax fish. Simultaneously, an L-shaped permeable weir is installed upstream of the first spawning area to intercept sediment and prevent siltation in the deep pool area. A cross-flow regulating component is installed around the spawning ground to control the inflow rate into the spawning ground.

[0036] The following description, in conjunction with the accompanying drawings and embodiments, further illustrates the method for establishing spawning grounds for fish suitable for spawning and raising young, specifically including the following steps.

[0037] Step S1: Conduct bed roughness tests on the first and second spawning areas respectively to determine the riverbed roughness.

[0038] Traditional spawning ground designs tend to focus solely on spawning function, neglecting the survival needs of juvenile fish. In this invention, spawning ground restoration takes into account both the juvenile and dry season refuge needs of fish and the spawning season. A first spawning area is set up to provide refuge for juvenile fish during the dry season, and a second spawning area is set up for fish to spawn. Therefore, when calculating the riverbed roughness, bottom roughness tests need to be conducted separately for different spawning areas.

[0039] The substrate roughness test includes:

[0040] (1) Setting up the experimental setup. This example uses the schizothorax fish as an example. The main body of the experimental setup is a rectangular straight acrylic water tank. The tank is 18 m long, 50 cm wide, and 30 cm high, with a slope of 4‰. A triangular weir is set at the front of the tank to measure the water flow rate.

[0041] (2) Experimental method. The prepared substrate material was laid flat on the bottom of the flume, with a thickness sufficient to completely cover the flume bottom plate and accurately reflect the roughness of the riverbed. Different flow conditions were set up. After the water flow reached a stable state, the water level at the upstream and downstream sections of the flume was measured at different flow rates. The corresponding water depth, cross-sectional area, and hydraulic gradient of the flume were calculated for roughness analysis.

[0042] The calculation of riverbed roughness is based on the Chezy formula and combined with the compound riverbed roughness calculation method to determine the overall flume roughness. , ,in, For traffic, For the water flow area, The hydraulic radius of the cross section, For wet period, It is a hydraulic gradient.

[0043] Meanwhile, considering that the test flume's sidewalls are made of plexiglass and the bottom is riverbed material, the roughness 'n' calculated using the above formula is the overall flume roughness. To eliminate the influence of the plexiglass sidewalls on the riverbed roughness, the riverbed bottom roughness is calculated using the method for determining the roughness of a compound flume: ,in, For the roughness of the water tank, The total wetted perimeter of the cross-section. The wetted perimeter occupied by the side wall water tank, The wetted perimeter is the area occupied by the substrate material.

[0044] Step S2: Construct a hydrodynamic model based on the riverbed roughness, determine the water depth and flow velocity of the first and second spawning zones, and determine the sediment index based on the sediment composition of the corresponding spawning zones.

[0045] Fish habitat simulation was conducted using River2D software. A two-dimensional depth-mean-plane model was used to simulate hydrodynamic processes and determine the water depth and flow velocity in the first and second spawning zones.

[0046] The hydrodynamic model is based on the depth-averaged two-dimensional Saint-Venant equations and mainly includes three governing equations:

[0047] ;

[0048] The water depth and flow velocity can be obtained by inverse solving the hydrodynamic model.

[0049] In the formula, , , , H is the water depth. Let g be the density of water, g be the acceleration due to gravity, and U and V be the average flow velocities in the x and y directions, respectively. and These represent the riverbed slopes in the x and y directions, respectively. and These represent the frictional resistance in the x and y directions, respectively. , , , , , The x-axis represents the horizontal turbulent shear stress component, with the x-axis being the downstream direction and the y-axis being the cross-flow direction.

[0050] The substrate index is obtained by sampling the proportion of sand and gravel in the substrate composition of the first and second spawning areas.

[0051] In this embodiment, the simulated spawning grounds of the Schizothorax aquaticus are as follows: first spawning zone: water flow velocity: 0.2~0.5 m / s; water depth: 1.0~1.5 m; bottom substrate: mainly pebbles and small gravels. Second spawning zone: water flow velocity: 0.5~2.0 m / s; water depth: 0.15~1.0 m; bottom substrate: sandy floodplain composed of sand (including fine sand and very small gravels) and medium and small gravels, mixed with a small amount of large gravels or rocks. The sand content is 70%~80%, and the gravel content is 20%~30%. In the gravel composition, small gravels with a diameter of less than 4 cm account for 90%, and medium gravels with a diameter of 4-10 cm account for 10%.

[0052] Step S3: Obtain the substrate index, flow velocity index, and water depth index curves for the target fish species in the first and second spawning areas.

[0053] This embodiment still uses *Schizothorax* as an example. In the Heyuan region, *Schizothorax* typically spawn on gravelly riverbeds with relatively fast currents. The eggs are slightly sticky, sink to the bottom, and are easily carried by the current into the gaps between the gravel. Based on the survey results of *Schizothorax 'Severodon'* and *Schizothorax 'Pygmy'* by the Sichuan Provincial Fisheries Research Institute and the Institute of Hydro-Environmental Sciences, Chinese Academy of Sciences, combined with the results of this project's survey of typical spawning grounds for *Schizothorax*, the most suitable habitat for spawning of *Schizothorax* in the Heyuan region was found to be: water depth 0.5–1.5 m, flow velocity 0.5–2.0 m / s, and water temperature 10–15°C. Furthermore, considering the habitat requirements of *Schizothorax* at different life stages, the suitability requirements for flow velocity, water depth, and bottom sediment for spawning, juvenile rearing, and dry season refuge can be obtained. The suitability requirements for the spawning period are shown in Table 1. Figure 1 (Suitability requirements for flow rate) Figure 2 (Suitability requirements for water depth) and Figure 3 (Requirements for suitability of substrate) are shown.

[0054] Table 1 Suitability index for spawning period of schizothoracic fish

[0055]

[0056] Based on various spawning ground suitability indices of the target fish species, habitat simulation was conducted using River2D software. A depth-mean-plane two-dimensional model was used to simulate hydrodynamic processes, and habitat suitability was calculated based on the suitability indices of the target fish species.

[0057] Step S4: Based on the bottom sediment index, current velocity, and water depth of the first and second spawning areas, and combined with the suitability index curves obtained in step S3, determine the current bottom sediment index suitability index, current velocity suitability index, and water depth suitability index of the first and second spawning areas, respectively.

[0058] Step S5: Calculate the weighted available area of ​​the first and second spawning areas based on the current substrate suitability index, flow velocity suitability index, and water depth suitability index, and adjust the substrate, water depth, and flow rate of the corresponding spawning areas according to the weighted available area.

[0059] In this embodiment, after calculation and analysis using the weighted available area (WUA) model, under the flow conditions from March to September, the WUA of the spawning grounds of the schizothorax fish after habitat modification increased by 0.2% to 23.7% compared with that before modification. The modification scheme has a significant effect on increasing WUA and can effectively improve the habitat of the spawning grounds of the schizothorax fish.

[0060] In this step, if the calculated usable area with weights does not meet the set requirements, the substrate, water depth, and flow rate of the corresponding spawning area will be adjusted. For example... Figure 4 As shown, a cross-flow component and an L-shaped permeable weir are set up upstream of the first spawning area.

[0061] Cross-flow regulating components: such as Figure 5 and Figure 6 As shown, the bottom layer consists of individual gabion mesh pieces forming a continuous sheet, buried at the bottom of the riverbed to ensure the overall stability of the flow regulation component. The upper layer uses spaced individual gabion mesh pieces to divert water flow, preventing direct scouring of downstream permeable weirs, spawning grounds, and other structures. This regulates the flow velocity entering the spawning grounds to a suitable range for fish spawning, while the flow regulation component also provides safety protection for permeable weirs and spawning grounds. Each gabion mesh piece measures 1m x 1m x 0.5m (length x width x height), and is filled with large, unprocessed pebbles with a diameter of at least 20cm. The folded gabion mesh boxes are transported to the site and unfolded according to the design dimensions. The edge wires of adjacent mesh boxes are tied together with double-strand binding wire at a spacing of ≤20cm, and the bindings must be tightened (≥3 turns) to ensure a secure connection without loosening. The corners of the mesh boxes require denser binding (spacing ≤10cm) to enhance overall stability. The upper and lower layers of wire mesh cages must be aligned, and the layers must be connected with binding wire (≥4 binding points per square meter). Special connectors should also be used for fixation to prevent the upper layer of cages from sliding. For fixing the cages to the foundation: For non-rock foundations, anchor bolts (≥50cm deep) can be installed at the four corners and center of the bottom of the cage, passing through the cage and fixing it to the foundation; for rock foundations, expansion bolts can be used for fixation (bolt spacing ≤1.5m), ensuring a tight fit between the cage and the foundation.

[0062] like Figure 7As shown, the L-shaped permeable weir is located downstream of the cross-flow regulating component. The L-shaped permeable weir comprises a first weir body arranged laterally along the river channel and a second weir body connected upstream or at a predetermined angle to the shoreline; the first and second weir bodies are rigidly connected. The angle between the weir arm and the riverbank is between 20° and 30°, and the slope of the weir arm from the slope towards the riverbed is between 2% and 7%; the weir arm elevation is taken from the flow rate elevation. The foundation rock depth needs to be more than twice the height of the exposed structure. To preserve the flow gap, the foundation rock is exposed for 20 cm to block upstream sand. The weir crest width is 400mm, the upstream slope ratio is 1:3, the downstream slope ratio is 1:5, and the weir height is 1.2m. The permeable weir is made of reinforced gabion mesh, possessing a certain permeability, which is conducive to creating diverse habitats in local river sections and can retain some riverbed sediment, promoting the growth of native species.

Claims

1. A method for establishing spawning grounds for fish spawning and juvenile rearing, characterized in that, The method includes: Step S1: Conduct bottom roughness tests on the first and second spawning areas respectively to determine the riverbed roughness; the first spawning area is used for fish larval rearing and to provide refuge during the dry season, and the second spawning area is used for spawning of schizothorax fish; Step S2: Construct a hydrodynamic model based on the riverbed roughness, determine the water depth and flow velocity of the first and second spawning zones, and determine the sediment index based on the sediment composition of the corresponding spawning zones; Step S3: Obtain the substrate index suitability curve, current velocity suitability curve, and water depth suitability curve for the target fish in the first and second spawning areas; Step S4: Based on the bottom sediment index, current velocity, and water depth of the first and second spawning areas, and combined with the suitability index curves obtained in Step S3, determine the current bottom sediment index suitability index, current velocity suitability index, and water depth suitability index of the first and second spawning areas, respectively. Step S5: Calculate the weighted available area of ​​the first and second spawning areas based on the current substrate suitability index, flow velocity suitability index, and water depth suitability index, and adjust the substrate, water depth, and flow rate of the corresponding spawning areas according to the weighted available area.

2. The method for establishing a spawning ground for fish suitable for spawning and juvenile rearing according to claim 1, characterized in that, Step S1 includes: Substrate materials were laid in the flume according to the riverbed conditions of the first and second spawning zones, respectively. Different flow rates were set up, and after the flow stabilized, the water levels at the upstream and downstream sections of the flume were measured under different flow rates. The corresponding water depth, cross-sectional area, and hydraulic gradient of the flume were calculated, and the overall roughness of the flume was also calculated. , in, For traffic, For the water flow area, The hydraulic radius of the cross section, For wet period, For hydraulic gradient; Based on the comprehensive roughness of the water tank Calculate the roughness of the riverbed sediment: ,in, For the roughness of the water tank, The total wetted perimeter of the cross-section. The wetted perimeter occupied by the side wall water tank, The wetted perimeter is the area occupied by the substrate material.

3. The method for establishing a spawning ground for fish suitable for spawning and juvenile rearing according to claim 1, characterized in that, In step S1, hydrodynamic models of the first and second spawning zones are constructed based on River2D to simulate the flow velocity and water depth of the corresponding spawning zones under different flow rates.

4. The method for establishing a spawning ground for fish suitable for spawning and juvenile rearing according to claim 3, characterized in that, The hydrodynamic model is as follows: ； In the formula, , , , H is the water depth. Let g be the density of water, g be the acceleration due to gravity, and U and V be the average flow velocities in the x and y directions, respectively. and These represent the riverbed slopes in the x and y directions, respectively. and These represent the frictional resistance in the x and y directions, respectively. , , , , , The x-axis represents the horizontal turbulent shear stress component, with the x-axis being the downstream direction and the y-axis being the cross-flow direction.

5. The method for establishing a spawning ground for fish suitable for spawning and juvenile rearing according to claim 1, characterized in that, Step S4 involves adjusting the flow rate, water depth, water temperature, and substrate of the spawning area, including: A cross-flow assembly and an L-shaped permeable weir are installed upstream of the first spawning area, with the cross-flow assembly located upstream of the L-shaped permeable weir. The L-shaped permeable weir includes a first weir body arranged laterally along the river channel and a second weir body connected upstream or at a set angle to the shoreline, with the first and second weir bodies rigidly connected; the bottom layer of the cross-flow regulating component is an integral continuous piece formed by single gabion mesh, and the upper layer is single gabion mesh arranged at intervals.

6. The method for establishing a spawning ground for fish suitable for spawning and juvenile rearing according to claim 4, characterized in that, The L-shaped permeable weir is a reinforced gabion mesh structure.

Images