A habitat closed-loop restoration method for bait fish in a Yangtze finless porpoise migratory protection water area

Abstract

The present application belongs to the technical field of rare aquatic organism habitat restoration, and particularly relates to a Yangtze finless porpoise ex-situ protection water area bait fish habitat closed-loop restoration method, comprising: constructing an aquatic vegetation community in the shallow area of the ex-situ protection water area, the aquatic vegetation community being composed of reed, pondweed and cattail, and the ratio of the number of plants of the three being 2-3:4:3; arranging fish spawning facilities in the slow-flowing bay area of the ex-situ protection water area; supplementing bait fish into the water area, the bait fish being composed of fish with the following percentage of tail number: 40%-45% of Pseudolaubuca hibernalis, 25%-30% of Pseudogobio bangi, 15%-20% of small crucian carp with a body length of 6-10 cm, 5%-8% of Leucogastia elongata, and 3%-5% of Xenocypris davidi; and dynamically regulating the fish community structure. The present application constructs a bait fish habitat closed-loop restoration system of partitioned restoration of bait fish habitat substrate + precise supplementing + dynamic regulation of community, realizes long-term stable supply of bait fish, and solves the industry problems of bait resource attenuation, structure imbalance and inability to continuously supply in a semi-closed artificial channel.

Description

Technical Field

[0001] This invention belongs to the field of habitat restoration technology for rare aquatic organisms, specifically relating to a closed-loop restoration method for the habitat of prey fish in the ex-situ conservation waters of the Yangtze finless porpoise. Background Technology

[0002] Ex-situ conservation of the Yangtze finless porpoise is a core measure for the rescue and protection of Yangtze dolphins. Currently, the main conservation sites are closed or semi-closed waters such as the old course of the Yangtze River and the Jiajiang River, with typical examples of semi-closed waters including the Xijiang River and Jiajiang River in Anqing. These waters are isolated from the main stream of the Yangtze River through dam projects, forming a unique aquatic ecosystem. They are highly controllable by humans and have good population isolation effects, making them the core sites for the conservation and breeding of small populations of finless porpoises.

[0003] Currently, the industry's methods for restoring the habitat of the Yangtze finless porpoise mainly focus on common ecological restoration methods such as water purification (e.g., using chemical methods to treat sewage), shoreline ecological transformation (e.g., using concrete walls and masonry to protect the shoreline), hydrological scheduling optimization (e.g., regulating water supply in specific time and space), and conventional vegetation restoration (e.g., single reed restoration).

[0004] The old course of the Yangtze River is mostly a semi-enclosed waterway, resulting in a low success rate for native small fish to reproduce naturally. In addition, climatic factors such as drought have further compressed the living space of prey fish, so the restoration of prey fish resources is necessary.

[0005] Existing forage fish resource restoration technologies generally employ universal stock enhancement and release methods. These methods are only suitable for the renewal of forage fish in open natural water bodies such as rivers and lakes, because open waters have rapid water exchange and strong resilience, making them less susceptible to the effects of universal stock enhancement and release. However, semi-enclosed waters have long water exchange cycles and poor resilience. Universal stock enhancement and release methods cannot accurately control the types and quantities of forage fish flowing into semi-enclosed waters, nor can they predict factors affecting the survival of native forage fish resources. These adverse factors lead to the decline of forage fish resources in semi-enclosed waters, making a long-term stable supply impossible. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a closed-loop restoration method for forage fish habitats in the ex-situ conservation areas of the Yangtze finless porpoise. Targeting the unique ecological characteristics of the semi-enclosed waters of the Xijiang River in Anqing, this invention constructs a closed-loop restoration system for forage fish habitats, consisting of "zonal restoration of the forage fish habitat base + precise replenishment of forage fish + dynamic regulation of fish community structure." Specifically, habitat restoration enhances the endogenous reproductive efficiency of forage fish, supplemented by annual precise replenishment and predator control, achieving low-intervention, stable maintenance and long-term stable supply of forage fish, thus solving the industry-wide problems of forage fish resource depletion, structural imbalance, and unsustainable supply in semi-enclosed waterways.

[0007] The technical solution provided by this invention is as follows.

[0008] A closed-loop restoration method for the habitat of prey fish in the ex-situ conservation waters of the Yangtze finless porpoise includes: Step one involves zonal restoration of the prey fish habitat substrate in the ex-situ conservation area. This involves differentiated habitat substrate reconstruction based on the water depth and functional zoning differences within the ex-situ conservation area. Specifically: (1) Construct an aquatic vegetation community in the shallow waters of the ex-situ conservation area. The aquatic vegetation community consists of reeds, Vallisneria natans and Myriophyllum spicatum, with a planting ratio of 2-3:4:3. The role of this planting ratio includes the emergent plants (reeds) to dissipate waves and protect the banks, the submerged plants (Vallisneria natans and Myriophyllum spicatum) to create underwater habitats, and the vegetation community composed of the three plants to enhance the self-purification of the water body. At the same time, it is suitable for the habitat needs of bait fish such as scad and bream in the subsequent steps to avoid predators near the shore and move in the middle layer.

[0009] (2) Set up fish spawning facilities in the slow-flowing bay area of ​​the ex-situ protection water area to form a layered system for bait fish to inhabit, spawn, and raise their young, so as to realize the autonomous breeding and natural replenishment of bait fish. Step 2: Supplement the relocation protection area with prey fish, which shall consist of the following percentages of fish: 40%~45% of bream, 25%~30% of small crucian carp, 15%~20% of fine-scaled gudgeon, and 3%~5% of yellowtail gudgeon, totaling 100%; the total number of prey fish supplemented per acre of relocation protection area shall be 1000~2000. Step 3: Dynamically regulate the fish community structure: monitor changes in the number of fish species and fish resources, and replenish prey fish as needed before the following year's breeding season to ensure the generational renewal of prey fish populations; regularly remove predatory fish. Among them, supplementing forage fish as needed means: when the monitored forage fish resources is lower than 70% of the same period of the first year, 1,000 fish per mu will be supplemented; when the forage fish resources are between 70% and 90% of the same period of the first year, 500 fish per mu will be supplemented.

[0010] Preferably, in the above-mentioned closed-loop restoration method for the habitat of prey fish in the ex-situ conservation waters of the Yangtze finless porpoise, the shallow water area is a shallow drawdown zone with a water depth of 0-3m, and an aquatic vegetation community is constructed by interplanting reeds, Vallisneria natans, and Myriophyllum spicatum using a cutting propagation technique.

[0011] Preferably, the above-mentioned closed-loop restoration method for the habitat of prey fish in the ex-situ conservation waters of the Yangtze finless porpoise involves planting reeds in the nearshore drawdown zone with a water depth of less than or equal to 0.5m, with 4 reeds per square meter. And / or, in the drawdown zone where the water depth is greater than 0.5m and less than or equal to 2.0m, Vallisneria natans and Myriophyllum spicatum are planted together, with a planting density of 8 Vallisneria natans per square meter and a planting density of 2 Myriophyllum spicatum per square meter. And / or, in the deep water zone of the drawdown zone of the shoal, where the water depth is greater than 2.0m and less than or equal to 3.0m, plant foxtail grass at a planting density of 4 plants per square meter.

[0012] This aquatic vegetation community scheme can form a gradient vegetation community in the shallow drawdown zone of 0-3m. Reeds stabilize the shoreline and reduce wind and waves, while Vallisneria natans and Myriophyllum spicatum enrich the underwater habitat, providing hiding and spawning places for small prey fish and increasing the survival rate of fry. At the same time, the three plants absorb nutrients from the water, improve the bottom sediment of the water, reduce external pollution interference, and enhance the stability of the aquatic habitat in ex-situ conservation.

[0013] Preferably, in the above-mentioned closed-loop restoration method for the habitat of prey fish in the ex-situ conservation waters of the Yangtze finless porpoise, both *Sinocyclocheilus bream* and *Sinocyclocheilus bream* are selected from juvenile fish of the current year with a body length of 5cm to 8cm. And / or, both the fine-scaled gudgeon and the yellowtail gudgeon are selected from juvenile fish of the current year with a body length of 6cm to 9cm. They are easy to breed and survive.

[0014] Preferably, in the above-mentioned closed-loop restoration method for the habitat of prey fish in the ex-situ conservation waters of the Yangtze finless porpoise, the prey fish are released during the early spring breeding season each year.

[0015] Preferably, in the above-mentioned closed-loop restoration method for prey fish habitats in the Yangtze finless porpoise ex-situ conservation waters, in step two, 40% of the total number of fish are released into the shallow drawdown zone, 35% of the total number of fish are released around the fish spawning facility, and the remaining prey fish are released into the area between the shallow drawdown zone and the fish spawning facility. And / or, in step three, the method for supplementing the bait fish as needed is to supplement at a rate of 500 fish / acre to 1000 fish / acre.

[0016] Preferably, in the above-mentioned closed-loop restoration method for the habitat of prey fish in the ex-situ conservation waters of the Yangtze finless porpoise, the method of placing fish around the spawning facility is as follows: the placement area is a 10m radius radiating outward from the spawning facility, that is, the fish are placed in a ring-shaped area 10m outside the spawning facility. The spawning facility itself is not directly used for placement; this area is mainly used for spawning.

[0017] Preferably, in the above-mentioned closed-loop restoration method for the habitat of prey fish in the ex-situ conservation waters of the Yangtze finless porpoise, step two further includes adding 10 ml of lactic acid bacteria per square meter at a time. 8 10 9 The sterilized product. The lactic acid bacteria are specifically Bifidobacterium lactis.

[0018] Lactic acid bacteria 10 8 10 9 The method for preparing the sterilized product is as follows: The purchased Bifidobacterium lactis lyophilized powder was suspended and dispersed in sterile water, sterilized, and then diluted with sterile water to a concentration of 10.7 Cells / mL ~10 8 The concentration of lactic acid bacteria was calculated to obtain a diluted solution, and the corresponding number of lactic acid bacteria was added to each square meter at one time.

[0019] Preferably, in the above-mentioned closed-loop restoration method for the habitat of prey fish in the ex-situ conservation waters of the Yangtze finless porpoise, the fish spawning facilities include artificial fish nests and / or ecological floating islands, which concentrate on strengthening the spawning attachment substrate of small native fish and significantly increase the endogenous germination rate of larvae and juveniles.

[0020] Preferably, the above-mentioned closed-loop restoration method for the habitat of prey fish in the relocation protection area of ​​the Yangtze finless porpoise further includes setting up a barrier on the outside of the reeds in the shallow drawdown zone. This is used to block the erosion of the bank slope by wind and waves, reduce the suspension of bottom sediment caused by water turbulence, protect reed seedlings from being knocked down by the water flow, improve the survival rate of aquatic vegetation, and stabilize the transitional habitat between water and land. The material of the barrier includes, but is not limited to, polyethylene netting, and the height of the barrier is set at 30cm above the normal water level to dissipate waves, protect seedlings, and reduce the suspension of bottom sediment.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention is the first to design a closed-loop restoration system for bait fish habitats, which involves "zonal restoration of the substrate of bait fish habitats + precise replenishment of bait fish + dynamic regulation of fish community structure". The aquatic vegetation community consists of reeds, Vallisneria natans, and Myriophyllum spicatum, with a planting ratio of 2-3:4:3. Fish spawning facilities are set up in the slow-flowing bay area of ​​the ex-situ conservation waters. The bait fish consist of the following percentages of fish: 40%-45% of Basilidis bream, 25%-30% of bream, 15%-20% of small crucian carp with a body length of 6cm-10cm, 5%-8% of fine-scaled gudgeon, and 3%-5% of yellowtail gudgeon, with 1000-2000 fish per mu. Before the following year's breeding, bait fish are replenished as needed, and ferocious carnivorous fish are removed. This achieves a long-term stable supply of bait fish, requiring only one replenishment per year. The bait fish can reproduce on their own and supply the needs of the aquatic environment during the rest of the year.

[0022] This invention employs a synergistic combination of plant species and prey fish species, limiting the layering of reeds, Vallisneria natans, and Myriophyllum spicatum. Reeds provide wave absorption and habitat protection, while the two submerged plants create a three-dimensional spawning and habitat base. Five types of native prey fish are introduced in specific proportions. Upper-layer fish reproduce using the aquatic plants, while scraping fish regulate algae and maintain vegetation. The layered habitats of emergent and submerged plants are adapted to the different water layers for prey fish to inhabit and reproduce. The fish's metabolic nutrients supply the vegetation, forming a mutually beneficial closed loop that solves the problem of the gradual decline of prey fish resources in semi-enclosed waterways. Other plant combinations (such as reeds, Vallisneria natans, and Ceratophyllum demersum) or prey fish combinations (such as bream, gudgeon, minnow, silver gudgeon, and yellowtail gudgeon) lack sufficient community synergy and habitat adaptability, ultimately leading to a decrease in overall restoration effectiveness and failing to meet the stable supply of prey fish in enclosed environments.

[0023] (2) Existing restoration of the Yangtze finless porpoise migration course relies solely on vegetation reconstruction and regular replenishment of prey fish. The accumulation of organic matter in enclosed waters easily deteriorates water quality, affecting the digestive and reproductive capacity of prey fish. Large-scale replenishment of fish fry is required the following year, resulting in high management costs. In addition to solving the above problems by relying on the closed-loop restoration system of prey fish habitat base "zonal restoration + precise replenishment of prey fish + dynamic regulation of fish community structure", this invention also regulates the intestinal microecology of fish by adding sterilizing agents containing lactic acid bacteria, matching the filter-feeding and scraping feeding habits of prey fish such as scorpionfish, improving gonadal development and spawning and hatching efficiency, and strengthening the endogenous reproductive capacity of the water. This microecological regulation method forms a synergistic closed loop with the zoned vegetation and precise fish release system, breaking through the technical limitations of traditional methods that rely solely on external release to maintain the supply of prey fish.

[0024] (3) Strong adaptability to scenarios: The method of the present invention is applicable to closed and semi-closed old channels of the Yangtze River, such as the semi-closed old channel of the Xijiang River. It fills the gap in the closed-loop restoration technology of food in the migratory waters of the Yangtze finless porpoise and solves the problem that traditional technologies are not adaptable to open water bodies and cannot adapt to closed-loop ecosystems.

[0025] (4) Community structure optimization: By controlling the clearing of ferocious fish, the fish community structure is precisely optimized, and the proportion of small prey fish, the staple food of Yangtze finless porpoises, is greatly increased, which is in line with the feeding habits of Yangtze finless porpoises. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the construction of an aquatic vegetation community in Embodiment 1 of the present invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings.

[0028] Unless otherwise specified, all reagents used in this invention are commercially available, and all methods used are conventional techniques in the art.

[0029] Explanation of terminology in this invention: Yangtze finless porpoise ( Neophocaena asiaeorientalis *Neophocaena* is a small toothed whale belonging to the class Mammalia, order Cetaceans, family Phocenidae, and genus Neophocaena. It inhabits only the middle and lower reaches of the Yangtze River and the connected Dongting and Poyang Lakes. It is a Class I protected wild animal in China. It has a slightly spindle-shaped body, dark gray coloration, no dorsal fin, and a length of about 1.5 meters. Its diet consists mainly of small, mid-to-upper-level fish.

[0030] Ex-situ conservation waters: Semi-natural waters used for raising Yangtze finless porpoises in ex-situ conservation groups, usually enclosed or semi-enclosed water bodies such as the former course of the Yangtze River.

[0031] Shallows: sedimentary landforms with shallow water depth formed by siltation, which are often exposed intermittently depending on the flow rate.

[0032] Drawdown zone: A transitional zone between the highest and lowest water levels, where land is periodically submerged and exposed due to seasonal water level fluctuations or regulated storage and release. It is a water-land ecological transition zone.

[0033] Shoal drawdown zone: A drawdown zone that develops in shoal topography.

[0034] Reed: scientific name Phragmites australis Reed (Phragmites australis) is a perennial emergent native plant belonging to the genus Reed of the Poaceae family. When planted in the nearshore area of ​​shallow waters and drawdown zones, its upright stems protrude above the water surface, which can reduce wind and waves, stabilize the bank slope, and provide nearshore shelter and habitat for prey fish.

[0035] Vallisneria: scientific name Vallisneria natans ἐ is a perennial submerged native plant belonging to the genus *Vallisneria* of the family Hydrocharitaceae. The entire plant grows underwater, with soft and dense leaves that can attach fish eggs, providing hiding places for prey fish, while also purifying the water and cultivating planktonic food organisms.

[0036] Myriophyllum: scientific name Myriophyllum verticillatum L. ， It is a perennial submerged native plant belonging to the genus Myriophyllum in the family Myriophyllum. It has dense underwater branches, is tolerant of low light and deep water environments, expands the underwater activity range of prey fish, helps decompose organic matter in the water, and maintains the stability of water quality.

[0037] Ceratophyllum: scientific name Ceratophyllum demersum L. belongs to the genus Ceratophyllum in the family Ceratophyllaceae of the order Ranunculales in the class Dicotyledonous plants. It is a perennial submerged herbaceous plant.

[0038] Prey fish resources (abbreviated as prey fish): The general term for the fish that Yangtze finless porpoises usually prey on in ex-situ protected waters. They are usually less than 20cm in length and prefer to inhabit shallow waters.

[0039] Predatory carnivorous fish: Fish that primarily feed on small prey fish and exert significant competitive pressure on prey fish resources in ex-situ conservation waters, including the snakehead (Gastrodon spp.). Elopichthys bambusa ) and other species.

[0040] Bess's tadpole: scientific name Hemiculter bleekeri It belongs to the genus *Culter alburnus* of the subfamily Culterinae in the family Cypriniformes. It is a small, pelagic native fish widely distributed in the main stream, lakes, and old channels of the middle and lower reaches of the Yangtze River.

[0041] Bream-like creature: scientific name Pseudobrama simoni It belongs to the genus *Bream-like fish* of the subfamily Gnatinae in the family Cypriniformes. Commonly known as the "reverse fish," it is a small, mid-to-upper-level native fish widely distributed in the Yangtze River basin.

[0042] Small crucian carp: scientific name Carassius auratus The species belongs to the Cypriniformes order, Cyprinidae family, Cyprinoideae subfamily, and Carassius genus. The method of this invention specifically refers to small-sized crucian carp individuals with a body length of 6cm to 10cm.

[0043] Fine-scaled gudgeon: scientific name Xenocypris microlepis It belongs to the genus Gnatifidae of the family Cypriniformes and is a small to medium-sized resident fish native to the Yangtze River basin.

[0044] Yellowtail Gudgeon: Scientific name Xenocypris davidi It belongs to the genus Gnatifidae of the family Cypriniformes and is a common small to medium-sized native fish in the middle and lower reaches of the Yangtze River.

[0045] Silver Gudgeon: Scientific name Xenocypris argentea It belongs to the genus Gnatella in the family Cypriniformes (or the genus Gnatella in the family Gnatella).

[0046] Example 1: A closed-loop restoration method for the habitat of prey fish in the ex-situ conservation area of ​​the Yangtze finless porpoise (1) Investigation of the Anqing Xijiang Riverbank Slope Experimental Base before restoration A field survey conducted in 2024 collected 168 species (including infraspecific taxa) of vascular plants belonging to 117 genera and 52 families from the Xijiang River basin and its riparian mudflats in Anqing. The average density of herbaceous plants in the Xijiang River basin was 95 ind. / m². 2 The average biomass of herbaceous plants in the Xijiang River basin of Anqing is 1366.7 g / m³. 2 A total of 21 dominant species were identified.

[0047] The vegetation restoration of natural mudflats in the drawdown zone along the Xijiang River is constrained by hydrological rhythms. During the high water levels of summer each year, the above-ground parts of plants in this area gradually die due to prolonged submersion, while the underground propagules enter a dormant state. As the water level recedes in winter and spring, the riverbed is exposed, and dormant buds and roots sprout, completing the entire growth cycle. Considering the shoreline land use pattern: the middle section of the shoreline is mostly occupied by fishponds and farmland, while the upper and lower sections have open waters and gentle slopes, providing ample operational space. Therefore, this invention prioritizes the placement of restoration experiments in these two sections of mudflats. This site selection balances the intensity of hydraulic disturbance with construction accessibility, facilitating the implementation of subsequent observation and comparison schemes.

[0048] (2) Monitoring of vascular plants A plant community survey was conducted at the Xijiang Riverbank Slope Experimental Base in Anqing. Qualitative and quantitative data were collected from both the water-direction and land-direction riparian vegetation in sample plots and transects. Qualitative collection primarily recorded all plant species in both the water-direction and land-direction riparian zones. Quantitative collection of water-direction vegetation used aquatic plant clips (collection area 0.1m²). 2 Two sampling points were set up along the water depth gradient, with two samplings at each point. Species composition and cover within the sampling plots were recorded, and biomass was calculated. Quantitative sampling of the terrestrial riparian zone was mainly carried out using the quadrat method.

[0049] (3) Monitoring methods for aquatic biological resources such as fish (3.1) Setting up monitoring sampling points Based on the principles of uniformity and representativeness, sampling points were set up within the experimental base to monitor the water environment and aquatic biological resources. Monitoring was conducted before and after ecological restoration to identify changes in the water environment and assess the effectiveness of the ecological restoration.

[0050] (3.2) Monitoring equipment Multi-mesh barbed wire: Mesh sizes are 1.2cm, 2cm, and 4cm, each 15m wide; 6cm, 8cm, 10cm, and 14cm, each 20m wide; net length 125m; net height 1.5m.

[0051] Shrimp trap net: mesh size 1.6cm, net width and height 40cm, net length 10m.

[0052] (3.3) Monitoring methods Fish collection: Using the multi-mesh gillnets of (3.2), two nets were placed at each sampling point. The nets were set up on the afternoon of the day before sampling and left for 12 hours. All catches were collected the next day.

[0053] Using the shrimp traps (3.2), three traps were placed at each sampling point. The traps were set on the afternoon of the day before sampling and left for more than 12 hours. The catch was collected the next day.

[0054] All catches were counted by species, including weight and number of fish, and net yield was recorded. Biological measurements were taken for each species, including total length, body length, and weight.

[0055] Underwater acoustic survey: The acoustic survey used a split-beam scientific fish finder, employing dedicated software for acoustic data acquisition. GPS was connected to a laptop via an RS232 interface to dynamically obtain latitude and longitude location information. The transducer was suspended vertically downwards at a depth of 1 meter on the port side of the small survey vessel, using a bioecho sampling method along the navigation cross-section at a speed of 7 knots. The survey route was designed using an equidistant parallel cross-section approach for underway surveys. Acoustic data analysis was performed using the acoustic data processing software Echoview, employing the echo integration method to estimate fish resource density.

[0056] (4) Experimental setup In areas along the Xijiang River (i.e., the relocation and conservation area for the Yangtze finless porpoise) where human disturbance is relatively minor, the near-water zone is dominated by phytoeshy grasses and *Carex esculenta*, transitioning upwards to a reed-*Reedia spp.* community. As the ground rises, the dominant species gradually change to a mixed grass assemblage consisting of *Artemisia capillaris*, *Leonurus japonicus*, *Aster tataricus*, *Erigeron tigrinum*, and *Cynodon dactylon*. In the scattered fishponds or natural depressions along the riverbank, aquatic plant life forms are relatively complete: the submerged layer contains *Hydrilla verticillata* and *Potamogeton crispus*, the floating layer commonly contains *Trapa natans*, *Lemna minor*, and *Euryale ferox*, while the emergent layer is dominated by *Typha orientalis* and *Reedia spp.*. This pattern reflects the selection effect of water level fluctuations and soil moisture gradients on species distribution and provides a basis for selecting a reference system for subsequent remediation experiments.

[0057] This invention takes into account factors such as the purpose, function, and time requirements of vegetation restoration along the Xijiang River riparian zone, and sets up an implementation group and a control group.

[0058] The specific repair methods are as follows: Step 1: Construct an aquatic vegetation community in the shallow water area. The aquatic vegetation community consists of reeds, Vallisneria natans, and Myriophyllum spicatum. The planting ratio of reeds, Vallisneria natans, and Myriophyllum spicatum is 2:4:3. This creates an underwater habitat, enhances the self-purification of the water body, and adapts to the habitat needs of prey fish such as scad and bream that need to avoid predators near the shore and move in the middle layer. The shallow water area is a drawdown zone with a water depth of 0.5m to 3m.

[0059] Reference Figure 1 Reeds were planted in the nearshore drawdown zone where the water depth was less than or equal to 0.5m. The reeds were planted by cuttings, with 4 plants per square meter and a soil depth of 15cm, for a total of 10 mu (approximately 1.65 acres).

[0060] On the side of the reeds (far shore side), in the drawdown zone where the water depth is greater than 0.5m and less than or equal to 2.0m, Vallisneria natans and Myriophyllum spicatum are planted together, with a ratio of Vallisneria natans to Myriophyllum spicatum of 4:1. The planting density of Vallisneria natans is 8 plants per square meter, and the planting density of Myriophyllum spicatum is 2 plants per square meter.

[0061] On the adjacent (far shore) side of the mixed planting area, in the deep water zone of the shallow water drawdown zone with a water depth greater than 2.0m and less than or equal to 3.0m, plant foxtail grass at a planting density of 4 plants per square meter.

[0062] Artificial fish nests were constructed in the slow-flowing bay area: the main frame was assembled from environmentally friendly PVC pipes, with each frame measuring 1m long x 1m wide. Attachment substrates were vertically suspended inside the frame, consisting of alternating layers of sterilized palm fiber and polyethylene mesh. Each substrate was 60cm high, with 10 substrates suspended per frame, providing a total attachment area of ​​6m². 2 A float is placed at the top of the frame, and a concrete block is attached to the bottom, allowing the fish nest to float in the water. The fish nests are spaced 5 meters apart and arranged in a staggered, quincunx pattern to avoid obstructing water flow. During installation, the weight of the block and float is adjusted so that the upper layer of the fish nest is 30 cm above the water surface and the lower layer is 20 cm below the bottom sediment. Installation is completed one week before the annual spring breeding season (usually late March) to match the natural breeding rhythm of fish such as the scorpionfish. After the breeding season ends (late June to early July), and monitoring confirms that the eggs have mostly hatched and all fry have emerged, the fish nests are collected, cleaned, disinfected, dried, and stored for reuse in the following year.

[0063] Step two: Replenish the water with bait fish, which consist of the following percentages of fish: 40% *Pterocarya stenoptera*, 30% *Pterocarya stenoptera*, 20% *Carassius amurensis*, 5% *Gnaphalium affine*, and 5% *Gnaphalium affine*. Details are as follows:

[0064] All bait fish have passed inspection and quarantine, have no external damage, and are in normal vitality. The seedlings are all juveniles born in the current year: the body length of the bream and the small crucian carp is 5cm~8cm; the body length of the small crucian carp is 6cm~10cm; the body length of the fine-scaled gudgeon and the yellowtail gudgeon is 6cm~9cm.

[0065] A total of 2,000 fish of five forage fish species were released into each acre of the experimental base waters. The concentrated release period was selected during the early spring breeding season, corresponding to early April, when the surface water temperature was stable at 15℃~18℃. This release time matches the natural breeding rhythm of native fish species, allowing the fry to enter the breeding season immediately after adapting to the aquatic environment, effectively expanding the annual population base and increasing the natural breeding scale of forage fish. Simultaneously, it coordinates with the placement of artificial fish nests, completing the release within 5 days after the nests are laid, ensuring that spawning groups can quickly utilize the spawning attachment medium. The release operation was carried out on sunny mornings, avoiding strong winds, rain, and sudden temperature changes to reduce stress on the fry. 40% of the total number of fish were released into the shallow drawdown zone, 35% were released into a circular area within 10 meters of the spawning facilities, and the remaining forage fish were released into the area between the shallow drawdown zone and the spawning facilities.

[0066] Step 3: Dynamically regulate the fish community structure: The number of fish species and fish populations are monitored quarterly to determine the replenishment amount of prey fish for the following year. "When the prey fish population is found to be below 70% of the same period in the first year, 1000 fish per mu (approximately 0.067 hectares) are replenished; when it is between 70% and 90% of the same period in the first year, 500 fish per mu are replenished to ensure the generational renewal of the prey fish population." In this example, in the second year, a total of 1000 fish of 5 prey fish species are released per mu of the experimental base waters. Predatory carnivorous fish are regularly removed quarterly to maintain their proportion in the total fish population at ≤5%.

[0067] Example 2: A closed-loop restoration method for the habitat of prey fish in the ex-situ conservation area of ​​the Yangtze finless porpoise. The repair method is basically the same as that in Example 1, with the following differences: Another 10-mu experimental base was selected in a less disturbed area along the Xijiang River for the experiment. The baseline survey confirmed that the water depth gradient, bottom sediment conditions and initial community structure of the base were consistent with those of the base in Example 1.

[0068] In areas where baitfish are present, apply 10g of lactic acid bacteria per square meter at a time. 9 The sterilization of individual prey fish supplements the types of food they consume, promotes their reproductive efficiency, and reduces the total amount of prey fish needed to be replenished in the second year.

[0069] In a specific embodiment of the example, lactic acid bacteria 10 9 The method for preparing the sterilized product is as follows: The purchased Bifidobacterium lactis lyophilized powder (Shandong Aicai Biotechnology Co., Ltd., specification 10 billion / g) was suspended and dispersed in sterile water at room temperature, and the concentration of the dispersion was 10. 9 CFU / mL, steam sterilized at 121℃, then diluted with sterile water at room temperature to 10. 8The diluent is prepared by dispensing 10 mL of the solution per square meter at a time.

[0070] Experimental results show that in the second year of Example 2, only 500 fish of 5 different bait species need to be added per acre, which is 50% less than in Example 1.

[0071] Control group 1: The repair method is basically the same as that in Example 1, with the following differences: Another 10-mu experimental base was selected in a less disturbed area along the Xijiang River for the experiment. The baseline survey confirmed that the water depth gradient, bottom sediment conditions and initial community structure of the base were consistent with those of the base in Example 1.

[0072] Change the foxtail algae to goldfish algae.

[0073] Both the control group and the examples used algae native to the old course of the Yangtze River. The purpose was to compare the effects of different native species on the restoration effect.

[0074] Control group 2: The repair method is basically the same as that in Example 1, with the following differences: Another 10-mu experimental base was selected in a less disturbed area along the Xijiang River for the experiment. The baseline survey confirmed that the water depth gradient, bottom sediment conditions and initial community structure of the base were consistent with those of the base in Example 1.

[0075] Replace the 5 bait fish with other common bait fish combinations: 40% of the fish species, 30% of the fish species, 20% of the small crucian carp with a body length of 6-10cm, 5% of the silver gudgeon (juvenile fish with a body length of 3-5cm, belonging to the same genus but a different species as the yellowtail gudgeon), and 5% of the yellowtail gudgeon.

[0076] Control group 3: The repair method is basically the same as that in Example 1, with the following differences: Another 10-mu experimental base was selected in a less disturbed area along the Xijiang River for the experiment. The baseline survey confirmed that the water depth gradient, bottom sediment conditions and initial community structure of the base were consistent with those of the base in Example 1.

[0077] Only the vegetation restoration method described in Example 1 was used.

[0078] Control group 4 The repair method is basically the same as that in Example 1, with the following differences: Another 10-mu experimental base was selected in a less disturbed area along the Xijiang River for the experiment. The baseline survey confirmed that the water depth gradient, bottom sediment conditions and initial community structure of the base were consistent with those of the base in Example 1.

[0079] Only the bait fish release method of Example 1 was used.

[0080] Explanation of variable control for each group: Before the deployment of all experimental plots in the examples and control groups, a uniform baseline survey was conducted to ensure that the water depth gradient, substrate type, hydraulic disturbance intensity, initial biological community structure, and water quality baseline values ​​were consistent, and interference from non-experimental variables was strictly controlled.

[0081] (5) Ecological restoration effect assessment (5.1) Evaluation of the effect of vascular plant restoration (including reeds) Experimental statistics were performed on Examples 1, 2, Control Groups 1, 2, 3, and 4. The monitoring period was one year, and the changes in indicators before and after repair were compared. The results are shown in Table 1.

[0082] Table 1. Ecological Restoration Effects of Reeds Initial restoration area (mu) 10 10 10 10 10 / Survival area (mu) after 1 year 7.35 8.17 5.51 6.98 6.13 / Reed vegetation restoration rate (%) calculated by area 73.5 81.7 55.1 69.8 61.3 / Note: " / " indicates that there is no relevant data.

[0083] In Table 1, the reed vegetation restoration rate is defined as the proportion of the area where reeds survive and form a stable community one year after restoration, relative to the initial total planting area, used to characterize the planting effectiveness of the target emergent plant.

[0084] Comparing the initial restoration area and survival area of ​​each group reveals that the actual situation on-site was affected by factors such as the sudden rise in water level during the summer flood season, the thin bottom mud in the drawdown zone of the bank slope, and strong hydraulic disturbance, which put some pressure on plant fixation and survival. However, the comparison results between Example 1 and Control Group 2 show that the differences in fish combinations mainly affect the growth rate of forage fish populations and community stability, and have no significant direct impact on the survival of higher plants. The comparison results of single factors in Control Groups 3 and 4 with the composite factors in Example 1 show that the restoration effect of the "vegetation + fish combination" is better than the sum of the effects of the two alone.

[0085] Two surveys of fish reproduction showed that, in Example 1, the number of fish eggs attached to artificial fish nests in May 2024 increased by 111.3% compared to the same period in May 2023. In Example 2, the number of fish eggs attached to artificial fish nests in May 2024 increased by 135.4% compared to May 2023. In Control Group 1, the number of fish eggs attached to artificial fish nests in May 2024 increased by 63.4% compared to May 2023. In Control Group 2, the number of fish eggs attached to artificial fish nests in May 2024 increased by 79.9% compared to May 2023. In Control Group 3, the number of fish eggs attached to artificial fish nests in May 2024 increased by 20.8% compared to May 2023. In Control Group 4, the number of fish eggs attached to artificial fish nests in May 2024 increased by 18.4% compared to May 2023. Control Group 4 did not undergo vegetation restoration, resulting in a significant decrease in fish egg numbers, which negatively impacted fish survival.

[0086] In addition to reeds, the total surviving area of ​​*Vallisneria natans* and *Myriophyllum spicatum* was simultaneously monitored to assess vascular plants, and the overall survival rate of *Vallisneria natans* and *Myriophyllum spicatum* was calculated. The results showed that the survival rates of submerged plants in Examples 1 (81.6%) and 2 (85.1%) were both above 80%, significantly higher than those in Control Groups 1 (54.8%), 2 (63.3%), and 3 (50.1%). Vegetation stratification gradually formed, and habitat heterogeneity continued to improve. Control Group 4 did not undergo vegetation restoration, so its survival rate was not statistically analyzed.

[0087] (5.2) Evaluation of the effectiveness of fish resource restoration This assessment excludes the five parent species of artificially introduced bait fish and their stocking amounts, and only counts the changes in the species and resource quantity of native wild fish. It excludes the direct interference of artificial propagation and objectively reflects the natural benefits of habitat restoration.

[0088] ① Changes in fish species The results are shown in Table 2. The native fish species in Examples 1 and 2 showed the highest growth rates, with Example 2 reaching a maximum of 13.04%.

[0089] Table 2 Changes in the number of native fish species before and after restoration Before restoration (May 2023) 22 22 22 22 22 21 The following year (May 2024) 24 26 21 20 20 22 growth rate(%) 9.09 18.18 -4.55 -9.09 -9.09 4.76 ② Changes in fish resources The results are shown in Table 3. The fish resources in Examples 1 and 2 showed the highest growth rates.

[0090] Table 3 Changes in fish resources before and after restoration Before restoration (May 2023) 32.4 33.1 31.6 32.0 31.5 31.8 The following year (May 2024) 40.9 43.6 35.4 36.0 29.4 30.7 growth rate(%) 26.23 31.72 12.03 12.5 -6.67 -3.46 Tables 2 and 3 show the monitoring results across the entire year and season, excluding interference from seasonal migration and vertical migration of fish, to verify the long-term stability of the restoration effect.

[0091] (5.3) Overall Analysis of Ecological Restoration Effects Based on habitat assessment and diagnosis and analysis of limiting factors, ecological restoration measures such as vegetation restoration, habitat reconstruction and restocking were implemented to address typical problems in ex-situ waters, thereby rebuilding riparian plant communities and creating suitable spawning and foraging habitats for fish.

[0092] Control group 1: The restoration effect was weaker than that of the example group, which is presumably related to the species' ecological niche matching degree: the community synergy between Elodea and Reed and Vallisneria was insufficient, the stratified habitat creation and water purification capacity were weaker than those of the Myriophyllum spicatum combination, and the habitat adaptability with prey fish was also low, which ultimately led to a decrease in the overall restoration efficiency. The specific mechanism needs further verification.

[0093] Control group 2: The repair effect was weaker than that of the example group, which is speculated to be related to the functional adaptability of the bait fish: The replacement fish combination had a low degree of matching with aquatic vegetation in terms of feeding habits and habitat layer utilization, and could not form a stable "vegetation-bait fish" synergistic system. The specific synergistic mechanism needs to be studied in depth.

[0094] The main reason for the poor repair effect in control groups 3 and 4 is that only single-factor repair was performed.

[0095] After the remediation measures were implemented, continuous monitoring for one year showed that the core indicators such as permanganate index, ammonia nitrogen, total phosphorus, and total nitrogen all met the Class II standard of the "Surface Water Environmental Quality Standard" (GB 3838-2002). Among them, the improvement in water transparency and total phosphorus in Examples 1 and 2 was significantly better than that in the control group.

[0096] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the inventive concept of this invention, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0097] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If such modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A closed-loop restoration method for the habitat of prey fish in the ex-situ conservation area of ​​the Yangtze finless porpoise, characterized in that, include: Step 1: Construct an aquatic vegetation community in the shallow waters of the ex-situ conservation area. The aquatic vegetation community consists of reeds, Vallisneria natans, and Myriophyllum spicatum, with the ratio of the number of plants of the three species being 2-3:4:

3. Set up fish spawning facilities in the slow-flowing bay area of ​​the ex-situ conservation area. Step 2: Supplement the relocation protection area with prey fish, which shall consist of the following percentages of fish: 40%~45% of Bass bream, 25%~30% of bream, 15%~20% of small crucian carp with a body length of 6cm~10cm, 5%~8% of fine-scaled gudgeon, and 3%~5% of yellowtail gudgeon, totaling 100%; the total number of prey fish supplemented per acre of relocation protection area shall be 1000~2000. Step 3: Dynamically regulate the fish community structure: monitor changes in the number of fish species and fish resources, supplement food fish as needed before the following year's breeding season, and eliminate predatory fish. Among them, supplementing forage fish as needed means: when the monitored forage fish resources is lower than 70% of the same period of the first year, 1,000 fish per mu will be supplemented; when the forage fish resources are between 70% and 90% of the same period of the first year, 500 fish per mu will be supplemented.

2. The method for closed-loop restoration of habitats for prey fish in the ex-situ conservation waters of the Yangtze finless porpoise according to claim 1, characterized in that, The shallow water area is the drawdown zone of shallow water with a depth of 0-3m.

3. The method for closed-loop restoration of habitats for prey fish in the ex-situ conservation waters of the Yangtze finless porpoise according to claim 2, characterized in that, Plant reeds in the nearshore drawdown zone where the water depth is less than or equal to 0.5m, with 4 plants per square meter; And / or, in the drawdown zone where the water depth is greater than 0.5m and less than or equal to 2.0m, Vallisneria natans and Myriophyllum spicatum are planted together, with a planting density of 8 Vallisneria natans per square meter and a planting density of 2 Myriophyllum spicatum per square meter. And / or, in the deep water zone of the drawdown zone of the shoal, where the water depth is greater than 2.0m and less than or equal to 3.0m, plant foxtail grass at a planting density of 4 plants per square meter.

4. The method for closed-loop restoration of habitats for prey fish in the ex-situ conservation waters of the Yangtze finless porpoise according to claim 1, characterized in that, Both the bream and the bream were selected from juvenile fish that were born in the current year and had a body length of 5cm to 8cm. And / or, both the fine-scaled gudgeon and the yellowtail gudgeon are selected from juvenile fish that are 6cm to 9cm in length and born in the current year.

5. The method for closed-loop restoration of habitats for prey fish in the ex-situ conservation waters of the Yangtze finless porpoise according to claim 4, characterized in that, The optimal time for releasing bait fish is during the early spring breeding season each year.

6. The method for closed-loop restoration of habitats for prey fish in the ex-situ conservation waters of the Yangtze finless porpoise according to claim 5, characterized in that, In step two, 40% of the total number of fish are released into the shallow water drawdown zone, 35% of the total number of fish are released around the fish spawning facility, and the remaining prey fish are released into the area between the shallow water drawdown zone and the fish spawning facility. And / or, in step three, the method for supplementing the bait fish as needed is to supplement at a rate of 500 fish / acre to 1000 fish / acre.

7. The method for closed-loop restoration of habitats for prey fish in the ex-situ conservation waters of the Yangtze finless porpoise according to claim 6, characterized in that, The area surrounding a fish spawning facility refers to the ring-shaped area within 10 meters of the fish spawning facility.

8. The method for closed-loop restoration of habitats for prey fish in the ex-situ conservation waters of the Yangtze finless porpoise according to claim 1, characterized in that, Step two also includes adding 10 ml of lactic acid bacteria per square meter. 8 10 9 Each sterilized item.

9. The method for closed-loop restoration of habitats for prey fish in the ex-situ conservation waters of the Yangtze finless porpoise according to claim 1, characterized in that, Lactic acid bacteria 10 8 10 9 The method for preparing the sterilized product is as follows: The lyophilized Bifidobacterium lactis powder was suspended and dispersed in sterile water, sterilized, and then diluted with sterile water to a concentration of 10. 7 Cells / mL ~10 8 The concentration of lactic acid bacteria was calculated to obtain a diluted solution, and the corresponding number of lactic acid bacteria was added per square meter.

10. The method for closed-loop restoration of habitats for prey fish in the ex-situ conservation waters of the Yangtze finless porpoise according to claim 1, characterized in that, The fish spawning facilities include artificial fish nests and / or ecological floating islands.

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