Community Structure Characteristics and Changes in Fish Species at Poyang Lake after the Yangtze River Fishing Ban

Abstract

To understand the fish community structure characteristics and changes in Poyang Lake after the Yangtze River fishing ban in 2021, seven sampling stations were established, namely in Hukou, Lushan, Duchang, Yongxiu, Nanjishan, Ruihong, and Poyang, for fishery resource surveys between 2020 and 2021. The results showed that 93 fish species were identified, belonging to 11 orders, 20 families, and 61 genera, which was an increase of 4.5% from before the fishing ban. Of these, 52 Cyprinidae species were identified, comprising the highest proportion (55.91%). Four invasive alien species (hybrid sturgeon, Cirrhina mrigala, Piaractus brachypomus, and Mugil cephalus) were identified, and the number of alien species in Poyang Lake was higher than before the fishing ban. Carnivorous and mid-lower-level fish showed a significant increase, accounting for 47.31% and 38.71% of the total species, respectively. Compared with the Yangtze River before the fishing ban, the body length and body weight of the main economic fish in Poyang Lake increased by 6.10–61.26% and by 15.14–291.57%, respectively. In terms of age structure, the proportion of major economically important fish aged 1 or 2 years decreased significantly, while the proportion of older fish increased substantially. There was little difference in the diversity of fish communities at different stations in Poyang Lake. In terms of biodiversity, the Shannon–Wiener index ranged from 2.158 to 2.909, with Poyang having the highest value and Nanjishan the lowest. Margalef’s index ranged from 4.265 to 6.459, with Lushan having the highest value and Nanjishan the lowest. Pielou’s index ranged from 0.617 to 0.822, with Duchang having the highest value and Nanjishan the lowest. Hence, the Yangtze river fishing ban has played an important and positive role in the restoration of fishery resources in Poyang Lake. However, long-term tracking and monitoring are needed to provide information to comprehensively evaluate the ecological impact of the Poyang Lake fishing ban.

1. Introduction

As the longest river in China, the Yangtze River has a diverse ecological environment, is one of the richest biodiversity areas in the world, and is one of the 35 priority ecoregions for conservation by the World Wide Fund for Nature (WWF). Poyang Lake is the largest freshwater lake in China and is one of the two existing large lakes connected to the Yangtze River [1]. The lake is a key water body involved in the ten-year fishing ban on the Yangtze River. Starting from 1 January 2018, a phased implementation of the fishing ban was implemented on the 332 aquatic life reserves (including 53 aquatic flora and fauna nature reserves and 279 aquatic germplasm resources reserves) in the Yangtze River Basin. The four aquatic life reserves (three aquatic flora and fauna nature reserves and one aquatic germplasm resources reserve) in Poyang Lake were included, with a total area of 1314.23 km² and spanning eight counties (cities and districts) in the vicinity of the lake. On 1 January 2020, a complete fishing ban was implemented for the Jiangxi section of the Yangtze River and the Poyang Lake Aquatic Reserve. Since 1 March 2020, all commercial fishing operations and any other activities that might harm the fish resources or fishery conditions of Poyang Lake have been prohibited. As of 31 October 2020, all retired fishing boats and nets were put under unified management. On 1 January 2021, a comprehensive fishing ban was implemented in Poyang Lake.

Poyang Lake is a key natural lake that connects with the mid-lower Yangtze River. It is an important feeding and fattening ground for fish that migrate to the Yangtze River, as well as a breeding ground for fish that migrate across the mouth of the Yangtze River [2,3]. Thus, Poyang Lake occupies a special place in the protection of Yangtze River fish germplasm resources and fish population conservation. As a typical floodplain lake at the mid-lower Yangtze River, the complex hydrological dynamics of Poyang Lake promote the spatiotemporal heterogeneity of the landscape and facilitate the material, energy, and biological exchange among various landscape elements while influencing the succession of various communities. In this sense, Poyang Lake contains rich and diverse biological resources. Field surveys and monitoring before the Yangtze River fishing ban recorded a total of 136 fish species in Poyang Lake between 1955 and 2000, and 101 fish species between 1997 and 2000 [2,4]. In 2010, 72 fish species were recorded in Poyang Lake; 89 fish species were recorded between 2012 and 2013; 62 fish species were recorded between 2018 and 2019; and 52 fish species were detected in 2019 [5,6,7]. Overall, a total of 212 fish species were recorded from 1980 to 2000. However, the number of fish species decreased to 174 for the period 2000–2017 [8]. In 2018, 106 fish species were observed in Poyang Lake and its tributaries during water restoration projects [9]. At that time, 37.7% of the indigenous fish species and 36.7% of the migratory fish species were not detected, indicating a significant change in the fish species composition [8].

To address these emerging problems, investigations have been performed on the community structure of fish in Poyang Lake, with sampling taking place before the comprehensive ban on commercial productive fishing in 2020. These studies showed that during their wintering period, fish in the Yangtze River-connecting waterways of Poyang Lake largely inhabited the three water areas north of Hukou County, Xieshan Mountain, and near Pingfeng Mountain. There has been relatively little research on the community structure of fish in Poyang Lake after the Yangtze River fishing ban. This study investigated fishery resources in Poyang Lake, in the Jiangxi section of the mainstream of the Yangtze River, and at the estuaries of the “Five Rivers” that flow into Poyang Lake in the period 2020–2021 after the fishing ban came into effect. The composition and biodiversity of fish species were analyzed, and the characteristics and changes of fish community structure were explored. The aim of this study was to provide a reference for the comprehensive evaluation of the ecological impact of the fishing ban on Poyang Lake and fish diversity conservation and biological integrity assessment.

2. Materials and Methods

2.1. Study Area and Sampling Sites

Situated in northern Jiangxi Province and on the south bank of the mid-lower Yangtze River, Poyang Lake is the largest inland freshwater lake in China and an internationally renowned wetland. Covering the area between 115°47′ E and 116°45′ E, and 28°22′ N and 29°45′ N, the water level of the lake is affected by the surface runoff of the “Five Rivers” (the Ganjiang River, the Fuhe River, the Xinjiang River, the Raohe River, and the Xiuhe River) as well as incoming water from the Yangtze River. Poyang Lake plays an important role in regulating and storing water before it is discharged into the Yangtze River at the outlet. The Ganjiang River gradually branches out into its tributaries south of Nanchang, with the main branch being joined by the Xiuhu River and flowing into Poyang Lake at Wucheng. The segment of the Ganjiang River from Wucheng to Zhuxikou is designated as the western waterway. The main branch is joined by the Fuhe River and the Xinjiang River as it enters Poyang Lake and flows to Ruihong Town, Yugan County. The segment from Ruihong Town to Zhuxikou is designated as the eastern waterway. The two waterways merge at Zhuxikou and enter the Yangtze River at Hukou, known as the waterway to the Yangtze River. The Nanjishan of Poyang Lake is a national-level nature reserve. Occupying a large area of sparsely populated land with abundant natural resources, it is an ideal wintering and stopover site for migratory water birds and comprises an apt representation of the Poyang Lake ecosystem. Between 2020 and 2021, seven sampling stations were set up in Hukou, Lushan, Duchang, Yongxiu, Nanjishan, Ruihong, and Poyang for fishery resource surveys. The position, number and investigation frequency of sampling stations are listed in

Table 1. The location and sampling profile of fisheries survey stations in Poyang Lake.

Position	Number of Sampling Sites (Water Areas)	Investigation Time	Total Investigation Frequency
Hukou	2 (Bali River: the west part of the main stream of the Yangtze River; Pingfeng: the watercourse between Poyang Lake and the Yangtze River)	April–June, July–August, September–October, November–December	16
Lushan	1 (the watercourse between Poyang Lake and the Yangtze River)	April–June, July–August, September–October, November–December	8
Duchang	2 (Zhuxikou; Poyang Lake District)	April–June, July–August, September–October, November–December	16
Yongxiu	2 (the mouth of the Ganjiang River; the mouth of the Xiuhe River)	April–June, July–August, September–October, November–December	16
Nanjishan	1 (Poyang Lake District)	July–August, November–December	4
Ruihong	2 (the mouth of the Xinjiang River and Fuhe River; Poyang Lake District)	April–June, July–August, September–October, November–December	16
Poyang	1 (Longkou: the mouth of the Raohe River)	April–June, July–August, September–October, November–December	8

and the map of the Poyang Lake area and 7 sampling stations are shown in Figure 1.

2.2. Investigation Method

Fish caught 10 km up- and downstream of the sampling station were collected. Fishing was carried out via active collection by research boats equipped with gillnets (mesh sizes: 2.5 cm, 6 cm, 8 cm, 10 cm, 12 cm, each of 100 m) and fishing baskets (length × height × width = 18 m × 0.33 m × 0.45 m, mesh = 0.8 cm). Collection locations and vessel numbers were recorded. The total length (to the nearest 0.1 cm), body length (to the nearest 0.1 cm), and weight (to the nearest 0.1 g) of the fish were measured. Fish that were difficult to identify on site were fixed in 10% formaldehyde solution after measuring their total length, body length, and weight and were taken back to the laboratory for further assessment.

Classification Method

The classification, Chinese names, and scientific names of the fish were determined using the latest taxonomic data, with the “Chinese Freshwater Fish”, “Fauna Sinica-Cypriniformes, Osteichthyes”, “Fauna Sinica-Siluriformes, Osteichthytes”, and “Latin-Chinese Dictionary of Fish Names by Classification System” as the primary references [10,11,12,13]. The sample collection time at each sampling station was 3–5 days.

2.3. Data Analysis and Statistics

2.3.1. Historical Data

Fish data from 2002 to 2019 were historical data collected by the authors’ research group with the same survey methodology as this study.

2.3.2. Fish Species Classification

Fish were classified with reference to the existing literature. The fish in Poyang Lake were divided into three categories according to their feeding habits: (1) carnivores feeding on vertebrates or invertebrates; (2) herbivores feeding on aquatic vascular plants or algae; (3) omnivores with both carnivorous and herbivorous feeding. Another way of classification was by the preferred habitats in water: (1) top-level fish: those often living in the upper water layer; (2) mid-lower-level fish: those often living in the middle and lower layers of the water; (3) bottom-level fish: those often living in the bottom water layer.

2.3.3. Catch per Unit Effort (CPUE)

Catch per unit effort refers to the average weight or quantity of fish caught per day within a period of time. This study used the catch per vessel per day as a measurement. All research fishing boats fished for the same 10 h per day, and the number of people on board each boat was usually two.

2.3.4. Dominant Fish Species

The Index of Relative Importance (IRI) [14] was used to evaluate the importance of a fish species in the community. The equation is:

IRI = (PN + PW) × F

where PN is the number percentage of a species; PW is the weight percentage of a species, and F is its frequency of occurrence across all sampling periods. Species with IRI >1000 were designated as dominant species, and those with 100 ≤ IRI < 1000 were important species. Dominant and important species were collectively referred to as main species.

2.3.5. Biodiversity

The diversity of fish in Poyang Lake was measured using several biodiversity indices: the Shannon–Wiener diversity index (H′), Margalef’s richness index (D), and Pielou’s evenness index (J′). The equations are:

$$\mathrm{Shannon-Wiener} \mathrm{diversity} \mathrm{index}: H^{\prime } = -{\displaystyle \sum _{i=1}^S{\mathrm{P}}_i\ln {\mathrm{P}}_i}$$

Margalef’s richness index: D = (S − 1)/lnN,

Pielou’s evenness index: J′ = H′/lnS,

where n_i is the number of fish species i; N is the total number of fish; P_i is the number percentage of fish species i in the total number of fish N, P_i = n_i/N and S are the total number of fish species at the sampling site.

3. Results

3.1. Fish Community Composition

A total of 14,333 fish were collected during the period 2020–2022. The catch weighed 10,300.048 kg in total. Ninety-three fish species were identified, belonging to 11 orders, 20 families, and 61 genera (

Table 2. Trends of fish species composition in Poyang Lake during the past 40 years.

Year	Number of Species Collected	Exotic Species	Feeding Habit			Habitat Water Horizon
			Carnivores	Herbivores	Omnivores	Top-Level	Mid-Lower	Bottom-Level
Before 1980	117	1	55	4	58	25	41	51
1982–1990	103	1	52	4	47	24	35	44
1997–2000	101	1	49	4	48	25	37	39
2012–2013	89	1	40	4	45	20	33	36
2020–2021	93	4	44	4	45	20	37	36

). Of these, 52 Cyprinidae species were identified, comprising the highest proportion (55.91%), followed by nine Bagridae species at 9.68%. There were 54 fish species collected from the Bali River section of the Yangtze River and the mouth of the Raohe River, respectively, 84 species from Poyang Lake, 56 species at the mouth of the Ganjiang River, 54 species at, and 60 species at the mouth of the Xinjiang River and Fuhe River.

A total of 44 carnivorous fish species, 45 omnivorous fish species, and four herbivorous fish species were collected (

Table 3. The composition, ecological types and distribution of fish species in Poyang Lake.

Species	Ecotype	The Bali River Section of the Yangtze River	Poyang Lake District	The Mouth of the Ganjiang River	The Mouth of the Xiuhe River	The Mouth of the Raohe River	The Mouth of the Xinjiang River and Fuhe River.
Acipenseridae
1. Acipenser sinensis	C; B		△
2. Hybrid sturgeon (Acipenser × Huso dauricus) *	C; B		△
Engraulidae
3. Coilia ectenes	C; U	△	△	△	△	△	△
4. Coilia brachygnathus	C; U	△	△	△	△	△	△
Salangidae
5. Neosalanx jordani	C; U		△
6. Protosalanx hyalocranius	C; U		△				△
Anguillidae
7. Anguilla japonica	C; L	△				△
Catostomidae
8. Myxocyprinus asiaticus	O; L	△	△				△
Cyprinidae
Danioninae
9. Zacco platypus	O; U			△
10. Opsariichthys bidens	O; U	△	△	△
Leuciscinae
11. Mylopharyngodon piceus	C; B	△	△		△		△
12. Ctenopharyngodon idella	H; L	△	△	△	△	△	△
13. Squaliobarbus curriculus	O; L		△	△			△
14. Ochetobius elongatus	C; L		△	△
15. Elopichthys bambusa	C; U		△	△			△
Culterinae
16. Sinibrama macrops	O; L	△
17. Pseudolaubuca sinensis	O; U		△	△		△	△
18. Pseudolaubuca engraulis	O; U
19. Toxabramis swinhonis	C; U		△	△		△
20. Hemiculter leucisculus	O; U		△	△		△	△
21. Hemiculter bleekeri	O; U		△	△	△	△	△
22. Culterichthys erythropterus	C; U		△	△	△	△
23. Culter alburnus	C; U	△	△	△	△	△	△
24. Culter mongolicus	C; U	△	△	△	△	△	△
25. Culter dabryi	C; U	△	△	△	△	△	△
26. Culter oxycephaloides	C; U						△
27. Parabramis pekinensis	H; L	△	△	△	△	△	△
28. Megalobrama mantschuricus	O; L	△	△	△	△	△	△
29. Megalobrama amblycephala	H; L		△	△	△	△	△
Xenocyprinae
30. Xenocypris argentea	O; L	△	△	△	△		△
31. Xenocypris davidi	O; L		△	△			△
32. Xenocypris microlepis	O; L		△				△
33. Pseudobrama simoni	O; L		△	△	△	△	△
Hypophthalmichthyinae
34. Hypophthalmichthys molitrix	H; U	△	△	△	△	△	△
35. Hypophthalmichthys nobilis	C; U	△	△	△	△	△	△
Gobioninae
36. Hemibarbus labeo	C; B	△	△
37. Hemibarbus maculatus	C; B	△	△	△	△	△	△
38. Paracanthobrama guichenoti	O; L		△	△	△	△
39. Pseudorasbora parva	O; L		△		△		△
40. Sarcocheilichthys sinensis	O; L	△	△	△	△	△
41. Sarcocheilichthys kiangsiensis	O; L	△	△	△	△
42. Sarcocheilichthys nigripinnis	O; L	△	△	△		△	△
43. Squalidus argentatus	O; L	△	△	△	△	△	△
44. Squalidus nitens	O; L	△	△
45. Coreius heterodon	O; B		△	△	△
46. Rhinogobio typus	O; B	△	△	△	△	△	△
47. Abbottina rivularis	O; B	△	△	△	△	△	△
48. Microphysogobio tungtingensis	C; B		△
49. Saurogobio dabryi	O; B	△	△	△	△	△	△
Acheilognathinae
50. Acheilognathus gracilis	O; L		△
51. Acheilognathus macropterus	O; L	△	△	△	△	△	△
52. Acheilognathus chankaensis	O; L		△		△	△	△
53. Acheilognathus taenianalis	O; L		△	△	△	△	△
54. Rhodeus ocellatus	O; L		△			△	△
55. Rhodeus sinensis	O; L		△		△
56. Paracheilognathus imberbis	C; L		△			△	△
57. Paracheilognathus himantegus	O; L		△			△	△
Labeoninae
58. Cirrhhina mrigala *	O; B		△
Cyprininae
59. Cyprinus carpio	O; B	△	△	△	△	△	△
60. Carassius auratus	O; L	△	△	△	△	△	△
Cobitidae
61. Parabotia fasciata	O; B	△	△	△		△	△
62. Cobitis sinensis	O; B	△	△
63. Cobitis macrostigma	O; B	△	△				△
64. Misgurnus anguillicaudatus	O; B	△	△	△	△	△	△
65. Paramisgurnus dabryanus	O; B	△	△			△
Siluridae
66. Silurus asotus	C; B	△	△	△	△	△	△
67. Silurus meridionalis	C; B	△	△			△	△
Bagridae
68. Pelteobagrus fulvidraco	C; B	△	△	△	△	△	△
69. Pelteobagrus eupogon	C; B	△	△	△	△	△	△
70. Pelteobagrus vachelli	C; B	△	△	△	△	△	△
71. Pelteobagrus nitidus	C; B	△	△	△	△	△	△
72. Leiocassis longirostris	C; B	△
73. Leiocassis crassirostris	C; B	△	△	△		△	△
74. Pseudobagrus pratti	C; B		△
75. Pseudobagrus albomarginatus	C; B	△	△	△		△	△
76. Hemibagrus macropterus	C; B	△	△				△
77. Clarias fuscus	C; B		△		△	△	△
Hemiramphidae
78. Hyporhamphus intermedius	O; U	△	△			△
Synbranchidae
79. Monopterus albus	C; B	△	△	△	△	△	△
Serranidae
80. Siniperca chuatsi	C; L	△	△	△	△	△	△
81. Siniperca kneri	C; L	△	△	△		△	△
82. Siniperca scherzeri	C; L		△		△	△	△
83. Siniperca roulei	C; L	△	△
Eleotridae
84. Odontobutis obscura	C; B	△	△			△	△
Gobiidae
85. Rhinogobius giuroiuns	C; B	△	△		△		△
Belontidae
86. Macropodus chinensis	O; L		△	△	△		△
87. Macropodus opercularis	O; L			△
Channidae
88. Channa argus	C; B	△	△	△	△	△	△
89. Channa asiatica	C; B	△
Mastacembelidae
90. Macrognathus aculeatus	C; B	△
91. Macrognathus sinensis	C; B		△			△
Mugilidae
92. Mugil cephalus *	O; B		△
Characidae
93. Piaractus brachypomus *	O; L		△

Where H: herbivorous fish; O: omnivorous fish; C: carnivorous fish; U: upper Layer fish; L: lower-middle layer fish; B: bottom layer fish; △ collected during this surveillance; * alien species.

). Twenty species of upper-level fish, 36 species of mid-lower-level fish, and 37 species of bottom-level fish were collected. Four species of migratory fish were collected, for 4.30% of the total number of fish species. These were Acipenser sinensis, Anguilla japonica, Coilia ectenes, and Mugil cephalus. A total of four protected fish species were collected, comprising 4.30% of the total number of fish species. These were A. sinensis, A. japonica, Myxocyprinus asiaticus, and Leiocassis longirostris. Four alien species were identified, comprising 4.30% of the total number of fish species. These were hybrid sturgeon (Acipenser × Huso dauricus), Cirrhina mrigala, Piaractus brachypomus, and Mugil cephalus.

3.2. Fish Community Composition and Variation in Poyang Lake

Previous fish resource surveys in Poyang Lake have recorded a total of 134 fish species (the same species registered under different names was counted as one species) from 26 families and 12 orders (

Table 4. The dynamics of fish fauna in Poyang Lake in the last 40 years.

Year	Acipenseriformes	Anguilliformes	Clupeiformes	Salmoniformes	Cypriniformes	Siluriformes	Cyprinodontiformes	Beloniformes	Synbranchiformes	Perciformes	Pleuronectiformes	Tetraodontiformes	Mugiliformes	Characoidei
Before 1980	2	1	3	3	70	17	1	1	1	14	2	2	0	0
1982–1990	0	1	3	4	61	18	1	1	1	12	1	1	0	0
1997–2000	0	1	3	4	62	14	1	1	1	14	0	0	0	0
2012–2013	1	1	2	3	56	10	1	1	1	12	1	0	0	0
2020–2021	2	1	2	2	58	12	0	1	1	12	0	0	1	1

). Of these, 71 species belonged to the family Cyprinidae, comprising 53.0%; 12 species (9.0%) belonged to the family Bagridae; eight species (6.0%) belonged to the family Cobitidae, and five species (3.7%) belonged to the family Serranidae. There were also four species in the family Salangidae and four species of the family Amblycipitidae, each comprising 3.0% of the total. Less than three species were identified for all other families. In the years leading to 1980, 117 fish species were identified in Poyang Lake, and 103 fish species were recorded between 1982 and 1990, including one alien species. Between 1997 and 2000, 101 fish species and one alien species were recorded, and 89 fish species and one alien species were identified between 2012 and 2013. In this survey, 93 fish species were recorded, including four alien species, hybrid sturgeon (Acipenser × H. dauricus), C. mrigala, P. brachypomus, and M. cephalus. The number of alien species in Poyang Lake has increased, while Psephurus gladius, Tenualosa reevesii, Cynoglossus joyneri, Takifugu ocellatus, and Takifugu obscurus have not been detected from 2001 to 2021. P. gladius and T. reevesii are considered extinct. Neither the order Cyprinodontiformes nor Tetraodontiformes have been observed for the past decade.

3.3. Community Structure Variation in Commercially Important Fish Species

The variation in body length was 6.10–61.26% between 2012 and 2021, with Mylopharyngodon piceus showing the smallest increase in body length and Siniperca chuatsi showing the largest increase (

Table 5. The body length composition of major economic fishes in Poyang Lake.

Species of Fish	The Body Length in 2012 (cm)			The Body Length in 2021 (cm)			The Amplitude of Variation (%)
	Range	Average Value	Sample Size	Range	Average Value	Sample Size
Mylopharyngodon piceus	11–82	24.6	101	9.4–80	26.1	58	6.1
Ctenopharyngodon idella	8.7–70	29.5	108	11.3–82	44.7	331	51.53
Hypophthalmichthys molitrix	11.5–74	28.4	173	18.6–64.3	39.9	434	40.49
Hypophthalmichthys nobilis	12.2–77.5	32.9	85	16.2–86	52.3	240	58.97
Cyprinus carpio	8.1–94.5	21.4	185	5.8–56.3	29.0	126	35.51
Carassius auratus	5.9–17.6	10	118	5.8–26.2	12.9	629	29
Siniperca chuatsi	8–46.4	19.1	109	11.5–51	30.8	224	61.26
Silurus asotus	15.2–107.5	30.1	92	12.1–135	37.2	43	23.59
Culter alburnus	12.1–62.3	25.1	99	8.9–67.5	32.4	113	29.08

). In terms of weight, the corresponding change was 15.14–291.57%, with S. chuatsi showing the largest increase and Cyprinus carpio showing the smallest increase (

Table 6. The body weight composition of major economic fishes in Poyang Lake.

Species of Fish	The Body Weight in 2012 (g)			The Body Weight in 2021 (g)			The Amplitude of Variation (%)
	Range	Average Value	Sample Size	Range	Average Value	Sample Size
Mylopharyngodon piceus	20–12,500	533	101	17.3–8725	714	58	33.96
Ctenopharyngodon idella	29–6500	810	108	31.3–12,800	2183	331	169.51
Hypophthalmichthys molitrix	27–6250	744	173	8.7–5730	1385	434	86.16
Hypophthalmichthys nobilis	40–10,500	1086	85	85.6–12,830	3335	240	207.09
Cyprinus carpio	15–17,500	687	185	5.4–4032	791	126	15.14
Carassius auratus	7–219	37	118	4.8–435	79	629	113.51
Siniperca chuatsi	10–2508	261	109	28–6540	1022	224	291.57
Silurus asotus	30–10,500	512	92	18.5–20,300	1377	43	168.95
Culter alburnus	16–2650	266	99	7–3800	694	113	160.9

). In terms of age structure, which was judged by the annual lines on the scales of the fishes, the proportion of major economically important fish aged 1 or 2 years at maturity decreased significantly in 2021 compared to 2012, while the proportion of more mature fish increased substantially (

Table 7. Percentage age composition of major fish harvesting in Poyang Lake in 2012.

	1+	2+	3+	4+	5+
Culter alburnus	66%	27%	6%	1%	/
Siniperca chuatsi	80%	17%	/	/	/
Silurus asotus	49%	37%	7%	4%	3%
Carassius auratus	100%	/	/	/	/
Cyprinus carpio	86%	7%	3%	1%	3%
Hypophthalmichthys nobilis	71%	21%	5%	2%	1%
Hypophthalmichthys molitrix	82%	11%	6%	/	1%
Ctenopharyngodon idella	54%	19%	15%	11%	1%
Mylopharyngodon piceus	56%	28%	13%	2%	1%

and

Table 8. Percentage age composition of major fish harvesting in Poyang Lake in 2021.

	1+	2+	3+	4+	5+
Culter alburnus	42%	10%	26%	21%	1%
Siniperca chuatsi	36%	20%	22%	21%	1%
Silurus asotus	47%	21%	14%	14%	5%
Carassius auratus	99%	1%	/	/	/
Cyprinus carpio	76%	12%	12%	/	/
Hypophthalmichthys nobilis	27%	41%	28%	3%	1%
Hypophthalmichthys molitrix	67%	32%	1%	/	/
Ctenopharyngodon idella	35%	34%	26%	5%	1%
Mylopharyngodon piceus	62%	29%	7%	/	2%

).

3.4. Community Structure Characteristics of Fish Species

The average catch per unit effort for Poyang Lake was 58.22 kg/boat/day. The highest CPUE was 204.5 kg/boat/day at Hukou, and the lowest was 17.10 kg/boat/day at Nanjishan (

Table 9. Catch per unit of fishing effort (CPUE) of different fishing gears and fish diversity in each section of Poyang Lake.

Position	Netting Gear	Day	CPUE (kg/Ship/Day)	Shannon–Wiener Diversity Index	Margalef’s Richness Index	Pielou’s Evenness Index
Hukou	Drift net, fish cage	20	204.5	2.586	6.355	0.692
Lushan	Trammel net, fish cage	20	27.65	2.724	6.459	0.696
Duchang	Trammel net, fish cage	20	44.60	2.900	5.225	0.822
Yongxiu	Trammel net, fish cage	20	32.67	2.825	5.482	0.761
Nanjishan	Trammel net, fish cage	10	17.10	2.158	4.265	0.617
Ruihong	Trammel net, fish cage	20	57.34	2.375	4.859	0.653
Poyang	Trammel net, fish cage	20	23.67	2.909	5.015	0.812

). The biodiversity indices used in this study were the Shannon–Wiener index, Margalef’s richness index, and Pielou’s evenness index (Table 8). The average value of the Shannon–Wiener index was 2.64, with the highest number being 2.901 at Poyang and the lowest being 2.158 at Nanjishan. The average value of Margalef’s richness index was 5.38. The highest value was 6.459 at Lushan, and the lowest was 4.265 at Nanjishan. The average value of Pielou’s evenness index was 0.72, with the highest value being 0.822 at Duchang City, and the lowest being 0.617 at Nanjishan. The dominant species at the Hukou, Lushan, Duchang, Yongxiu, Nanjishan, Ruihong, and Poyang sampling sites were, respectively, Cyprinus carpio and Megalobrama terminalis; Hypophthalmichthys nobilis, Coilia brachygnathus, and M. terminalis; H. nobilis, Ctenopharyngodon idella, and Hypophthalmichthys molitrix; H. molitrix, H. nobilis, and M. terminalis; Carassius auratus, H. nobilis, and Paracanthobrama guichenoti; H. nobilis and H. molitrix; H. molitrix, C. idella, and M. terminalis. Species with the highest IRI were C. carpio, H. nobilis, H. molitrix, C. acratus, and H. molitrix in the Hukou, Lushan, Duchang, Yongxiu, Nanjishan, Ruihong, and Poyang sampling sites, respectively (

Table 10. Dominant species and fish harvesting composition in each section of Poyang Lake.

Position/ Species		Parabramis pekinensis	Ctenopharyngodon idella	Culter dabryi	Coilia brachygnathus	Siniperca chuats	Carassius auratus	Cyprinus carpio	Hypophthalmichthys molitrix	Culter mongolicus	Culter alburnus	Megalobrama terminalis	Megalobrama amblycephala	Coilia ectenes	Hypophthalmichthys nobilis	Leiocassis longirostris	Paracanthobrama guichenoti
Hukou	N (%)	1.58	0.32	0.32	2.21	6.15	1.10	9.15	2.68	1.56	0.47	28.39	-	12.46	7.73	11.04	-
	W (%)	0.11	0.13	0.00	0.02	0.40	0.03	82.14	2.18	0.18	0.08	3.21	-	0.13	6.32	2.20	-
	IRI	<300	<300	<300	<300	<300	<300	4057	<300	<300	<300	316	-	699	624	736	-
Lushan	N (%)	0.86	0.20	8.47	29.98	2.18	6.04	0.66	2.94	4.16	2.49	12.48	0.20	2.69	2.74	-	0.25
	W (%)	0.67	1.06	3.75	3.71	4.40	1.67	1.90	22.69	1.32	2.08	14.65	0.43	0.65	37.03	-	0.03
	IRI	<300	<300	1222	3369	658	771	<300	2563	548	456	2679	<300	334	3977	-	<300
Duchang	N (%)	6.55	6.55	0.25	11.09	1.18	13.36	1.93	5.04	1.34	0.59	6.81	0.42	3.19	6.55	-	13.86
	W (%)	39.43	26.85	0.02	0.50	2.43	0.54	1.67	14.28	0.07	0.42	8.12	0.42	0.28	39.43	-	0.45
	IRI	<300	3341	<300	1159	<300	1391	<300	1932	<300	<300	14.92	<300	348	4598	-	1431
Yongxiu	N (%)	4.95	4.61	4.07	7.39	5.97	16.81	2.37	9.97	1.97	1.02	15.12	1.08	1.83	4.95	-	4.47
	W (%)	26.41	13.79	1.62	0.52	11.28	2.64	4.83	22.26	2.41	1.55	6.45	1.33	0.35	26.41	-	0.15
	IRI	429	1840	569	791	1725	1945	720	3222	437	<300	2157	<300	<300	3137	-	463
Nanjishan	N (%)	0.77	0.88	2.87	1.93	0.28	23.28	0.33	0.17	1.16	0.39	4.08	0.55	-	0.77	-	26.14
	W (%)	27.85	17.64	1.48	0.55	1.11	9.06	0.55	1.55	6.47	0.98	7.19	1.87	-	27.85	-	1.70
	IRI	<300	1852	435	<300	<300	3234	<300	<300	763	<300	1127	<300	-	2862	-	2784
Ruihong	N (%)	1.53	1.78	0.74	2.32	2.81	6.16	1.13	8.04	0.69	0.89	5.42	3.55	1.68	1.53	-	1.13
	W (%)	78.23	3.18	0.28	0.94	3.55	0.14	1.10	6.93	0.65	0.08	1.11	1.34	0.16	78.23	-	0.02
	IRI	<300	496	<300	325	318	630	<300	1497	<300	<300	654	489	<300	5982	-	<300
Poyang	N (%)	1.68	4.19	9.78	12.66	0.28	13.69	3.82	5.40	1.40	1.86	12.94	1.68	0.74	1.68	-	0.47
	W (%)	10.81	17.22	6.96	1.95	0.99	2.85	8.69	23.77	2.39	4.57	5.04	1.74	0.17	10.81	-	0.14
	IRI	638	2141	1674	1461	386	1654	1251	2917	<300	510	1798	<300	<300	937	-	<300

).

4. Discussion

4.1. Post-Fishing Ban Variation in the Fish Community Composition

The prevalent fish species in Poyang Lake belong to the families Cypriniformes and Cyprinidae, exhibiting the compositional characteristics of fish communities in East Asian rivers and lakes [15]. In recent years, the fish community composition has been affected by factors such as flooding, water temperature, water turbidity, and the fishing ban. The 1996 and 1998 Yangtze River floods brought large numbers of farmed fish and migratory fish into Poyang Lake, resulting in a significant change in the species composition of the lake [16]. Since the implementation of the Yangtze River fishing ban, it has had a positive effect on the recovery of fish communities in the lakes of the middle and lower reaches of the Yangtze River. Hu et al. performed a quantitative study of the characteristics of water and sediment movement in the lake and the changes in the lake basin from the influence of sedimentation and erosion as well as the hydrological and ecological effects, using measured data of sediment transport in and out of the lake from 1956 to 2020 [17]. They found that before 2000 Poyang Lake was largely dominated by sedimentation and, from 2001 to 2010, both sedimentation and erosion were present in the lake basin. From 2011 to 2020, the lake basin was entirely under the influence of erosion. The water temperature in Poyang Lake showed a lateral trend of gradual increase from north to south, and from west to east. This is because the northern part of the lake is a waterway to the Yangtze River, where water runs deep and flows fast, resulting in strong heat dissipation. Compared to the west bank, the east bank of the main lake has a lower flow velocity, and the flow is affected by the bay. This region thus features low wind–wave mixed energy, and heat is not transferred effectively in the lateral direction. The water is emerald-green in color, and the sunlight penetrates relatively deep. From 2010 to 2019, although the distribution of fish species changed along environmental gradients, the similarity among communities increased, and there was a tendency towards uniformity [7]. In the years leading up to 1980, 117 species of fish were recorded in Poyang Lake. Between 1982 and 1990, 103 species of fish were recorded, including one alien species. From 1997 to 2000, 101 fish species were recorded, including one alien species. Between 2012 and 2013, 89 fish species were recorded, including one alien species. In this study, 93 fish species were recorded, including four alien species. The composition of fish species in Poyang Lake is thus constantly changing, although less than 90 species play a dominant role in the structure of the fish community. The fish population in Poyang Lake reached a peak in 1998. However, the variety of fish species in the lake showed a declining trend in 2012–2013. The increase in the number of species in 2020–2021 following the Yangtze River fishing ban is small, while the increase in exotic species is obvious.

Further analysis showed that the species identified at various stations in Poyang Lake and the Jiangxi section of the Yangtze River mainstream were similar, consisting largely of Cyprinidae, particularly omnivorous and bottom-level species. The fish in Poyang Lake are primarily bottom-level and omnivorous types. However, after the comprehensive ban on commercial fishing in 2020, there were significant increases in carnivorous and mid-lower-level fish. It has been speculated that, after the ban, carnivorous fish had abundant food and were not threatened by fishing, and this benefited their population recovery. In contrast, carnivorous and mid-lower-level fish are the main targets of commercial fishing. After the fishing ban, it became easier to collect samples of these species for research purposes and monitoring, as manifested by the increase in the observed number of species.

Strong spatial distribution characteristics were also seen in the species composition, with the highest number of fish species observed in Poyang Lake. Significant differences in fish species exist among the sampling sites at river mouths. Sixty species of fish were identified at the mouths of the Xinjiang and Fuhe Rivers, while only 45 species were found at the Xiuhe River mouth. For other rivers, at least 54 species of fish species were identified at their river mouths. Among the five rivers, Ganjiang River contributes the highest average flow into Poyang Lake per year, about 54.2% of the total influx into the lake. The Raohe River contributes the smallest flow volume into Poyang Lake (9.4%), followed by the 9.8% of the Xiushui River, while the Xinjiang River and the Fuhe River contribute 14.5% and 12.1%, respectively [18,19]. In summary, there may not be a close relationship between the number of fish species identified at a river mouth and the average influx into the lake at that location. The Xiushui River is located in the mountains of northwestern Jiangxi Province, with its mouth also in the northwest. We thus speculate that the habitat characteristics of the Xiuhe River and the gradual increase in water temperature of Poyang Lake in the north–south and west–east directions is one reason for the relatively low number of fish species found at the mouth of the Xiuhe River. Zhang et al. classified 24 sampling sites into the Xiushui group and the Poyang Lake group [15]. In this study, the IRI values of Hukou (C. carpio and M. terminalis), Lushan (H. nobilis, C. auratus, M. terminalis, H. molitrix, and C. dabryi), Duchang (H. nobilis, C. idella, H. molitrix, M. terminalis, P. guichenoti, C. acratus, and C. brachygnathus), Yongxiu (H. molitrix, H. nobilis, M. terminalis, C. idella, and S. chuatsi), Nanjishan (C. acratus, H. nobilis, P. guichenoti, C. idella, and M. terminalis), Ruihong (H. nobilis and H. molitrix), and Poyang (H. molitrix, C. idellus, M. terminalis, C. dabryi, C. acratus, C. brachygnathus, and C. carpio) were ≥1000, making them the dominant species. Poyang Lake attracts fish with different movement and migration habits by providing targeted spawning grounds and foraging conditions. Fish that lay buoyant eggs periodically choose river and lake habitats for spawning and fattening [20], while fish that produce sticky eggs choose coastal areas with dense water grass for spawning and open water for wintering and seeking refuge [21]. Hukou is well connected with the mainstream of the Yangtze River and tributaries such as the Ruihong and Xinjiang Rivers. Hukou features rich ecological niches and a complex hydrological and sediment environment that enable it to support greater biodiversity [22]. The higher hydrologic connectivity facilitates greater ecological niche breadth, accommodating varied fish species [23]. Strong interspecific competition may have resulted in the relatively low number of dominant species at this location.

4.2. Post-Fishing Ban Variation in the Community Diversity

The habitat environment and the activities of fish induce changes in their community structure and diversity [24,25]. For the fish community in Poyang Lake, the key area for fishery resources has changed from water areas around the three mountains, Poyang County, and Yugan County in 2010 to Hukou County, Xingzi County, and Xinjian County in 2019. In other words, the key areas moved from the lake center to the Yangtze River waterway and closer to the mainstream of the Yangtze River [7]. This study produced similar findings. Generally speaking, there was little difference in the diversity of fish communities at different stations in Poyang Lake. In terms of biodiversity, the Shannon–Wiener index ranged from 2.158 to 2.909, with Poyang having the highest value and Nanjishan the lowest. Margalef’s index ranged from 4.265 to 6.459, with Lushan having the highest value and Nanjishan the lowest. Pielou’s index ranged from 0.617 to 0.822, with Duchang having the highest value and Nanjishan the lowest. The diversity of the fish community depends on two factors: the number of species and the evenness of their distribution. When the number of species is constant, a more even distribution of species gives rise to higher diversity [26]. The sampling frequency at Nanjishan was only half that of other stations, which could be the reason for its relatively low biodiversity indices. It should be noted that research on the Yangtze River finless porpoises (Neophocaena asiaeorientalis) in Poyang Lake shows that at mid-low water levels, the species is most frequently spotted in water bodies around the three mountains, Longkou, and between Kangshan and the mouths of the three rivers. At high water levels, porpoises are most frequently seen in water bodies around Duchang County and the three mountains. There is partial overlap between the areas with the highest occurrence of Yangtze River finless porpoises and those with high fish diversity [27].

The number of fish species in Poyang Lake increased after the fishing ban in the Yangtze River compared with the number before the fishing ban. The number of fish species collected in this study increased to 93 from the 89 species identified in the 2012–2013 study. Alien species showed the most significant change in species, and the trend of premature maturity, small size, and low quality among major economically important fish species was effectively curbed. Only one alien species was identified in the 2012–2013 study, while four were found in this study, namely hybrid sturgeon (Acipenser × Huso dauricus), Cirrhina mrigala, Piaractus brachypomus, and Mugil cephalus. Some researchers have pointed out that research on the fishing industry of Poyang Lake should consider the invasion of alien species [7], as this is thought to be an important reason for the decline of indigenous fish resources. The presence of some exotic fish has been recorded in Poyang Lake. These fish species may enter Poyang Lake through escaping farming facilities, artificial introductions, or natural dispersal with currents. The Poyang Lake Basin is an area heavily and adversely affected by invasive fish species in Jiangxi Province. Alien species such as hybrid sturgeon, C. mrigala, Piaractus brachypomum, and M. cephalus are found extensively in the lake, the mainstream and tributaries of the Five Rivers, and their associated water bodies, posing a danger to the fish population, the aquatic ecosystem, and the biodiversity of indigenous fish in the invaded water bodies. There is currently a lack of effective measures for the prevention and control of these invasive species. We recommend undertaking a systematic study on the type, distribution, transmission pathway, invasion mechanism, and ecological impact of these species in the Poyang Lake Basin to identify areas for improvement in existing prevention and control measures and thereby protect the indigenous fish population and the local aquatic system.

4.3. Impact of the Yangtze River Fishing Ban on the Restoration of Fishery Resources in Poyang Lake

The ban on fishing in the Yangtze River has replenished the fish resources of Poyang Lake, especially the resources of the “four major carp” (herring, grass carp, silver carp and bighead carp) have increased significantly. Compared to 2012, increases in body length and weight were observed among the major economically important fish species in 2021, with the increases in the carnivorous fish species Siniperca chuatsi being the most prominent. In addition, a significant increase in proportion of fish in more mature age groups was found. The Yangtze River fishing ban policy has had a positive impact on the changes in body length, body weight, and age of major economic fish in Poyang Lake. Studies on the effect of the Yangtze River fishing ban on Coilia ectenes of Poyang Lake, a species that migrates upstream, also indicated that the two years of fishing ban have so far benefitted the population recovery of this migratory fish [28]. Our two-year study also showed that among all seven stations, Hukou scored the highest catch per unit effort, followed by Ruihong and Duchang. It should be noted that higher values of catch per unit effort were observed at the mouths of the Fuhe and Xinjiang rivers near Ruihong and at Zhuxikou near Duchang compared to sampling sites in the lake. Nanjishan, as a representation of the Poyang Lake ecosystem, had the lowest catch per unit effort of 17.10 kg/boat/day, revealing the massing of fish in the channels connecting the Yangtze River and Poyang Lake, and Poyang Lake and other rivers. Significant differences in community composition and biodiversity remain in different regions, possibly due to the interconnectivity between Poyang Lake and Yangtze River, and the effective replenishment of lake fish by the “Five Rivers”. Hence, we recommend the continued and increased monitoring and management of key water areas such as the Yangtze River waterway, Poyang Lake waterway, and the mouths of the “Five Rivers” to fully realize their potential in supporting and maintaining the fish diversity of Poyang Lake.

However, from the perspective of available fishery resources, compared to historical peaks, the amount of fishery resources at Poyang Lake has shown a trend of increase followed by decrease. The fishing yield between 1949 and 1980 was 3.72 × 10⁴ t. In the 1990s, the amount of fishery resources increased continuously, reaching an average annual supply of 4.26 × 10⁴ t. Since the end of the 20th century, the supply of fishery resources has declined to an average annual volume of 2.94 × 10⁴ tons (a 30.8% drop). In 1998, the supply of fishery resources reached a peak of 7.19 × 10⁴ t. The lowest supply occurred in 2017, with only 27.0% of the volume in 1998. Jiang et al. suggested that there was a significant change in the fish community structure in Poyang Lake during 2010–2019 [29]. While small fish remained the dominant species, a significant miniaturization was observed in several fish species, possibly due to overfishing. At the same time, interference from human activities has increased in Poyang Lake, especially in areas farther from the mainstream of the Yangtze River such as Poyang County, Xinjian County, and Yugan County. However, will the ten-year fishing ban on the Yangtze River significantly help the restoration of fishery resources in Poyang Lake? As suggested by Yang et al. [30], the discovery of Mugil cephalus, a euryhaline nearshore fish, at two sampling sites, one at the center of the main lake (S9) and one in the waterway to Yangtze River (S20), in October 2020 could be the result of the fishing ban. However, enhanced restoration of natural habitats is critical to the life cycle of various fish species, including spawning and nursery habitats. Also, stricter management of pollutants entering the lake and management of water levels to mimic natural fluctuations will help accelerate the recovery of fish resources in Poyang Lake. They concluded that the fishing ban eliminated the pressure on the ecosystem from fishing and promoted the recovery of fishery resources and the upstream movement of fish, and the conclusions of this study also indicate that the effects of fishing closures on fish stocks are positive. Hence, we believe that the fishing ban on the Yangtze River has played an important and positive role in the restoration of fishery resources in Poyang Lake. However, the restoration of fishery resources in Poyang Lake is a long-term and complex process that requires continuous conservation and management measures. The implementation of the fishing ban policy is a positive start, but more scientific monitoring and reasonable ecological regulation are needed in the future to ensure the sustainable use of fishery resources and the long-term health of the ecological environment in Poyang Lake.

5. Conclusions

In this study, a total of 93 species of fish were found in seven stations of Poyang Lake, of which 55.91% were Cyprinidae species. Meanwhile, the number of alien species (hybrid sturgeon, Cirrhina mrigala, Piaractus brachypomum, and Mugil cephalus) increased after the fishing ban. The ecological types of fish in Poyang Lake showed that 47.31% and 38.71% of the total species were carnivorous and mid-lower-level fishes. For the main economic fish in Poyang Lake, the body length and body weight increased, and the proportion of older fish increased substantially. Moreover, the diversity of fish communities at different stations in Poyang Lake showed no significant difference. Generally, the Yangtze River fishing ban has played an important and positive role in the restoration of fishery resources in Poyang Lake.