The number and biodiversity of fish are the most significant indicators of the health of a waterbody. In China, there are more than 1100 species of freshwater fish, 70% of which inhabit the rivers [1
]. Although the total number is notable among worldwide statistics, the biodiversity has been continuously declining with increasing anthropogenic and economic development. In fact, as early as 1998, 92 species of the freshwater fish were listed in the China Red Data Book of Endangered Animals: Pisces [3
], which shows that four species unfortunately have gone extinct and 28 species have become endangered. The loss of biodiversity greatly exceeds the world average [4
]. It is the adverse anthropogenic impacts on the freshwater ecosystem that must first be to blame. Both notorious industrialisation and urbanisation are major hindrances to sustainable development in China. Against the background of abrupt population expansion, many irrational activities associated with urbanisation have led to deterioration of the aquatic environment, such as unsustainable exploitation of water resources, improper river modification, pollutant discharge and exotic species invasion.
In 2018, China’s 13th National People’s Congress inserted the term “ecological civilization” into the country’s constitution for the very first time, indicating that the notion has now been raised up to the national strategy level as a main focus paralleling economic and social development [5
]. In the field of aquatic environment, Chinese government has established a series of policies aimed toward balanced water resources exploitation and aquatic ecosystem protection and restoration. In April 2015, the State Council of China promoted the “Action Plan for Prevention and Control of Water Pollution,” a milestone also known as the “Ten-point Water Plan,” the primary objective of which was to substantially improve the country’s water quality and aquatic ecological situation by the year 2020 [6
]. More recently, legislation also has been enhanced. In 2018, the revised Water Pollution Prevention and Control Law came into force, aiming at boosting aquatic environmental protection and restoration from a legal standpoint [7
]. The effects of water quality on aquatic biodiversity have been comprehensively reviewed, and accordingly a series of protection areas have been established throughout the country. All these actions demonstrate that the priority of public policy has shifted from mainly social and economic progress to also include environmental conservation for healthy aquatic ecosystems and sustainable hydrologic cycles.
However, the practical situation suggests an aquatic ecological deficit would remain. What is worse, knowledge of the ecosystemic constitution of freshwater fish (including migratory fish) of river basins over much broader areas of China, as well as specific factors influencing the biodiversity, is far from sufficient. The reported monitoring data over the past few decades were either not comprehensive or lacked continuity. As a result, the conservation and restoration of aquatic ecosystems have been performed nationwide without a reliable scientific basis and have even tended to be too formalistic and/or disorganised. To make contributions for sound river basin management in China, a pioneering study on the ecological situation (especially the fish biodiversity) was initiated in the Yangtze River Basin. The necessity and significance of the scientific basis and the truly ecological notion would be emphasized. Besides, the comprehensive and continuous basin-scale scientific investigation, as well as the “ecological river” concept-oriented conservation and restoration action, would be timely advocated.
2. Materials and Methods
As shown in Figure 1
, the Yangtze River originates from glaciers on the Qinghai–Tibet Plateau at its westernmost point, heads toward the East China Sea and eventually enters the Pacific Ocean. Along the way, it flows across the southwestern and central parts of China before reaching its outlet in Shanghai (the economic centre of the country). With a length of 6300 km and a catchment area of 1.8 million km2
, the Yangtze River is the third largest river in the world. Having the biggest discharge volume, it also supports the world’s largest hydroelectric power station, i.e., the Three Gorges Dam. Designated as part of the latest national development strategies, the Yangtze River Economic Belt includes about 40% of the country’s population and aggregate economy and is on the way of high-speed development. In its development planning outline issued in 2016, “ecology first” and “green development” form basic principles. Unfortunately, the Yangtze River Basin had long been sustaining extremely severe destruction of aquatic habitats [8
]. In a multi-year study undertaken by the China Europe Water Platform (CEWP) project, a China–Austria cooperating project, etc., representative tributaries of the lower basin of the Yangtze River were thoroughly and continuously investigated. The main study area was the East Tiaoxi River Basin, one of the best epitomes of the environmental issues of the Yangtze River Basin (Figure 1
). With a mainstream length of 152 km and a catchment area of 2267 km2
, the East Tiaoxi River is the largest river flowing into Lake Taihu, the third largest freshwater lake in the Yangtze River Basin. This lake with scenic beauty has been drawing focuses of worldwide researchers, ironically due to its notorious chronic water pollution problems such as eutrophication [9
Regarding fish species and communities, the joint research focused primarily on the following: (1) spatiotemporal distribution, (2) natural and anthropogenic influences, (3) habitat requirements of certain key species and (4) river health assessment based on fish-based index of biological integrity (FIBI). Regarding FIBI system development, 24 metrics were selected as candidate metrics, which covered five attributes of fish assemblage, i.e., species richness and composition, trophic composition, tolerance/intolerance, reproductive guilds, and fish abundance and health condition. Two FIBI systems were then established for the upper reaches (eco-zone of evergreen broad-leaf forest) and middle-lower reaches (eco-zone of urban and suburban agricultural areas), respectively. The detailed system composition, as well as the criteria of metric scoring and assessment, was described by Huang et al. [10
] Geographic Information System (GIS) was one of the major tools used to facilitate the entire research. Detailed field investigation was carried out at 55 sampling sites of the East Tiaoxi River Basin (Figure 1
), by wading in the upper reaches (reservoirs excluded) and by boat in the middle-lower reaches, respectively. In the shallow reaches fish were sampled using specific backpack electrofisher at the main habitat units such as riffle, glide and pool, while in the middle-lower reaches local boat electrofisher was used. The samples were identified to species level, followed by data processing using methods such as sample-based rarefaction curve and cluster analysis to reveal fish distribution patterns [11
]. The spatiotemporal variation of fish communities and the associations of fish density and richness with environmental variables (influencing factors) were also investigated using methods such as non-metric multidimensional scaling and canonical correspondence analysis based on fish abundance data [11
]. Note that the major natural factors focused on included distance to source, altitude, stream width, stream velocity, stream depth and pH, and the major anthropogenic factors covered residential area, revetment, farmland and factory.
In this study, we recorded 84 species of fish, 35 of which were endemic. The main results are presented in Table S1, Figures S1 and S2
. Inspiringly, certain endangered species in the neighbouring country Japan were found to be locally flourishing (Figure 2
). Owing to the devastation of habitats as well as the blockage of breeding migration routes, the once common Leptobotia tchangi
Fang, 1936 has almost disappeared and hence was called a “natural monument” by the Japanese Ministry of the Environment. For similar anthropogenic reasons, Vanmanenia stenosoma
Boulenger, 1901 and Acheilognathus chankaensis
Dybowski, 1872 are both at risk of extinction in Japan. The detailed investigation of their habitat requirements (stream depth, stream velocity, pebble size, etc.) provided valuable information for further protection and restoration initiatives in both China and Japan. Taking Leptobotia tchangi
for instance, it was found that its density had positive correlation with stream velocity, while its body size positively correlated with pebble size (see Figure S3 and S4
). On the other hand, the once-famous Coilia ectenes
Jordan & Seale, 1905 of high culinary and economic value now can rarely be observed, as the deterioration of water quality, devastation of habitats and overharvesting in the Yangtze River led to the drastic decline of this diadromous fish in the past few decades [16
]. Meanwhile, another variety featuring freshwater migration—Coilia nasus taihuensis
Yuan, Lin, Liu & Qin, 1977—has emerged in Lake Taihu and tributaries of the East Tiaoxi (Figure 2
), reminding people of the dramatic ecological change induced by human activities. Furthermore, according to the results of river health assessment (Tables S2 and S3
), 24 out of 45 monitoring sites were determined to be “healthy” or “fair,” while the rest were either “poor,” “very poor” or “null.” Based on the strategy of identifying conservation priority areas first, 21 locations with high fish biodiversity were determined to be hotspot protection areas, including the habitats of all the above-mentioned key species (see Figure 2
). GIS-based tools significantly increased the accuracy of protection activities.
By comprehensively researching the influences on the richness of fish species, natural factors were identified, including distance to source, altitude, stream width, stream velocity, stream depth and pH (Table S4, Figure S5
). More importantly, the study also revealed the impacts of anthropogenic activities (Figure S6, Table S5
), especially the negative influences (Figure 2
). In addition to common adverse effects such as from water pollution and ship disturbance, we found the impact of local privatised stone mining to be non-negligible. With no regard for the aquatic environment, the stone powder and other residuals from mining and transportation freely entered the adjacent waterbodies, which seriously suffocated the fish by getting stuck in their gills. Besides, other ubiquitous practices such as river training works and water pollution control projects have been continuously converting river environments from their original states to artificial states, thereby causing serious loss of the basic ecological functions of the rivers. The entire study area has locally been subjected to various negative impacts by human activities, such as the expansion of floodways, constrictions caused by bridge crossings, river realignments due to cutoffs and restoration activities, changes in resistance of dikes, weirs and riprap, river diversion for water intakes, dams and grade control structures, sediment supply from deforestation, increased runoff due to impervious cover, increased nutrient loads and aggravated bank erosion (see Figure 3
for examples). From one October to the next, engineering construction had degraded a hotspot with 15 fish species and 216 individuals to a silent-spot with only 6 species and 20 individuals in just a year. Only where the aquatic habitats were maintained in a good state and rich with hydrophytes was satisfactory fish biodiversity observed (Figure 2
). Ironically, the “submerged plants” area would have been reclaimed without this study at river basin scale. The flora presents relevant ecological significance, including the ability to mitigate negative impacts resulting from stone mining. However, it was completely neglected in previous conservation and restoration schemes, as regular surveys on water quality and fish biodiversity were conducted randomly and only at the local level, thus failing to draw the whole picture.
We have also noticed inappropriate perceptions and practices of protection and restoration, which require urgent correction. For example, only fish regarded as flagship species and/or included in the national protection list draw broad attention, such as Acipenser sinensis
Gray, 1835 and Neophocaena
Palmer, 1899. Normal fish species, including ones presented in Figure 2
, are usually ignored. However, based on the theory of a healthy ecosystem as well as the experience and lessons of many developed countries, all the species within a specific ecosystem must be equally conserved, as they all interrelate and interdepend. Swayed by the impractical expectation of instant effects as well as influenced by the urbanisation tendency in river basin planning, various kinds of supposedly ecological engineering measures are prevailing in riparian areas. Energy-consuming modes of wastewater treatment plants and facilities have been transplanted to the riparian areas. Since they fulfil the dream of ameliorating water pollution overnight, such palliatives make it seem to be quite desirable for local government to handle the inspection and assessment based on directives from higher authorities. Also, popular artificial wetlands have been constructed here and there, with the main focus being on water purification and aesthetics rather than biodiversity conservation. Even worse, a large amount of money has been invested to the artificial landscape projects with no true ecological idea involved, such as a hydrophilic platform (Figure 4
). These supposedly ecological measures swiftly satisfy human desires but go against the laws of nature. With dramatically changed land cover and land use in the riparian areas, the vulnerable habitats for fish and other living creatures are apt to be even further degraded. According to the theory of ecological integrity, it is a natural and undisturbed state with physical, chemical and biological integrity that should be the right goal of ecological restoration [17
The master plan for the development of the Yangtze River Economic Belt has become one of China’s principal national strategies. Because the primary goal of water-related environmental policies in China has fundamentally changed as conservation and restoration gain top priority, some measures have been taken as essential, such as a 10-year ban on fishing in the Yangtze River starting in 2020. However, this case study revealed that current practices apparently fail to keep pace with the central government’s directives. The present situation in the Yangtze River Basin is still sounding the alarm and causing critical concern among the public. As the biodiversity of freshwater fish keeps on decreasing mainly due to anthropogenic impacts, it is apparent that there has been a serious lack of scientific basis and truly ecological action for sound river basin management.
Comprehensive and continuous scientific investigation at river basin scale is proposed to track riverine fish biodiversity and to further understand the influencing factors. We believe that accurate identification of ecological protection red lines and relevant hotspot protection areas, more targeted action plans and technical guidelines for normalising conservation and restoration activities would be achieved only on the basis of data from scientific study in accordance with the theory of ecological integrity. The results of this exemplary study reveal significant insight into the highly anticipated nationwide practices. To support the initiative, we recommend that the relevant government bodies—such as the Ministry of Science and Technology and the affiliated National Natural Science Foundation of China—set up special funds for long-term fundamental research on the ecological environment and biological resources of the Yangtze River Basin. All involved local authorities should also take responsibility for routine environmental monitoring and assessment. Further, we advise that the supposedly ecological engineering measures for conservation and restoration, together with the destructive pollution control and treatment practices, be strictly prohibited by policy and institutional means [18
], which recently have received positive reply from the prime minister. Meanwhile, scientific data and the know-how for effective environmental conservation and restoration must be delivered to and shared among all the stakeholders, especially the government decision-makers in this Chinese case. From the viewpoint of ecological integrity, the real concept of “ecological river” needs to be advocated and put into practice, which aims at recovering the original structure and ecological functions of a river and hence make it regain the resilience and stability in order to maintain acceptable quality under long-term or sudden disturbance [13
]. Last but not least, to ensure the success of the whole cause, more stringent legislation and regulations must be enacted and enforced.
Water resources management is the epitome of China’s environmental issues, and significant aquatic biodiversity loss in the major river basin shows the severity of the challenges. Heading toward sustainable development, China must make its great power accountable and lead the way by taking “scientific” and “ecological” action.