Influencing Aspects of Fish Diversity Patterns in the Middle and Lower Yangtze River

Human-caused changes to landscapes and rivers have fundamentally affected patterns of freshwater biodiversity throughout the world’s aquatic systems. Previous studies have shown that small and medium-sized streams experienced a sharp decline, but there has been less focus on the patterns and drivers of fish biodiversity in larger river systems.

The research team led by Professor Chen Yuchun of the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences, in collaboration with Michigan State University, Washington University and JCI, demonstrated the roles of lake-river connectivity, wetland extent, and human stress factors in shaping the alpha and beta diversity patterns of fish. Migratory and non-migratory populations in the middle and lower reaches (MLR) of the Yangtze River. The results were recently published in natural ecology.

In this study, the researchers examined the relationship between wetland extent, a range of human stressors, including urbanization, fishing pressure, navigation, shoreline modification, and three classifications of fish aggregation data—all species, non-migratory species, and migratory species. It was sampled along the river-lake connection slopes of Dongting and Puyang lakes.

Based on the distance between the sampling areas and Puyang Lake or Dongting Lake, the researchers used cluster analysis to divide the sample access into three parts, including MLR1, MLR2, and MLR3. MLR1 was located near Dongting Lake and further upstream. The region closest to Poyang Lake was MLR2, which was located in the middle. The MLR3 access was furthest from Dongting and Poyang lakes and was located downstream.

To discover patterns of spatial diversity of fish (alpha and beta) in the middle and lower Yangtze River, the researchers performed a one-way multivariate analysis of variance. The results showed that MLR3 had the lowest species richness and the largest total beta diversity (dBC) compared with the other two clades for both species and non-migratory species.

In addition, the researchers performed a redundancy analysis and a distance-based redundancy analysis to facilitate mechanistic interpretations of associations between explanatory variables and the diversity of alpha and beta fish. River and lake connection, wetland extent, and fishing pressure greatly affected alpha and beta diversity. Nesting species were mainly related to the amount of wetland, and showed the strongest associations with non-migratory fish species. Turnover was primarily associated with river lake conductance (mainly Poyang Lake), especially for migratory species.

Maintaining fish diversity in this large river ecosystem requires protecting hydrological connectivity and wetland habitats, as well as reducing fishing pressure. The results of this study will help better inform fish conservation efforts in the Yangtze River.