Initial recovery of fish faunas following the implementation of pen-culture and fishing bans in floodplain lakes along the Yangtze River

Sediment eDNA reveals damming triggered changes in algal and fish communities at the Three Gorges Reservoir in China

With the rapid development of water conservation projects around the world, the potential impacts of damming on river ecosystems have attracted widespread attention. Here, we employed the environmental DNA (eDNA) records of the sediment core profiles to explore the effects of the dam construction on algal and fish community structure and biodiversity in the Three Gorges Reservoir in China for the past few decades. We detected 242 genera of algae and 62 species of fish in the sediment cores of the Xiangxi River estuary, the main tributary of the reservoir. The structure of algal and fish communities was changed significantly before and after damming. The dominant species in the algal community shifted from Cyanophyta to Bacillariophyta, while the dominant species in the fish community remained Cypriniformes, and the species diversity fluctuated greatly after damming. In addition, the Non-metric Multidimensional Scaling (NMDS) analysis showed that the composition of algal communities differed significantly among different sequences, while the differences among fish community groups were relatively small. The total nitrogen (TN) and total phosphorus (TP) in sediments were expected to be the main factors, affecting the abundance of eDNA in algae and fish in sediments. Our research emphasizes the progressiveness of sediment eDNA in retrieving the historical dynamics of biological communities, and especially, obtaining the temporal succession trend of biological communities is crucial to understanding the impact of dam construction on the reservoir ecosystem.

Effect of the ten-year fishing ban on change of phytoplankton community structure: Insights from the Gan River

The Yangtze River is one of the largest riverine ecosystems in the world and is a biodiversity hotspot. In recent years, this river ecosystem has undergone rapid habitat deterioration due to anthropogenic disturbances, leading to a decrease in freshwater biodiversity. Owing to these anthropogenic impacts, the Chinese government imposed a "Ten-year fishing ban" (TYFB) in the Yangtze River and its tributaries. Ecological changes associated with this decision have not been documented to evaluate the level of success. This study evaluates the success of the TYFB by analyzing the changes in phytoplankton communities and comparing them to periods before the TYFB was imposed. A total of 325 phytoplankton species belonging to 7 phyla and 103 genera dominated by Chlorophyceae and Bacillariophyceae were identified. Species diversity according to the Shannon-Wiener ranged between 1.19 and 3.00. The results indicated that phytoplankton diversity increased, while both density and biomass decreased after the TYFB. The health of the aquatic ecosystem appeared to have improved after the TYFB, as indicated by the phytoplankton-based index of biotic integrity. Significant seasonal and spatial differences were found among the number of species, density, and biomass of phytoplankton, where these differences were correlated with pH, water depth, chlorophyll-a, permanganate index, transparency, copper, ammonia nitrogen, and total phosphorus based on redundancy analysis. Results from this study indicate that the TYFB played an important role in the restoration of freshwater ecosystem in the Yangtze River and its tributaries.

Short-term responses of macroinvertebrate assemblages to the "ten-year fishing ban" in the largest highland lake of the Yangtze basin

The rapid decline of freshwater biodiversity caused by overfishing has led to the implementation of a series of conservation measures, including fishing bans. However, existing studies have mostly focused on the effects of fishing bans on economically important species, while impacts on freshwater macroinvertebrates in lake ecosystems have been rarely studied. This study used a before-and-after methodology to determine the short-term effects of the "ten-year fishing ban" on the macroinvertebrates of the Dianchi Lake, the largest highland freshwater lake in the upper Yangtze basin, between 2015 and 2022. Following the fishing ban, the overall macroinvertebrate species richness (median [interquartile]) across sites increased from 4 [2-6] to 5 [4-7]. The total density increased from 128 [80-272] to 212 [140-325] n/m². The median biomass increased from 0.18 [0.08-0.41] to 0.51 [0.26-2.36] g/m². In particular, the Chironomidae density in the offshore sites increased from 16.00 [0.00-32.00] to 33.30 [16.00-48.00] n/m², and the biomass increased from 0.03 [0.00-0.09] to 0.16 [0.07-0.22] g/m². Within the inshore sites, the aquatic insect density increased from 4 [1.33-15.33] to 56 [22.00-86.67] n/m². The Malacostraca density increased from 34.67 [11.67-95.33] to 110 [53.33-223.33] n/m², and the biomass increased from 0.43 [0.11-1.00] to 1.48 [0.50-2.00] g/m². Two endangered Margarya species were rediscovered at multiple sites compared to the pre-fishing ban period. A significant change in macroinvertebrate community structure across the lake was observed, which can be largely attributed to the fishing ban. The immediate increase in species richness, density, and biomass of most macroinvertebrate species suggests a combination of effects from both reduced exploitation pressure and lessened disturbances on lake habitats. The findings indicate that the fishing ban is beneficial for the recovery of most macroinvertebrate species in freshwater lakes.