Spatial distribution patterns of fish egg and larval assemblages in the lower reach of the Yangtze River: Potential implications for conservation and management

Abstract

1. River fish diversity is threatened by anthropogenic environmental alteration to landscapes. The early life-history stages of fish play an important role in maintaining diversity and population recruitment and can be heavily influenced by landscape patterns. Information on temporal and spatial distribution patterns of fish eggs and larvae is also important for biodiversity conservation and management of fish resources.2. The Yangtze River possesses a high diversity of fishes, including many commercially important species. The economy along the lower reach of the river is well developed, and most of the area is experiencing high pressure from human impacts. This section of the Yangtze River connects with the largest freshwater lake in China at the upstream end and flows into the estuary at the downstream end. These two landscape features are likely to have a significant impact upon the spatial distributions of fish egg and larval assemblages.3. Environmental variables, fish eggs, and larval assemblages were sampled in three locations, at Hukou, Anqing, and Jingjiang, in the lower reach of the Yangtze River.The results suggest that the higher number of species and greater abundance in upstream sites reflect the critical function of connectivity of Poyang Lake with the river for fish recruitment in the lower Yangtze. The delayed bloom of larval fish, occurrence of estuarine species, and a lower species number and abundance of freshwater fish downstream reflect the influence of tidal intrusion from the estuary.4. This study highlights the value of maintaining natural river-lakes connectivity in the Yangtze River as a conservation measure. The connected river-lake system should be designated as a priority area for fish resource protection in the lower reach of the Yangtze River. We recommend further measures to break down barriers between the river and other lakes and to restore the natural lateral connectivity of the floodplain ecosystem.

Longitudinal drifting pattern of larval assemblages in the lower reach of the Yangtze River: Impact of the floodplain lakes and conservation implementation

“…Limnological attributes of floodplain lakes are thought to provide better physical characteristics than in the main channel for the reproduction of some freshwater fish, such as higher water temperatures, lower turbidity, and cleaner and shallower habitats (Lorig et al, 2013). In our previous research, daily water temperature collecting at HK, AQ and JJ locations showed an obvious longitudinal pattern increasing in the upstream direction especially in early spawning months (Ren et al, 2021). For example, the mean value of water temperature was 22.3°C at HK, which was significantly higher than at AQ (21.8°C) and in turn higher than at JJ (21.5°C) in the early spawning season (from Mid‐April to June) (Ren et al, 2021; Appendix S1).…”

“…In our previous research, daily water temperature collecting at HK, AQ and JJ locations showed an obvious longitudinal pattern increasing in the upstream direction especially in early spawning months (Ren et al, 2021). For example, the mean value of water temperature was 22.3°C at HK, which was significantly higher than at AQ (21.8°C) and in turn higher than at JJ (21.5°C) in the early spawning season (from Mid‐April to June) (Ren et al, 2021; Appendix S1). In the present research, the total magnitude of larval abundance increased longitudinally in the upstream direction, and the spawning time and duration of reproduction for all eight dominant species (six river–lake migratory and two lake–sedentary species) also showed an earlier spawning period or increased spawning duration in the same direction (Table 2; Figure 5).…”

“…Fishery surveys studied in HK region in Poyang Lake showed that the annual fish biodiversity, average abundance and biomass were significantly higher during the prevailing spawning season (May to August) than in other periods, which indicated active migration occurring between Poyang Lake and the Yangtze River (Hu et al, 2011). In our previous study, the number of species for eggs and larval fish collected at HK area was significantly higher than at Anqing (AQ) and Jingjiang (JJ) (Ren et al, 2021). For example, 46 larval species were collected at HK, which was higher than at AQ (42) and JJ (31), especially for river–lake migratory species and lake–sedentary species (Ren et al, 2021).…”

“…In our previous study, the number of species for eggs and larval fish collected at HK area was significantly higher than at Anqing (AQ) and Jingjiang (JJ) (Ren et al, 2021). For example, 46 larval species were collected at HK, which was higher than at AQ (42) and JJ (31), especially for river–lake migratory species and lake–sedentary species (Ren et al, 2021). In the present research, our result showed that the larval species and abundance were highest at WJ both in 2014 and 2015(Figure 4).…”

“…Larval fish also provide a sensitive tool for monitoring the potential recruitment effects of floodplain lakes to the main channel of the river (Converse et al, 1998;Lorig et al, 2013). Additionally, knowledge of larval assemblages is relatively limited in the lower reach of the Yangtze River, except our previous study that focuses on the annual spatial and temporal of larval assemblages (Liu et al, 2019;Ren et al, 2016Ren et al, , 2021. Thus, in the present research, we investigated larval fish assemblages during the prevailing spawning season along the longitudinal reduction gradient of floodplain lakes in the lower reach of the Yangtze River.…”