Relationship between environmental variables and egg abundance of the four major Chinese carps, downstream of the Three Gorges Reservoir

Abstract

Reservoir “eco‐operation” is an ecological flow regulation measure, such as mimicking a flood process to stimulate fish spawning. Since 2011, the Three Gorges Reservoir (TGR) eco‐operation trials have been carried out to facilitate the spawning of the four major Chinese carps (FMCC) below the Gezhouba Dam. Until now, the response of FMCC spawning to new hydrologic conditions is seldom documented. Using ecological monitoring data from 2012 to 2017, this study analyses annual variations in environmental factors and FMCC spawning, and the correlations between them. During the date of FMCC egg occurrence, there was no significant difference both in annual mean water temperature (TEM) and water transparency (TRA) among years, while there was significant difference in annual mean river flow. The annual egg abundance of FMCC ranged from 135 to 610 million, with an average of 286 million. The peak spawning of FMCC occurred 3 to 5 times annually, while the scattered spawning occurred about 2 to 3 times. Classification and Regression Trees and Random Forests were used to model the daily egg abundance of FMCC. Daily flow (FLO) and flow increase multiple (FIM) were determined as the most important factors for FMCC spawning. The models predicted daily egg abundance of FMCC in the Shashi section could reach to 3.16 × 107 ind. for FLO exceeding 10,000 m3/s and FIM below 49.12. The results might be helpful to deeply understand the role of flood peak process on fish spawning and the optimization of TGR eco‐operation on FMCC spawning.

Variation of heat flux and ecological impact on fish reproduction in the middle reaches of Yangtze River

“…At the optimal temperature, the gonads of domestic fish develop rapidly, which in turn promotes their spawning and reproduction. We know that when the WT is lower than 18℃, the immaturity of the gonads will inhibit the spawning and reproduction activities 24 , so the relationship between the natural reproduction time and the time when the WT reaches 18℃ for the first time is worth exploring (Figure 6). We found that the first spawning date of the FMCC every year occurs after the date when the WT first reached 18°C, which confirms the fact that the spawning WT of the FMCC is greater than 18 °C； Before impoundment, the TGR's WT typically reaches 18°C between the middle and end of April; however, due to the influence of "stagnant heat" in the reservoir's water storage, the WT reaches 18°C around May after impoundment.…”

Ecological responses of spawning habitat suitability to changes in flow and thermal regimes influenced by hydropower operation

“…The mainstream of the Yangtze River is divided into the Upper Yangtze reach, upstream of Yichang, with a length of 4504 km; the Middle Yangtze reach, from Yichang to Hukou, with a length of 955 km; and the Lower Yangtze reach, downstream of Hukou, with a length of 938 km (Figure 1 [a]) (Yang et al, 2018). FMCC, namely, grass carp ( Ctenopharyngodon idella ), black carp ( Mylopharyngodon piceus ), silver carp ( Hypophthalmichthys molitrix ) and bighead carp ( Hypophthalmichthys nobilis ), are endemic and economic fish species in China, whose breeding and nursing habitats are mainly located in the Middle Yangtze reach (Xu et al, 2020). The 380 km reach with a spawning scale extending from Yichang to Chenglingji historically accounted for 42.7% of total FMCC egg production in the mainstream of Yangtze River (Yi et al, 1988).…”

River Damming Impacts on Fish Habitat and Associated Conservation Measures

“…FMCCs are freshwater fish whose adults migrate upstream to spawning sites during flood seasons and spawn semi‐buoyant drifting eggs (Figure 8). The fertilized eggs drift a long distance for development, and then juvenile fish swim into riparian lakes, which serve as nursery habitats (Q. Chen et al., 2021; W. Xu et al., 2020; B. Yi et al., 1988). The spawning activity of FMCCs requires a minimum flow velocity to trigger the release of eggs (Q. Chen et al., 2021), and the drifting eggs require a suitable flow velocity to keep them suspended (Garcia et al., 2013; M. Li et al., 2013; Q. H. Yang et al., 2014; P. Zhang et al., 2021).…”