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

Abstract

AbstractReservoir “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.