Ecological Flow Assessment to Improve the Spawning Habitat for the Four Major Species of Carp of the Yangtze River: A Study on Habitat Suitability Based on Ultrasonic Telemetry

Abstract

Four major species of Chinese carp, namely black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idellus), silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), are important economic freshwater fish varieties in China. They primarily inhabit and breed in the Yangtze River. Unfortunately, the construction and operation of the Gezhouba Dam and the Three Gorges Dam have dramatically changed the hydrodynamic conditions in the middle reaches of the Yangtze River, leading to a sharp decline in the reproduction rates of these carp. The egg abundance of the four species of carp downstream from the Three Gorges Dam reached 8.35 billion in 1965, but abundance during 2005-2012 was only 0.25 billion. One of the main reasons was that the hydrodynamic conditions of the spawning ground could not meet the four species' breeding requirements. However, due to the limitations of traditional detection tools, the spawning characteristics of these four species of carp were still unclear. In this study, the ultrasonic telemetry and a three-dimensional hydrodynamic model were utilized to build the habitat suitability index (HSI) curves for the four species of carp. The habitat suitability model was then built based on HSI curves to assess spawning habitat quantity under different flow conditions. Finally, the habitat suitability model in the Yidu spawning ground was validated using 32 groups of sampling data in 2015 and 2017. The statistical results showed that the most suitable velocity ranged from 0.78 m/s to 0.93 m/s. The most suitable water depth ranged from 14.56 m to 16.35 m, and the most suitable Froude number ranged from 0.049 to 0.129. The habitat suitability model simulation results indicated that when the discharge was between 15,000 m 3 /s and 21,300 m 3 /s, the weighted usable area (WUA) values in both the Yidu and Zhicheng spawning grounds would remain at a high level. The validation results showed that most spawning activities occurred at a high level of WUA, and that the daily spawning egg numbers increased with the WUA value. Therefore, discharges of between 15,000 m 3 /s and 21,300 m 3 /s could be recommended as ecological operation target flows. We propose a feasible ecological operation scheme by setting the initial flow at 15,000 m 3 /s and maintaining the daily discharge increase at 1500 m 3 /s for 4 days.

Changes in the flow regimes associated with climate change and human activities in the Yangtze River

“…Four major Chinese carps, that is, grass carp, black carp, silver carp, and bighead carp, are the most important economic freshwater fish in China. Their egg abundance downstream of the TGD was 8.35 billion in 1965 and decreased to merely 0.25 billion after construction of the TGD (Yu et al, ). The effective breeding population size of the Chinese sturgeon, the largest anadromous fish in the Yangtze River, decreased by more than 24% after the closure of the TGD in 2003 (Huang & Wang, ).…”

Elevated Temperatures Shorten the Spawning Period of Silver Carp (Hypophthalmichthys molitrix) in a Large Subtropical River in China

“…The discharge suitability index (DSI) and the temperature suitability index (TSI) were applied to define the discharge and temperature suitability for silver carp' spawning (Yu et al, 2018). The DSI was calculated as DSI i = D i D max , where DSI i is the discharge suitability index of the discharge bin i, D i is the value of larvae abundance weighted by the number of spawning occurrences of the discharge bin i, D max is the maximum value of larvae abundance weighted by the number of spawning occurrences across all discharge bins.…”

“…Determining the impact of global warming on fish spawning (e.g., spawning time) is challenging, since spawning characteristics are also regulated by other factors such as hydrographic parameters, spawning population stocks (Gillet and Dubois, 2007;Paumier et al, 2020). Generally, warm temperature and increases in river discharge can trigger spawning initiation (Yu et al, 2018), while spawning stock abundance mainly determines the interannual variability in larvae production (Glover et al, 2020). However, in some cases (e.g., a cold winter), temperature and river discharge affect larval abundance of some species (e.g., Clupea harengus membras) more significantly than spawning stock size (Ojaveer et al, 2011).…”

“…Their spawning timings vary slightly in different regions: mid-May to the beginning of July in the Caspian Basin (Abdusamadov, 1987); from mid-May to mid-June in Arkansas (Freeze and Crawford, 1983); from June to early August in the Amur River (Gorbach and Krykhtin, 1989); from May to August in the Yangtze River (Zhang et al, 2000); and early April to early October in the Pearl River in China (Shuai et al, 2018). In China, some researchers consider the occurrences of silver carp eggs and larvae to be stimulated by high water discharge (Shuai et al, 2018;Yu et al, 2018). However, this fish can reproduce in the Wabash River without changes in discharges (Coulter et al, 2016).…”

Fuzzy Representation of Environmental Flow in Multi-Objective Risk Analysis of Reservoir Operation

“…0.9~1.2 ⁄ and > 1.2 ⁄ . Yu et al (2018) believes that the flow velocity suitable for FMCC survival and reproduction in the middle Yangtze River was 0.63~1.83 ⁄ . By summarizing the relevant studies, we set the environmental flow velocity range as:…”