Abstract
Schizothorax prenanti is an endemic fish in the mountain rivers of southwestern China with unique protection value. To further explore the vortex motion of hydraulic habitats, which is closely related to the fish breeding process, the cross-sectional vorticity was used to evaluate the hydraulic conditions of the natural spawning habitat of S. prenanti. A coupled level-set and volume-of-fluid (CLSVOF) three-dimensional (3D) model was applied to simulate the hydraulic habitat of the Weimen reach, a typical natural spawning ground for S. prenanti in the upper Yangtze River. The model was used in conjunction with the Wilcoxon rank sum test to distinguish the distributions of vertical vorticity in spawning and non-spawning reaches. Statistical analysis revealed that the cross-sectional vorticity in spawning reaches was significantly greater than in non-spawning reaches, with likely biological significance in the spawning process. The range of cross-sectional mean values of vorticity was 0.17 s-1–0.35 s-1 in areas with concentrated fish sperm and eggs; the minimum value was 0.17 s-1, and the majority of values were greater than 0.26 s-1. Based on this study, a vague-set similarity model was used to assess the effectiveness of ecological restoration by evaluating the similarity of the cross-sectional vorticity of the natural spawning reach and rehabilitated spawning reach after implementing ecological restoration measures. The outcome might provide a theoretical basis for the recovery of damaged S. prenanti spawning grounds and act as an important complement for the assessment of recovery effectiveness and as a useful reference for the coordination of ecological water use with the demands of hydraulic and hydropower engineering.
Highlights
Schizothorax prenanti, a semi-migratory fish endemic to China that matures in inland waters, is a Class-II provincial protected animal and an important commercial fish that inhabits the upper reaches of the Yangtze River and tributaries such as the Jinsha, Dadu, Minjiang, and Qingyi [1]
To further examine vorticity and improve our current index system, the present study examines the cross-sectional vorticity of the spawning grounds of S. prenanti through field investigations, numerical simulations, rank sum tests and vague set analyses
Limited studies have examined the effects of vorticity characteristics on fish spawning grounds, though this subject is gradually attracting the attention of researchers
Summary
Schizothorax prenanti, a semi-migratory fish endemic to China that matures in inland waters, is a Class-II provincial protected animal and an important commercial fish that inhabits the upper reaches of the Yangtze River and tributaries such as the Jinsha, Dadu, Minjiang, and Qingyi [1]. Lamourou et al [12] and Moir et al [13, 14] suggested that local hydraulic metrics influence spawning habitats with varying importance and indicated that the Reynolds number or Froude number may be useful single descriptors of hydraulic habitat because they are dimensionless and comparable between different river sizes and fish species. These measurements fall short of a full description of the hydraulic habitats because the spatial variation of the complex flow fields has not been described for spawning grounds
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