Transport of invasive carp eggs and the effect of river turbulence

Abstract

Bighead (Hypophthalmichthys nobilis), silver (Hypophthalmichthys molitrix) and grass (Ctenopharyngodon Idella) carps are important food sources in East Asian while considered an invasive species in North America due to their extremely large population and detrimental effects on native fishes. These species are mass spawners with similar reproductive characteristics. Suspension of eggs is believed to be necessary and predictive of successful recruitment. Dependence on suspension makes them incline to spawn in turbulent zones in rivers. Egg transport models have been used to understand egg drift process of invasive carps, among which FluEgg is widely used. FluEgg has been tested and applied in both rivers and laboratory experiments. However, the limitation of FluEgg is the uncertainty caused by its usage of one-dimensional (1-D) hydraulic data and parameterization of hydrodynamics in the complex large river. The objective of this research is to develop a multi-dimensional modeling framework to better reflect the inherent physics of eggs transport associated with river turbulence. First, we developed a fully three-dimensional (3-D) stochastic egg drift model, namely SDrift. Based on egg characteristics as a function of post-fertilization time and temperature, SDrift applies Markov-chain random walk to simulate stochastic movement of eggs, and can be coupled with prescribed hydrodynamics parametrization using field-survey data or simulated 3-D hydrodynamics. Second, the performance of SDrift was compared with FluEgg and evaluated using experimental and simulated results in two idealized channels and a representative reach of the Lower Missouri River. To apply SDrift on a large river, we processed a fully 3-D high-resolution (4x4x0.4 m, 49,053,215 cells) computational fluid dynamics (CFD) modeling using Reynolds-averaged Navier Stokes (RANS) simulation in an 8-km long reach in the Lower Missouri River. The hydrodynamics model was calibrated and validated with field measurements of water-surface elevation and velocity under different discharge conditions. With the simulated hydrodynamics, SDrift was applied to elucidate egg transport processes in a highly engineered large river. The modeling results show the strong effects of localized turbulence on egg transport due to in-steam hydraulic structures and strong morphological variations in the river. Finally, a field survey of river turbulence was carried out at a representative sandbar island within a short spatial range in the Lower Missouri River. The measurement data allow evaluations of river turbulence structures and testing of the validity of classic turbulence parameterization. The measurements and evaluations provide information on the spatial scale of turbulence variabilities that may be important in ecologically relevant habitats.