Study On The Movement Characteristics Of Drifting Fish Eggs

In recent years,the construction of large-scale water conservancy and hydropower projects and the human activities have changed the original river morphology,squeezed the living space of fish,blocked the fish migration,destroyed the original fish habitat,and reduced the amount of fish resources.In order to protect the fish resources,various departments use ecological operation,ecological restoration and other methods to create suitable hydrological and hydrodynamic conditions and meet the needs of fish breeding.The amount of the fish early-stage resources is an important indicator to measure the effect of the ecological operation and remediation.The estimation still uses the method of estimating the average density of fish eggs proposed by Yi Bolu in the 1960s.This method has problems such as large error and poor accuracy,which is insufficient to evaluate the effect of the ecological operation.At the same time,the range of spawning grounds deduced from fish eggs' development time and the average river flow velocity are too large to guide the fish habitat restoration and spawning grounds protection.Therefore,it is urgent to establish a new method based on the laws of fish eggs'movement to accurately locate fish spawning grounds and estimate fish early-stage resources,so as to propose measures for fish resources protection.In this paper,particle tracking velocimetry(PTV)technique is used to carry out laboratory flume experiments of fish eggs' movement.The characteristics of fish eggs'movement under approximately constant uniform flow are systematically analyzed,and the relationship between the velocity of fish eggs' movement,the trajectory slope of fish eggs'movement and the velocity of water is preliminarily quantified.At the same time,the physical force analysis is applied to simplify the force of fish eggs,and the equation of fish eggs'movement under the condition of constant uniform flow is deduced.The theoretical deduction and the results of experiment are compared and summarized to reveal the movement characteristics,main influencing factors of fish eggs and the mechanism of action.Taking the tributary of Ouchi River as the research area,the model fish eggs were used to carry out field drifting experiments to explore the drifting trajectory and velocity characteristics of fish eggs in natural rivers.On this basis,a fish eggs movement model was established based on Fluent software,and the model was calibrated and validated by laboratory fish eggs' movement flume experiment data.Using the model established in this paper,the movement of fish eggs released from different locations in Ouchi River was simulated,the drifting velocity and trajectory of fish eggs were analyzed,and the methods of estimating fish early resources and locating spawning grounds based on the model were discussed.The main conclusions of this paper are as follows:(1)The Velocity and Traj ectory Characteristics of Fish Eggs' MovementThe fish eggs' longitudinal velocity was linear increase with the increasing flow longitudinal velocity under the condition of constant uniform flow.The fish eggs'vertical velocity had no significant relationship with the flow longitudinal velocity.In lower velocity condition,the trajectories of eggs' movement had a linear decrease trend and the slope of trajectories slowed down with the increase of flow velocity.When the flow velocity increased to a certain value,the trajectory changed from simple linear sinking to the wave-and-roll type sinking,and quite a few individual eggs jumped suddenly.(2)Theoretical Analysis of Fish Eggs'MovementIn this paper,the equation of fish eggs' movement under constant uniform flow is solved analytically.Comparing the theoretical deduction with the results of laboratory flume experiment,the movement characteristics,main influencing factors of fish eggs'movement and the mechanism were revealed.It was found that the movement equation of fish eggs'movement overestimated the longitudinal velocity,vertical velocity and trajectory slope of fish eggs.(3)Analysis of Drifting Characteristics of Fish Eggs in Natural RiversThe drifting density of fish eggs in natural rivers decreases with the increase of drifting distance,and there are differences in drifting density of fish eggs at different locations in rivers.The drifting velocity of fish eggs lagged behind the flow velocity at all sampling sections,and there were slight differences in drifting velocity of fish eggs thrown at different locations in the river cross-section.The drifting trajectory direction of fish eggs is consistent with direction of the main stream,which is affected by river topography,hydrodynamic conditions,specific gravity and particle size of fish eggs.(4)Construction and Application of Numeric Model of Fish Egg' MovementA fish eggs movement model was established based on the Fluent software,and the model was calibrated and validated by laboratory fish eggs' movement flume experimental data.Using the model established in this paper,the movement of fish eggs released from different locations(left bank,middle and right bank)in Ouchi River was simulated,and the drifting characteristics of fish eggs in natural rivers were analyzed statistically.The results show that the model can simulate well the drifting movement of fish eggs in natural rivers.The methods for estimating early fish resources and locating spawning grounds in natural rivers using fish eggs movement model were explored.