Simulating mobile populations in aquatic ecosystems

Many aquatic species of management interest, such as endangered, sport, or commercially valuable fish, move extensively within a hydrosystem as they use different habitats for spawning, rearing, feeding, and refuge. Engineering tools are presently inadequate to simulate movement by such species as part of the water resources planning and management. We describe how fixed grid-cell methods can be coupled with mobile object-oriented modeling methods (called Eulerian–Lagrangian methods) to realistically simulate movement behavior of fish in the complex hydraulic and water quality fields of aquatic ecosystems. In the coupled system, the Lagrangian framework is used to simulate the movement of symbolic fish (that is, an individual fish, schools of fish, or some aggregate of the population), and the Eulerian framework is used to simulate the physicochemical regimes that influence fish movement behavior. The resulting coupled Eulerian–Lagrangian hybrid modeling method is based on a particle-tracking algorithm supplemented with stimuli-response rules, that is, the numerical fish surrogate.