This research aims to develop a dynamic state variable model to predict changes in fish density on an estuarine tidal mudflat. Flounder, Pleurnectes flesus, is the model organism. Input data include environmental variables such as temperature, salinity, oxygen concentration, turbidity and possible toxicants. Biotic input variables are the density of of prey, predators and competitors. Using the input, the model produces maps of the optimal habitat use of flounder on the intertidal mudflats during flooding.