A REGIONAL ORGANISM EXCHANGE MODEL FOR SIMULATING FISH MIGRATION

A grid-based, spatially-explicit Regional Organism Exchange (ROE) mode l is presented as a framework for integrating aquatic ecosystems and f ish population processes at the landscape level. Active fish movements across a grid cell boundary were predicted, based on environmental to lerance ranges. The model was designed to be easily modified for any a quatic system, migratory life-stage, or trophic community. ROE was spe cifically developed to understand how large-scale physical patterns (i .e., tidal and freshwater intrusions) and landscape biological process es (i.e., primary production and foraging behavior) control migration of stenohaline fishes in the estuarine lagoon of Laguna de Terminos, M exico. A migration response matrix for temperature, salinity, food ava ilability, birth, and mortality was used to control cell-to-cell popul ation movements. Internal cell processes included logistic population growth, trophic interactions, and ecosystem feedback parameters. Outpu t data maps from the ROE model showed how population spatial distribut ions were linked to spatial and temporal patterns of water quality. Ho wever, the most significant parameter affecting long-term population s tability was birth rate; an internal cell variable. It was concluded t hat the simulation of large, density-dependent, spatial processes such as migration can be understood with a grid-based mechanistic ROE mode l because its rule-based design for movement allowed organisms to resp ond to ecological processes and adjust to changing environmental condi tions.