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Simple models which predict the dispersion and input of organic waste from cage fish farms can be used as management tools for the siting of farms and assessing the potential for enrichment of the benthic ecosystem. A modification of the sediment model originally described by Gowen et al. (1988) is presented. The modifications include: variation in bottom topography; changes in current speed with depth; correction of horizontal current flow in response to changing depth. Data from a fish farm in Chile are used to compare simulations of dispersion and sediment loading from the original and modified models.

Some forms of aquaculture cause significant impact on the natural environment and hence there is considered to be a need to control aquaculture developments. One approach would be to predict the impact prior to development and relate the predictions to predetermined standards. Predicting the otential for eutrophication requires the quantification of the amount of soluble waste being released from fish farms; use of numerical models to predict eutrophication in terms of enhanced phytoplankton biomass; establishment of environmental quality objectives and standards. This paper discusses the second and third requirements. Predictive models ranging from empirical relationships between variables to complex ecosystem models have been developed for managing eutrophication of lakes and coastal waters. The use of different types of model are discussed in the context of aquaculture development and it is concluded that empirical models should be used by regulatory authorities as a screening tool to provide a quantitative prediction of the potential for eutrophication. The establishment of environmental quality objectives and standards should be an integral part of any framework plan for aquaculture development. It is suggested that chlorophyll, rather than dissolved nutrients is a more appropriate variable to use as a standard for eutrophication associated with the growth of phytoplanton. It is concluded that there is a requirement for scientifically based values of standards to be set for coastal waters