Setting Carrying Capacity limits

Site specific capacity thresholds are determined through the licensing process, where benthic impact modelling (AutoDEPOMOD) is used to set peak biomass thresholds on the basis of predicted impacts on seabed infaunal diversity. The development consent process (planning consent administered by Local Authority also considers a number of other environmental impacts through Environmental Impact Assessment) may limit site specific biomass on the basis of expected environmental impacts or the ability of a site to use (discharge) medicines to treat pathogen infections.

At a water body level (sea lochs), simple models are employed to predict a precautionary threshold for assimilative capacity based on the predicted nutrient enhancement and benthic impacts arising from cumulative discharges from multiple developments in the water body. The models used and the framework in which the outputs are used are explained in the referenced report.6 These are simple precautionary models able to be used across all 100+ sea lochs that support aquaculture in Scottish waters (Figure 4).

Efforts to produce more sophisticated estimates of assimilative carrying capacity have been made and complex multilayer coupled physical biological models have been developed to improve estimates of assimilative capacity at a water body level, but application of these in a robust way across multiple water bodies requires extensive forcing data and significant effort and expense. It is hoped future efforts will improve estimates, but for the time being, monitoring data suggest the current regime is sufficiently precautionary to prevent eutrophication effects arising from cumulative discharges from marine finfish aquaculture.