A comparison between far-field and near-field dispersion modelling of fish farm particulate wastes

An important consideration in the design of fish farms is the fate of the resultant particulate wastes. Consequently, this study is aimed at investigating the validity of an existing near-field regulatory model that assesses the fate of particulate wastes arising from fish farms. The results from the near-field regulatory model have been compared with those from a far-field model to assess the implications of the near-field model focusing on a 1km-by-1km area around the fish farm and ignoring any cumulative impacts of other fish farms in the area. The study has been undertaken at a site located on the west coast of Scotland encompassing Loch Shuna and Loch Melfort, which contain eight fish farms. The far-field dispersion modelling was undertaken using a layered three-dimensional tidal model with a coupled dispersion module. This study has demonstrated a number of benefits through using a far-field model to simulate particulate waste dispersion resulting from fish farms as opposed to using a near-field model. The far-field model accounts for the spatial variability in tidal currents, which can be important in coastal areas; it also allows the impacts of multiple fish farms operating in combination to be assessed over a larger area. In addition, it was found that compared with the far-field modelling, the near-field modelling has the potential to underestimate the benthic impacts of fish farms.