Improving understanding of fish farm organic waste dispersal in higher energy environments

Organic waste from open cage fish farms can negatively impact the benthos if the quantities of settling material exceed the natural assimilative capacity of the seabed. The amounts of total organic material which are allowed to be released are thus regulated in most countries where open-cage fish farming takes place. In Scotland, limits on settling organic waste are one of the main factors determining the maximum fish biomass permitted at a farm site. Computer models of the dispersal of total organic waste to the seabed have become an important tool in both initial site licencing, but also continued site monitoring. Introduction to Executive Summary:The main organic waste dispersal model used in Scotland is DEPOMOD. Originally developed in the late 1990s this model has gone through several upgrades, the latest version being NewDEPOMOD. The original model was developed and calibrated for relatively sheltered, low dispersal sea-loch sites with muddy seabed, where the model’s predictive capability has proven to be generally high. However, many newer fish farms have been developed in more dispersive sites. Despite NewDEPOMOD incorporating a relatively sophisticated waste resuspension sub-model, problems have been encountered with accurately predicting the benthic footprint of fish farm organic waste at these more dispersive sites. The main aim of the INCREASE project was to try and improve our understanding of why these predictive problems are occurring and to suggest future work to address any issues identified.