The use of mathematical models by the regulator to support the setting of licenses of marine discharges from the cage fish farm industry

The Scottish Environment Protection Agency (SEPA) is the environmental regulator in Scotland responsible for licensing all discharges to controlled waters, which includes coastal waters. For marine aquaculture, which is principally based on Atlantic salmon (Salmo salar) raised in cages, this translates into a license for the discharge of waste feed and feces (set as a maximum stock biomass limit) and mass of chemotherapeutant used for disease control. To support SEPA in setting these licenses a methodology has been developed through which mathematical models can be used to advise on limits for consent applications. The regulatory framework requires calculation of consent parameters on a site-specific basis. These cover the major chemical therapeutants, both those released in a dissolved and in a solid phase, and may be extended to cover benthic impacts of biomass. To facilitate this, SEPA has developed suitable modeling standards in tandem with practical predictive models, which can be run on the limited site-specific data and information normally available. The paper outlines the Scottish regulatory framework, thinking behind SEPA's philosophy, types of models and standards developed, and looks at the advantages and disadvantages of the system for both the regulator and fish farmer. Finally, the way forward for future development is investigated including the options of moving further offshore and thus reducing impact in the coastal zone, or the greater use of technology to reduce emissions and waste entering the environment.