Sea lice management measures for farmed Atlantic salmon (Salmo salar) in Scotland: Costs and effectiveness

Cultured and wild Atlantic salmon around the world are affected by sea lice. Salmon culturing countries have policies in place to minimize sea lice abundance on cultured salmon in open net pens in the marine environment. To adhere to these policies, salmon producers deploy a range of management measures against sea lice throughout the production cycle. The cost effectiveness of these sea lice management measures is not well quantified. This study provides estimates for cost effectiveness in Scotland of (1) individual sea lice management measures and (2) integrated management strategies that span an entire production cycle. Estimates were based on the cost-effectiveness ratio, in which costs consist of those associated with equipment, implementation, environment and side effects (mortality). Effectiveness was based on interviews and expert opinions. For single measures, skirts and the use of in-feed medicines had the best cost-effectiveness. Cleaner fish, fresh or brackish water baths, the physical removal measures (thermolicer and hydrolicer) and medicinal baths were among the next most cost-effective measures, followed by hydrogen peroxide baths. Tarpaulins were more cost-effective than well boats due to lower costs under the assumption of equal effectiveness. Direct comparison of cost effectiveness among measures may not always be constructive as they are deployed at different times in the production cycle and their functionality is different. A holistic approach to sea lice management, a common practice in industry as shown by the integrated management strategies, may reduce risk of developing resistance. For the single measures, carbon costs were insignificant compared to other costs. If measures would have a lasting effect on production through to harvest, such as ongoing increased mortality as a result of a management measure, carbon costs may become significant. Better quantification of effectiveness is important because the scarcity of data led to uncertainty that had a large impact on cost-effectiveness estimates. Generally, this study demonstrated a lack of reliable publicly available data and lack of standardization of data, which constrains research. Highlighted gaps in knowledge can serve as a guide to improve further understanding.