The Institute of Aquaculture was commissioned by the Scottish Aquaculture Research Forum (SARF) to carry out a study on the “Technical Considerations of closed containment sea pen production for some life stages of salmonids”. The final report, for which the lead author was Dr Roy Clarke, was recently published on the SARF website. Closed containment sea pens replace the net of traditinal fish pens with an impermeable material which can either be flexible (plasticised fabric) or rigid (fibreglass or concrete). Pumps must then be used to ensure an adequate exchange of water to maintain fish health. An example of a commercial system (AgriMarine) is shown in the following video:

The study investigated the technical and economic use of a closed containment sea pen nursery system for production of larger (circa 1 kg) fish for stocking in conventional cage systems with a view to reducing the duration of the marine on-growing phase in conventional open cages. This modified production strategy would reduce the time of exposure to sea lice, allow the capture of some of the solid waste from the culture operation and potentially allow more efficient use of ongrowing sites as the rate of throughput in those sites could be substantially increased.

In the last 5 years or so, there has been considerable activity, mainly in Norway, concerning the development of novel marine aquaculture systems with a focus on reducing the environmental impact of marine fish farming and enabling marine aquaculture to move further offshore. The study reviewed the available systems and also worked with Scottish equipment providers on feasible concepts and their capital and operating costs. This particularly considered how closed containment systems could be integrated into current production patterns for both salmon and trout prodction and the potential benefits in terms of reducing the need for sea lice treatments and optimising use of biomass consent limits.

As an associated component of the project, MSc student Danielle Maitland considered options for capture and treatment of solid wastes from these systems. From an environmental perspective, this would be one of the major benefits of investing in closed containment.

In summary, a financial model was used to express the total additional costs to produce 1,000 g post-smolts which took account of capital depreciation costs and operating costs incurred in addition to the “normal” costs for a conventional system. On this basis, the total derived additional costs per post-smolt were between £1.59 and £2.48 per post –smolt. When expressed as a cost per kg of salmon sold, this is equivalent to an additional production cost of £0.37 to £0.57/kg.

The study was intended to support strategic analysis by both commercial companies and policy organisations with an interest in the future of the Scottish salmon industry.