Assessing the Benefits and Challenges of Recirculating Aquaculture Systems (RAS) for Atlantic Salmon Production

Abstract

Land-based recirculating aquaculture systems (RAS) are used routinely for rearing juvenile Atlantic salmon in freshwater (to seawater-tolerant smolts). These systems potentially also offer a promising alternative to sea pen farming of Atlantic salmon in the drive to satisfy increasing global market demands and reduce pressures on marine fisheries and ecosystems. Several technological challenges need to be overcome and key knowledge gaps addressed to realize the potential of seawater RAS for post-smolt grow-out. Firstly, seawater RAS requires cost-effective technological solutions for maintaining the quality of recirculating seawater and treating and disposing of high-salinity wastewater. Technology within RAS also needs to cater for the different physiological requirements of distinct life stages of Atlantic salmon (from eggs to table-ready fish), to maximize fish welfare and growth, and to ensure high product quality. In this review we draw attention to interacting physical, chemical and biological components of RAS, which need to be managed systemically when optimizing and maintaining freshwater and seawater aquaculture systems. We then briefly review published local- to global-scale sustainability indicators, quantified through life-cycle analysis (LCA), to facilitate comparisons between lanf-based RAS and sea-based closed containment aquaculture systems. Existing ‘cradle to gate’ LCAs focus on production efficiency, energy consumption and carbon accounting, and call into question the sustainability of geographically extensive production of Atlantic salmon using RAS, for example in hot, dry climates. These LCAs, however, often do not account for major benefits of RAS, including reduced food miles (to market), the removal of direct environmental threats to farmed salmon (including from sea lice) and reciprocal risks to marine ecosystems from sea pen farming. We conclude that judgements on the efficiency and sustainability of RAS, compared to other farming methods, for upscaling Atlantic salmon production to meet rising global demands need to be assessed more holistically, adopting systems-wide approaches.

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