RAS vs Net Pen Salmon Farming: Comparing Welfare Outcomes

Land-based recirculating aquaculture systems (RAS) and open sea net pens represent contrasting approaches to salmon farming, each with distinct welfare implications.

Key Facts

Norway produces approximately 1.5 million tonnes of Atlantic salmon annually, mostly in open sea net pens; RAS production is growing globally.
Sea lice (Lepeophtheirus salmonis) infestations in net pen salmon cause chronic skin lesions, feeding impairment, and significant mortality — estimated at over 50 million fish annually in Norway.
RAS eliminates sea lice exposure by isolating fish from open water but introduces chronic stress from high water recirculation noise and artificial environments.
Stocking densities in RAS can exceed 80 kg/m³, while Norwegian regulations limit net pens to 25 kg/m³.
RAS water quality management reduces antibiotic use significantly; net pen operations contribute to antibiotic resistance in marine environments.
Transport and pre-slaughter handling stress, acute in both systems, is a key welfare bottleneck common to all salmon farming methods.

Welfare Considerations

Both RAS and net pen systems impose welfare costs, but their nature differs significantly. Net pen salmon face endemic parasite pressure from sea lice, unpredictable storm damage, escape risks, and wild predator stress. RAS salmon face chronic sensory stress from artificial environments, high noise, and potentially greater crowding. Neither system provides conditions remotely resembling natural salmon habitats of rivers and oceans. Welfare researchers argue that the choice between systems should be guided by welfare outcome data rather than environmental considerations alone. Current evidence suggests sea lice in net pens represent a more acute welfare problem than RAS noise, but RAS technology is rapidly evolving and welfare data are still emerging.

What You Can Do

Support research funding for welfare indicators in both RAS and net pen systems, enabling evidence-based comparisons.
Choose salmon certified under welfare-inclusive schemes where available, or reduce salmon consumption overall.
Advocate for mandatory welfare monitoring and reporting for all commercial salmon farming operations.
Support policies that phase out the most harmful net pen practices, such as chemical sea lice treatments with documented non-target impacts.
Follow and share research from institutions like the Institute of Marine Research (Norway) on salmon welfare science.