Aquaculture enclosures have typically prioritised ergonomic and economic requirements over concerns for fish welfare. Various integral farming practices, such as handling and crowding of fish stock, also have a high risk of evoking strong stress responses in fish and consequently impacting their welfare. As fish welfare becomes a priority for the salmon farming industry, improving rearing conditions for these fish is critical. Environmental enrichment (EE) is a proven avenue for improving the quality of life of farmed animals by helping captive animals to meet their physiological and behavioural needs. More specifically, structural enrichment (SE) provides this stimulus by adding novel structures / objects into the rearing environment resulting in additional physical complexity / heterogeneity. The benefits of using SE within terrestrial farming has been widely demonstrated, whereas the needs of aquatic farmed animals for such enrichment have comparatively been overlooked. There have indeed been studies on salmonids demonstrating the benefits of incorporating SE (including improved growth, survival, physiological stress responses, and fin conditions of farmed salmon). Previous studies have focused solely on juvenile salmon in freshwater farming, neglecting investigations into potential effects of SE in sea pens on farmed salmon welfare. This study aims to investigate the impact of SE, using kelp-based structures, on farmed Atlantic salmon welfare. Six commercial sea pens (n = 50–60,000 salmon) will be used , with 3 enriched with 2 ‘Kelprings’ (PVC and rope “lantern-like” structures covered in kelp) . The remaining three pens (i.e., unenriched/barren), serve as control samples. Following deployment of these Kelprings, 15-minute, bi-weekly video recordings will be captured systematically across all six pens (i.e., immediately following the first feed of every 14th day) over a three-month period. These recordings will be captured using feed cameras to ensure consistent, fixed POV recordings of the salmon behaviour. At the end of these three months, a putatively stressful event (grading) will be conducted on all salmon as part of the husbandry routines. In addition to behavioural analyses (including but not limited to Qualitative Behavioural Assessment [QBA]), fin / skin condition, growth, and mortality will be compared and assessed between enriched and unenriched pens. Expected outcomes are that salmon reared under structurally enriched sea cages will i) Have improved condition indices, and better fin / skin condition (owing to reduced conspecific aggression and abrasion against enclosure perimeters), ii) recover faster from stressful events (i.e., grading), and have shorter startle responses, iii) exhibit significantly more positive valence in their behavioural expressivity, as captured by QBA, iv) have improved mortality rates in the event of an intervention / significant disturbance. Principal Components Analysis (PCA) of the QBA scores will identify the perceived patterns of expressive characteristics across the video recordings of salmon behaviour, and reveal any potential dimensions of salmon expressivity. These components of the QBA scores will then be compared across the different treatments (enriched vs. unenriched salmon) The results from this study will provide insights into the potential benefits of structural enrichment for farmed salmon at the seawater rearing stage (with unique insights obtained from evaluating the emotional states through QBA) , which will be used to inform certification schemes on future welfare standards.