An integrated modelling approach for the stocking optimisation of a commercial-scale salmon-kelp IMTA system

Coastal Integrated Multi-Trophic Aquaculture (IMTA) systems, which combine the cultivation of extractive species like sugar kelp ( Saccharina latissima ) with fed species such as Atlantic salmon ( Salmo salar ), are often suggested as a way to diversify farm production and reduce environmental impact. However, commercial-scale IMTA faces challenges in synchronizing nutrient transfer and uptake between species, influenced by environmental and production factors. This study presents an integrated modelling approach to optimize stocking strategies in a commercial-scale salmon-kelp IMTA system located in Bantry Bay, Ireland. The modelling approach combines a salmon growth model, hydrography, and a re-parameterised Dynamic Energy Budget model for kelp growth. The study evaluates different stocking scenarios to assess their impact on nutrient cycling and biomass yields. Results from the simulations indicate that extending the kelp growing season considerably enhances kelp biomass yield and nitrogen assimilation, with the potential to mitigate up to 3.07 % of salmon-derived nitrogen waste under the scenarios investigated for this farm. The findings highlight the importance of timing in kelp stocking and suggest that early deployment could improve nutrient removal efficiency. This integrated modelling framework provides valuable insights for optimizing IMTA systems by improving species management and nutrient synchronisation at farm level. • Model suggests extended kelp season boosts yield, despite slow initial growth. • Model suggests early kelp stocking enhances nitrogen removal capacity. • Model suggests kelp timing, not salmon output, is key to IMTA optimisation at site.