Life cycle assessment of sea lice treatments in Norwegian net pens with emphasis on the environmental tradeoffs of salmon aquaculture production systems

Abstract

The development of food production systems and the adoption of diets with lower environmental burdens are critical to mitigate the threats from climate change and the erosion of biodiversity and ecosystems. Many consider seafood to be a viable alternative source of animal protein to the most polluting types of ruminant production, such as cattle and sheep. Farmed salmon is a popular finfish providing an alternative to meat, appreciated for its taste, the quality of its proteins, and its sources of marine omega 3. Despite significantly lower life cycle impacts than most land-based animal production, the salmon aquaculture industry faces substantial environmental challenges. In Norway, large production volumes concentrated in open marine cages led to the chronic contaminations of coastal areas by viruses and parasites. This reduces production efficiency, fish welfare and threatens the stocks of wild salmon. Permanent sea lice infestations in net pens force farmers to use new delousing methods, exacerbating the situation. The Norwegian aquaculture industry is unable to increase its production output sustainably and finds itself at a crossroads. Farmers are investing in alternative land-based and sea-based aquaculture systems without a comprehensive understanding of the environmental tradeoffs involved.

This work intends to improve our understanding of the environmental strengths and weaknesses of salmon aquaculture systems. I used Life Cycle Assessment (LCA) in most of my research to account for environmental impacts generated through life cycles and value chains. First, I reviewed the salmon LCA literature and applied a simple parametric statistical protocol to compare the LCA results of different salmon systems across studies. Then, I conducted LCA of the biological, mechanical, and chemical lice treatments used by the Norwegian aquaculture industry. The rationale for this work was the recent transformation of the treatment mix and the exclusion of treatments' impacts from the LCA of net pen salmons. Finally, I used the LCA of warmwater fish RAS farming in Sweden from Bergman and colleagues and an innovative winter fallowing to control sea-lice infestations in net pens suggested by Stene and colleagues to discuss the tradeoffs and future of aquaculture systems in Norway.

Despite small data samples and multiple confounding factors, the cross-study statistical comparison was successful for some portions of the data. I demonstrate that (1) sea-based systems require significantly less energy than land-based systems, (2) land-based systems have a significantly lower feed conversion ratio than sea-based systems, and (3) closed systems likely have a significantly lower eutrophying potential than open systems. Norwegian farmers' current lice treatment mix adds significant life cycle impacts to net pen salmons, especially for the carbon, marine toxicity, and energy footprints. The main impact drivers are the increased salmon mortality, the fuel use from ships, the production of hydrogen peroxide, and the construction of mechanical treatment units. However, preliminary observations suggest that adding the treatment impacts to the life cycle impacts of net pen salmons will have a negligible effect on system comparisons. Regarding the LCA methodology itself, I argue in favor of more data reusability and interoperability using the lice treatments LCA to showcase the possibility of sharing openly human and machine-readable inventories while respecting confidentiality agreements. I also highlight the limitations of LCA for the comparison of aquaculture systems, particularly with regards to impacts on biodiversity, ecosystems, and fish welfare.

Finally, based on the current state of knowledge, I argue against the large-scale development of land-based, offshore, and closed sea-based systems envisioned by some stakeholders in Norway. I recommend testing nature’s strategy suggested by Stene and colleagues to mitigate sea lice challenges and improve the environmental profile of open sea-based systems. A low technology solution like this could allow the industry to increase its production output by keeping more fish in the cages alive.