Review and advancement of the marine biotic resource use metric in seafood LCAs: a case study of Norwegian salmon feed

Seafood life cycle assessment (LCA) studies have adopted the primary production required (PPR) indicator to account for the impact of these production systems (e.g., capture fisheries or aquaculture) on the ecosystems they harvest wild inputs from. However, there exists a large diversity in the application of methods to calculate PPR, and current practice often does not consider species- and ecosystem-specific factors. Here, we critically examine current practice and propose a refined method for applying the PPR metric in seafood LCAs. We surveyed seafood LCAs that quantify PPR, or its derivatives, to examine the diversity of practice. We then defined and applied a refined method to a case study of the average Norwegian salmon feed in 2012. This refined method incorporates species-specific fishmeal and oil yields, source ecosystem-specific transfer efficiencies and expresses results as a percentage of total ecosystem production that PPR represents. Results were compared to those using previously applied methods based on the literature review, and the impact of uncertainty and natural variability of key input parameters was also assessed using Monte Carlo simulation. From the literature review, most studies do not incorporate species-specific fishmeal and oil yields or ecosystem-specific transfer efficiencies when calculating PPR. Our proposed method, which incorporated source species- and ecosystem-specific values for these parameters, provides far greater resolution of PPR than when employing global average values. When alternative methods to calculate PPR were applied to marine inputs to Norwegian salmon feeds, resulting PPR values were similar for some sources of fishmeal and oil. For other species, such as Atlantic herring from ecosystems with low transfer efficiencies, there was a large divergence in resulting PPR values. For combined inputs to Norwegian salmon feeds in 2012, the refined method resulted in a total PPR value that is three times higher than would result using the currently standard method signaling that previous LCA research may have substantially underestimated the marine biotic impacts of fishery products. While there exists a great diversity of practice in the application of the PPR indicator in seafood LCA, the refined method should be adopted for future LCA studies to be more specific to the context of the study.