Tropical pond-based aquaculture fulfils an essential role in the global food and food system as the main production system for popular species such as carps, catfish and shrimp. Aquaculture products are recognized as a relatively low impact animal protein source. Various actors in the seafood industry are embracing the adoption of LCA. However due to a lack of standardization and guidelines there is a risk of divergent LCA’s with differing results potentially leading to confusion for consumers.
The interest of the industry has led to several studies as well as the development of LCA tools for aquaculture production. As standardization and guidance from the PEFCR and FAO LEAP are lacking this has led to development of the underlying methods through engagement with industry, NGO’s, academia, and government organizations. One of the main issues has been the direct and indirect greenhouse gas (GHG) emissions from tropical aquaculture ponds, the main GHGs from tropical aquaculture ponds are Nitrous oxide and methane. The inclusion of these GHG emissions is necessary to be included for consistency and completeness as the GHG emissions associated with terrestrial livestock products is commonly included. In this presentation we present the current state of the emission modelling approach and identify the primary gaps for further research.
Because of the complex interactions of feed, excretion and the food web in aquaculture ponds it is not feasible to use a fate-based model based on the digestion of the animal as proposed in the first version for public consultation of the PEFCR for marine fish when dealing with tropical pond systems . Therefore, a mass balance approach was applied for emissions of nutrients to water.
Direct N2O emissions within the aquaculture pomds were based on the volatilization of surplus nitrogen in the water as by-products of nitrification and denitrification processes within the pond, using the conversion rate of surplus N to N2O: 0.71%. For indirect emissions of N2O due to nitrogen released as dissolved inorganics or particulate matter into the environment a conversion factor of 1% was used. Methane emissions could have a significant contribution to the total footprint of tropical aquaculture and have been been included based on the IPCC wetlands guidance.
The current state of the emission methodology provides an indication that the contribution of the direct GHG emissions lies in the order of 10-30% of the total footprint of tropical aquaculture production. The current methodology can capture the effects of basic farm management practices such as feed protein content, FCR and productivity allowing producers to improve their footprint. However, many management practices that could influence the GHG emissions cannot be reflected in this emission model. Further research is needed to provide insight into all the factors that influence GHG emissions. This requires more direct measurements of the flows of GHGs and the relation of these emissions to pond management.