Greenhouse gas emissions from aquaculture: a life cycle assessment of three Asian systems.
The rapid growth and development of global aquaculture has raised questions regarding the potential associated greenhouse gas (GHG) emissions. To gauge the scale of GHG emission in Asia, where growth has been greatest, a preliminary study was carried out on three aquaculture systems: Nile tilapia (Oreochromis niloticus) in Bangladesh, Indian major carps (Catla catla, Cirrhinus cirrhosus, Labeo calbasu, Labeo rohita) in India, and striped catfish (Pangasianodon hypophthalmus) in Viet Nam. The analysis was intended to improve understanding of where and how GHG emissions arise in Asian aquaculture, and highlight weaknesses in the currently available data. This approach will guide future studies on how to develop cost-effective ways of improving aquaculture performance and reducing emissions, and how to improve data collection. Primary data were collected from April to June 2014, using questionnaires to guide interviews at 5 or 6 feed mills and 10-12 farms per country. The units covered a range of approaches to feed manufacture and farming, to demonstrate the different methods used in each of the three aquaculture systems. Secondary data was used to determine the related GHG emissions from cradle to farm-gate. For each of the three systems, life cycle assessment models were prepared, from pre-farm, through the farming system, to harvest. The models were not continued to market, as so many different markets were found that it was not feasible to make a representation. Output from the models showed distinct differences in the emissions associated with the three systems. The striped catfish system in Viet Nam had the lowest emissions (1.37 kg CO2e/kg live weight fish), followed by the Nile tilapia in Bangladesh (1.58 kg CO2e/kg live weight fish), and Indian major carps in India having the highest emissions (1.84 kg CO2e/kg live weight fish), when excluding emissions from land use change. Although the ranking remained the same, the magnitude of emissions increased in all three systems, when including land use change in the model. The production of feed was the largest source of GHG emissions for all three systems, being mainly associated with the production of the raw materials. Transport of the raw materials to the mills, and of feed from the mills to the fish farms, were also significant sources of GHG emissions. There were differences in feed mill energy requirements between countries, possibly reflecting variation in technology applications and efficiencies. High economic feed conversion ratios (eFCRs) exacerbated the impact of feed on GHG emissions, as more feed was required to produce one kilogram of fish. In particular, the Indian major carps showed high FCRs (1.0-5.0); the FCRs for striped catfish in Viet Nam and for Nile tilapia in Bangladesh were low (1.6-1.9 and 1.1-2.0 respectively). The study highlighted a recent increase in the use of commercial feed in Bangladesh and India, reducing the FCRs. Farming systems in the different countries required varying quantities of energy, reflecting the relative need for pumping to exchange water in the ponds, and other energy requirements on the farms, such as lighting and transport. The report highlights the variation within every stage of production in each of the three aquaculture systems in Asia: raw materials used, energy use in the mills, transport methods for moving the feed to the farm, farming methods, survival of fish to harvest, and feed conversion ratios. The magnitude of this variation, in India and Bangladesh in particular, showed that significant work is needed to communicate and execute better feed formulation and farming practices. The report recommends methods which could reduce emission intensities related to the farming systems. Applying best practices uniformly on farms, and thus increasing efficiencies, appear to be major factors needing improvement.