This paper was published in the March 2021 edition of International Aquafeed
The ability to evaluate the environmental impact of different aquaculture production systems is key towards building a stronger global food system combining social, environmental and economic aspects of sustainability.
Nutrition should remain the cornerstone of strategic thinking as the challenge is to assure a global population the required intakes in terms of vitamins, minerals, amino acids and fatty acids. As the science and the industry are already working hand in hand, providing clear guidance to the industry about fishery management and fish stocks assessment, it is important that nutrition be considered as a much-needed science, as we know that human nutrition gaps can lead to widespread negative health consequences. The current gap of EPA/DHA, among others, shouldn’t be overlooked. A recent paper from Helen Hamilton et al. [Hamilton et al., 2020. Systems approach to quantify the global omega-3 fatty acid cycle. Nature Food] highlighted that the current human nutritional supply is estimated to be only 30% of the demand.
Aquaculture has been the fastest growing protein sector for many years, with an average annual expansion rate comprised between 6 and 8%, making it a key contributor to food security. In 2015, the contribution of farmed species to seafood surpassed the one of wild-caught fish for the first time. The global aquaculture sector is already valued at $243.5 billion (2019) and may take about $150 billion to $300 billion in investments and capital alone to meet the demand for seafood by 2030 (Towards a Blue Revolution from The Nature Conservancy and Encourage Capital, 2019).
The production of the non-fed aquaculture species (seaweeds and other aquatic plants in marine and freshwater systems; bivalve molluscs such as mussels, oysters and abalone; some species of freshwater crayfish, and some freshwater finfish species) keeps increasing but is being exceeded by the rate of growth of the fed species (such as salmon, shrimps, trout, seabass). Fed aquaculture products are growing in popularity and are driving the demand.
These considerations have their importance when it comes to assessing the environmental impacts of aquaculture. An interesting research paper in Nature [MacLeod, M.J., Hasan, M.R., Robb, D.H.F. et al. Quantifying greenhouse gas emissions from global aquaculture. Sci Rep 10, 11679 (2020)] focuses on greenhouse gas emissions across aquaculture systems globally. It finds that “global aquaculture accounted for approximately 0.49% of anthropogenic GHG emissions in 2017, which is similar in magnitude to the emissions from sheep production. The modest emissions reflect the low emissions intensity of aquaculture, compared to terrestrial livestock (in particular cattle, sheep and goats)”.
This doesn’t come as a surprise when we know that fish have the ability to convert a greater proportion of the protein and energy they receive from feed and turn it into human food than what terrestrial livestock can. Therefore, their contribution to food security is high. This also contributes to making fish a sustainable resource to be used in the production of marine ingredients. Fish has some very clear advantages as “livestock”. They live in water, so they are weightless and don´t have to use energy on standing upright. They therefore don´t need a strong and heavy bone structure. Fish also burn carbohydrates more efficiently that land animals. They are cold-blooded so they don´t use energy to uphold a high and stable body temperature. Finally, fish has a very effective reproduction. A fertile female salmon can produce between 6 - 10 000 salmon fry. The energy consumption to reproduce is therefore very low compared with land animals like pork, chicken or cows.
If we compare the energy “yield” to produce the edible parts of salmon with land animals like pork and chicken, salmon comes out on top. The energy retention (the part of the energy from the feed we find in the edible part of the animal produced) is 23% for salmon. The number for pork is 14% and for chicken it´s 10 %. So, we get around double the amount of food from salmon as we do from pork and chicken per unit feed we use in production (source: Global Salmon Initiative, Sustainability report 2019).
Diving into some more detailed findings of MacLeod et al.’s “Quantifying greenhouse gas emissions from global aquaculture” report, it is interesting to note that sources of GHG emissions differ depending on fish species. The authors explain that “species predominantly reared in Asia (i.e., Indian major carps, freshwater catfishes and cyprinids) have higher rice methane (CH4) emissions, while the carnivorous salmonids have more emissions associated with fishmeal and higher crop land use change (LUC) emissions (arising from soybean production), reflecting their higher protein rations”.
This study provides valuable insights into understanding what it takes to feed a population with protein. Every food production system generates impacts and a step-by-step approach can help understand where strategic thinking is needed to improve current processes in relation to water aeration, pumping, etc) or feed combinations.