Climate change and aquaculture: potential impacts, adaptation and mitigation

This document addresses the potential impacts of climatic change on the aquaculture sector and to a lesser extent the contribution of aquaculture to climate change. In order to achieve these objectives, the status of this subsector in relation to the total food fish supply, recent changes therein and other related aspects are analysed with a view to addressing potential adaptations and mitigation. Currently, the proportionate contribution of aquaculture to food fish consumption approximates 45 percent; this is also reflected in the increasing contribution of aquaculture to total fisheries figures recorded in the gross domestic product (GDP) of some of the main producing countries. Considering human population growth and stagnation in the growth of capture fisheries, it is expected that the supply of food fish from aquaculture will be required to increase even further to meet future demand for fish. Aquaculture is not practised evenly across the globe and to evaluate the potential impacts of climate change, the document analyses current aquaculture practices in relation to: three climatic regimes, vis-a-vis tropical, subtropical and temperate; in relation to environmental types vis-a-vis marine, fresh and brackish waters; and in relation to geographic divisions by continents. It is seen that aquaculture is predominant in tropical and subtropical climatic regions and geographically in the Asian region. Furthermore, the most cultured commodities are finfish, molluscs, crustaceans and sea weeds, but species that feed low down in the food chain predominate. The geographic and climatic concentration of aquaculture necessitates, for the time being, a focus on the development of adaptive strategies for addressing or mitigating climate change impacts in these regions, especially if the predicted gap between supply and demand for food fish Climate change implications for fisheries and aquaculture – Overview of current scientific knowledge 152 is to be realised through aquaculture. However, we cannot disregard the potential for aquaculture growth in other regions. The main elements of climate change that could potentially impact on aquaculture production – such as sea level and temperature rise, change in monsoonal rain patterns and extreme climatic events and water stress – are highlighted and the reasons for such impacts evaluated. By virtue of the fact that the different elements of climate change are likely to be manifested or experienced to varying degrees in different climatic zones, the direct impacts on aquaculture in the different zones are considered. For example, it is predicted that global warming and a consequent increase in water temperature could impact significantly and negatively on aquaculture in temperate zones because such increases could exceed the optimal temperature range of organisms currently cultured. Such impacts may be balanced with positive impacts that might occur as a result of climate change, such as enhanced growth and production in tropical and subtropical zones. However, positive impacts are unlikely to occur without some potential negative impacts arising from other climatic change elements (e.g. increased eutrophication in inland waters). In both instances possible adaptive measures for reducing or maximizing the impacts are considered. An attempt is also made to deal with the climatic change impacts on different culture systems, for example, inland and marine systems and different forms of culture practices such as cage culture. Furthermore, it is likely that diseases affecting aquaculture will increase both in incidence and impact. Nearly 65 percent of aquaculture production is inland and concentrated mostly in the tropical and subtropical regions of Asia. Climate change impacts as a result of global warming are likely to be small on aquaculture practises taking place in such systems and if at all positive, brought about by enhanced growth rates of cultured stocks. On the other hand, climate change will impact on water availability, weather patterns such as extreme rain events, and exacerbate eutrophication and stratification in static (lentic) waters. The influence of the former on aquaculture is difficult to project. Some adaptive measures related to the location of farms are discussed here. However, based on current practices, particularly with regard to inland finfish aquaculture that is predominantly based on species feeding low in the food chain, the greater availability of phytoplankton and zooplankton through eutrophication could possibly enhance production. On the other hand, in marine cage culture, adaptive measures will revolve around the introduction of improved technologies to withstand extreme weather events. Sea level rise and consequent increased salt water intrusion in the deltaic areas of the tropics where there is considerable aquaculture production is likely to occur. Adaptations to related impacts will involve the movement inland of some operations that culture species with limited saline tolerance. Equally, aquaculture is seen as an adaptive measure to provide alternative livelihood means for terrestrial farming activities that may be no longer possible and or cost effective due to sea water intrusion and frequent coastal flooding. One of the most important, though indirect, impacts of climate change on aquaculture is considered to be brought about by limitations on fishmeal and fish oil availability (for fish feeds) as a result of a reduction in raw material supplies. Other types of raw materials might also be affected. The negative impacts are likely to be felt mostly in the temperate regions where the finfish aquaculture is based entirely on carnivorous species. Adaptive measures to counteract these impacts are suggested. The ecological cost of different aquaculture species and systems, as opposed to other sources of animal protein production, is presented and the indirect contribution to carbon emissions is considered. As a mitigation measure to curtail the contribution of aquaculture to carbon emissions, it is suggested that the consumer is made aware of the carbon emissions associated with various products, in the same way that traceability is indicated. In this context, it is demonstrated that on the whole aquaculture is less energy costly and could contribute to carbon sequestration more than other terrestrial farming