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72 million square kilometres. That is the size of the world’s oceans within the exclusive economic zones estimated to be environmentally suitable to farm fish and shellfish. The estimate, based on several parameters such as temperature, dissolved oxygen concentration, productivity and salinity, is the result of a study conducted by centre researcher Max Troell and colleagues from the University of British Columbia, Canada.
The study, published in PLOS One, shows that since most ocean-based mariculture operations are exposed to natural environmental conditions, the physical and chemical properties of the waters affect growth and survival, and consequently, the potential for mariculture expansion.
Despite the rather specific estimate, the researchers add caution to interpretation of the results. "Technological, social, financial, ecological and resource availability are all factors constraining future expansion of the aquaculture industry," Troell explains.
Marine farming has since the 1980s steadily expanded but growth rate has slowed down slightly over the past ten years. Ocean areas with environmentally suitable conditions for mariculture remain much larger than areas in which it is currently practised.
This is particularly evident in Africa, the Caribbean and along the Atlantic coast of South America. These regions have been identified as suitable hotspots for expansion of many mariculture species, yet total mariculture operations account for only 1,3% of global production.
“Some reasons for this gap relate to poor economic conditions, lack of supporting infrastructure, political instability, limited foreign investment and inadequate value chain linkages, ”Troell explains. Other notable areas where conditions are good included the Gulf of Mexico, the Caribbean Sea, the East China Sea, the Yellow Sea, the Sea of Japan and the Banda See off the coast of Timor-Leste.
Concerns regarding the environmental sustainability of mariculture also play an important part in explaining why the business has not expanded. Particularly, if expansion of farming marine carnivorous species further increases the demand for fish resources in feeds it could result in further stress on fish stocks and marine ecosystems. But there are promising progress being made, including development of alternative and innovative feed ingredients and more efficient and affordable technologies. Troell adds ”Many seafood outcompete livestock in terms of environmental impacts, and this creates incentives for further expansion of the aquaculture industry.
But Troell and his colleagues also argue that future studies need to become more detailed when identifying suitable areas for mariculture, accounting for pollution, expansion of other marine activities and effects from climate change.
The researchers obtained a list of farmed species from the Sea Around Us mariculture database (SAU). The database is derived largely from the Food and Agricultural Organisation (FAO) database, with augmented information from national statistics to subdivide annual mariculture production by sub-national units (e.g., provinces, states), in addition to countries and taxa, for the period 1950 to 2010. They extracted the species’ names of all fish and invertebrates reported in the database (307 in total). Records that are not reported at the species level (i.e., with genus and species specified) were excluded from the analysis. Following the minimum occurrence data requirements for species distribution models, they only retained species that occurred in more than seven sub-national units. This is to ensure a greater model accuracy with higher numbers of occurrence locations. Environmental parameters included: temperature, dissolved oxygen concentration, chlorophyll-a concentration, salinity, pH, silicate concentration, current velocity and euphotic depth.
Max Troell is a system ecologist mainly working with environmental problems associated with aquaculture. This work focuses on inter-linkages between aquaculture and fisheries, on different spatial scales.
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