Primary drivers for cage culture and their relevance for African cage culture

摘要

Although the use of cages for holding and transporting fish for short periods is historic particularly in China, the development of modern cage culture for food production and ornamental purposes has evolved substantially in recent decades only, bothin systems design and impact on total aquaculture production. This paper explores key drivers that have influenced cage culture in Europe and elsewhere to draw on lessons that may be of relevance to African cage culture development. Conservative estimates suggest that around 3 million tonnes of fish are produced in cages notably in coastal environments, in Europe, the Americas and Asia. The drivers for the rapid uptake of cage culture have been largely technical, market driven and species' dependent, whereas the drivers affecting recent change to continued expansion and management are largely regulatory, both of which may have direct relevance for emerging cage farming in Africa. The direction and emphasis for African countries may depend on whether the products are intended for domestic or international markets. The widespread uptake of cage farming has been driven by its relatively low cost compared with land based systems, versatility of material use and construction and perhaps more importantly easier access to open waterbodies. The flexibility and adaptability of cages for culture have enabled cages to be used for all stages of the product flow from breeding and seed production to final production for consumption. In addition to markets, the expansion of the subsector and its impact on production, however, has been primarily driven and facilitated by research and development in and assured availability of high quality of seed and feed, both of which are current constraints in sub-Saharan Africa, A modest 100 tonnes tilapia unit requires around half million fry and 150-200 tonnes of pelleted feed. Therefore, for any meaningful sectoral cage culture development in Africa priority should be given to addressing these drivers. Although set-up capital costs may be lower than land based operations, capital and operational costs can be high and therefore access to finances will also have to be considered. Market forces have also been prominent in steering changes in cage farming. Decline in prices, traceability, biosecurity and public pressure have necessitated management changes and such lessons may be relevant to African countries. The rapid expansion phase of cage culture in Europe and the Americas has been recently tempered by the potential forthe nutrient inputs to approach the carrying capacity of enclosed or partially enclosed farmed waterbodies. More recently in Europe, the new EU Water Directive aims to harmonize environmental regulations across the EU with respect to water quality standards, and may require the industry to adapt to enable future expansion. Lessons from these and other initiatives will be relevant to Africa. Whilst such emerging regulatory frameworks will vary for coastal and inland waterbodies, the primary drivers in each environment type will be influenced by competition for water by multiple users, selection of and benchmark tolerance levels set for indicators, skills and organization of environmental groups in influencing these processes. The infancy of cage farming in Africa does provide an ideal opportunity for countries to establish realistic baseline indices and indicators to facilitate and promote well-planned cage farm sites and management practices both in inland and coastal waters.