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Sustainable Aquaculture Magazine - December 2017

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19 Background Atlantic bluefin (Thunnus thynnus) are the tuna species with the biggest commercial interest to fishermen and farmers in Europe. They are found in the Atlantic, the Mediterranean and the North Sea and can grow up to 700kg. They are highly valued in both local and over- seas sashimi markets, fetching on average €20 to €50 per kilogram. However, this demand, combined with the industrialisation of Europe's fishing fleet over the course of the 20th century, has resulted in a history of severe overfishing. By the early 2000s, it was thought that the stock size had been reduced to such a low level that a total collapse was a realistic possibility. As tuna-fishing operators looked to increase profitabil- ity by adding more value and volume to their catches, the tuna-fattening sector started to develop. Since then a number of purse seine vessels have focused on the capture of live tuna to on-grow in captivity. These purse seiners mostly target young-adult and mature tuna that are carefully caught and towed back to fattening farms. Upon arrival, the tuna are transferred to large floating cages where they are fattened to attain a more mar- ketable size and to improve the fat percentage of the meat. Currently there are 54 companies with total farm- ing capacity of 53,606 tonnes per annum involved in the fattening of Atlantic bluefin tuna (ABT) in the Med- iterranean and these account for the vast majority of tuna aquaculture output. A number of NGOs and consumers have expressed their concerns about these operations. Because it is difficult to train adult to tuna to eat pelleted feeds, the on-growers use locally caught fresh fish as feed. This process has a very low feed-conversion ratio (FCR), "By the early 2000s, it was thought that the stock size had been reduced to such a low level that a total collapse was a realistic possibility" First hatchery-produced Atlantic bluefin tuna sold in the Netherlands - hatched by IEO in Spain, farmed by Ricardo Fuentes and eventually sold to sustainable seafood trader Jan van As in 2014 ©Jan van As

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