Fattened in cages and shipped to Japan

The vast majority of the bluefin tuna caught by purse seiners in the Mediterranean are destined for fattening in cages, to supply a new market in Japan for a cheaper version of the highly valued maguro for sushi and sashimi.

The tuna are transferred directly from the purse seine net into the nets of a tug boat. The tug then tows the tuna to so-called tuna farms located in various places around the Mediterranean.

Life on the farm
The caged tuna are fed once a day on herring, sardines, anchovies, and squid. They are fattened in this way for 6-7 months, and sometimes up to two years. This maximizes the price for each fish: the greater the fat content, the greater the price on the Tokyo fish market.

However, this practice is not very efficient: 10-25kg of feed fish are needed to produce just 1kg of tuna. This has led to increased pressure on some feed fish stock, such as anchovies and sardinella.

Located not far offshore, the farms can also cause pollution of coastal habitats. Regulation has lagged behind this new industry, with many tuna farms operating illegally and flouting local laws.

Shipped to Japan
The majority of tuna caught in the Mediterranean end up on giant tuna-reefer vessels - industrial cargo vessels that deep-freeze the tuna onboard for shipment primarily to Japan. Farmed tuna are slaughtered and frozen after the fattening season (October to March). Some tuna are frozen directly after catching during the fishing season (May to July), while others are also air freighted to Japan fresh.