Photo credit with caption: Greenpeace
Additional review: Abdel Rahman El Gamal (Founder of the website)
This photo shows a tug towing a tuna cage between fishing grounds in Libya and tuna farms in Sicily, Italy.
It may worth adding that the fattening of Bluefin tuna in Italy started in 2001 by a 4-cage farm located in Sicily, the number of farms and cages increased afterwards. In tuna fattening, captured Bluefin, go through fattening in large floating cages with a diameter of 50 m and 25 m depth.
Caged tuna are fed with herring, sardines, anchovies, mackerel and squid for 3 to 8 months. Depending on the water temperature the fish are fed 5 to 8% of the estimated body weight/day. This feeding system is extremely inefficient as about 20 to 25 kg of fish is required to add a kilogram weight to the caged tuna. In addition to the increase of tuna weight during the fattening, the increase of their fat content is targeted to allow for better price in commercial tuna markets, especially the Sushi Market in Japan.
Tuna fattening is certainly an important fishery activity throughout various activities including capturing the tuna required for fattening, transporting the captured tuna to fattening cages, capturing the fish needed to feed tuna and move the harvest to tuna markets. However, most of mentioned activities raise negative images which could be summarized in the possible depletion of juvenile tuna population, draining the seas of fish used as tuna food. Moreover, the excess feed and feces of caged tuna are polluting the near shore waters.
In conclusion, the sustainability of tuna fattening in cages will depend on the availability of economically sound methods of hatchery production to avoid the use of wild-caught juveniles. Equally important, is the improvement in artificial feed formulation to eliminate or reduce baitfish consumption.