Mediterranean fishing is largely artisanal, but the world's first large-scale industrial fishery was in fact born here -- coastal trapping of bluefin tuna, practiced not only in Sicily but also in places like Algeria, Croatia, France, Libya, Morocco and Spain for over a thousand years.

This traditional fishery began to decline in the 1960s, and now the traps have mostly been replaced by purse seiners and longliners, which represent the only true industrial fishing fleet on the Sea.

Catches of the high-value, far-ranging bluefin reached a high point of 39 000 tonnes in 1994, but by 2002 dropped by nearly half that amount, to 22 000 tonnes.

Today, they only make up around three percent of the total catch in the Mediterranean, though their economic importance is disproportionately high, due to overseas demand.

The largest driver of that demand is the sushi and sashimi market in Japan, which prizes the tunas' belly meat. There, a single large adult bluefin tuna can sell for US$50 000 or more.

The United States is another important destination, with annual demand for bluefin tuna running around 24 000 tonnes -- more than an entire year's catch in the Mediterranean.

"Sea ranching" a cause for concern

Adding to the pressures on bluefin tuna are captures of juvenile fish used as "seed stock" in tuna-fattening operations.

Also known sea-ranching or captured-based aquaculture (CBA), this is a practice in which tuna are caught in the wild and then penned and fattened using aquaculture techniques prior to harvesting.

FAO estimates that production of bluefin tuna via CBA currently runs around 25 000 tons a year, up from 10 000 tonnes just five years ago. Production is primarily concentrated in Croatia, Malta, Spain and Turkey.

According to the most recent edition of FAO's flagship report on fisheries, The State of World Fisheries and Aquaculture (SOFIA), CBA of bluefin tuna raises some serious concerns, as it has opened new markets and is putting increased pressure on the stock.

At the same time, captures of "seed stock" may be going unreported, handicapping efforts to assess the stocks' status.

Additionally, FAO has stressed the need to develop manufactured feeds for penned fish, rather than using imported raw fish.