The study released Tuesday by the International Union for Conservation of Nature says almost half of the species of sharks and rays in the Mediterranean and at least 12 species of bony fish are threatened with extinction due to overfishing, pollution and the loss of habitat.
Commercial catches of bluefin tuna, sea bass, hake and dusky grouper are particularly threatened, said the study by the Swiss-based IUCN, an environmental network of 1,000 groups in 160 nations.
"The Mediterranean and eastern Atlantic population of the Atlantic bluefin tuna is of particular concern," said Kent Carpenter, IUCN's global marine species assessment coordinator.
He cited a steep drop in the giant fish's reproductive capacity due to four decades of intensive overfishing. Japanese diners consume 80 percent of the Atlantic and Pacific bluefins caught and the two tuna species are especially prized by sushi lovers.
In January, a 754-pound (342-kilogram) bluefin tuna fetched a record 32.49 million yen, or nearly $396,000, in Tokyo at the world's largest wholesale fish market — about $526 per pound ($1,157 per kilogram).
Fishing in the Mediterranean is regulated by U.N. treaties, the European Union and separate laws among the 21 nations that border the sea.
Last November, the International Commission for the Conservation of Atlantic Tunas voted to cut the bluefin fishing quota in the eastern Atlantic and Mediterranean from 13,500 to 12,900 metric tons annually — about a 4 percent reduction. It also agreed to improve enforcement of quotas on bluefin.
Environmental groups, however, wanted bluefin fishing slashed or suspended and were upset with the limited action.
The IUCN study, which began in 2007 and included 25 marine scientists, is the first time the group has tried to assess native marine fish species in an entire sea.
The study blames the use of highly effective trawlers and driftnets for the incidental capture and killing of hundreds of marine animals with no commercial value. But it also concluded there's not enough information to properly assess almost one-third of the Mediterranean's fish.
"Even though marine resources in the Mediterranean Sea have been exploited for thousands of years and are relatively well studied, the data deficient group may in fact include a large proportion of threatened fishes," the study said, calling for more research.
The U.N. Food and Agriculture Organization says fish stocks continue to dwindle globally despite increasing efforts to regulate catches and stop overfishing