The warning was made as the Mediterranean’s oversized fishing fleets embarked on Wednesday at the beginning of a two-month fishing season.
Increased demand for the fish in Japan has triggered an explosion in the size of the Mediterranean fleet, with many of the boats using illegal spotter planes to guide them to the warm-water tuna.
Pirate fishing vessels also hunt the bluefin, whose dried, dark red meat once fed Roman armies.
“Whichever way you look at it, the Mediterranean bluefin tuna collapse trend is dramatic, it is alarming and it is happening now,” said Sergi Tudela, Head of Fisheries at WWF Mediterranean.
WWF is calling for the immediate closure of the Mediterranean bluefin tuna fishery to give the species a chance to recover.
The group points to catches in 2007 that were only a quarter of the levels 50 years ago, with most of the decline happening in recent years.
WWF also says the average sizes of the mature tunas caught off the coast of North Africa has been cut in half since the 1990s. Before the growth of large-scale industrial fishing, individual tunas sometimes weighed in at nearly 2,000 pounds (900kg).
The loss of these giant tunas -- able to produce many more offspring than medium-sized individuals -- is a sign that the reproductive capacity of the species is greatly reduced, WWF says.