WWF scientists hope to work with traditional Spanish fishermen, who have seen catches fall by more than 80 per cent in the past 20 years.
The World Wildlife Fund has resumed its bluefin tuna tagging project to map fish migration in the Mediterranean off northern Spain.
Al Jazeera's Nick Clark joins an expedition led by scientists and environmentalists who say the bluefin tuna could effectively disappear by 2012 if there is no change to current mismanagement and overfishing.
For thousands of years, fishing boats across the Mediterranean have put out to sea, working rich and abundant waters. At one time, the bluefin tuna was so plentiful that it fed the Roman legions.
But not any more - the Mediterranean bluefin tuna has been so overfished in recent times that the breeding stock is on the verge of collapse.
"The bluefin is being fished beyond all viable limits," says Pablo Cermeno, team leader of the World Wildlife Fund's sea-going research unit.
"The numbers are shocking - we're on the verge of disaster."
Cermeno and a team of marine biologists and tuna specialists are aboard the yacht Columbus as it embarks on the tuna trail, an ambitious tagging programme designed to reveal more about a fish thought to migrate thousands of kilometres across oceans.
On one of its expeditions, the Columbus headed to sea out of Roses port on the Catalan coast of Spain.
Tagging the bluefin
Sixteen kilometres off shore, hooked lures are cast into the sea. After many fruitless hours, the Columbus heads across the wide expanse toward a frenzied flock of gulls darting into the waves.
|The Columbus has been tagging bluefin tuna 16km off the coast of Spain [Courtesy: WWF]
Suddenly, we see the hallmark boiling swirl of feeding tuna and the gold bullion of the ocean is hooked.
A juvenile bluefin - a glistening, writhing torpedo of sheer muscle - weighing some 30kg is hauled on board.
The eyes are covered to calm the fish and quickly an incision is made into its belly. The tracker tag is inserted, the wound stitched and the bluefin returned to the sea, where it quickly recovers.
"The tag is basically a computer chip which records round-the-clock data like the tuna's location, diving depth, body temperature and surrounding water temperature," Cermeno says.
Some devices are "pop-up" satellite tags. At a pre-programmed date, they detach from the tuna and float to the ocean surface where they transmit data via satellite back to the lab.
Others are permanent archival tags which record data over years. Some of these will be retrieved by fishermen who are encouraged to return them in exchange for a 300 euro reward.
"Tagging studies have already given new insights into the bluefin," explains Cermeno.
"A key finding was that up to 30 per cent of the population may cross the Atlantic Ocean but they always swim home to spawn in either the Gulf of Mexico or the Mediterranean Sea. Knowledge like this has major implications for the way the fisheries are managed."
Despite the WWF's warnings, the bluefin tuna industry says claims of imminent stock collapse are exaggerated.
Al Jazeera visited an offshore tuna farm run by Balfego, Spain's biggest bluefin tuna company, where circular pens anchored to the sea bed contain thousands of captured wild tuna.
They are being fattened - every day 55 tonnes of fish are pumped in to feed the caged shoals.
"We think that right now and we have the scientific proof [that] the tuna population is not about to collapse, certainly not in our part of the Mediterranean which is well protected by the Spanish Government," says Juan Serrano, Balfego's director-general.
"In fact our studies show quotas are already working and the population is on the increase. But certain countries like France and Italy have to cut their fishing fleets to reflect the quotas - Libya and Turkey too."
Divers drop into the water and then we hear a muffled bang as a bluefin takes a sub-aqua bullet to the head. Within moments, 300kg of prime tuna is hauled from the deep.
Like 90 per cent of the Mediterranean catch, this fish - valued at more than $10,000 - will end up in Japanese restaurants as high-grade sushi.
Right now Balfego have around 8,000 tuna in the cages, which amounts to tens of millions of dollars worth of fish.
And that is just one company's quota; Balfego are allowed to catch 1,000 tonnes a year. WWF estimates that 60,000 tonnes are fished from the Mediterranean a year - more than twice the legal limit. It's a very, very profitable business.
But Balfego say that all their fish are bar-coded and traceable and that they are making every effort to sustain the fishery, even embarking on an experimental spawning programme.
Daily fish auction
We drive south along the coast to Palamos, where the daily fish auction is in full swing. The only tuna on offer is the cheaper, more plentiful albacore and bonito.
When available, bluefin is considered too expensive for merchants and there are strict rules governing its sale.
"All fish legally caught have to have a certificate with the date of capture and the name of the boat," says Octavi Obiol who runs Peixos de Palamos, a fish supplier to many of the world's top restaurants.
"If I don't have the details of where the fish came from, I won't buy it."
However, there are those who ignore the quotas and deal in illegal fish which scientists say severely impacts the bluefin breeding population.
"In 2001, bluefin caught on the Libyan coast weighed an average 124kg. Last year that dropped to 64kg," Sergi Tudela, head of fisheries at WWF Mediterranean, says.
"The population of tuna that are capable of reproducing is being wiped out. The Mediterranean bluefin fishery is collapsing as we speak. WWF has no choice but to urge its immediate closure."
There has also been a strong push for the bluefin to be listed on Appendix 1 of the Convention on International Trade in Endangered Species.
This listing would put it in the same endangered category as the blue whale.