Evidence is emerging of unregulated and probably illegal tuna fishing in Libyan waters during this year's conflict.
Signals recorded from boats' electronic "black boxes" show a large presence inside Libyan waters, a major spawning ground for the endangered bluefin tuna.
Several strands of evidence, including a letter from a former industry source, suggest the involvement of EU boats.
The issue will be aired this week at the annual meeting of Iccat, which regulates tuna fishing in the region.
The European Commission believes any fishing in Libyan waters this year could be judged illegal.
EU Fisheries Commissioner Maria Damanaki told BBC News that she is also investigating whether Italian authorities made bilateral deals with Libya on tuna-fishing, which would contravene EU regulations.
The annual meeting of Iccat - the International Commission for the Conservation of Atlantic Tunas - opens in Istanbul on Friday, preceded by two days of talks within its Compliance Committee, which will begin to assess whether rules have been broken.
After the Libyan civil conflict began in February, Ms Damanaki's office was set to request a suspension of all tuna fishing in Libyan waters, given that the breakdown in governance made regulation difficult.
On 7 April, Libyan authorities, in one of a series of letters obtained by BBC News, told Iccat that because of the "recent and exceptional circumstances" they were going to suspend all tuna fishing in their waters voluntarily.
Three weeks later, Libya sent another letter to Iccat cancelling the suspension, without citing its reasons.
Iccat chairman Fabio Hazin asked Libya to reconsider. It was too late to procure international observers for the vessels, as regulations require, he said; and Iccat members did not have the time needed to discuss and approve Libya's proposed fishing plan.
In response to further correspondence, Dr Hazin and Compliance Committee chairman Christopher Rogers told Libyan official Nuredin Esarbout that "fishing by the Libyan fleet... in 2011 might be in contravention" of Iccat rules.
Ms Damanaki further warned that any catches would be "well on track to be deemed illegal".
She asked EU member states to "monitor the activities of your national operators" to make sure they were not catching or trading potentially illegal fish.
She also warned that she stood ready to use recently adopted EU rules on illegal fishing against anyone involved in such activities.
Under Iccat rules, all purse seine boats - the type most common in bluefin operations - have to be equipped with a Vessel Monitoring System (VMS), an electronic gadget that transmits information including the boat's location every six hours.
The statistical report prepared for the forthcoming meeting - also obtained by BBC News - includes a map showing the number of VMS signals received from various locations in the Mediterranean during the 2011 fishing season.
The biggest bursts of activity are in the spawning grounds where bluefin gather in the early summer; and this includes the waters off the Libyan coast.
This map does not show which vessels were operating there, although Iccat is believed to have this information.
According to environmental groups that monitor tuna-fishing ports, vessels authorised to fish in Libyan waters did not do so, remaining in French and Maltese ports all season.
If that is correct, it implies that boats from other Iccat member states were operating there, which would be illegal.
As well as the area extending 12 nautical miles off the coast which is the Mediterranean standard for territorial waters, Libya claims the whole of the Gulf of Sirte covering 57,000 sq km (22,000 sq miles) and a further "exclusive fishing zone" extending 62 nautical miles into the Med.
It is one of six main spawning grounds that purse seine vessels target. The nets are drawn around the roiling shoals like a basket, and the fish are subsequently transferred to cages that are slowly towed to "ranches" or "farms" for fattening before death and sale.
A letter recently sent to WWF and Greenpeace - which work closely together on the bluefin issue - by an experienced hand in the bluefin tuna fishery says illegal operations have been rife in the southern part of the Mediterranean for years.
At different times, he says, operators based in Spain, France, Malta and Italy have been involved.
In 2010, Italy voluntarily closed tuna fishing in its own waters. But, the informant writes, Italian fishermen were transported to Libya by means that evaded border controls, and fished there instead.
He also accuses EU fleets of using planes to spot aggregations of spawning tuna, which has been banned since 2006; catching undersized fish; and operating with such little regard for bad weather that entire hauls of fish ended up dead in the water.
"Would you like to know where all these dead fish are? They are on the sea floor!", he writes.
Government inspectors, he says, "can be bought for a cigarette packet".
The letter has been forwarded to Iccat.
Although reports from fisheries academics and environment groups have regularly condemned aspects of the Mediterranean bluefin industry down the years, first-hand reports from people this close to the industry are rare, partly because of intimidation.
But, the source says, he is moved to "repentance" because of the "incredible things" he has seen.
His letter is very specific, naming companies, locations, activities, time periods and catch sizes.
How closely the source's claims are related to the European Commission investigation of possible bilateral deals between Italy and Libya is not clear, as Ms Damanaki preferred not to elaborate on the nature of that investigation.
From an ecological point of view, a plunder in Libyan waters would be disturbing.
The northern bluefin was classified as endangered on the internationally accepted Red List earlier this year.
Environment groups are urging Iccat and the EU to act swiftly.
"The real plundering of the bluefin tuna population in Libyan waters by local and foreign fleets makes a strong case for a ban of the fishery in those waters from 2012," said Sergi Tudela, head of WWF's Mediterranean fisheries operation.
"Actually, this area must be turned into a bluefin tuna sanctuary protecting one of the most important breeding grounds for this iconic species," he told BBC News.
WWF and the other environment groups involved in the issue continue to warn that the basic problem across the region is over-capacity - there are simply too many boats that need to exceed their catch quotas in order to turn a profit.
Last month, a report from the Pew Environment Group calculated that 140% more bluefin flesh entered the market from the Mediterranean than was declared by fishing boat skippers.
"Fifteen years after tuna farming started in the Mediterranean, it's still impossible to know the biomass of tuna originally caged in every farm, which prevents achieving traceability in this fishery," said Dr Tudela.
"The moment has come for Iccat Parties to ban tuna farming."
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