So far tuna Census studies were all centered on the oceans

Are there one or two stocks of bluefin tuna in the Mediterranean How many genetically distinct populations swim in its warm waters At what percentage mounts their rate of hybridization with the populations of the Atlantic 60 as assess it scientists Even more Finally, how to organize migration flows of this case Launched in August in Palma de Mallorca with the collaboration of the Spanish Oceanographic Institute and the Principality of Monaco, the Mediterranean tuna monitoring program devised by the World Wild Foundation is the most ambitious project of tracing never realized in these waters. "It is inadmissible to know so little about a case over which it exercises so much pressure," justifies Denis Ody, which returned the first campaign of tagging on the "Columbus", the science vessel of the Foundation.

So far, tuna Census studies were all centered on the oceans. Tag Foundation Giant, created in 2006 by a group of researchers at Stanford University, and placed tags on 1.005 individuals of the species of bluefin tuna in the Atlantic and 596 others in the Pacific. The European programme copy the principle: for three years, Spanish and French scientists will travel the great blue by campaigns, successive to mark tens of small and large specimens.

With the help of darts

For adults, they will use electronic markers capable of recording a year of data on the temperature, depth and light intensity. The recorder automatically rises to the surface and transfers its data to the Argos satellite. "The marking needs to approach the animal close enough for throwing a DART." "Several thousands of dollars the marker, the shooter has interest to adjust his shot", explains Denis Ody.

The recorded data are compressed before transmission and synthesized histograms and profiles. To trace the route of the fish, scientists are based on the analysis of light levels on twenty-four hour periods. They thus determine dawn, noon and dusk, and raises the stopwatch. Noting the difference with GMT (Greenwich Mean Time) time, they can precisely calculate longitude.

The latitude is more complex to deduct. The first data is provided by the measurement of the length of the day, the changes may indicate the distance of distance from the equator. But calculated data are not fine. To improve their geolocation, scientists have developed algorithms that also take into account the temperature of the water. The information can then be cut with measurements taken by satellites. "Precision is of the order of the degree, which is quite sufficient to trace the route of migration", says Sergi Tudela, responsible fisheries in the Mediterranean of the WWF (specially) and tuna specialist program.

The data collected will establish more effective sustainable management plans for the tuna as well as for fishing which depends on. "Thanks to this information, we can put pressure on decision makers and allow them to make more thoughtful choices for the management of this threatened species," explains Sergi Tudela. It is estimated that the annual harvest in the region amounted to 60,000 tonnes, or more than double than what the law allows and especially more than four times the amount recommended by international scientists. The State of knowledge allows to suppose the existence of two stocks of bluefin tuna in the Mediterranean: the Western basin at the level of the area historically taken Balearic, and in the eastern part off the coast of the Turkey. The study will tell precisely which are the nurseries and will also help to reconcile the environmentalists and fishermen, at least in the field of statistics.