Mysteries of Mediterranean bluefin tuna come under the microscope

The most ambitious Mediterranean tuna tagging project yet will today start seeking answers to some key mysteries on the migratory behaviour of this most valuable but also most imperilled ‘prince of the sea’.

WWF scientists, launching the three-year On the Med tuna trail project in Spain’s Balearic Islands, hope to map tuna migrations around the Mediterranean and verify theories that there may be resident tuna populations in the eastern Mediterranean that never venture into the Atlantic.

“It is scandalous that we know so little about a species we are putting under such huge pressure from illegal fishing and oversized fleets,” said Dr Pablo Cermeño, WWF Mediterranean’s Tuna Officer.

“WWF’s new tagging project will shed new light on tuna migratory routes and behaviour which will enable far more effective recovery and management plans both for the tuna and the fishery that depends on them.”

On the Med tuna trail will also be a race against time to gather data before the overstretched fishery collapses. Current annual catches taking ever smaller and more juvenile fish are estimated to be in the region of 60,000 tonnes – double the level allowed by law and four times the amount considered sustainable by international scientists.

Very few tagging studies have been done in the eastern Atlantic and Mediterranean so far, with activity focusing instead mostly on the western Atlantic. WWF’s tagging project, which will collect, among others, information on position and depth of the high speed fish, will fit adult fish (over 40kg) with ‘pop-up’ tags that record information at a frequency of once per minute, and which release from the fish at a specified time and float to the surface for the data to be read by satellite.

Important lifecycle information on the bluefin will also come from ‘archival’ tags clipped onto juvenile fish and recovered at point of catch – wherever that may be.

“The plan behind this project is to fill the gap between the little we do know about bluefin behaviour in the Mediterranean and what we need to know,” said Dr Sergi Tudela, Head of Fisheries at WWF Mediterranean. “When we have better data, we would urge fisheries decision-makers to use it to make better-informed choices for the management of this endangered species.”

WWF’s tuna tagging activities – planned in partnership with key international scientific institutions and fishing stakeholders in the Mediterranean, and made possible thanks to financial help from the Prince Albert II of Monaco Foundation – will run to 2010.

Today’s On the Med tuna trail tagging launch will use tuna caught by recreational fishers in the Balearics, once the most significant breeding area for bluefin in the Mediterranean. WWF, which is calling for a recovery period moratorium on bluefin tuna fishing if effective rules for a sustainable fishery cannot be drawn up and enforced, is also promoting the establishment of a tuna sanctuary in the Balearics.

Further WWF tagging events across Mediterranean waters will roll out in September and in 2009.