TUNASAT

The TUNASAT project is a EU-funded project and a collaboration between Cefas and laboratories in Italy and Spain. There are two key objectives to the project; first to evaluate the effectiveness of available pop-up satellite tag technologies in European (principally Mediterranean) waters and second to investigate the migratory movements of bluefin tuna over extended periods.

The field phase of the project involved tagging 'giant' (>6ft long, >300kgs in weight) bluefin tuna off the coast of Corsica with two different types of satellite tags; simple pop-up tags that transmit final pop-up positions, and more complex Pop-up Archival Tags (PAT tags), which store information about daily (internal and external) temperature, times of sunrise and sunset, proportion of time at depth and final pop-up position.

The archival data can be used to calculate geographic position during the time that the tagged individuals are at liberty, thus vastly increasing the available biological and behavioural information available. Analysis of the efficacy of the tags has revealed significant failure of the geographical coverage of the orbiting Argos satellites through which data are returned. This has lead to a loss of data from the tags that 'popped off', a problem which the project was the first to identify and which Argos are now rectifying.

However, data from tags returned through the fishery, and from the data which could be downloaded through the satellite link ups, have shown that movements of tuna within the Mediterranean depended heavily on the age of the individuals and the availability of food. Young fish tended to stay in a relatively confined area of high productivity, whereas large adults undertook extensive migrations outside of the Mediterranean to latitudes considerably northward of those currently understood to be geographical limits.

This work links to research being undertaken on Atlantic bluefin tuna at Monterey Bay Aquarium, and is part of a larger effort to test established, but unproven, management hypotheses about the extent of migrations of bluefin stocks and the degree of mixing between stocks currently managed as separate stocks.