Study confirms the key role of the Balearic Islands in bluefin tuna reproduction

Marine currents play a fundamental role in determining the location of bluefin tuna spawning areas, which occur in very specific places, such as the Balearic Islands, where dispersal rates are particularly low, according to a scientific study.

The research, led by the Balearic Oceanographic Centre of the Spanish Institute of Oceanography (IEO-CSIC) and the Balearic Islands Coastal Observing and Forecasting System (SOCIB), shows that marine currents are key to the location of spawning areas, which are characterised by significant retention processes that prevent larvae from dispersing into areas that are unsuitable for their survival.

These areas, where food availability is adequate, temperature conditions ensure survival and currents favour retention, occur only in very specific locations, as is the case in the Balearic Islands.

In fact, during the reproductive season of species such as Atlantic bluefin tuna, currents in the western Mediterranean favour the transport of particles towards the Balearic Islands, making the area a particularly favourable environment for the larval development of tuna and other large pelagic fish.

The results of this research were obtained by combining time series of in situ oceanographic data, collected during campaigns carried out over more than a decade and integrated into a database called Ibamar, with high-resolution simulations from the Western Mediterranean Operational ocean forecasting model (WMOP) developed by SOCIB.

This integrated approach made it possible to reproduce marine circulation and analyse how physical processes control the transport and retention of particles. Specifically, the analysis was based on Lagrangian simulations for the period between 2009 and 2019, allowing researchers to assess the persistence of these patterns over time.

The results show that these retention patterns are persistent, although they display some interannual variability associated with changes in the oceanographic conditions of the region.

One of the factors that may modulate this variability is the position of the Balearic Front, an oceanographic structure associated with salinity gradients between water masses of different origins. The study reveals that shifts in this front play a key role in the dispersal and retention of particles, as they can significantly modify the residence time of eggs and larvae in spawning areas, with possible implications for the recruitment of large pelagic populations.

The work highlights the importance of integrating oceanographic observations and high-resolution numerical models to study complex processes that are difficult to observe directly in the ocean.

The study was carried out within the framework of the Baleatún, Tunawave and Tunibal projects, with the collaboration of the Mediterranean Institute for Advanced Studies, IMEDEA (CSIB-UIB), and the Andalusian Institute of Marine Sciences (ICMAN-CSIC).