Integrating reproductive ecology, early life dynamics and mesoscale oceanography to improve albacore tuna assessment in the Western Mediterranean

Albacore tuna is a pelagic top predator of high ecological and commercial relevance worldwide. Despite the importance of this species, there is only limited knowledge of its life cycle, reproductive dynamics and early life ecology. In the Mediterranean, where the assessment is based on data-poor methods, the status of the albacore population remains uncertain. Here we combine information from commercial fisheries, ichthyoplankton surveys and oceanographic data in the Western Mediterranean Sea to identify the geographical location of the main spawning areas and larval habitats. We applied this information to develop a habitat-corrected larval abundance index providing information on early life dynamics. The larval index was compared with fisheries-dependent indices used for the stock assessment of the Mediterranean albacore. The results allowed the identification of the main spawning grounds, located around the Balearic Sea, and the role of oceanographic conditions when studying larval abundances. The larval abundance index shows a significant negative trend during the last decade, indicating a potential reduction in the spawning stock biomass, which is consistent with the trend observed from the fisheries-dependent indices. We discuss how the systematic integration of information from ichthyoplankton surveys and hydrography to improve assessment is an example of operational fisheries oceanography in practice.