Spawning behaviour of Atlantic bluefin tuna (Thunnus thynnus) was investigated using electronic satellite tags deployed in the western Mediterranean spawning ground, around the Balearic Islands (years 2009-2011). All the fish were tagged underwater and released within schools. In general, the fish tagged in the same year/school displayed common migratory trends. Following extended residency around the Balearic Islands, most tagged tuna crossed the Strait of Gibraltar heading for the North Atlantic. Discrepancies between the migratory tracks reconstructed from this and previous electronic tagging studies suggest that the bluefin tuna Mediterranean population may comprise distinct units exhibiting differing migratory behaviours. The diving behaviour varied between oceanic regions throughout the migratory pathways, the shallowest distribution taking place in the spawning ground and the deepest at the Strait of Gibraltar. A unique diving pattern was found on the majority of nights while the fish stayed at the spawning ground; it consisted of frequent and brief oscillatory movements up and down through the mixed layer, resulting in thermal profiles characterized by oscillations about the thermocline. Such a pattern is believed to reflect recent courtship and spawning activity. Reproductive parameters inferred from the analysis of vertical profiles are consistent with those estimated in previous studies based on biological samples.

Hoolihan, J. P., Luo, J., Abascal, F. J., Campana, S. E., De Metrio, G., Dewar, H., Domeier, M. L., Howey, L. A., Lutcavage, M. E., Musyl, M. K., Neilson, J. D., Orbesen, E. S., Prince, E. D., and Rooker, J. R. 2011. Evaluating post-release behaviour modification in large pelagic fish deployed with pop-up satellite archival tags. – ICES Journal of Marine Science, 68: 880–889.

Abascal, F. J., Mejuto, J., Quintans, M., and Ramos-Cartelle, A. 2010. Horizontal and vertical movements of swordfish in the Southeast Pacific. – ICES Journal of Marine Science, 67: 466–474. In all, 21 swordfish (Xiphias gladius) were tagged with pop-up archival satellite tags in the Southeast Pacific. Despite problems of premature release, the information obtained provided insight into the horizontal and vertical behaviour of the species in the area. A consistent migratory pattern was observed, fish moving northwest by autumn and presumably returning south by early spring. Swordfish typically forage in deep water during the day and stay in the mixed layer at night, although this behaviour is occasionally modified. The maximum depth recorded was 1136 m, and dives deeper than 900 m were found in five of the six tags analysed. There was a significant positive relationship between average depth by night and visible moon fraction.