Determining bluefin tuna habitat through frontal features in the Mediterranean sea

The distribution patterns of bluefin tuna schools observed during the STROMBOLI EU project (2000-2002) were analysed in relation to oceanographic conditions. High-resolution radiometers (AVHRR and SeaWiFS) were used on a daily basis to derive maps of environmental variability. An edge detection technique was especially applied to estimate the position of frontal features. Using a variety of geostatistical and point process techniques, we were able to show that the distribution of bluefin schools was partially driven by the occurrence of transient fronts in the Gulf of Lions. This is believed to be mainly a trophic association, since enhanced convergence and retention processes occur at fronts, possibly leading to higher prey densities (e.g. anchovies). The spatial density and frequency of transient fronts may therefore have an influence on the foraging activity of bluefin tuna: the distribution and evolution of the thermal fronts in the western Mediterranean Sea are further detailed for the 2001-2004 period.