Body size and isotopic profiles enable discrimination between long-term resident and highly migrant contingents of Atlantic bluefin tuna.

The Atlantic bluefin tuna (ABFT) population ranges throughout the Atlantic Ocean and Mediterranean Sea, and consists of multiple contingents that use diverse habitats and show different movement patterns over the life cycle. Based on body size, elemental and isotopic data of C and N in muscle and liver, we analysed eastern-stock ABFT by comparing mid-sized individuals caught by hook-and-line gears with larger individuals harvested from traps in the Strait of Gibraltar (SoG). Our results show that trophic-related chemical markers have potential for separating temporarily sympatric contingents throughout the ABFT population range, reflecting size-dependent spatial distribution and differential patterns of residency and migration.

Common dolphinfish, Coryphaena hippurus, spawn at their easternmost Atlantic range adjacent to the Mediterranean Sea.

This study provides sound evidence of the spawning activity of common dolphinfish (Coryphaena hippurus) in the Gulf of Cadiz (southwest Spain) during summer months. Along with waters off Côte d'Ivoire, this area adjacent to the Mediterranean Sea is the easternmost Atlantic spawning ground documented for the species. All the fish analysed (5 males and 15 females) were at spawning stage, except the smallest female (61.

Global spatial risk assessment of sharks under the footprint of fisheries.

Effective ocean management and the conservation of highly migratory species depend on resolving the overlap between animal movements and distributions, and fishing effort. However, this information is lacking at a global scale. Here we show, using a big-data approach that combines satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries.

Spawning behaviour and post-spawning migration patterns of atlantic bluefin tuna (Thunnus thynnus) ascertained from satellite archival tags.

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.

Ultrastructure of oogenesis in the bluefin tuna, Thunnus thynnus.

Ovarian ultrastructure of the Atlantic bluefin tuna (Thunnus thynnus) was investigated during the reproductive season with the aim of improving our understanding of the reproductive biology in this species. The bluefin, like the other tunas, has an asynchronous mode of ovarian development; therefore, all developmental stages of the oocyte can be found in mature ovaries. The process of oocyte development can be divided into five distinct stages (formation of oocytes from oogonia, primary growth, lipid stage, vitellogenesis, and maturation).