Landings of European porbeagle rose to more than six thousand tonnes during the late 1940s but declined through the second half of the 20th century, leading to concerns that the north-eastern Atlantic stock was at risk. The true state of this stock, however, remains unknown. Indeed, several important features of the species' spatial ecology, such as the extent of migrations or the location of pupping areas, are based mostly on anecdotal reports.
Building knowledge in this field is difficult because porbeagles spend much of their time offshore and in deep pelagic habitat. The development of pop-up satellite archival tag (PSAT) technology is helping to improve this acquisition of information though, revolutionizing investigations into the distribution of this large migratory species.
For this article, PSATs deployed on adult or subadult female porbeagles reported migrations and behaviour over a full year for the first time in the eastern Atlantic. Nine migrations (eight female and one male) were reconstructed, providing evidence of the porbeagles returning to the Bay of Biscay during the summer months. This return of the females to a previously occupied location – a trait known as 'site fidelity' – suggests that the stock structure is more complex than assumed by the standard assessments that rely on a uniform spatial distribution hypothesis. This new data will help improve assessments of porbeagle stock status and distribution.
Tagging a porbeagle with a PSAT. Photo: Gérard Biais, Ifremer