Skipjack tuna (Katsuwonus pelamis) is a cosmopolitan species found in schools distributed mainly in tropical and subtropical waters of the three oceans, breeding opportunistically throughout the year over broad areas of the Atlantic Ocean. Skipjack tuna stocks have been historically exploited by two major gears (purse seine on the eastern stock and bait boat on the western stock) and by many countries throughout their range (ICCAT 2022).

In general, the Atlantic Ocean Tropical Tuna Tagging Programme (AOTTP) shows a minimal exchange between the eastern and western skipjack stocks, the separation between the two stocks is less clear for those tags released by the AOTTP close to the boundaries of the stock (5º S; 35º W) (ICCAT 2022). Also, skipjack spawning seems to be continuous in time and space; however, for obvious biological and oceanographical reasons, they will necessarily undergo seasonal and geographical variations. The combination of these spatial-temporal heterogeneities generates isolated micro cohorts, at least during their early life. Each of these cohorts will show its own movement pattern: showing E-W and N-S movements at a geographical scale that is typical of skipjack, i.e. very seldom moving at large distances over 1500 miles, at least in the Atlantic (Fonteneau 2015).

There remains some uncertainty around the stock structure of skipjack in the Atlantic (de Souza Corrêa et al. 2022) (Gaertner et al. 2008), but the hypothesis of separate Eastern and Western stocks is still the most plausible and is used by ICCAT for the assessment and management of this tuna species (ICCAT 2022) (ICCAT 2022).