Movement patterns and size distribution of little tunny (Euthynnus alletteratus) in the Eastern Central Atlantic Ocean: Insights from conventional tag release-recapture data

Abstract

This study investigates the movements, patterns, and size distribution of little tunny (Euthynnus alletteratus) in the Eastern Central Atlantic Ocean. Data were collected as part of the ICCAT Atlantic Ocean Tuna Tagging Programme (AOTTP) through conventional tag release-recapture experiments. The study analyzed data from 7870 tagged fish, of which 452 were recaptured between 2016 and 2020. The results indicated that little tunny could travel long distances, with some fish covering up to 600 Nm between Mauritania and Côte d’Ivoire. The movement patterns of tagged fish varied, and there appeared to be some exchange of fish between Senegal-Mauritania and the Gulf of Guinea through the Côte d’Ivoire Exclusive Economic Zone (EEZ). The recapture rate was the highest within the first month after release, with half of the tagged fish recaptured within this period, then approximately 17 % and 11.5 % of tagged fish were recaptured within 60 and 90 days, respectively. The size distribution of tagged and recaptured little tunny varied by area with statistically significant differences between Côte d’Ivoire – Gulf of Guinea and those from Mauritania to Liberia. The recaptured fish were larger than the tagged fish in all areas studied, suggesting a significant growth of individuals (4.2 cm per quarter). In conclusion, this study highlights the extensive movements and migration patterns of little tunny in the Eastern Central Atlantic Ocean. These findings suggest that factors such as Anchored Fish Aggregating Devices (AFAD) may influence the mobility of fish in certain areas and that the size distribution varies significantly between different regions.