Abstract
The EU purse seine fishery is composed of two major fleets targeting tropical tuna species in the IOTC ConventionArea. A common sampling design has been shared and developed by the French and Spanish scientists since the1980s with the aim to collect data on the fishing activities and the biological parameters of their fishery. Bothfleets have evolved simultaneously according to the development of the new technology and fishing practices.Thus, considering their similarities, their catches were historically assumed to be comparable. In the presentstudy, we review the validity of this hypothesis under the evolution of the fishing management in the IOTC areaof competence in recent years, focusing on the species composition of the catch and accounting for space andtime. We investigated the reporting data and the scientific samples at landing during the period 2010-2021 in 5°squares and quarters commonly exploited by the two fleets. As expected, the French and Spanish catch werehighly correlated and homogeneous whatever the fishing mode and the year. Scientific data were more stablethan the declaration due to the standardization of the measurement. However, since 2018, the species compositionstarted to slightly differ in catch under floating objects for the two datasets. The frequency of yellowfin tunaremained quite stable in the French fleet whereas it started to be lower in the Spanish reported catch. Oppositedynamic was observed for the skipjack but no pattern regarding the bigeye tuna. This recent trend needs to beconfirmed in the following years and further study on the differences in fishing strategies that have possibly ledto this change