Abstract
We explored the usefulness of Dynamic factor analysis (DFA) to detect common patterns in the sets of CPUEs for Atlantic yellowfin (Thunnus albacares) and for eastern Atlantic skipjack (Katsuwonus pelamis), respectively. For yellowfin, the most appropriate model, in terms of AIC, identified two common trends. The 10 yellowfin CPUE series could be divided into 3 groups based on factor loadings. The grouping corresponds in part to the geographic location of the fisheries (i.e., the western Atlantic area for group 1 and the northeastern tropical Atlantic region for group 2). The fact that the first group is constituted by CPUEs obtained from 3 different fishing gears (pole and line, purse seine and longline), operating at different depth levels, suggests that the regional trend reflects more a sub-population response to a local exploitation rate than to environmental conditions. In light of the present results, the CPUEs should be combined respectively into two regional indices before performing a unique combined index. For skipjack, results are less conclusive and further studies with explanatory factors are required to account for the fact that this species is seldom targeted by the tuna fisheries.