Interactions between oceanographic variables and population structure of the yellowfin tuna Thunnus albacares (Bonnaterre, 1788) in the Western Central Atlantic

Pelagic fish species, such as tunas, represent important resources for the fishing fleets of several countries. Identifying spatiotemporal distributions of abundance, structure of sizes, weights and influences of environmental variables is extremely important to promote sustainable catches and efficient management plans for fisheries stocks. This present study aimed to analyse the spatiotemporal distribution of Thunnus albacares, their relationships with oceanographic variables, as well as size and weight structure, and the proportions of life stages/phases in catches, mainly within the Brazilian Exclusive Economic Zone. Data were obtained on longline fleet catches; the sea surface temperature (SST) and chlorophyll-a (Chla) were measured in an area ranging from 42.2° to 24.8° W and 5.9° S to 8.8° N; the lunar cycle was also studied. Generalised Additive Models and spatial statistics techniques were used to model the effect of the variables on catch per unit effort (CPUE) and on length structure. The results indicate that the distribution, abundance and length structure of T. albacares are strongly associated with environmental (SST and Chla), temporal (year, months, seasons and moon phases) and spatial (latitude, longitude and hemisphere) variables. The comparison of catch sizes with the first length at maturity (L₅₀) indicated that approximately half of the catches are on young specimens, showing great variation over the years, reaching 74.8% in 2012. These results show that providences should be taken focusing on mitigating young specimens' capture and the sustainable exploitation of tuna in the Atlantic. The patterns of CPUE and length strongly support the feeding and spawning migration hypotheses.