Estimativas do coeficiente de capturabilidade na pesca do espadarte (Xiphias gladius) no atlântico sul

Abstract

The Brazilian pelagic longline fleet has a large area of activity in the South Atlantic and has been responsible in recent years for the second largest swordfish catch (Xiphias gladius) in the region. However, it is a fleet with vessels of different flags, fishing strategies and target species, which can make it difficult to interpret the results of the analyzes for stock assessment and, consequently, result in poorly informed management decisions. Fisheries stock assessment pass initially by obtaining standardized CPUE (Capture Per Unit of Effort) as valid relative abundance index. For the last assessment of the South Atlantic swordfish stock, different approaches were tested to obtain the Brazilian series, which included the direction of the fleet, changes in the configuration of the apparatus, historical changes in fishing strategies and changes in the shape of information. However, the series presented some inconsistencies related to high interannual variability and trends conflicting with the other series provided by the countries that exploit swordfish in the region. In order to obtain a better understanding about the inconsistencies of the Brazilian series and the origin of the observed conflicts, an analysis of the series of standardized CPUEs was performed after a detailed review in the database, in which inconsistencies within each trip were analyzed and eliminated, obtained a reduction in overdispersion of data and in the variability of the resulting standardized CPUE series. In the theory, the relationship between the standardized and nominal CPUE series would be that the former reflects variations in abundance, while the latter reflects the joint variability of species abundance and catchability, two key parameters to be estimated in stock assessments. However, time variable catchability is still poorly understood and estimated in most cases. Here, the nominal and standardized series of swordfish captured by the Brazilian longline fleet were used to obtain estimates of the variability of the catchability coefficient (q) over the years. In addition, a measure of influence of each explanatory variable used in standardization on annual q estimates was calculated. Estimates of variations in q and associated factors have broadened fishery knowledge, besides assisting in knowledge about the constructions of standardized CPUE series, which may be useful in designing appropriated approaches to their use in stock assessment models.