Variabilidade das espécies-alvo e adensamentos do espadarte (Xiphias gladius) capturados pela frota brasileira de espinhel pelágico no Atlântico tropical e subtropical oeste

Abstract

Tuna and like are among the most important in the marine environment from an economic and social point of view. On the other hand, many of these species are already being exploited to their maximum sustainable limit or are overexploited, with the aggravation of relatively high market demand. There is a clear need for ongoing inventory assessments and effective management to maintain or recover overexploited stocks. Among the main challenges for the sustainable management of marine resources is the achievement of relative abundance indexes that reflect the real state of the stock biomass. In view of this context, the present study initially analyzed the history of catching commercial pelagic longline fishing in Brazil from 1978 to 2018, focusing on the identification of fishing targets. Subsequently, the spatial distribution patterns of swordfish (Xiphias gladius) from the South Atlantic were investigated for the construction of abundance indicators. For this purpose, the available data on catch, effort and geographic location of the fishing bids, analyzed in the National Tuna and Related Data Bank (Banco Nacional de Dados de Atuns e Afins-BNDA), were analyzed. Then, a statistic was calculated with ratios between catches of the different species, which was used as an indicator of the direction of the fleet. The spatial densification structure was evaluated based on spatial autocorrelation calculations. The results of the initial analysis revealed a mosaic of flags, target species, technologies and fishing strategies, which can be grouped into three distinct moments. In the first (1978-1986) there is a predominance of leased vessels in the east, and the targeting for swordfish is accentuated. The second phase (1987-2001) was marked by an increase in the targeting for yellowfin tuna, mainly white. Finally, in the third phase (2002-2018), several vessels were leased, and there was an increase in the targeting for swordfish and blue sharks. In addition, the swordfish capture data from the Brazilian fleet showed a moderate degree of spatial dependence. In some cases the dependence is manifested in moves made with a distance of more than 1000 km between them. The size and distribution of densities have varied greatly over the years. Thus, the knowledge of these variations in the calculations of estimates of relative abundance indexes is essential to avoid misinterpretations when assessing the stock and, consequently, in fisheries management.