Uso do habitat e demografia do tubarão azul (Prionace glauca, Linnaeus, 1758) no oceano atlântico sul ocidental

Abstract

Elasmobranchs (sharks and rays) are species that present a great vulnerability to anthropogenic exploitation. The populations of these species have suffered significant declines mainly due to overexploitation caused by overfishing. The blue shark (Prionace glauca) is the most widely distributed and species in the world, being the most abundant in the pelagic fisheries in the oceanic region. Although it is a species highly exploited by fishing, P. glauca is considered as an almost endangered species in Brazil and in the world NT. However, conservation status may be linked to the absence or scarcity of information regarding their demographics and habitat use. For these reasons, the objective of the present study was to analyze the published evidence on the biology and fishing of the blue shark, to evaluate the use of the habitat (population and nursery area identification) through multi-elemental microchemical analyzes in vertebrae and to estimate demographic parameters of the blue shark (Prionace glauca) in the South Atlantic Ocean, in order to assist the sustainable management and conservation of the species. For the study of demography, a total of 798 P. glauca specimens were captured between the years of 1994 and 2002 on vessels operating in the South Atlantic Ocean. A matrix population model was constructed and thus, obtained the elasticity. Three scenarios were generated from natural mortality (M), total (Z) and equilibrium (Z '). In the real scenario, with an impact of fishing activity, the intrinsic population growth rate was -0.043, showing that the population decreases every year. The elasticity analysis showed that young are fundamental for the sustainability of the population. The multi-elemental analysis in the vertebrae of 7 specimens showed significant differences (Mann-Whitney U test, P <0.05). However, the proportions Sr: Ca, Mn: Ca and Cu: Ca exhibited a direct relationship, being significant among individuals (Kruskal-Wallis, P <0.05). Blue shark is considered to be deficient in demographic data and habitat use, such information is necessary because of the current fishing effort to which the species is subjected. Conservation measures are necessary since declines are already being recorded.