Seletividade do matapi para captura do camarão da Amazônia no baixo rio Tocantins, Amazônia, Brasil.

Abstract

The species Macrobrachium Amazonicum shrimp (Heller, 1862), popularly known as the Amazon-shrimp, is widely exploited by artisanal fisheries in Para. It is the species most consumed regionally, taking a socio-economic importance to the state. However, there are no legal provisions for development of fisheries of amazon-shrimp, which is justified by the lack of information about the biology and the dynamics of the species. Therefore, the aim of this study was to evaluate the selectivity of matapi and the fishing gear used to catch M. amazonicum, at the lower Tocantins River. The study was conducted in the vicinity of the area of the municipality of Abaetetuba islands. Sampling occurred in March of 2013 (rainy season) and June of 2013 (dry season) at three sampling sites in the communities of Perpétuo Socorro, Santa Maria e São Miguel. Thirty matapis were used at every collection site, with spacing between battens 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 mm, all with babassu baits. Each matapi was covered with a mosquito net of the type which has been called as overmatapi with the function of not letting some individuals that escape through the matapi splices. Fisheries occurred at nighttime, with an average duration of 12 hours. The shrimps harvested were frozen in a 1 kg plastic bags. Information about the location of capture, location of retaining (or matapi or overmatapi), date and the extent of the spacing between the splices of matapi were noted. The shrimps were sent to the laboratory for crustacean of the Research and Fisheries Resources and Management Center of the North Coast – CEPNOR, in Belém. In the laboratory, the specimens passed by the identification, sexing and biometrics process. The Kruskal-Wallis test was used to compare mean total length and weight and the condition factor of the specimens with 5% error; the weight/length ratios were analyzed by t test with bilateral error of 5%; and selectivity for the construction of the curves of selection. The results demonstrated that males are bigger and females are heavier. The weight/length relationship were positively correlated, differed between the sexes (t = -4.59; p <0.0001), whereas males and females exhibited negative allometry. The condition factor was higher in the rainy season. The matapi with splices spacing 5 mm is the most suitable for fishing this species of shrimp, taking into account the capture of 50% of the adult population. These information observed enhance the evidence of overexploitation of M. amazonicum in the lower Tocantins, making necessary a discussion and implementation of the most appropriate sustainable fisheries management of this species in the region.