Selectivity of matapi used in catching Macrobrachium amazonicum in the lower Rio Tocantins, Amazon, Brazil

Abstract

The study aimed to determine the selectivity of matapi used in catching Amazon-shrimp, Macrobrachium amazonicum (Heller, 1862), the lower Tocantins River. The fishing was carried out during the rainy season and the dry season of 2013 in three sampling points. Thirty matapis were used for every collection point, with spacing between battens 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 mm, all with babassu baits. The Kruskal-Wallis test was used to compare mean total length and weight and condition factor of the specimens with 5% error; the weight/length ratios were analyzed by bilateral t test with α=5%; and the selectivity for 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 allometric growth. The condition factor was higher in the rainy season. The matapi with spacing of 5 mm of splices is the most suitable for fishing, taking into account the capture of 50% of the adult population and the captured volume