Caracterização ecogeomorfológica das áreas de desova de quelônios de água doce (gênero podocnemis) no entorno da Ilha do Bananal, Rio Araguaia

Abstract

The biggest concentration of nests of the population of amazon turtle (Podocnemis expansa) of the center-west of Brazil occurs nearby the Bananal Island, in sand bars. In this area it also has important nesting of tracajá (Podocnemis unifilis). Both the species can use the same sand bars, but the nesting places normally do be the same set. Each turtle species takes advantage of the place that presents geomorphologic characteristics appropriate to the hatching success of their eggs. The amazon turtle nest has 50 cm and 70 cm in depth where 40 up to 160 eggs are laid. Tracajás is less demanding about the characteristics of the sand bars, and its nests are shallower (between 10cm and 20cm in depth) and smaller clutch size (from 10 to 25 eggs). This work analyzes the ecomorphologic characteristics of the sand bars that are used as nesting areas. It has a set of factors that influence in the choice and the reproductive success of the Podocnemis genera turtles. The temperature of the nests, due to the sun heat, is controlled by the depth of the egg chamber, by the texture and by the mineralogical composition of the sand bars. The bar area chosen as the nest site emerges in the period of dry and the nesting occurs, generally, between July and October. The return of the rainy season varies throughout the years and it is common that the sudden ascent of the level of the rivers floods the nests, killing the embryos and the hatchling. The nesting places of the amazon turtle in the studied areas have two common characteristics: the nesting usually occurs at highest part of the sandbars and the presence of deep pools in the neighborhoods where the turtles stay before the nesting. Tracajás is less selective in choose the nest places that can occur in diverse environments.