Geological characteristics of the nesting areas of the giant Amazon river turtle (Podocnemis expansa) in the Crixás-Açu river in Goiás State, Brazil

Abstract

A large population of the giant Amazon river turtle (Podocnemis expansa) nests along the beaches of the Crixás-Açu River in the central western region of Brazil. In spite of the existence of several point bars in the area, only a selected group of beaches is used for nesting by P. expansa. Geological aspects, such as river width and depth, beach height -above 200 cm -with sandy sediments, were indispensable for the choice of these nesting sites. The relatively reduced dimensions of the point bars and the great number of turtles, which nest in the same local, contributed to the existence of a high nest concentration. The rapid rise of the Crixás-Açu River caused the flooding of the beaches and the drowning of hatchlings and embryos. It is estimated that nearly all the nests were lost. The height of the nesting place and the time of flooding related to the incubation period are decisive in embryo survivorship. The Retiro, Júnior, Assombrado and Limoeiro beaches, which are situated at heights of 183 to 310 cm, were inundated on 8 November 2000. The Barreira Branca beach, with a height of up to 380 cm was completely inundated on 13 December 2000. All of these beaches were flooded before the hatchlings emerged. KEY WORDSgiant Amazon river turtle, Araguaia basin, Crixás-Açu River, nesting, Podocnemis expansa Características geológicas das áreas de nidificação da tartaruga-daamazônia (Podocnemis expansa) no rio Crixás-Açu no Estado de Goiás, Brasil RESUMO Uma das maiores populações de tartaruga-da-amazônia (Podocnemis expansa) da região Centro-Oeste do Brasil nidifica ao longo das praias do rio Crixás-Açu no estado de Goiás. Apesar de existirem inúmeras barras em pontal na área, apenas um seleto grupo de praias foi eleito como ponto de nidificação pela tartaruga-da-amazônia. Aspectos geológicos, tais como um substrato constituído por sedimentos arenosos, a presença de locais amplos e profundos no rio, e patamares elevados, acima de 200 cm foram imprescindíveis à escolha dos pontos de desova. As dimensões relativamente reduzidas das barras em pontal e o grande número de indivíduos a desovarem no mesmo local fazem

Neonatal biometry and characterization of Amazonian Turtle nests (Podocnemis expansa)

“…Thus, nest depth may cause the incubation temperature of the eggs to be adequate for the better development of the hatchlings, and thus, allow more eggs to hatch. Davenport (1997) andFerreira Júnior &Castro (2006) found that the temperature of nests varies according to the depth. Besides, Pignati and Pezzuti (2013) found that nests close to the vegetation have lower temperatures than nests located in areas of lower vegetation cover.…”

Nesting of Phrynops geoffroanus (Testudines: Chelidae) on sandy beaches along the Upper Xingu River, Brazil

“…Phrynops geoffroanus lays its eggs in synchrony with the variation in level of the Xingu River, as do other species of Amazonian turtles, such as Podocnemis expansa (Schweigger, 1812) (ALHO & PÁDUA 1982, FERREIRA JÚNIOR & CASTRO 2006, Podocnemis sextuberculata (Cornalia, 1849) (PEZZUTI & VOGT 1999) and P. unifilis (FERREIRA JÚNIOR & CASTRO 2010). When nesting occurs on the beaches, the duration of incubation should be compatible with the low water period, and hatching should take place before the beaches flood.…”