On clutch size and hatching success of the South American turtles Podocnemis expansa (Schweigger, 1812) and P. unifilis Troschel, 1848 (Testudines, Podocnemididae).

Paulo Emilio Vanzolini

doi:10.1590/s0001-37652003000400002

Abstract

Data on clutch size and hatching success of P. expansa were gathered for seven beaches traditionally used by the species and re-analyzed statistically by means of regression analysis, of the number of eggs on the number of females (or nests) and of the number of young on the number of eggs. All regressions were linear, passed through the origin and had excellent fits. Average clutch size varied from 75 to 123, and presented geographic differentiation: (i) Rio Orinoco, (ii) Rio Trombetas + Rio Branco and (iii) Rio Juruá + Rio Purus. Average hatching success was ca. 83%. In P. unifilis there was also geographic variation in clutch size, the Iquitos area showing the highest values. Hatching success of P. unifilis was uniformly high: only one sample, from Iquitos, had less than 90% success. The outstanding fit of the clutch size regressions leads one to consider egg volume variability, which was found to be high in both species, in contradiction with current optimal egg size theory.

Highlights

Turtles whose reproductive cycle is geared to the alternation of river flood/low flow are sensitive to the damming of large rivers for hydroelectric projects, which unavoidably involves regularization of regime, and obliteration of fluvial cycles
This is the case with the South American species of Podocnemis
P. expansa was described by Schweigger in 1812

Summary

Introduction

Turtles whose reproductive cycle is geared to the alternation of river flood/low flow are sensitive to the damming of large rivers for hydroelectric projects, which unavoidably involves regularization of regime, and obliteration of fluvial cycles. This is the case with the South American species of Podocnemis. P. expansa (“tartaruga”, turtle par excellence) is a widely distributed (Wermuth and Mertens 1996), very large, even spectacular animal, whose females lay their eggs communally, in herds frequently very numerous, on traditional beaches. Due to gregarious egg-laying, and to irrational human predation, it has been the object of much concern, and effort is currently being spent on conservation

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