Herbert Meier & Ingo Schaefer Fig. 8. The embryo will be clearly visible after four weeks of incubation. subside, while they can rather be found in the lagoons with their reduced currents that form at times of high water. Nevertheless it needs to be contemplated as to how far varying water depths indicate seasonal changes. According to information obtained from native human inhabitants of the natural habitats, matamatas lay their eggs in September/October when water levels are beyond their maxima. The eggs are deposited very close to the water, so that it is important for the turtles to pick a time when their clutches are unlikely to be flooded, which means a time when water levels have begun to subside continually. The hatchlings then emerge in February/March around the start of the next rainy season when water levels begin to rise once more. The availability of game fish for the local people likewise depends on water levels: The Indians catch more fish during low water than at times of high water. We create a similar situation through seasonally rationing the turtles’ food: more food (200 g or more per specimen) is made available during the time of low water, in our case, in winter, when water exchanges are limited. Courting (and mating?) activities intensify in summer when “food is scarce” and peak around February/March. Seasonally fluctuating water exchanges are still continued in 2008, as are the varying amounts of food. Another criterion promoting seasonality in the greenhouse maintained by Meier is to be found in the natural diel and annual seasonal cycles. While these fluctuations are little expressed and may therefore be irrelevant in the natural habitats, there is still a chance that they might have gained in importance after more than ten years of keeping. Oviposition In nature it appears to happen more often that a clutch is covered only insufficiently. The reason for this is certainly the available substrate. Compacted loamy soils that have superficially dried out by the sun make it quite impossible for the turtles to excavate proper nest pits. Fig. 9. Another week or two to go until hatching: the baby turtle has pierced the shell of its egg all on its own and lies on its back. 28 RADIATA 17 (3), 2008
The Matamata, Chelus fimbriata Fig. 10. A matamata has left its egg a few days prematurely. Fig. 11. A hatchling immediately after leaving its egg. Fig. 12. A juvenile matamata of a few days of age. Fig. 13. A juvenile Chelus fimbriata. Fig. 14. A juvenile matamata of a few days of age. RADIATA 17 (3), 2008 29
