ALVES-JUNIOR, JRF et al. Reproductive indices in natural nests of giant Amazon river turtles Podocnemis expansa (Schweigger, 1812) (Testudines, Podocnemididae) in the Environmental Protection Area Meanders of the Araguaia river. Braz. J. Biol. [online]. 2012, vol.72, n.1, pp.199-203.
ISSN 1519-6984. http://dx.doi.org/10.1590/S1519-69842012000100024.
The conservation management of the giant amazon river turtles in the medium Araguaia river
The nesting beaches of giant south american river turtle Podocnemis expansa (picture) were monitored during the 2008 reproductive season, in the Environmental Protection Area Meanders of the Araguaia River, state of Goiás, Brazil, by researches of Chico Mendes Biodiversity Conservation Institute and Uberlândia Federal University.
A total of 29.538 live hatchlings were collected from the nests and after the two-week period in the nursery, 29.251 were released on the banks of the Araguaia river, representing a mortality rate of 0.97% in the nursery. Hatched eggs represented 94.63% and unhatched eggs 94.63%, while survival and mortality rates were 94.24% and 5.76%, respectively. Oil eggs were not observed in the evaluated nests.
In general, excessive management of the reproductive process of chelonians can impair the trophic chain and interfere in the population dynamics of other species existing at a location, insofar as it changes the availability of food, and is therefore not recommended.
The reproductive efficiency of the wild population of P. expansa can be affected by many environmental factors such as temperature, humidity and rainfall. In addition, men-maid factors like the presence of chemical in the water and the potential for infectious disease also have significant impact. The reproductive indices data obtained from this study are indispensable for future investigations of hatching anomalies.
The goal of this study was to determine the percentage of hatched and unhatched eggs, hatchling survival and mortality, and the average number of live and dead hatchlings, unhatched eggs and total number of eggs of P. expansa from natural nests on that region.
Although the status of natural populations is unknown, the basis of turtle preservation activities involves nest and hatchling protection and management.
The hatchlings were removed from the egg chambers and counted only when they were considered "mature". It was also recorded the number of live hatchlings, dead hatchlings and unhatched eggs.
The hatchlings removed from the egg chambers were taken to a nursery located at the headquarters of the Amazonia Chelonia Project, where they were kept for 15 days to lose their egg odor, after which they were released on the river bank.
The mean total number for eggs and of dead hatchlings per female were lower than many reported works to the state of Amazonas. However, the mean number of live hatchlings and the hatching rate in the researched region were higher than those found by the aforementioned papers.
The high standard deviation in the number of dead hatchlings and unhatched eggs, found in this study, was attributed to the total loss of some nests caused by the low level of these nests in relation to the water sheet of the Araguaia river, which resulted in their partial inundation, altering the proper humidity coefficient for embryo development.
The specialized bibliography states that hatchlings should be kept in nurseries for periods of up to 15 days, sufficient time for hardening of the carapace, umbilical cicatrization and elimination of the characteristic strong odor of the fat of the egg. This procedure hinders predation by natural enemies and increases the chances of survival of hatchlings, thus justifying keeping them for 15 days in the nursery in order to reduce predation pressure.
The most common predators of P. expansa eggs and hatchlings on the studied locale are the black-headed vulture (Coragyps atratus), the carcara plancus (Polyborus plancus), the yellow-headed caracara (Mivalgo chimachima), the tegu lizard (Tupinambis teguixin), the ring-tailed coati (Nasua nasua), crab-eating fox (Cerdocyon thous), fishes of the genus Serrasalmus spp, piraiba (Brachyplatystoma filamentosum) and jau (Paulicea luetkeni), and crocodiles like Paleosuchus spp. e Caiman crocodilus, end many others.
This work was financial supported by São Paulo Foundation of Research Financial Support, Chico Mendes Biodiversity Conservation Institute and Uberlândia Federal University.
Rafael Antônio Machado Balestra