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Methods
| Fieldwork occurred in August (nesting season) and October (hatching season) of 2012 and 2013, covering approximately 200 km of the river. In nesting season campaigns, nest searching occurs in the early morning hours, when we can locate the nests by the female turtle tracks. We marked each nest with a stake, georeferenced it, and opened most of them to count the total number of eggs and to measure environmental variables (distance to the river, nest height, slope, egg-chamber depth, depth to the first egg, and vegetation cover, and collected substrate samples to analyze sand granulometric fractions). The incubation period was recorded based on evidence such as female tracks, egg characteristics, and egg pigmentation to determine the oviposition date (Pezzuti & Vogt, 1999). The distance to the river was measured linearly from nests to the riverbank with 50 m measuring tape. The nest height was estimated with hoses filled with water and measuring tape, as described by Pantoja-Lima et al. (2009). We used an inclinometer (Starret) to verify the slope at the nest site. The egg-chamber depth, the distance from the surface of the nest to the bottom of the egg chamber, and the depth to the first egg were all measured with a millimeter rule (Pignati, Fernandes, Miorando, Ferreira, et al., 2013). The canopy coverage was estimated with a spherical densiometer model C (Lemmon 1956). We collected a sample of approximately 200g of sediment from the surface of 43 nests and classified it in particle size fraction with the sieve system (Folk 1974) in the Geology Laboratory of Federal University of Pará (UFPA). Canopy coverage estimation and granulometric analysis were made only for 2012 nests. A portion of 30 nests (24.74%) were unmanipulated to compare the hatching rate with manipulated nests. We recorded total and partial nest losses in all campaigns. The mortality causes were determined based on egg characteristics and external nest elements, such as predator tracks, distribution of shells from consumed eggs around the nests, and excavation characteristics on the nest surface. We counted the hatched and unhatched eggs in the hatching campaigns to determine the hatching rate. For the sex ratio analysis, five hatchlings per nest from 43 nests were humanly euthanized. We fixed in formalin 10% and then stored in alcohol 70% at the Laboratory of Aquatic Ecology and Fisheries in the UFPA. The sex identification was performed by the external analysis of gonad morphometry as described by Malvasio et al. (2012). Malvasio, A., Nascimento-rocha, M., Santos, D., Ataídes, G. De, Nascimento-rocha, J. M., & Santos, H. D. (2012). Morfometria e histologia das gônadas de machos e fêmeas recém-eclodidos de Podocnemis expansa e Podocnemis unifilis (Testudines, Podocnemididae). Acta Scientiarium, 34(1), 105–112. https://doi.org/10.4025/actascibiolsci.v34i1.7257 Pantoja-Lima, J., Pezzuti, J. C. B., Teixeira, A. S., Félix-Silva, D., Rebêlo, G. H., Monjeló, L. A. dos S., & Kemenes, A. (2009). Seleção de Locais de Desova e Sobrevivência de Ninhos de Quelônios Podocnemis no Baixo Rio Purus, Amazonas, Brasil. Revista Colombiana de Ciencia Animal, 1(1), 37–59. Pezzuti, J. C. B., & Vogt, R. C. (1999). Nesting Ecology of Podocnemis sextuberculata (Testudines, Pelomedusidae) in the Japurá River, Amazonas, Brazil. Chelonian Conservation and Biology, 3(3), 419–424. Pignati, M. T., Fernandes, L. F., Miorando, P. S., Ferreira, P. D., & Pezzuti, J. C. B. (2013). Nesting Site and Hatching Success of Podocnemis unifilis (Testudines: Podocnemididae) in a Floodplain Area in Lower Amazon River, Pará, Brazil. South American Journal of Herpetology, 8(3), 175–185. https://doi.org/10.2994/sajh-d-13-00006.1 |
