Artificial incubation of yellow-headed sideneck turtle Podocnemis unifilis eggs to reduce losses to flooding and predation, Cojedes and Manapire Rivers, … (original) (raw)
Related papers
2010
Although widespread in South America, the yellow-headed sideneck turtle Podocnemis unifilis is considered 'Vulnerable' in Venezuela. A large proportion of eggs of this riverine species may be lost due to predation (including collection by humans) and flooding. As a technique to enhance reproductive success, transfer of wild-laid eggs to protected zones for incubation has been successfully carried out. This study undertaken in 2009, evaluated the hatch success of clutches transferred to artificial nest chambers at protected locations compared with natural clutches left in situ along stretches of the Cojedes and Manapire rivers (Venezuela). Along the Cojedes River, 78 turtle nests were located, 27 of which were excavated and eggs transferred for incubation. In the Manapire River, 87 nests were located, eggs from 13 of which were transferred for incubation. In the Cojedes River, 28.2% of study clutches (n=22) were lost due to predation and flooding; in the Manapire River, 85% of nests (n=74) were lost due to predation (humans and other animals). At Cojedes River, hatching success of eggs in artificial nests was 88.2% and 63.2% in natural nests. At Manapire River, hatching success of eggs in artificial nests was 42% and 0% in natural nests.
Conservation …, 2010
Although widespread in South America, the yellow-headed sideneck turtle Podocnemis unifilis is considered ‘Vulnerable’ in Venezuela. A large proportion of eggs of this riverine species may be lost due to predation (including collection by humans) and flooding. As a technique to enhance reproductive success, transfer of wild-laid eggs to protected zones for incubation has been successfully carried out. This study undertaken in 2009, evaluated the hatch success of clutches transferred to artificial nest chambers at protected locations compared with natural clutches left in situ along stretches of the Cojedes and Manapire rivers (Venezuela). Along the Cojedes River, 78 turtle nests were located, 27 of which were excavated and eggs transferred for incubation. In the Manapire River, 87 nests were located, eggs from 13 of which were transferred for incubation. In the Cojedes River, 28.2% of study clutches (n=22) were lost due to predation and flooding; in the Manapire River, 85% of nests (n=74) were lost due to predation (humans and other animals). At Cojedes River, hatching success of eggs in artificial nests was 88.2% and 63.2% in natural nests. At Manapire River, hatching success of eggs in artificial nests was 42% and 0% in natural nests
Journal of Zoology, 1998
Mortality factors and hatching success of 422 terecay turtle (Podocnemis unifilis) nests on seven beaches in the Nichare and Tawadu Rivers, Venezuela, were studied following the oviposition phase. Beaches (3.4-28.4 km2), predominantly sandy, and bordered by riparian vegetation, were searched to record nest numbers and their distribution. Elevation and surrounding plant cover were measured for each nest. Most nests were found close to the vegetation's edge (0-11 m), at a significant distance from the water's edge (21-80 m), in more open ground, and along the highest points of the beach (1-2.5 m above the water's edge). Nest density was positively correlated with beach elevation but not with beach dimensions. Most nests were concentrated in less than 10% of beach area, along the upper 20% of the beach. Average clutch size was 20.1±1.7 eggs, but larger clutches were found significantly further away from vegetation. No significant correlation between hatching success and clutch size was found.A large proportion of nests were subject to animal and human predation but environmental factors (especially flooding) affected some. The major cause of egg loss was human predation. Most clutches collected by humans were found away from vegetation, on the upper 10-20% of beaches, in exposed unvegetated sites. Animals preyed upon those nests along the vegetation's margin (1-2 m) in the upper 0-9% of beaches, in sites of high plant cover (75-100%). Nests reaching the incubation phase were mainly located in the open areas, which are more prone to human predation. About three-quarters of nests showed high hatching rates (91-100%). However, hatchability was highest furthest away from the vegetation. Our results indicate that humans are collecting eggs mostly from sites in which nests have the larger clutches and the higher potential hatching success. Because of this relationship between nest viability and location, sustainable yield programmes must consider where harvesting can take place and must avoid the application of standard harvests per nest.
Survival of the terecay turtle (Podocnemis unifilis) in the Nichare-Tawadu Rivers, Venezuela
Journal of Zoology, 1998
Mortality factors and hatching success of 422 terecay turtle (Podocnemis uni®lis) nests on seven beaches in the Nichare and Tawadu Rivers, Venezuela, were studied following the oviposition phase. Beaches (3.4±28.4 km 2 ), predominantly sandy, and bordered by riparian vegetation, were searched to record nest numbers and their distribution. Elevation and surrounding plant cover were measured for each nest. Most nests were found close to the vegetation's edge (0±11 m), at a signi®cant distance from the water's edge (21±80 m), in more open ground, and along the highest points of the beach (1±2.5 m above the water's edge). Nest density was positively correlated with beach elevation but not with beach dimensions. Most nests were concentrated in less than 10% of beach area, along the upper 20% of the beach. Average clutch size was 20.1 1.7 eggs, but larger clutches were found signi®cantly further away from vegetation. No signi®cant correlation between hatching success and clutch size was found.
2020
Nesting site selection is of great ecological and evolutionary importance for turtles, because it is a key determinant of individual reproductive success. In this study we evaluated the effects of two types of nesting substrate (sand bank and clay banks) on the incubation success of a generalist nesting species, Podocnemis unifilis, in a floodplain area in the Brazilian Amazon. Nesting characteristics were recorded during the nesting seasons of 2012–2014, when 634 nests were monitored throughout the incubation period. Mean size of laying females did not vary between substrate types (sand = 24.71 cm; clay = 25.44 cm; P = 0.2054), nor was clutch size related to females’ sizes. However, females that nested on sand bank exhibited a clearer pattern of nest positioning relative to distances to vegetation and water line than those laying eggs on clay banks. Mean egg size (40.24 ± 2.68 mm) and weight (21.09 ± 5.46 g) did not vary between types of nesting substrate, and there was no variatio...
Canadian Journal of Zoology, 2006
The hatching success of leatherback turtles, Dermochelys coriacea (Vandelli, 1761), is influenced by heterogeneously distributed ecological factors. However, the hatching success according to nest-site selection has rarely been studied and little is known about the role of nest-site selection and infertile (yolkless) egg production on the predation rate and development of fertile eggs in leatherback turtle nests laid in French Guiana. A field study of 99 leatherback turtle nests was conducted to quantify the relationships between hatching success and (i) the nest-site selection (i.e., vegetation line, sea tide line) and (ii) the infertile eggs, especially their state after incubation (i.e., hydrated or dehydrated) and their effects on predation rate. We found that hatching success on this beach was very low (38.2%). This study illustrates that nest-site selection influences the predation rate and the dehydration of yolkless eggs, while the production of yolkless eggs by leatherback turtles has consequences on nest success. The proportion of yolkless eggs in the clutch, as well as their status at the end of incubation (hydrated or not, preyed upon), correlates with predation rate, development of yolked eggs, and hatching success. There was a significant relationship between nest location (relative to high tide line and vegetation line) and both the predation rates of eggs and the percentage of dehydrated yolkless eggs within a clutch. The production of yolkless eggs was related to hatching success and supports the hypothesis that yolkless eggs have a positive effect on the future of the clutch.