SURVIVAL OF NESTS OF THE TERECAY TURTLE (PODOCNEMIS-UNIFILIS) IN THE NICHARE-TAWADU RIVERS, VENEZUELA

Mortality factors and hatching success of 422 terecay turtle (Podocnem is unifilis) 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. Elevatio n 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 d istance from the water's edge (21-80 m), in more open ground, and alon g the highest points of the beach (1-3.i m above the water's edge). Ne st density was positively correlated with beach elevation but not with beach dimensions. Most nests were concentrated in less than 10% of be ach area, along the upper 20% of the beach. Average clutch size was 20 .1+/-1.7 eggs, but larger clutches were found significantly further aw ay from vegetation. No significant correlation between hatching succes s and clutch size was found. A large proportion of nests were subject to animal and human predation but environmental factors (especially fl ooding) affected some. The major cause of egg loss was human predation . Most clutches collected by humans were found away from vegetation, o n the upper 10-20% of beaches, in exposed unvegetated sites. Animals p reyed upon those nests along the vegetation's margin (1-2 m) in the up per 0-9% of beaches, in sites of high plant cover (75-100%). Nests rea ching the incubation phase were mainly located in the open areas, whic h are more prone to human predation. About three-quarters of nests sho wed high hatching rates (91-100%). However, hatchability was highest f urthest away from the vegetation. Our results indicate that humans are collecting eggs mostly from sites in which nests have the larger clut ches and the higher potential hatching success. Because of this relati onship between nest viability and location, sustainable yield programm es must consider where harvesting can take place and must avoid the ap plication of standard harvests per nest.