Hatching Success of the Leatherback Turtle (Demochelys coriacea) in Natural Nests at Playa Grande, Costa Rica
Schwandt, Andrea J.
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Playa Grande, Costa Rica supports a population of about 1500 nesting leatherback turtles, making it the third most important nesting beach in the world and the most important beach in the Pacific. During the 1993-94 nesting season, effects of poaching and predation were studied on this beach, hatching success and fate of the eggs released in natural nests were determined, and relationships between hatching success and various biotic and abiotic factors were examined. A sample of 82 nests was studied; 68 (82.9 %) of these remained undisturbed and survived until hatching. Tidal effects accounted for the majority of nest loss, destroying two clutches (2.4 % of the total) by frequent inundation and 7 clutches (8.6 %) by washing them away. Poaching and predation, which caused the death of 1.3 % and 2.4 % of the clutches, respectively, was much less prominent on Playa Grande than on other nesting beaches, due to extensive patrolling of the beach at night. 14.6 %of the study nests were oviposited below the high tide line, and the effects of tide resulted in significantly fewer of these nests surviving to hatching than those oviposited in the open beach area or within the vegetation. The mean emergence success for successful clutches was 54.2 %; most of the eggs which failed to hatch were infertile, possibly due to a lack of viable sperm in the population. Hatching success was negatively related to the number of yolked eggs in the clutch and positively related to the number of smaller, yolkless eggs deposited on top of the clutch. Yolkless eggs may serve as a thermal buffer or a source of moisture, and may prevent sand from falling into the spaces between yolked eggs, aiding in diffusion of 02 into the nest. Nests laid 0-5 m from the vegetation had a significantly lower hatching success than those laid 5-10 m from it and contained more maggot-infested eggs, due possibly to sand in this area containing more moisture. Repeated nesting attempts for 10 individual turtles indicate that ultimate hatching success may be related to the reproductive condition of the mother turtle.