Abstract
Leatherback sea turtles (Dermochelys coriacea) nest on dynamic, erosion-prone beaches. Erosive processes and resulting nest loss have long been presumed to be a hindrance to clutch survival. In order to better understand how leatherbacks cope with unstable nesting beaches, I investigated the role of beach erosion in leatherback nest site selection at Playa Gandoca, Costa Rica. I also examined the potential effect of nest relocation, a conservation strategy in place at Playa Gandoca to prevent nest loss to erosion, on the temperature of incubating clutches. I monitored changes in beach structure as a result of erosion at natural nest sites during the time the nest was laid, as well as in subsequent weeks. To investigate slope as a cue for nest site selection, I measured the slope of the beach where turtles ascended from the sea to nest, as well as the slopes at other random locations on the beach for comparison. I examined temperature differences between natural and relocated nest sites with thermocouples placed in the sand at depths typical of leatherback nests. Nests were distributed non-randomly in a clumped distribution along the length of the beach and laid at locations that were not undergoing erosion. The slope at nest sites was significantly different than at randomly chosen locations on the beach. The sand temperature at nest depths was significantly warmer at natural nest sites than at locations of relocated nests. The findings of this study suggest leatherbacks actively select nest sites that are not undergoing erosive processes, with slope potentially being used as a cue for site selection. The relocation of nests appears to be inadvertently cooling the nest environment. Due to the fact that leatherback clutches undergo temperature-dependent sex determination, the relocation of nests may be producing an unnatural male biasing of hatchlings. The results of this study suggest that the necessity of relocation practices, largely in place to protect nests from erosion, should be reevaluated to ensure the proper conservation of this critically endangered species.
Highlights
The leatherback sea turtle (Dermochelys coriacea), once among the most abundant of the world’s marine turtles (Pritchard 1982), has become listed as an IUCN critically endangered species (Sarti-Martínez 2000)
This threat stems from the dynamic, erosion-prone nature of leatherback nesting beaches (Eckert 1987), where erosion has been estimated to be responsible for 36-50% leatherback nest loss (Mrosovsky 1983)
Some management programs have implemented the practice of nest relocation, where leatherback eggs are physically relocated from natural nest sites to other areas of the beach deemed more stable
Summary
The leatherback sea turtle (Dermochelys coriacea), once among the most abundant of the world’s marine turtles (Pritchard 1982), has become listed as an IUCN critically endangered species (Sarti-Martínez 2000). Some management programs have implemented the practice of nest relocation, where leatherback eggs are physically relocated from natural nest sites to other areas of the beach deemed more stable. I predicted that beach slope would be used by leatherbacks coming ashore as a cue for assessing nest site stability Another objective of my research was to examine whether current nest relocation practices at Playa Gandoca have the potential to affect sex ratios of hatchlings. Over 50% of naturally deposited nests at Playa Gandoca are relocated to other areas of the beach deemed more stable, largely in response to presumed threats of erosion, as part of current conservation protocols (Chacón & Eckert 2007, this study). To investigate whether relocation practices were having a similar effect at Playa Gandoca, I tested the hypothesis that nest relocation influences the temperature of the nest environment
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