Factors that control the emergence of green turtle hatchlings from the nest

Sea turtle hatchlings typically emerge at night and temperature has often been suggested as controlling the timing of emergence. Models based on threshold temperatures, above which hatchling activity is inhibited, are not fully compatible with the observed temporal distribution of emergence. This study reports on the temporal pattern of hatchling emergence and associated sand temperature profiles and tidal regimes at Heron I., in the southern Great Barrier Reef, Australia. A new model is proposed on the basis of sand temperature gradients instead of the absolute temperature of the sand surface. The excellent fit between the temperature gradient model and the observed pattern of emergence suggests that it is the temperature gradient in the top 10cm of the sand column rather than an absolute temperature per se that turtle hatchlings use to time their emergence.