Low reproductive success of leatherback turtles, Dermochelys coriacea, is due to high embryonic mortality

We examined the mechanism responsible for low reproductive success in leatherback turtles (Dermochelys coriacea) at Playa Grande, Costa Rica: low egg fertilization versus high rates of embryonic death. Leatherbacks at this beach had a high rate of fertility ((X) over bar = 93.3% +/- 2.5%, n = 819). We incubated 10 eggs from every clutch encountered of 19 females during 3 months of the 19981999 nesting season. Fertility rate of some females decreased during the nesting season, but overall was high. Detection of fertility was difficult using standard methods because fertility rates cannot be determined accurately from nests excavated after hatching because of egg decomposition. Removal and incubation of eggs from nests provided a better estimate. Embryonic death, particularly in the beginning of incubation before embryos are visible to the unaided eye, was the cause of low hatching success in this population. Hatching success increased with increasing fertility and differed between females, with some mothers having 71-81% success and others 23-32%. Embryonic death and not low egg fertility drives poor recruitment at Playa Grande. Improved conservation of this species at Playa Grande will require a better understanding of the mechanism behind embryonic death. (C) 2003 Elsevier Ltd. All rights reserved.