Survival from egg to maturity in a declining population of loggerhead sea turtles, Caretta caretta
Previous estimates of survival rates of sea turtle eggs or hatchlings to adulthood depend upon the assumption that their populations are neither increasing nor decreasing in numbers. The assumption is made in spite of the fact that recent interest in sea turtle demography stems from the belief that populations are in decline. This paper presents estimates of the survival rate from egg to maturity necessary to maintain a population of loggerhead turtles, Caretta caretta, at its present observed rate of decline. Conventional demographic equations were used along with values of adult survivorship, fecundity and alternative estimates of age at maturity from the literature. Results indicate that the proportion of eggs surviving to adulthood lies between 0.0009 and 0.0018 in this declining population, as opposed to an estimated value of 0.0025 in the unlikely event that the population is stationary. These results suggest that previous studies have overestimated survival of eggs or hatchlings to maturity in sea turtle populations. The methodology may be used to assess gross survivorship from egg to adulthood in increasing or decreasing populations of any species in which adults and eggs are more easily studied than are juveniles.
Frazer, N. B. 1986. Survival from egg to maturity in a declining population of loggerhead sea turtles, Caretta caretta. Herpetologica 42:47-55.