Estimating the number of green and loggerhead turtles nesting annually in the Mediterranean

Abstract

Most species of marine turtle breed every two or more years and it is the norm for females to lay more than one clutch of eggs within a nesting season. Knowing the interval between breeding seasons and the clutch frequency (number of clutches laid by an individual in a breeding season) of females allows us to assess the status of a nesting population. At Alagadi Beach, Northern Cyprus, over a period of 6 years (1995–2000), we attributed 96% of green Chelonia mydas and 80% of loggerhead Caretta caretta turtle clutches to known individual females. This intensive level of monitoring enabled us to estimate the clutch frequency for both species. Using four different methods we estimated clutch frequency to be 2.9–3.1 clutches per female for green turtles and 1.8–2.2 clutches per female for loggerhead turtles. The median interval between nesting seasons for green turtles was 3 years, and for loggerhead turtles it was 2 years. Utilizing these parameters and available data from other beaches that are monitored regularly, we estimate that there are 2,280–2,787 logger-head and 339–360 green turtles nesting annually at these sites in the Mediterranean. This highlights the Critically Endangered status of this population of green turtles. Furthermore, as conventional beach patrols underestimate clutch frequency, these population estimates are likely to be optimistic.