Age and growth determination by skeletochronology in loggerhead sea turtles (Caretta caretta) from the Mediterranean Sea

Skeletochronology was applied to humerus bones to assess the age and growth rates of loggerhead sea turtles (Caretta caretta) in the Mediterranean Sea. Fifty-five dead turtles with curved carapace lengths (CCL) ranging from 24 to 86.5 cm were collected from the central Mediterranean. Sections of humeri were histologically processed to analyze annual growth marks. Two approaches were used to estimate the somatic growth in the form of a von Bertalanffy growth function. The first approach was based on calculating the total number of growth marks, which corresponds to the age of turtles at death. The second approach estimates the carapace length at old growth marks in order to provide the growth rate of each turtle. The observed individual growth rates ranged from 1.4 to 6.2 cm yr-1, and showed both elevated inter- and intra-individual variability possibly related to the environmental variability experienced by turtles during their lifetime. Both approaches gave similar results and suggest that Mediterranean loggerhead turtles take 14.9 to 28.5 years to reach a CCL of 66.5 to 84.7 cm. This size corresponds to the average size of nesting females found in the most important Mediterranean nesting sites and can be considered the approximate size at maturity.