Age and growth of loggerhead sea turtles (Caretta caretta) of coastal Georgia : An assessment of skeletochronological age-estimates

Abstract

Loggerhead sea turtles stranded on Cumberland Island (CI), Georgia provide skeletal samples to estimate the ages of individual turtles by skeletochronology. An initial study in 1986 used an average-thickness of humeral cross-section protocol to estimate individual ages and the minimum carapace length (CL) of nesting females to predict the average age at sexual maturity for the CI sample. The original data and two new CI samples are analyzed by average-thickness, correction-factor, and regression-growth protocols to reassess the original age estimates, to test the reliability of the three protocols, and to predict growth rates and age of sexual maturity. All protocols show moderate to high variation in one or more steps of the calculations of the age-estimates. The lowest variation occurs in the correction-factor protocol, and this protocol's assumption for the estimation of the number of resorbed growth layers matches best the observed pattern of bone growth in Caretta. The skeletochronological results show growth patterns (von Bertalanffy model) with asymptotes of 96 - 117 cm curved carapace length (CCL) and growth coefficients of 0.040 - 0.106 for the CI samples. These patterns predict sexual maturity occurring from 20 - 63 yr, assuming 92 cm (SCL) as the mean size at sexual maturity. Growth rate estimates range from 30 - 40 mm yr 1 for 40 - 49 cm SCL turtles to 10 - 35 mm yr 1 for 80 - 89 cm straight carapace length (SCL) turtles.