Age and growth of loggerhead sea turtles in southern Brazil

The juvenile and subadult stages of loggerhead sea turtlesCaretta carettaare poorly studied in Brazil. We present age estimates and a growth model for loggerhead sea turtles in the South Atlantic Ocean obtained through skeletochronological analysis of humeri from both neritic and oceanic stage individuals. The age estimation was based on the number of growth marks in the humerus; however, for larger turtles early growth marks were resorbed and therefore it was necessary to use a correction factor to account for the lost growth marks. The estimated ages indicate that the oceanic stage lasts 8 to 19 yr (average: 11.5 yr). Schnute’s growth model was fit to age-at-length data, as its shape is versatile and it does not require data from all life stages (i.e. hatchlings through adults near asymptotic size). However, because the shape of Schnute’s curve was almost linear for the age window comprising our data, a linear regression ultimately provided a better fit to the data, yielding an age at maturation estimate of 32 yr. Somatic growth rates were calculated through incorporation of the Body Proportional Hypothesis into conversion of growth mark measurements to estimates of carapace length. Growth rates from neritic stage South Atlantic loggerheads were similar to those reported for neritic loggerhead sea turtles from the North Atlantic Ocean, but were lower than those of oceanic loggerheads from the South Atlantic Ocean. This finding suggests that local environmental conditions influence loggerhead sea turtles’ growth rates as well as the energy expenditure during migrations, energy allocation and genetic origin.