Estimates of age and growth in a population of green sea turtles (Chelonia mydas) from the Indian River lagoon system, Florida: a skeletochronological analysis

Abstract

The Indian River lagoon system harbors a dynamic population of juvenile green sea turtles (Chelonia mydas). This foraging or developmental population occupies the lagoon year-round and periodically experiences cold-stunning events that kill a portion of the population. A sample of 59 C. mydas (28-74 cm straight carapace length) from the December 1989 cold-stunning event was aged by skeletochronology, yielding age estimates of 3-14 years. Mean growth-rate estimates range from 30 to 52 mm/year for most age and size classes, with means for the 6- to 11-year age classes (44-49 mm/year) not significantly different but greater than those of the youngest and oldest classes (3-5 and 12 years old, respectively) (32-38 mm/year). Because of the lack of adults and near-adults in the sample, growth models (e.g., Gompertz) do not yield biologically realistic asymptotes, hence they do not provide accurate estimates of age at sexual maturity. The age estimates suggest that the western Atlantic C. mydas change from a pelagic to a neritic life predominantly as 5- to 6-year-olds and, in central Florida, juveniles may live in a developmental habitat for 6 or more years.

Navigation and seasonal migratory orientation in juvenile sea turtles

“…Thus, the majority of loggerheads used for these experiments were probably at least 7·years old. Estimates of ages for juvenile green turtles inhabiting inshore waters in Florida range from 2·years at 21·cm to 7·years at 44·cm, indicating that the green turtles obtained for our study were at least 2·years of age (Zug and Glor, 1998).…”

Back-calculating length from skeletal growth marks in loggerhead sea turtlesCaretta caretta

“…Early studies by Zug and his colleagues (Zug et al 1986, Parham & Zug 1997) used ventral radius measurements from the center of the medullary cavity to the ventral edge of the humerus cross-section. Later works by Zug and his colleagues switched to the use of long-axis (lateral) diameter measurements as described here (Zug et al 1995, Zug & Glor 1998. The study by Bjorndal et al (2003) of pelagic stage loggerheads returned to the use of ventral radius measurements taken from the center of the medullary cavity to the ventral edge of the humerus, on an axis perpendicular to the longitudinal axis of the cavity.…”

Kemp's Ridley Sea Turtle Saga and Setback: Novel Analyses of Cumulative Hatchlings Released and Time-Lagged Annual Nests in Tamaulipas, Mexico

“…At approximately 8-10 inches (20-25 cm) carapace length, juveniles leave the pelagic environment and enter nearshore developmental habitats such as protected lagoons and open coastal areas rich in sea grass and marine algae. Growth studies using skeletochronology indicate that green sea turtles in the western Atlantic shift from the oceanic phase to nearshore developmental habitats after approximately 5-6 years (Bresette et al 2006;Zug and Glor 1998). Within the developmental habitats, juveniles begin the switch to a more herbivorous diet, and by adulthood feed almost exclusively on seagrasses and algae (Rebel 1974), although some populations are known to also feed heavily on invertebrates (Carballo et al 2002).…”