Abstract
Somatic growth rate data for wild sea turtles can provide insight into life‐stage durations, time to maturation, and total lifespan. When appropriately validated, the technique of skeletochronology allows prior growth rates of sea turtles to be calculated with considerably less time and labor than required by mark‐–recapture studies. We applied skeletochronology to 10 dead, stranded green turtles Chelonia mydas that had previously been measured, tagged, and injected with OTC (oxytetracycline) during mark–recapture studies in Hawaii for validating skeletochronological analysis. We tested the validity of back‐calculating carapace lengths (CLs) from diameters of LAGs (lines of arrested growth), which mark the outer boundaries of individual skeletal growth increments. This validation was achieved by comparing CLs estimated from measurements of the LAG proposed to have been deposited closest to the time of tagging to actual CLs measured at the time of tagging. Measureable OTC‐mark diameters in five turtles also allowed us to investigate the time of year when LAGs are deposited. We found no significant difference between CLs measured at tagging and those estimated through skeletochronology, which supports calculation of somatic growth rates by taking the difference between CLs estimated from successive LAG diameters in humerus bones for this species. Back‐calculated CLs associated with the OTC mark and growth mark deposited closest to tagging indicated that annual LAGs are deposited in the spring. The results of this validation study increase confidence in utilization of skeletochronology to rapidly obtain accurate age and growth data for green turtles.
Highlights
Understanding growth rates, life-stage durations, and age at maturation is critical for modeling sea turtle population trends and guiding management decisions for these threatened and endangered species (Heppell et al 2003)
This validation allows prior growth rates to be calculated from successive LAG diameters of Hawaiian green turtles
The current study extends the carapace length in which annual LAGs have been verified to 85.5 cm SCL, as we were able to indirectly validate annual LAG deposition in CM-10, which was not included in Snover et al.’s (2011) direct validation due to the lack of a visible OTC mark
Summary
Understanding growth rates, life-stage durations, and age at maturation is critical for modeling sea turtle population trends and guiding management decisions for these threatened and endangered species (Heppell et al 2003). Growth rate data are usually acquired through long-term capture, mark, recapture studies of wild populations of sea turtles (Heppell et al 2002). Analyzing growth marks retained in the bones of sea turtles through the technique of skeletochronology has provided an alternate and comparatively rapid means of acquiring a record of growth rates throughout life for individuals (Avens and Snover 2013). Skeletochronology has been applied to several species of sea turtles, allowing estimates of life stages, growth rates, age at maturation, and total lifespan (reviewed by Avens and Snover 2013).
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