Characterization of size-at-age and somatic growth patterns for Kemps ridleys in the Gulf of Mexico using skeletochronology

With appropriate validation and calibration, the technique of skeletochronology, or analysis of skeletal growth marks (GMs), has the potential to provide age data (Castanet et al. 1993), as well as growth rates comparable to those yielded by traditional mark-recapture methods (Campana 1990, Casale et al. 2011). For the Cheloniid sea turtles, skeletochronological analysis has typically focused on the humerus bone located in the upper portion of each front flipper, as early assessments indicated that this bone exhibits the least amount of resorption, or destruction of early GMs throughout life (Zug 1986). In the Atlantic, annual GM deposition in Kemp?s ridley humeri has been validated using several methods (Snover 2002; Snover and Hohn 2004) and a proportional relationship between humerus and somatic growth has been demonstrated (Snover 2002), allowing validated back-calculation of straightline carapace lengths (SCLs) from GM diameters. Together, these findings provided a foundation for estimation of growth rates, juvenile stage durations, and mean age at maturation for Kemps ridleys stranded in the mid-Atlantic region of the U.S. east coast during the mid- to late 1990s (Snover et al. 2007a). Previous, un-validated skeletochronological analysis has been conducted using humeri of Kemp?s ridleys in the Gulf of Mexico that predominantly stranded during the late 1970s and early 1980s (Zuget al. 1997). However, to address validation and collect longer-term age and growth data, additional skeletochronological analysis for Kemp's ridleys in the Gulf of Mexico is still needed.

Each humerus was flensed of tissue, boiled, dried, and histologically processed (decalcified, microtomed, stained, mounted on a microscope slide) according to the methods of Avens et al. (2012). Sequential, partial, digital images of histologically processed humerus sections were taken at 4? magnification and partial images were then pieced together using Adobe Photoshop to form complete, calibrated, digital images of entire humerus sections that could be used for GM counts and measurements. Two readers conducted independent assessments followed by joint assessments to reach consensus regarding the number and placement of the lines of arrested growth or LAGs that demarcate the outer edges of GMs for all 340 humeri. In addition, digital diameter measurements of all LAGs in each humerus section image have been completed for all 340 humeri.

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