Snover and Hohn: Validation and interpretation of skeletal marks in Caretta caretta and Lepidochelys kempu 



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(Chelonia mydas; Zug and Glor, 1998; Zug et al., 2002) 

 and Kemp's ridley (Lepidochelys kempii; Zug et al., 

 1997) sea turtles. In each of these studies, the authors 

 used various protocols to estimate the number of lay- 

 ers lost. Any protocol estimating the number of layers 

 lost to resorption relies on the concept that the spatial 

 pattern of the LAGs is representative of the growth of 

 the animal. To confirm this assumption, researchers 

 must establish a correlation between bone dimensions 

 and body size (Hutton, 1986; Klinger and Musick, 1992; 

 Leclair and Laurin, 1996). 



Two of the studies that have applied skeletochronology 

 to sea turtles have demonstrated annual GMs in both 

 juvenile (Klinger and Musick, 1992) and adult (Coles et 

 al., 2001) loggerhead sea turtles. Numerous additional 

 studies have applied skeletochronology to sea turtles. 

 To date, the technique has been applied to loggerhead 

 (Zug et al., 1986; Zug et al, 1995; Bjorndal et al., 2003), 

 green (Bjorndal et al., 1998; Zug and Glor, 1998; Zug 

 et al., 2002), Kemp's ridleys (Zug et al., 1997), and 

 leatherback [Dermochelys coriacea) (Zug and Parham, 

 1996) sea turtles. What is needed for the appropriate 

 application of skeletochronology to sea turtle species 

 is additional validation of annual GMs and a guide to 

 their interpretation. Furthermore, because resorption is 

 a problem in sea turtle bones, the validation of a pro- 

 portional allometry between bone and somatic growth 

 is necessary to enable back-calculation. 



In this study, we address each of these issues for 

 Kemp's ridley and loggerhead sea turtles by examining 

 humeri from known-age animals. We analyzed each 

 humerus without prior knowledge of the animal's age 

 and we present the results of our analyses, including 

 reinterpretations of bones for which we were incorrect 

 in our age assessments. The purpose of this study was 



to use known-age samples both to validate the likeli- 

 hood that GMs are annual and as a learning tool for the 

 best guide to interpreting GM in wild animals. 



Materials and methods 



We obtained samples from two known-age loggerhead 

 and 13 known-age Kemp's ridley sea turtles (Table 1). 

 In addition, we collected samples from 240 wild logger- 

 head and 262 wild Kemp's ridley sea turtles. With the 

 exception of one loggerhead, CC-1, all of the sea turtles 

 died in the wild and samples were retrieved from the 

 carcasses. Sample CC-1 died in captivity. 



Sample preparation 



Zug et al. (1986) analyzed skeletal elements of the cra- 

 nium and right forelimb of loggerhead sea turtles and 

 determined that the humerus was most suited to skeleto- 

 chronology studies. Therefore, we also used the humerus. 

 Specimens arrived as either dried bones or whole flippers. 

 For flippers, we dissected out the humerus, which v/as 

 then flensed, boiled, and air-dried for at least two weeks. 

 We cross-sectioned each humerus at a site just distal to 

 the deltopectoral crest. At this site, the ratio of cortical 

 to cancellous bone is highest (Zug et al., 1986), and the 

 region immediately distal to the insertion scar of the 

 deltopectoral muscle on the ventral side of the bone maxi- 

 mizes that ratio (see Zug et al., 1986 for diagrams of the 

 loggerhead sea turtle humerus). This site also provided 

 a landmark that allowed us to section at equivalent sites 

 on every humerus. 



We removed 2-3 mm thick sections at that site us- 

 ing a Buehler® isomet low speed saw. This section was 



