Snover and Hohn: Validation and interpretation of skeletal marks in Caretta caretta and Lepidochetys kempii 



687 



Discussion 



Validation of the annual nature of growth marks 



Our results supported annual deposition of GMs in log- 

 gerhead and Kemp's ridley sea turtles. The headstarted 

 and older CWT Kemp's ridley sea turtles in particular 

 highlighted the likelihood of annual marks. These ani- 

 mals displayed sharp and regularly spaced LAGs that 

 were consistent with the actual ages of the animals. 

 The results from the CWT Kemp's ridley sea turtles also 

 emphasized the difficulties in interpreting early GMs. 

 From these animals we concluded that in general Kemp's 

 ridley sea turtles deposit a poorly defined annulus in 

 their first year and well-defined LAGs starting with the 

 end of the second year and in following years. 



For loggerhead sea turtles, only CC-2 spent any time 

 in the wild. The number of GMs deposited after the 

 animal was released (determined from the appearance 

 of the anomalous triplet of LAGs) was consistent with 

 the number of years for which the animal was at large, 

 considering that the first mark was deposited at release. 

 This indicated that not less than one GM was deposited 

 per year, and that additional or supplemental LAGs 

 or annuli indistinguishable from annual lines may be 

 deposited under extreme conditions, such as at the time 

 of release into the wild. Fortunately, in this case, these 

 extreme conditions were not frequent enough to have a 

 serious impact on age estimates. For the life-time cap- 

 tive animal, CC-1, our estimated minimum age was 

 five years shorter than the actual age of 29.4 years and 

 clearly demonstrated that not more than one GM was 

 deposited each year. Because of the relatively large size 

 of the sea turtle humerus, in comparison to phalanges 

 of amphibians, rapprochement did not appear to be a 

 problem in our attempts to discern LAGs. This bone 

 was similar in appearance to adult wild loggerhead and 

 Kemp's ridleys sea turtles with rapprochement of the 

 peripheral LAGs and resorption of most of the interior 

 GMs. Although accurate age estimates cannot be made 

 of these bones through skeletochronology, if rapproche- 

 ment correlates to the timing of sexual maturity, counts 

 of the compressed GMs can provide valuable informa- 

 tion on postreproductive longevity and adult survival. 

 This information can be combined with average age at 

 reproductive maturation for piecing together the life 

 history of sea turtles. Although our sample size for 

 loggerhead sea turtles was very small (two), the size 

 complements a tetracycline-injection study that previ- 

 ously validated annual GMs for juvenile loggerhead 

 sea turtles from Chesapeake Bay (Klinger and Musick, 

 1992). In addition, an adult loggerhead sea turtle from 

 that same study stranded dead 8.25 years after in- 

 jection and provided evidence of annual deposition of 

 growth marks in adults (Coles et al., 2001). 



The indirect validation results for Kemp's ridley sea 

 turtles highlighted the cyclic nature of bone growth; 

 bone deposition increases from late spring through early 

 summer to fall and no bone deposition occurs from De- 

 cember to spring. From this information we inferred 



10 



11 



B 



-9- 

 -10- 



11 



=14/15= 



16 



12 



13 



17 



19, 



20 



c 



-24- 



"./-23- 



.-22- 



J2.Y 



J20- 



Figure 4 



Images of different portions of the humerus cross-sec- 

 tions of CC-1 (Caretta caretta). Black bar represents 1 

 mm in length for all views. (A and Bl The outer edge 

 of the bone is at the top of the photo. (C) The outer 

 edge of the bone is towards the bottom of the photo. For 

 all views, lines of arrested growth (LAGs) are labeled 

 with numbers; low numbers represent the most recently 

 deposited LAGs (near the outer edge of the bone) and 

 higher numbers represent the earlier LAGs. 



that LAGs form annually in the spring for Kemp's rid- 

 ley sea turtles that strand along the mid- to southeast 

 U.S. Atlantic coast and that these LAGs are visible at 

 the edges of the bones by late spring to early summer. 



