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Fishery Bulletin 102(4) 



fixed in 109c formalin then decalcified by using a com- 

 mercial decalcifying agent (RDO, Apex Engineering 

 Products Corporation, Calvert City, Kentucky). Time 

 to decalcification varied with the size of the bone and 

 the strength of the solution, usually between 12 and 36 

 hours. Following decalcification, 25-f.im thick cross-sec- 

 tions were made by using a freezing-stage microtome. 

 Sections were stained in Erlich's hematoxylin diluted 

 1:1 with distilled water (Klevezal, 1996) and mounted 

 on slides in 100% glycerin. 



Known-age sea turtles 



We received the humeri from each of two captive, known- 

 age loggerhead sea turtles after they died (Table 1). The 

 first specimen, CC-1, was held in an outdoor tank during 

 the summer months and inside a greenhouse during the 

 winter months (this turtle was the same captive female 

 noted in Swartz, 1997). The second, CC-2, was raised in 

 captivity for two years then released from Panama City, 

 Florida, into the Gulf of Mexico. 



For the Kemp's ridley sea turtles, we received humeri 

 from 13 dead known-age animals (Table 1). The head- 

 start Kemp's ridleys were raised in captivity for one 

 year, then released as part of a binational program oper- 

 ated jointly by state and federal U.S. agencies and the 

 Instituto Nacional de la Pesca (INP) of Mexico (Klima 

 and McVey, 1995). The coded-wire-tagged (CWT) Kemp's 

 ridley sea turtles were tagged and released as hatch- 

 lings. This tagging program is operated jointly by the 

 U.S. National Marine Fisheries Service (NMFS) Galves- 

 ton Laboratory and the INP of Mexico as a means of 

 gaining a better understanding of the early life history 

 of the Kemp's ridley sea turtle (Caillouet et al., 1997). 



Using the methods described previously, we prepared 

 stained thin-sections from the humeri. Without prior 

 knowledge of the animal's history, the number of visible 

 LAGs was quantified for each bone and a minimum age 

 estimated. Our age estimates were then compared to 

 the age information available for each animal. 



Indirect validation of annual growth marks 



Peabody (1961) and Castanet et al. (1993) suggested that 

 the correlation between the width of the last zone formed 

 and the date of death provided an indirect means of vali- 

 dating that deposition of the LAG occurs annually and at 

 the same time of year for an individual population. We 

 applied this method to 76 wild Kemp's ridley sea turtles 

 for which humeri displayed between one and five LAGs. 

 Each of these animals had stranded dead along the 

 Atlantic coast between Maryland and North Carolina. 

 Thin-sections were prepared of the humeri as described 

 above. We quantified the width of the last zone formed 

 by measuring the outside diameter of the whole section 

 (D ) and the diameter of the last competed LAG (D L ), 

 between the lateral edges of the bone on an axis paral- 

 lel to the dorsal edge. The amount of bone growth after 

 the last LAG (D -D L ) was plotted against the Julian 

 stranding date, with the assumption that stranding 



date approximated date of death. Least-squares linear 

 regressions were fitted to the data. 



Validation of the relationship between 

 LAG diameter and body size 



In order to relate GM diameters to somatic growth rates, 

 there must be a constant proportionality between bone 

 growth and somatic growth (Chaloupka and Musick, 

 1997). To address this proportionality, we took eight 

 morphometric measurements of 240 wild loggerhead and 

 262 wild Kemp's ridley humeri, using digital calipers 

 or a tape measure when dimensions were beyond the 

 range of the calipers. Measurements of maximum length, 

 longitudinal length, proximal width, distal width, delto- 

 pectoral crest width, lateral diameter at sectioning site, 

 ventral to dorsal thickness at sectioning site, and mass 

 were recorded. We compared these measurements with 

 the carapace length, measured as standard straight-line 

 length (SCL) from the nuchal notch to the posterior end 

 of the posterior marginal, using a least-squares linear 

 regression. For mass, the data were natural-log trans- 

 formed to form a linear regression. 



Results 



Known-age Kemp's ridley sea turtles 



Three Kemp's ridley sea turtles captive for one year 

 and then released were recovered 4.5 to 6.5 years after 

 hatching (Table 1). Sample LK-1 had minimal resorp- 

 tion and four complete GMs, each comprising one zone 

 followed by a LAG. An additional zone was seen at the 

 periphery and the LAG that would complete this last 

 GM was not yet visible at the outer edge of the humerus 

 cross-section. From GM counts and death date, we esti- 

 mated the age of this animal accurately at five years 

 (Fig. 1). Sample LK-2 retained five completed and one 

 incomplete GM; however, we observed a large area of 

 resorption in the interior region of the cross-section 

 that potentially obscured additional GMs. We aged this 

 animal at a minimum of 5.5 years, the actual age being 

 6.5 years. Sample LK-3 displayed four completed GMs 

 and one incomplete mark. Without prior knowledge of 

 this animal's age, we estimated the age accurately at 

 4.5 years based on layer count and time of death. 



Ten of the Kemp's ridley sea turtle samples were 

 tagged and released after hatching, and no time was 

 spent in captivity (Table 1). Results from these ten re- 

 covered animals allowed us the opportunity to study 

 and interpret the early GM patterns in noncaptive ani- 

 mals. The first year mark for Kemp's ridley sea turtles 

 appeared to be a poorly defined annulus, as evidenced 

 by LK-4 (Fig. 2A). In turtles greater than two years 

 old, similar first year marks also appeared more or less 

 distinctly (Figs. 2B and 3). Additional marks, which can 

 only be interpreted as supplemental lines given the age 

 of the animal, appeared between GM one and the outer 

 edge of the bone in LK-6 (Fig. 2B) and LK-10. Specimens 



