688 



Fishery Bulletin 102(4) 



triple LAG 



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Figure 5 



Image of a section of the humerus cross-section of 

 CC-2 (C. caretta). Outer edge of bone is towards the 

 bottom of the photo. Solid lines (upper left I highlight a 

 series of triple lines of arrested growth (LAGs); curved 

 dashed lines highlight the three diffuse LAGs. Black 

 bar represents 1 mm in length. 



Most studied species of reptiles and amphibians deposit 

 GMs within their bones (Castanet et al., 1993; Smirina, 

 1994). For some of these species, the annual nature of the 

 GM has been validated (e.g.. Tucker, 1997; de Buffrenil 

 and Castanet, 2000; Trenham et al., 2000). For others, 

 it is consistent with their ecology that the marks must 

 represent annual events (Castanet et al., 1993). Growth 

 marks observed in loggerhead (Zug et al., 1986; Zug et 

 al., 1995; Coles et al., 2001), Kemp's ridley (Zug et al., 

 1997), and green (Zug and Glor, 1998; Zug et al., 2002) 

 sea turtles are similar in structure to those observed in 

 other species of reptiles and amphibians. Drawing on 

 previous studies of reptiles and amphibians, validation 

 studies on sea turtles, and the evidence presented in this 

 article, we assert that GM in bones of sea turtles are 

 likely deposited primarily with an annual periodicity. 



Given these results, on the surface it seems contradic- 

 tory that in two validation studies annual GMs could 

 not be confirmed. For serpentine species, Collins and 

 Rodda (1994) injected brown snakes with a fluorescent 

 marker and kept them in captivity for one year under 

 two different feeding regimes. Five or six GMs vary- 

 ing in distinctness were identified beyond the fluores- 

 cent marks in bone cross-sections. Statistical analyses 

 showed that these marks may relate to shedding events. 

 It is unclear if the GM pattern prior to captivity was 

 similar to what was seen after the fluorescent mark. 

 The forced feeding component of that study may have 

 induced higher growth rates than would be found in 

 nature, causing the shedding events to appear as his- 

 tological marks in the bone. 



In a sea turtle study, Bjorndal et al. (1998) did not 

 find GMs in the humeri of green sea turtle bones. They 

 suggested that the tropical marine habitat of the study 



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250 



350 

 Julian date 



450 



550 



Figure 6 



Julian date of stranding plotted against the amount of 

 bone deposited peripherally to the last LAG in Kemp's 

 ridley sea turtles (L. kempii: n = 76). D represents 

 the outside diameter of the humerus, D L represents 

 the diameter of the last LAG. Julian dates on x-axis 

 equate to 20 June through 19 June; therefore num- 

 bers that are greater than 365 represent the Julian 

 date plus 365. Solid lines represent linear regressions 

 that were run separately for 6 months. 20 June to 31 

 November I filled squares) and 1 December to 19 June 

 (open squares). The regression for the first six months 

 was significant (P<0.006i and the regression for the 

 second six months was not significant lP= 0.27 1. 



population (approximately 21°07'N) allowed for con- 

 tinual activity and growth and inhibited GM forma- 

 tion. However, GMs have been clearly demonstrated 

 in green sea turtles from the coastal waters of Florida 

 (approximately 29°N) (Zug and Glor, 1998) and Hawaii 

 (approximately 22°N) (Zug et al., 2002). Other studies 

 of reptiles and amphibians in tropical and warm tem- 

 porate climates have reported distinct GMs in species 

 that remain active year-round (i.e., do not hibernate 

 or estivate) (Patnaik and Behera, 1981; Estaban et al., 

 1996; Guarino et al.. 1998). 



Interpretation of anomalous LAGs 



Although our sample sizes were small, especially for log- 

 gerhead sea turtles, several characteristics were noted 

 in the analyses of the samples that would affect how 

 anomalous LAGs are interpreted. Three interpretations 

 of double and bifurcating LAGs are provided. The first 

 interpretation is that if double LAGs appear frequently 

 in individual bones and throughout the sample, they 

 likely indicate an ecology that has two growth cycles 

 per year (Castanet et al., 1993). In this case the two 

 LAGs are distinct from each other over the entire bone 

 cross-section. This pattern was observed in the newt 

 Triturus marmoratus living at a high altitude where 

 the animals had both winter and summer dormancy 

 periods (Castanet and Smirina. 1990; Caetano et al., 

 1985; Caetano and Castanet, 1993). The second inter- 

 pretation of double LAGs is that they result from a brief 



