682 



Abstract — Numerous studies have 

 applied skeletochronology to sea turtle 

 species. Because many of the studies 

 have lacked validation, the applica- 

 tion of this technique to sea turtle 

 age estimation has been called into 

 question. To address this concern, we 

 obtained humeri from 13 known-age 

 Kemp's ridley (Lepidochelys kempii) 

 and two loggerhead (Caretta caretta) 

 sea turtles for the purposes of examin- 

 ing the growth marks and comparing 

 growth mark counts to actual age. We 

 found evidence for annual deposition 

 of growth marks in both these spe- 

 cies. Corroborative results were found 

 in Kemp's ridley sea turtles from a 

 comparison of death date and amount 

 of bone growth following the comple- 

 tion of the last growth mark (n=76). 

 Formation of the lines of arrested 

 growth in Kemp's ridley sea turtles 

 consistently occurred in the spring for 

 animals that strand dead along the 

 mid- and south U.S. Atlantic coast. 

 For both Kemp's ridley and loggerhead 

 sea turtles, we also found a propor- 

 tional allometry between bone growth 

 • humerus dimensions) and somatic 

 growth (straight carapace length i, 

 indicating that size-at-age and growth 

 rates can be estimated from dimen- 

 sions of early growth marks. These 

 results validate skeletochronology as 

 a method for estimating age in Kemp's 

 ridley and loggerhead sea turtles from 

 the southeast United States. 



Validation and interpretation of annual 

 skeletal marks in loggerhead (Caretta caretta) 

 and Kemp's ridley (Lepidochelys kempii) sea turtles 



Melissa L. Snover 



Duke University Marine Laboratory 



135 Duke Marine Lab Road 



Beaufort, North Carolina 28516 



Present addresss: Pacific Fisheries Environmental Laboratory 



1352 Lighthouse Ave. 



Pacific Grove, California 93950 

 E-mail address: melissa snover g noaa gov 



Aleta A. Hohn 



Center for Coastal Fisheries and Habitat Research 

 National Marine Fisheries Service, NOAA 

 101 Pivers Island Road 

 Beaufort, North Carolina 28516 



Manuscript submitted 1 5 August 200,3 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 ii June 2004 by the Scientific Editor 



Fish. Bull. 102:682-692 (2004 I. 



The basic tenet of skeletochronology is 

 that bone growth is cyclic and has an 

 annual periodicity in which bone for- 

 mation ceases or slows before new, rel- 

 atively rapid bone formation resumes 

 (Simmons, 1992; Castanet et al„ 1993; 

 Klevezal, 1996). This interruption of 

 bone formation is evidenced within 

 the primary periosteal compacta by 

 histological features, which take two 

 forms in decalcified and stained thin- 

 sections. The most common form is a 

 thin line that appears darker than the 

 surrounding tissue, termed the "line 

 of arrested growth" (LAG) (Castanet 

 et al., 1977). The second, less-common 

 form is a broader and less distinct line 

 that also stains darker, referred to as 

 an annulus (Castanet et al., 1977). 

 Alternating with LAGs or annuli are 

 broad zones that stain homogeneously 

 light, and represent areas of active 

 bone formation. Together, a broad 

 zone followed by either a LAG or an 

 annulus represents a skeletal growth 

 mark (GM) (Castanet et al., 1993). To 

 apply skeletochronology to a species, 

 the annual periodicity of the GM must 

 be validated. 



Validation studies are necessary 

 not only to confirm the annual nature 1 

 of the GM but also to identify and in- 

 terpret anomalous LAGs. Anomalous 

 LAGs that are a common problem in 

 skeletochronology studies of reptiles 



and amphibians include double (Chin- 

 samy et al., 1995; El Mouden et al., 

 1997; Guarino et al., 1998), splitting 

 (Guarino et al., 1995; 1998; Coles et 

 al., 2001), and supplemental (Guarino 

 et al, 1995; Lima et al., 2000; Tren- 

 ham et al., 2000) lines. In addition to 

 anomalous LAGs, there are two other 

 difficulties typical in skeletochronol- 

 ogy studies; compression of LAGs at 

 the periphery of the bone and resorp- 

 tion of the innermost LAGs. In older 

 animals the GMs are compressed at 

 the outer periphery of the bone as a 

 result of decreased growth. Francil- 

 lon-Vieillot et al. (1990) term this 

 phenomenon "rapprochement" and it 

 is a problem when the LAGs become 

 too close together to be differentiated 

 — usually in the small phalangeal 

 bones used in amphibian studies lEg- 

 gert and Guyetant. 1999; Lima et al., 

 2000; Leclair et al.. 2000). 



In addition to anomalous and com- 

 pressed LAGs, the loss of early GMs 

 through endosteal resorption is an- 

 other problem with skeletochronol- 

 ogy. Although this does not present a 

 problem with most amphibian species 

 (Kusano et al., 1995; Castanet et al., 

 1996; Sagor et al., 1998), the prob- 

 lem is extreme in skeletochronology 

 studies of loggerhead (Caretta caretta; 

 Klinger and Musick. 1995; Zug et al., 

 1995; Parham and Zug, 1997), green 



