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Fisher/ Bulletin 100(1) 



Our goal in this study was twofold. First, 

 we used humerus growth-increment data to 

 estimate ages of a sample of Hawaiian green 

 seaturtles from various locations in the ar- 

 chipelago and developed a growth model for 

 the general Hawaiian population; geograph- 

 ic variation in growth will be addressed in a 

 subsequent paper. Second, we compared two 

 different methods of deriving the age esti- 

 mates, the so-called "correction-factor" meth- 

 od described by Parham and Zug ( 1998) and 

 a newer approach, the "spline-integi'ation" 

 method, introduced in the present study. 



Materials and methods 



Our sample consisted of 104 individuals 

 of C. mydas, collected from the islands of 

 Hawaii, Kauai, Lanai, Maui, Oahu, and the 

 Northwestern Hawaiian Islands; the Oahu 

 sample predominated with 64 individuals. 

 All individuals were measured to the near- 

 est 0.1 cm straight carapace length (SCL). 

 The smallest individual was a 5.3-cm-SCL 

 hatchling. The smallest posthatchling was 

 a pelagic juvenile (of assumed Hawaiian 

 origin) recovered from the former squid 

 driftnet fishery north of the island chain. 

 All other posthatchling turtles were from 

 coastal Hawaiian waters, found stranded dead and re- 

 trieved by the National Marine Fisheries Service's Hawai- 

 ian Islands Seaturtle Stranding Network. The salvaged 

 turtles ranged from 28.7 to 96.0 cm SCL. The sample was 

 divided into eight 10-cm size classes; representation was 

 roughly equivalent for the middle six classes (Fig. 1). The 

 30-39 cm sample contained only turtles in the upper quar- 

 tile of this size class. Each turtle was necropsied and its 

 right humerus removed for skeletochronological examina- 

 tion. The necropsy data included a complete set of carapace 

 measurements, organ condition evaluations, and informa- 

 tion on fibropapilloma tumor occurrence and severity; see 

 Work and Balazs (1999a, 1999b) for details on the entire 

 data set. In addition to the skeletochronological data, we 

 used only the SCL measurements and tumor-evaluation 

 observations in the present study. 



Where possible, we selected tumor-free individuals for 

 the present analysis because our goal was to examine the 

 overall growth pattern for normal Hawaiian Chelonia my- 

 das. Because the prevalence of fibropapillomatosis is high 

 in the wild Hawaiian population (Murakawa et al., 2000), 

 we included in our sample individuals with fibropapillo- 

 mas. but otherwise appearing normal, in order to ensure 

 adequate representation in the larger size classes. Healthy 

 animals were those showing no evidence of weight loss or 

 other indicators of illness and no evidence of disruption 

 or retardation of normal growth. Individuals with tumors 

 represented 27'7r of the 50-59 cm, 507^ of 60-69 cm, 76% 

 of 70-79 cm, 73% of 80-89 cm, and 17% of 90-99 cm SCL 

 size classes (Fig. 1). 



20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99 

 Straight carapace lengtti (cm) 



Figure 1 



Size (straight carapace length) distribution of the Hawaiian Chelonia 

 mydas skeletochronological sample. The members of each class are segre- 

 gated into individuals without (shaded bar) and with (black bar) fibropapil- 

 loma tumors. Tumors in our sample are present only in larger turtles. 



Our skeletochronological data derived from cross-sec- 

 tions (0.6-0.8 mm thick) from the middle of the humeral 

 shaft just distal to the deltopectoral crest and at the nar- 

 rowest diameter of the diaphysis (Zug et al., 1986). On 

 each specimen, we counted the number of visible growth 

 layers and measured the widths (long-axis diameters) of 

 the humerus at each successive growth cycle and the 

 width of the resorption core. Bone sections were taken 

 from mid-shaft, the narrowest location of the bone, be- 

 cause the humerus retains the gi'eatest number of perios- 

 teal growth layers there, and hence this location permits 

 the most accurate estimation of the number of growth cy- 

 cles (periosteal layers) and the relative rates of growth 

 (=successive humerus diameters). 



We used two procedures for estimating the total num- 

 ber of growth layers, and hence age, of each turtle. In the 

 correction-factor (CF) method, as described in Parham and 

 Zug ( 1998), the turtle's age is estimated as the number of 

 growth layers observed in the outer region of the humerus 

 section plus the predicted number of resorbed growth lay- 

 ers represented in the remodeled core of the humerus. The 

 latter, unobservable component is estimated as C (i? - R[^), 

 where R is the radius of the absorption core, Rf^ is the ra- 

 dius of a hatchling's humerus (before the beginning of in- 

 crement formation), and C is the so-called correction fac- 

 tor The correction factor is a constant "aging rate" (yr/mm) 

 assumed to apply to the resorption core, and calculated 

 as the reciprocal of the mean growth layer width in small 

 turtles. The mean growth layer width was estimated from 

 129 periosteal growth layer widths observed in 34 turtles 



