Morphological Characteristics of the Carapace of the Hawksbill Turtle, Eretmochelys imbricata, from Cuban Waters

Abstract

Hawksbill turtles, Eretmochelys imbricata (Linnaeus, 1766), from Cuban waters of the Caribbean were analyzed to determine the relationships between straight carapace length (SCL) and either straight carapace width (SCW) or body weight (Wt). The regression equations were SCW = 0.9136(SCL)0.951 (R2 = 0.923, n = 315) and Wt = 4.17 10–4(SCL)2.68 (R2 = 0.798, n = 289), respectively. The regression equations between the first costal width (C1W) and either SCW or Wt were SCW = 3.223(C1W)0.847 (R2 = 0.919, n = 156) and Wt = 1.416 x 10–2(C1W)2.426 (R2 = 0.740, n = 133), respectively. There was no difference in slopes of the C1W-SCL relationship between wild and captive raised turtles as analyzed by ANCOVA. Thus, I pooled the group data and re-calculated the C1W and SCL relationship as SCL = 4.353(C1W)0.848 (R2 = 0.953, n = 340). This result indicated that SCL measurements could be estimated based on C1W measurements and that the C1W-SCL relationship could be applied to captive raised or wild hawksbills. It is clear that the SCL-SCW and C1W-SCW relationships were more similar to the relationship in the hawksbill turtles from Puerto Rican waters than to those captured in Australian waters, although there was no significant geographic difference between specimens from the Caribbean and Australian INTRODUCTION The external morphology and sizes of marine turtles offer a great amount of useful biological information. Comparisons of the morphologies among populations provide a better understanding of evolutionary and genetic relationships, whereas comparisons of the body sizes among individuals and populations help to clarify physiological and ecological relationships. It has been reported that body size is connected to body temperature (Spotila and Standora 1985), metabolic rate (Prange and Jackson 1976), growth rate (Bjorndal and Bolten 1988), and clutch size (Witzell 1985). Because it is relatively easy to measure the morphological characteristics of marine turtles, there have been a number of studies of carapace size in various populations of the hawksbill turtle, Eretmochelys imbricata (Linnaeus, 1766) (Witzell 1985). However, because of the difficulty of gathering specimens and determining the sex of immature turtles, these studies often had only a small sample size and hadn’t dealt with the distinction between females and males. Morphological studies of the carapace in the hawksbill have been compiled for Australia (Limpus 1992) and Puerto Rico (van Dam and Diez 1998). Until now, there has been no report on carapace shapes in turtles found in Cuban waters. Many wild adult hawksbill carapaces have been measured in Cuba but no immature turtle carapace measurement data are available. The goal of this study was to collect more data of wild and captive raised turtles, to analyze these data altogether, and to discuss geographical variations in the carapace morphology of hawksbill turtles. MATERIALS AND METHODS To determine the relationships between straight carapace length (SCL) and straight carapace width (SCW), SCL and weight (Wt), and the first costal width (C1W) and SCW or between C1W and Wt, I used measurement data from 315 hawksbill turtles captured by fishery net in Cuban waters from 1995 to 1998. Thirty-two of the 315 were captured from Doce Leguas Key, southwest of Cuba in 1995 and 1998, 48 from Nuevitas, northeast of Cuba in 1995 and 1996, and 235 from Isla de Pinos, southeast of Cuba in 1996. For the relationship between C1W and SCL, I added measurements from 184 captive raised hawksbill turtles that had hatched on Doce Leguas Key and were raised at breeding facilities on Isla de Pinos. I did not classify turtles by sex because there is no sexual difference in the hawksbill carapace (Limpus 1992). I measured select morphometrics of 156 wild and 184 captive raised hawksbill turtles (Figure 1). Measuring sites were SCL, SCW, Wt, and C1W (Figure 1). Vernier calipers (± 0.5 cm) were used to measure SCL and SCW, C1W was measured using a tape measure (± 0.1 cm) from whole turtle’s carapaces, and Wt was measured using a spring scale (up to 20 kg ± 0.05 kg, from 20 kg to 90 kg ± 1kg) from turtles which were either drowned within 24 hrs or alive (see Figure 2). I estimated the relationships between log10 SCL, log10 SCW, or log10 Wt and log10 C1W by calculating the allometry equation Y = aXb for the data presented in Table 1. Then I compared slopes of the regression lines log10 SCL vs log10 C1W between wild and captive raised individuals Manuscript received January 9, 2003; accepted January 6, 2004