Differences in the morphological body condition index of sea turtles between species and size classes

Abstract

The body condition of animals is an important indicator of their habitats and the effects of anthropogenic activities and pollution. Body condition indices calculated from morphometric measurements have been widely employed as they are easy to use and inexpensive. In sea turtles, Fulton's condition index, calculated as the bodyweight divided by the cube of straight carapace length (SCL), has been commonly used and it has been proposed that an index of ≥1.2 indicates a good body condition. However, comparing Fulton's condition index between different species and size classes is problematic as it does not consider the mass-length relationship. In this study, we conducted a meta-analysis to evaluate the differences between sea turtles. A literature review indicated that most studies reported the SCL-based Fulton's condition index for green turtles (Chelonia mydas), followed by loggerhead turtles (Caretta caretta) and hawksbill turtles (Eretmochelys imbricata). Therefore, we compared the values reported for healthy turtles of these three species. Meta-analysis supported the adequacy of 1.2 as a threshold in juvenile and adult green turtles and large juvenile and adult loggerhead turtles. High Fulton's condition index values were found for hatchlings and post-hatchlings of all three species and small loggerhead turtle juveniles. Low Fulton's condition index values were found for hawksbill turtles, particularly small juveniles. The differences in the Fulton's condition index between species and size classes indicated that it should be used carefully as a threshold for health condition evaluation.

Variations in body condition of green turtles (Chelonia mydas) in two nearby foraging grounds indicate their sensitivity to foraging habitats

“…The BCI values of both the Kudat Mainland and Balambangan Island aggregations were generally comparable with the global mean of healthy green turtles (1.31 in small juveniles, 1.41 in large juveniles and adults; Nishizawa & Joseph, 2022). No serious damage or fibropapilloma tumours also indicate good body condition of green turtles at both Kudat Mainland and Balambangan Island.…”

“…turtles were dominant compared to Brunei Bay. It should be noted that the catching technique in this study was suitable for catching smaller turtles although it cannot be ruled out that larger green turtles were missed by the surveys of the Kudat Mainland foraging aggregations.The BCI values of both the Kudat Mainland and Balambangan Island aggregations were generally comparable with the global mean of healthy green turtles (1.31 in small juveniles, 1.41 in large juveniles and adults;Nishizawa & Joseph, 2022). No serious damage or fibropapilloma tumours also indicate good body condition of green turtles at both Kudat Mainland and Balambangan Island.…”

Health status and genetic compositions of green turtles (Chelonia mydas) foraging in Brunei Bay

“…The body condition of foraging green turtles in Brunei Bay was relatively good, as Fulton's BCI was within the range of apparently healthy green turtles (1.25-1.36 for small juveniles, 1.34-1.47 for large juveniles and adults) [17]. Mildly affected tumours were observed from only two individuals; thus, the fibropapilomatosis is less prevailed in Brunei Bay in comparison with Indonesia [5].…”

“…The assessment of sea turtle health using tools such as the body condition index, which is calculated through morphometric measurements [10,11], and hematology parameters obtained from blood samples [12,13], are valuable indicators. However, regional, and ontogenetic differences necessitate the establishment of baseline and reference intervals to monitor sea turtle populations effectively [14][15][16][17]. Additionally, the prevalence of fibropapilloma [18] or epibiotic load [19,20], and their relationship with hematology parameters, provide insight into the overall health of sea turtle populations.…”