Abstract

Body condition evaluation provides an important index for wildlife health assessment.¹ In sea turtles, body condition is typically evaluated through subjective body condition scoring and/or a calculated body condition index, BCI=([mass (kg)/straight carapace length (cm)³]×10,000). Body condition scoring is visually subjective and can produce highly variable results, while BCI calculation allows for greater repeatability between evaluators but requires body mass measurement, which can be difficult in field situations.^2,3 One solution is to use ultrasonography as a noninvasive, rapid proxy for body condition estimation. The goal of this study was to validate ultrasonography of subcutaneous fat depth to estimate body condition in green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtles using two types of portable ultrasound technologies, the IBEX^® EVO^® and the Renco Lean-Meater^®. The EVO^® is a veterinary certified ultrasound with advanced imaging software, while the Lean-Meater^® is designed for livestock backfat measurement. These ultrasounds were used to measure subcutaneous fat depth on the carcasses of 10 green turtles (mean ± SD BCI: 1.26±0.20) and eight loggerheads (mean ± SD BCI: 1.10±0.19). Ultrasonography-guided measurements were taken at four anatomic locations (dorsal shoulder, dorsal neck, lateral neck, and dorsal base of hind flipper) on each turtle’s body, with the flippers positioned in neutral, flexion, and extension. For each anatomic site, fat biopsies were collected via dissection and measured manually. Bland-Altman bias plots in conjunction with Passing-Bablock regression analyses were used to evaluate the level of agreement between subcutaneous fat measurements taken using the two ultrasound machines, and between ultrasound-assisted measurements and gross measurements. In green turtles, the dorsal shoulder region in flexion gave the lowest level of bias in measurements given by the two ultrasound machines (2 mm bias [95% limits of agreement (LoA): -1.64–2.04]), and a statistically significant level of agreement between measurements (R²=0.59, p=0.006). In loggerheads, the lateral neck in neutral position gave the lowest level of bias in ultrasound measurements (1.3 mm [95% LoA: -1.04–1.30]); however, the level of agreement was not statistically significant (R²=0.36, p=0.212). For green turtles, measurement of subcutaneous fat in the dorsal shoulder region using the EVO^® (but not the Lean-Meater^®) with the flipper extended resulted in the lowest level of bias (0.05 mm [95% LoA: -0.53–0.52]), and the level of agreement between the two measurements was statistically significant (R²=0.68, p=0.001). In loggerheads, the lateral neck in flexion gave the lowest level of bias (0.3 mm [95% LoA: -0.63–0.69]); however, the level of agreement between measurements using the two different machines was not statistically significant (R²=0.17, p=0.559). In loggerheads, moderate-to-strong linear relationships were observed between BCI and ultrasound measurements of the lateral neck (Lean-Meater^®: R²=0.55; EVO^®: R²=0.70) and the dorsal hind flipper (EVO^®: R²=0.66) using linear regression, but not for the other anatomic sites, nor for any anatomic sites in green turtles. This data suggest that ultrasound-assisted measurement of subcutaneous fat depth may be a suitable proxy for BCI in loggerheads, which in conjunction with physical examination and clinical blood data provides a means to assess nutritional status.

Acknowledgements

We thank collaborating organizations that assisted in carcass collection and transport: Florida Fish and Wildlife Conservation Commission, Loggerhead Marinelife Center, Brevard Zoo, the Clinic for the Rehabilitation of Wildlife, and Ecological Associates, Inc. Thanks to Wendy Marks, Skyler Klingshirn, Hunter Brown, and Derek Aoki for assistance with data collection and necropsies.

*Presenting author
⁺Student presenter

Literature Cited

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2.  Bjorndal KA, Bolten AB, Chaloupka MY. 2000. Green turtle somatic growth model: evidence for density dependence. Ecol Appl 10:269–282.

3.  Stacy NI, Bjourndal KA, Perrault JR, Martins HR, Bolten AB. 2018. Blood analytes of oceanic-juvenile loggerhead sea turtles (Caretta caretta) from Azorean waters: reference intervals, size-relevant correlations and comparisons to neritic loggerheads from western Atlantic coastal waters. Cons Physiol 6(1):coy006.