Adipose tissue estimation of foraging and nesting green turtles Chelonia mydas using bioelectrical impedance analysis

Abstract

Adipose tissue is the main energy store in sea turtles and fluctuates in response to dietary conditions and external stressors. Monitoring programmes commonly use body condition indices (BCIs) to infer the nutritional and health status of sea turtle populations. However, BCIs have poor predictive power for estimating adipose tissue. We introduce the use of bioelectrical impedance analysis (BIA) as a portable technique to estimate adipose tissue in green turtles Chelonia mydas. The aims of this study were to estimate adipose tissue of green turtles on the Great Barrier Reef (Australia), and to examine whether adipose tissue is a more sensitive indicator than BCI. Turtles (n = 250) were sampled at 3 foraging sites and at a nesting beach with differing levels of anthropogenic impact. Differences in adipose tissue, Fulton’s BCI, and body mass across study sites and life stages were assessed by conducting linear mixed effects models. BIA estimates of mean adipose tissue revealed significant differences across life stages and sampling sites, that were not found using BCI data. Mean adipose tissue was estimated to be 4.6 ± 0.6% (% body mass ± SD) and was not correlated with mean BCI (1.2 ± 0.1). Adipose tissue was not reduced in turtles foraging at sites with a high level of anthropogenic impact. Adult turtles had significantly higher adipose tissue values than juveniles and subadults. Adult females measured during and shortly before nesting season had the highest adipose tissue values (%). BIA is a practical method for estimating adipose tissue, and we recommend this technique for consideration in sea turtle monitoring programmes.