Evaluation of scute thickness to infer life history records in the carapace of green and loggerhead turtles

Abstract

Use of scute in biochemical studies to infer ontogenetic changes of habitat and diet in sea turtles is becoming more frequent because scute is an inert tissue with continuous growth that can record habitat and diet changes through time. Changes are detectable through biochem- ical markers such as stable isotopes and trace elements. These studies are critical for the manage- ment of endangered sea turtles because location and foraging requirements of these animals must be known in order to be able to provide effective protection measures. However, scute thickness is not homogeneous throughout the carapace. Depending on where in the scute a sample is col- lected, a different version of the history of an individual turtle could be obtained. Our goal was to determine where on the carapace the thickest scute is found in green turtles Chelonia mydas and loggerhead turtles Caretta caretta and whether this area reveals the longest life history of the tur- tle based on stable isotopes of carbon and nitrogen. Our results show that regardless of size, the thickest part of the scute is found in the central region of the second lateral scute in green turtles and of the third lateral scute in loggerheads. Furthermore, the thickest areas do provide the longest records of the history of green turtles and, perhaps, of loggerhead turtles. We were able to observe a clear shift of habitat from the stable isotope values in the central region of the scute of several green turtles that was not observed in the posterior margin. Thus, the central region site should be used to collect scute tissue as this provides information on the life history of sea turtles over the longest period of time.