Cold-blooded divers: temperature-dependent dive performance in the wild hawksbill turtle Eretmochelys imbricata

Abstract

Sea turtles are diving ectotherms that are influenced by the temperature of the ambient water, although swimming activity can temper this influence via increased body temperatures enhanced by the thermal inertia of these large animals. We successfully equipped 3 nesting hawksbill turtles Eretmochelys imbricata with time–depth recorders (TDRs) to monitor water temperature and dive depth over the duration of the re-migration interval between 2 successive nesting seasons. Data sets for up to 22 mo were obtained, showing fluctuations in water temperature over the seasons. Nocturnal dive behaviour of the turtles at their foraging grounds revealed an increase in dive duration with decreasing water temperatures in winter. A model is provided to estimate dive duration for the range of temperatures experienced by this species in the wild. The data on vertical velocity during ascent and descent phases as a parameter for activity failed to show thermal dependence. It is concluded that changes in water temperature have an effect on the behavioural ecology of Hawksbill Turtles.