Seasonal diving patterns and body temperatures of juvenile green turtles at Heron Island, Australia

Abstract

This study compared diving patterns of juvenile green turtles, Chelonia mydas, in a coral reef habitat during summer and winter. Dataloggers were deployed on green turtles at Heron Island, Australia, during December 2000 and August 2001 so that dive variables and ambient water temperature (T W ) could be monitored. Cloacal temperatures (T B ) were recorded from green turtles upon capture to assess their ability to maintain a thermal gradient between T B and T W . Data show that green turtles altered diving behaviour seasonally. Green turtles spent significantly more time in shallow water (<1 m) during winter than during summer. Dive depth for dives that exceeded 1 m was 2.9 ± 0.4 m (mean ± SEM) during summer and 4.4 ± 0.6 m during winter. Dive duration in summer (13.1 ± 1.2 min) was approximately half the dive duration in winter (24.3 ± 1.6 min), and surface interval in summer (0.6 ± 0.1 min) was one-third that of the surface interval in winter (1.8 ± 0.1 min). The observed changes in behaviour may be due to seasonal changes in environmental and physiological factors. There was no statistically significant difference between T B and T W during summer or winter.