This project investigates the diving physiology of turtles in order to assess the ability of these reptiles to adapt to increased threats of climate change and pollution, and to understand the high mortality from by-catch of marine turtles during fisheries activities. Turtles differ from other divers such as marine mammals in that they primarily store oxygen in their lungs and, in addition, have a three-chambered heart, in which a single ventricle selectively shunts blood primarily to either the lungs or the body. Turtles also survive long dormant periods, during which the blood is devoid of oxygen and filled with high concentrations of lactic acid. With this tolerance for lack of oxygen, it is unclear why there is such high mortality of marine turtles during short periods of net entanglement. Self-contained physiological data loggers will be applied to one species of freshwater turtle and two species of marine turtles in order to document heart rate, blood oxygen depletion, and blood lactate concentrations during a variety of conditions including undisturbed spontaneous dives and net entanglement. Because of the dependency on lung oxygen, it is hypothesized that a) heart rate will not decrease during dives, b) the rate of blood oxygen depletion will correlate with heart rate during dives, c) that the magnitude and degree of cardiac shunting will vary under different diving conditions, and d), in contrast to most dives, high lactate levels will occur during net entanglement due to struggling. This project features collaboration of Scripps Institution of Oceanography, the University of California Irvine and the University of Tokyo (marine turtle studies). Broader impacts of the project include training of the post-doctoral fellow, graduate students, and undergraduates, outreach programs to high school students in the United States, teaching of a class in diving physiology at the University of Tokyo, and the development of a blood lactate sensor/recorder that can be applied to other diving and exercise physiology studies in the future.