Respiratory flow and tidal volume scale with body mass in sea turtles but not breath duration

The ventilatory capacity of sea turtles is an important factor in their diving ability because they spend most of their time submerged. However, there is limited information on the relationship between the ventilatory capacity and body mass of sea turtles. To investigate the allometric scaling of the functional ventilatory capacity, we measured respiratory flow, tidal volume, and breath duration of spontaneous breaths in 40 sea turtles from 3 species (loggerhead, Caretta caretta; green, Chelonia mydas; hawksbill, Eretmochelys imbricata) of various body sizes (range: 0.7-120.6 kg) on land and in water. The results showed that the ventilatory capacity did not differ on land or in water. The respiratory flow and tidal volume increased with body mass with an allometric exponent of 0.76-0.80 and 0.87-0.89, respectively. In contrast, the breath duration and the ratio of tidal volume to the maximum lung volume were constant. These results suggest that sea turtles increase respiratory flow by increasing tidal volume with increasing body mass rather than prolonging breath duration, which may allow them to reduce the surface interval to breathe. This study improves the understanding of the ventilatory capacity of sea turtles.