MEPS 386:275-286 (2009)  -  DOI: https://doi.org/10.3354/meps08084

ABSTRACT: Data loggers were utilized to record depth, temperature, biaxial motion and swimming speed for female green turtles Chelonia mydas between nesting events in Thailand. The present study demonstrated clear alternations in swimming effort with depth. Both resident and maximum dive depths significantly affected flipper beat frequency, suggesting that turtles change flipper beat frequency with current buoyancy in ways similar to other diving mammals and birds. Body angles became steepest during the initial phases of descent and ascent, but were <60°. Swimming speeds were related to flipper beat frequency and current buoyancy. Swimming speeds based on the dominant stroke frequency during the inter-nesting period (0.18 to 0.21 Hz) were estimated at 0.52 to 0.60 curved carapace lengths s^–1. These values are similar to the modal speeds of the leatherback turtles Dermochelys coriacea and the mean speeds during the initial descent of the loggerhead turtles Caretta caretta. We calculated the dynamic body acceleration (DBA) as the index of activity during the descent and ascent phases and found a relationship between maximum dive depth and DBA. Although active stroking during deeper dives may result in a shorter dive duration, daytime dives (ca. 16 to 26 m) were deeper than those observed during the night (ca. 9 to 13 m). This result suggests a beneficial reproductive strategy for females that involves changes in vertical space, for example, to obtain refuge from energy-consuming encounters with males or predators.

KEY WORDS: Diving behaviour · Chelonia mydas · Sea turtles · Flipper beat frequency · Swimming speed · Body angle