Respiratory frequency, dive behaviour and social interactions of leatherback turtles, Dermochelys coriacea during the inter-nesting interval

Abstract

We collected simultaneous dive Time Depth Recorder (TDR) data and video images from free swimming adult female leatherback turtles, Dermochelys coriacea, during the first 24 h after nesting on the beach, in order to determine relationships between dive parameters, activity, overall respiratory frequency and behaviour. We identified three different underwater locomotory activities (subsurface swimming, V-shaped dives and U-shaped dives) from video and TDR data that varied in their mean depth, duration and a number of other parameters. Overall respiratory frequency (overall f R) was significantly different between all locomotory activities, with turtles taking 1.7±0.1 breaths min −1 while subsurface swimming, 0.78 breaths min −1 after V-shaped dives and 0.57 breaths min −1 after U-shaped dives. Descent rates and ascent rates were significantly faster in U-shaped dives (descent 0.19±0.010 m s −1, ascent 0.28±0.015 m s −1) than in V-shaped dives (descent 0.10±0.008 m s −1, ascent 0.12±0.012 m s −1). Flipper stroke rates were significantly lower during the bottom component of U-shaped dives (0.18±0.02 strokes s −1) than during the descent (0.29±0.03 strokes s −1) or ascent (0.29±0.03 strokes s −1). From overall f R and flipper stroke rate data, we inferred that turtles used less energy during U-shaped dives than the other activity types. We recorded interactions between male turtles and the study females that lasted up to 11 min, during which male turtles displayed the characteristic courtship behaviour of sea turtles. It appeared that females attempted to avoid males by aborting ascent and extending dive duration to swim to the sea floor when males were present.