Flipper beat frequency and amplitude changes in diving green turtles, Chelonia mydas

Using a turtle-borne camera system, changing flipper beat frequency and amplitude were measured in five diving green turtles (Chelonia mydas Linnaeus 1758) in the Bahia de los Angeles, Mexico (28 degrees 58'N, 113 degrees 33'W). These observations were made between June and August 2002. Turtles worked hardest (i.e., had the highest flipper beat frequency and amplitude) at the start of descents when positive buoyancy is predicted to oppose their forward motion. During the later part of descents, turtles worked less hard in line with opposing buoyancy forces being reduced. For example, flipper beat frequency declined from about 60-80 beats min(-1) at the start of descent to around 25-40 beats min(-1) after 30 s of the descent. At the start of ascents the flipper beat frequency was around 30 beats min(-1), lower than on descent, and declined as the ascent progressed with often passive gliding for the final few meters to the surface. This pattern of effort during diving appears to apply across a range of marine reptiles, birds and mammals suggesting that graded effort during descent and ascent is an optimum solution to minimising the cost of transport during diving.