Flipper movement during sea turtle diving

Depth and flipper movements were simultaneously measured during 23 dives for a free-swimming green turtle (Chelonia mydas) at Ascension Island. A few characteristic dive profiles that have been widely reported in hard-shelled turtles were recorded. Flipper movements revealed that, on dives to midwater, there was generally active swimming, compared to long periods of inactivity on dives to the seafloor. During all dives, there were clear changes in the flipper beat frequency during the descent. On leaving the surface, flippers beats occurred quickly (typically 30–40 beats min−1) and then as the descent continued the frequency declined (typically to about 10–14 beats min−1). These observations match the general pattern reported for other air-breathing divers for increased effort at the start of the descent to overcome initial positive buoyancy