The diving behaviour of green turtles at Ascension Island

For six green turtles, Chelonia mydas, that had nested on Ascension Island in the South Atlantic, we used time-depth recorders to examine their diving behaviour during the subsequent internesting interval (10-12 days). All th e turtles performed dives where they remained at a fixed depth for a long p eriod, surfaced briefly and then dived to the same depth again. It is gener ally believed these dive profiles are caused by the turtles resting on the sea bed. The maximum depth that turtles routinely reached on these resting dives was between 18 and 20 m, with resting dives deeper than 20 m being ex tremely rare. Resting dive duration increased significantly with deeper div es. From this relationship, and assuming that turtles with fully inflated l ungs at the surface need to dive to 19 m to achieve negative buoyancy, we e stimated for two turtles that the oxygen consumption during resting dives w as 0.016 and 0.020 litres O-2/kg per h, respectively. This is similar to th e value predicted from the allometric scaling relationship for the minimal oxygen consumption of turtles. We calculated that the energy conserved by r esting during the internesting period may appreciably increase the reproduc tive output of females. (C) 2000 The Association for the Study of Animal Be haviour.