Changes in behaviour during the inter-nesting period and post-nesting migration for Ascension Island green turtles

Satellite transmitters were attached to green turtles Chelonia mydas while they were nesting on Ascension Island in the South Atlantic (7 degrees 57'S , 14 degrees 22'W) and individuals were subsequently monitored during the i nter-nesting period and the post-nesting migration to Brazil. During the in ter-nesting period, data from the transmitters suggested that turtles gener ally stayed within 5 km of the nesting beach on which they had originally b een observed. During both the inter-nesting period and migration, turtles w ere submerged the vast majority (> 95 %) of the time, suggesting that they neither basked at the surface nor drifted passively during migration to any great extent. There was a clear dichotomy in submergence behaviour, with s ubmergences tending to be of short duration during postnesting migration (m ean = 7.3 min, 3318 h of data from 5 individuals) and of longer duration du ring the inter-nesting period (mean = 22.1 min, 714 h of data from 5 differ ent individuals). As submergence duration is generally linked to activity l evels in sea turtles. this pattern suggests that turtles were comparatively inactive during the inter-nesting period and comparatively active during m igration. During both the inter-nesting period and the post-nesting migrati on, diel submergence patterns were detected with dive duration tending to b e longer at night. As the turtles migrated WSW from Ascension Island, there was a reduction in their speed of travel. A numerical model of the near-su rface currents suggested that this reduction was associated with the weaken ing of the WSW now of the prevailing South Atlantic Equatorial Current.