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"57'S, 14"22'W) and individuals were subsequently monitored during the inter-nesting period and the post-nesting migration to Brazil. During the inter-nesting period, data from the transmitters suggested that turtles generally stayed within 5 km of the nesting beach on which they had originally been observed. During both the inter-nesting period and migration, turtles were submerged the vast majority (>95%) of the tune, 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 submergences tending to be of short duration during postnesting migration (mean = 7.3 rnin, 3318 h of data from 5 individuals) and of longer duration during the inter-nesting period (mean = 22.1 min, 714 h of data from 5 different in&viduals). As submergence duration is generally linked to activity levels in sea turtles, this pattern suggests that turtles were comparatively inactive during the inter-nesting period and comparatively active dunng migration. During both the inter-nesting period and the post-nesting migration, die1 submergence patterns were detected with dive duration tending to be 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-surface currents suggested that this reduction was associated with the weakening of the WSW flow of the prevailing South Atlantic Equatorial Current.