MEPS 189:263-273 (1999)  -  doi:10.3354/meps189263

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

G. C. Hays1,*, P. Luschi2, F. Papi2, C. del Seppia3, R. Marsh4

1School of Biological Sciences, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, Wales, UK
2Dipartimento di Etologia, Ecologia, Evoluzione, University of Pisa, Via A. Volta 6, 56126 Pisa, Italy
3Centro di Studio per la Faunistica ed Ecologia Tropicali del CNR, Via Romana 17, 50125 Firenze, Italy
4James Rennel Division, Southampton Oceanography Center, Empress Dock, Southampton SO14 3ZH, United Kingdom

ABSTRACT: 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 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 submergences tending to be of short duration during post-nesting migration (mean = 7.3 min, 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 individuals). 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 during migration. During both the inter-nesting period and the post-nesting migration, diel 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.

KEY WORDS: Green turtle · Chelonia mydas · Satellite tracking · Submergence · Ascension Island

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