INFLUENCE OF SURFACE CURRENTS ON POST-NESTING MIGRATION OF GREEN SEA TURTLES NESTING ON WAN-AN ISLAND, PENGHU ARCHIPELAGO, TAIWAN

Abstract

The relationships between ambient flows and the migration corridors of green turtles (Chelonia mydas) nesting at Wan-an Island, Penghu Archipelago in Taiwan Strait were determined. Six turtles deployed with Argos-linked satellite tags from 1996 to 2004 were used. The ambient flows were derived from the combination of ship board measurements, a global tidal model, and the geostrophic flows derived from sea surface height anomalies. The results showed that there were, basically, three migrating patterns. Turtles that migrated northeastward rode the main surface currents, traveling 2000 km in a month. The swimming speeds along the track were less than 0.5 m s^(-1). More than half of their migration energy was spent in adjust their headings against the tidal currents. Turtles that travel southward against the current had swimming speeds over 1 m s^(-1). These turtles corrected their headings and increased swimming speeds when they encountered oceanic eddies that deflected them from their destination. For the third migration pattern, turtles used the coast landmarks as migration guides, swimming constantly at 0.7 m s^(-1). Their migration distance was proportional to the swimming speed with little influence from the flows in shallow coastal waters. All three patterns showed very good compass sense in migration orientation and the swimming speeds were related to the ambient current.