English abstract
We followed the movements of 9 adult female olive ridley turtles Lepidochelys olivacea after nesting on Masirah Island, Oman, using satellite tracking. Their post-breeding migrations ranged from 85 to 796 km. Three individuals travelled north to foraging grounds in Pakistan, Iran and the United Arab Emirates. The other 6 turtles remained in Omani seas for extended periods (mean ± SD = 171.3 ± 109.4 d; range = 40 to 310 d). These locally resident turtles experienced biannual cooling of sea temperatures due to the effect of the west Arabian Sea upwelling which was not experienced by those that migrated to the north. Indications of disparity in turtle size between foraging locations are identified for the first time in this species. The majority of turtles (8) settled in coastal areas of water depth <100 m. Two locally resident turtles remained in very shallow water (<40 m depth) where they were capable of extended dive durations (>100 min) in water warmer than 21°C, which is a feature unique to olive ridleys amongst sea turtles. They displayed a shift to shorter diving after breeding, indicating increased activity levels. The entire spatial footprint of olive ridley dispersal remained within a putative regional management unit (RMU) for this species in the western Indian Ocean, supporting its delineation. We reveal Oman's key role in conserving this demographic unit, with 6 turtles remaining within its national boundary. Our data add to the growing body of evidence that marine turtles show varied migration behaviours within populations, thus complicating their management.
