Vertical and horizontal habitat preferences of post-nesting leatherback turtles in the South Pacific Ocean

Abstract

Leatherback turtles are the largest and widest ranging turtle species, and spend much of their time in the offshore pelagic environment. However, the high seas have thus far received lit- tle management attention to protect their ecosystems and biodiversity. We tagged 46 female leatherback turtles with satellite transmitters at Playa Grande, Costa Rica from 2004 to 2007. In the present study, we analyzed the vertical and horizontal habitat preferences of these leatherback tur- tles in the South Pacific Ocean. The turtles exhibited short, shallow dives during their migration southward (mean depth: 45 m; mean duration: 23.6 min), followed by deeper, longer dives (mean depth: 56.7 m; mean duration: 26.4 min) in the South Pacific Gyre that probably indicated searching for prey. We integrated the horizontal movements with remotely sensed oceanographic data to deter- mine the turtles' response to the environment, and applied this information to recommendations for conservation in the pelagic environment. A generalized additive mixed model applied to the daily turtle travel rates confirmed that slower travel rates occurred at cooler sea surface temperatures, higher chlorophyll a concentration and stronger vertical Ekman upwelling, all of which are consid- ered favorable foraging conditions. The southern terminus (35 to 37° S) of the leatherback tracks was also in an area of increased mesoscale activity that might act as a physical mechanism to aggregate their prey, gelatinous zooplankton. However, this could also act as a thermal limit to their distribution. This characterization of leatherback habitat use could aid the development of management efforts within the South Pacific Ocean to reduce mortality of leatherback turtles from fisheries interactions.