Dive and beak movements patterns in leatherback turtles (Dermochelys coriacea) during internesting intervals in French Guiana
Résumé
1. Investigating the foraging patterns of free-ranging species is essential to estimate energy/time budgets for assessing their real reproductive strategy. Leatherback turtles Dermochelys coriacea (Vandelli 1761), commonly considered as capital breeders, have been reported recently to prospect actively during the breeding season in French Guiana, Atlantic Ocean. In this study we investigate the possibility of this active behaviour being associated with foraging, by studying concurrently diving and beak movement patterns in gravid females equipped with IMASEN (Inter-MAndibular Angle SENsor). 2. Four turtles provided data for periods varying from 7.3 to 56.1 h while exhibiting continuous short and shallow benthic dives. Beak movement ('b-m') events occurred in 34% of the dives, on average 1.8 +/- 1.4 times per dive. These b-m events lasted between 1.5 and 20 s and occurred as isolated or grouped (two to five consecutive beak movements) events in 96.0 +/- 4.0% of the recorded cases, and to a lesser extent in series (> five consecutive beak movements). 3. Most b-m events occurred during wiggles at the bottom of U- and W-shaped dives and at the beginning and end of the bottom phase of the dives. W-shaped dives were associated most frequently with beak movements (65% of such dives) and in particular with grouped beak movements. 4. Previous studies proposed wiggles to be indicator of predatory activity, U- and W-shaped dives being putative foraging dives. Beak movements recorded in leatherbacks during the first hours of their internesting interval in French Guiana may be related to feeding attempts. 5. In French Guiana, leatherbacks show different mouth-opening patterns for different dive patterns, suggesting that they forage opportunistically on occasional prey, with up to 17% of the dives appearing to be successful feeding dives. 6. This study highlights the contrasted strategies adopted by gravid leatherbacks nesting on the Pacific coasts of Costa Rica, in the deep-water Caribbean Sea and in the French Guianan shallow continental shelf, and may be related to different local prey accessibility among sites. Our results may help to explain recently reported site-specific individual body size and population dynamics.