Thermal and trophic habitats of the leatherback turtle during the nesting season in French Guiana

Understanding environmental cues determining behaviour and habitat use of species of conservation concern is crucial if one aims at implementing sustainable management of these natural resources. In this way, here, we investigate the thermal and trophic conditions encountered by the critically endangered leatherback sea turtle Dermochelys coriacea during its nesting season in French Guiana where high bycatch rates have been reported.Mean sea water temperatures obtained in situ by animal-borne recorders were 26.6 ± 0.7 °C in the water column, with all but one turtle remaining in water > 25 °C during the inter-nesting interval. In terms of prey availability, regular jellyfish stranding events were recorded during the nesting season, on a 1.25-km long section of the nesting beach. The occurrence of jellyfish was supported by benthic trawls performed on the continental shelf, with a total of 45.4 kg of jellyfish collected in 3.5 h exclusively in coastal waters 10 to 20 m deep where water transparency was between 0.8 and 3 m. This is consistent with the at sea distribution area of gravid leatherbacks during their inter-nesting intervals, as they spent almost 70% of their time diving in shallow (< 20 m deep) waters in front of the Maroni River estuary. In French Guiana, leatherback's gelatinous prey are thus present in very shallow water close to the nesting site and may be easily exploited by active gravid leatherbacks. This suggests that French Guiana female leatherbacks may be influenced by local trophic conditions and actively prospect productive areas overlapping with local fisheries ground.     

Gulps, wheezes, and sniffs: how measurement of beak movement in sea turtles can elucidate their behaviour and ecology

This study was performed to assess the extent to which an intermandibular angle sensor (IMASEN) may be used to elucidate the behaviour of six captive loggerhead turtles. The measuring system was glued to the beak of turtles and set to measure the intermandibular distance at 5 Hz while the turtles fed (on anchovies, squid, and live crabs), swam, rested, and breathed. The behaviour of the equipped turtles was filmed and compared afterwards to the sensor readings. The IMASEN output data allowed quantification of the number of food items ingested as well as the time between food seizure and deglutition and the type of food ingested. However, nonfeeding turtles exhibited regular jaw movements with a reduced amplitude of ca. 2.2 mm, which clearly differed from feeding movements and were caused by buccal oscillations. Such movements of the base of the buccal cavity generate a steady flow of water pass the chemosensory organs and were interrupted only during food ingestion, resting, and breathing. Breathing was clearly distinguishable by the IMASEN. The beak sensor is thus a reliable system to investigate a number of behaviours in sea turtles which encompass foraging, buccal oscillation, and respiratory frequency. It has potential for allocating time to different activities in free-ranging sea turtles and thus allows us to gain insight to their foraging and diving strategies.     

Fuel use and corticosterone dynamics in hatchling green sea turtles (Chelonia mydas) during natal dispersal

During their natal dispersal hatchling sea turtles depart their nest, beach and inshore areas quickly to move into offshore developmental habitat using their finite energy stores. Patterns of fuel use and endocrine responses that could facilitate hatchling sea turtle dispersal activity are poorly understood. This study, examined aspects of intermediary metabolism by measuring plasma fuel use and an endocrine response of hatchling green turtles (Chelonia mydas) during terrestrial and aquatic activity coinciding with natal dispersal. Specifically, we measured plasma concentrations of glucose, non-esterised free fatty acids and protein to gauge the contributions of carbohydrate, lipid and protein metabolism for fuelling natal dispersal. In addition, we measured plasma levels of the steroid hormone corticosterone (CORT) a hormone implicated in regulating a number of metabolic events associated with migration and energy use in vertebrates. During terrestrial activity, hatchlings ascended through the sand from their nests and exhibited significant increases in plasma CORT and lactate indicating intense periods of anaerobic activity. During swimming, all plasma metabolites, with the exception of plasma protein, peaked between 1 and 4 h post-beginning swimming activity. Plasma CORT peaked at between 3 and 5 h of swimming activity. These plasma concentrations are consistent with intensive activity inducing catabolism of carbohydrate, lipid and protein stores to support prolonged activity. These results are similar to other vertebrates and suggest a relatively uniform cascade of physiological processes during such arduous migratory events.