Habitat use and diving behaviour of gravid olive ridley sea turtles under riverine conditions in French Guiana
Résumé
The identification of the inter-nesting habitat used by gravid sea turtles has become a crucial factor in their protection.
Their aggregation in large groups of individuals during the inter-nesting period exposes them to increased
threats to their survival - particularly along the French Guiana shield, where intense legal and illegal
fisheries occur. Among the three sea turtle species nesting in French Guiana, the olive ridley appears to have
the most generalist diet, showing strong behavioural plasticity according to the environment encountered. The
large amounts of sediments that are continuously discharged by the Amazon River create a very unusual habitat
for olive ridleys, i.e. turbid waters with low salinity. This study assesses the behavioural adjustments of 20 adult
female olive ridleys under such riverine conditions. Individuals were tracked by satellite from Remire-Montjoly
rookery in French Guiana using tags that recorded the location and diving parameters of individuals, as well as
the immediate environment of the turtles including the in situ temperature and salinity. Data concerning potential
preyswas provided via collection of epifauna by a trawler. Multiple behavioural shifts were observed in both
horizontal and vertical dimensions. During the first half of the inter-nesting season, the turtles moved away from
the nesting beach (21.9±24.7 km ), performing deeper (12.6±7.4 m) and longer (29.7±21.0 min) dives than
during the second half of the period (7.4±7.8 km, 10.4±4.9mand 25.9±19.3 min). Olive ridleys remained in
waters that were warm (range: 26–33 °C) and which fluctuated in terms of salinity (range: 19.5–36.4 psu), in a
relatively small estuarine habitat covering 423 km2. If olive ridleyswere foraging during this period, the potential
preys that might be available were mostly crustaceans (43%) and fish (39%), as expected for the diet of this generalist
species during this period. This study highlights the numerous behavioural adaptations of this species in
response to the unusual riverine conditions of the French Guiana continental shelf.