The influence of ocean currents on Leatherback Turtle movements in the open ocean

Recent satellite tracking studies suggest that movements of adult Leatherback turtles (Dermochelys coriacea) in the open ocean are influenced by ocean currents.  A quantitative analysis of this association can provide important and novel insight on how Leatherback turtles interact with their environment and also provide a valuable tool for predicting potential effects of climate change and interactions with pelagic fishing gear.  Such analyses are difficult because of large and complex uncertainties in both satellite tracking data and in the estimation of ocean currents.  Using a combination of Argos satellite tracking data and oceanographic model predictions of current velocities, we present a state-space modelling approach that deals with uncertainties in the data and decomposes observed movements into two components: advective movement due to prevailing ocean currents; and, directed movement behaviour. The relative strengths of these components provide unique insight into the effects of ocean currents on turtle movements. Variability in movement types over time may be related to behavioural shifts between traveling, searching, and active foraging. This approach can easily be adapted to analyze movements of other pelagic species.